研究者詳細 - 山崎　秀雄

論文 - 山崎　秀雄

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The Three-Body Problem in Stress Biology: The Balance Between O2, NO, and H2S in the Context of Hans Selye’s Stress Concept

Yamasaki H.

Stresses ( Stresses ) 5 ( 2 ) 37 - 37 2025年06月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Hans Selye’s stress concept, first introduced in the 1930s, has undergone substantial evolution, extending beyond biology and medicine to influence diverse academic disciplines. Initially, Selye’s General Adaptation Syndrome (GAS) described nonspecific physiological responses to stressors exclusively in mammals, without addressing other biological systems. Consequently, the concept of stress developed independently in biology and medicine, shaped by distinct physiological contexts. This review provides a historical overview of stress research, highlights both parallels and divergences between the stress responses of plants and animals, and integrates insights from traditional Eastern philosophies. We propose an updated GAS framework that incorporates the dynamic balance among reactive oxygen species (ROS), reactive nitrogen species (RNS), and reactive sulfur species (RSS) within the broader context of oxidative stress. We highlight the ionotropic glutamate receptor (iGluR) family and the transient receptor potential (TRP) channel superfamily as minimal molecular architectures for achieving GAS. This perspective expands the classical stress paradigm, providing new insights into redox biology, interspecies stress adaptation, and evolutionary physiology.

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Spatiotemporal Characteristics Determining the Multifaceted Nature of Reactive Oxygen, Nitrogen, and Sulfur Species in Relation to Proton Homeostasis

Yamasaki, H; Itoh, RD; Mizumoto, KB; Yoshida, YS; Otaki, JM; Cohen, MF

ANTIOXIDANTS & REDOX SIGNALING ( Antioxidants and Redox Signaling ) 42 ( 7-9 ) 421 - 441 2025年03月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Seawater Tolerance of the Beach Bean Vigna marina (Burm.) Merrill in Comparison with Mung Bean (Vigna radiata) and Adzuki Bean (Vigna angularis)

Septiana, A; Nakamura, SP; Naomasa, RF; Yamasaki, H

AGRICULTURE-BASEL ( Agriculture (Switzerland) ) 15 ( 3 ) 228 - 228 2025年02月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Seawater intrusion into soils caused by global climate change and tsunami disasters is a significant factor contributing to soil salinization in coastal vegetation areas, posing a critical threat to agriculture and food security. This study aimed to evaluate the seawater tolerance of Vigna marina, a wild Vigna species, through comparative laboratory experiments with Vigna radiata (mung bean) and Vigna angularis (adzuki bean). Unlike V. radiata and V. angularis, the seeds of V. marina exhibited significant buoyancy in seawater, remaining afloat for at least 30 days. After this prolonged seawater incubation, V. marina seeds maintained a 100% germination rate, whereas V. radiata and V. angularis failed to germinate under the same conditions. The photosynthetic activity of V. marina seedlings, evaluated via the Fv/Fm parameter, remained stable even after seven days of seawater irrigation. In contrast, V. radiata and V. angularis perished under seawater irrigation. Furthermore, V. marina seedlings exhibited sustained growth under seawater irrigation, showing consistent increases in both fresh and dry weight. These findings confirm that V. marina possesses remarkable tolerance to seawater, a critical characteristic for cultivation in areas affected by seawater intrusion.

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Pleiotropic Functions of Nitric Oxide Produced by Ascorbate for the Prevention and Mitigation of COVID-19: A Revaluation of Pauling's Vitamin C Therapy.

Yamasaki H, Imai H, Tanaka A, Otaki JM

Microorganisms ( Microorganisms ) 11 ( 2 ) 397 2023年02月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Linus Pauling, who was awarded the Nobel Prize in Chemistry, suggested that a high dose of vitamin C (L-ascorbic acid) might work as a prevention or treatment for the common cold. Vitamin C therapy was tested in clinical trials, but clear evidence was not found at that time. Although Pauling’s proposal has been strongly criticized for a long time, vitamin C therapy has continued to be tested as a treatment for a variety of diseases, including coronavirus infectious disease 2019 (COVID-19). The pathogen of COVID-19, SARS-CoV-2, belongs to the β-coronavirus lineage, which includes human coronavirus, severe acute respiratory syndrome (SARS), and Middle East respiratory syndrome (MERS). This review intends to shed new light on vitamin C antiviral activity that may prevent SARS-CoV-2 infection through the chemical production of nitric oxide (NO). NO is a gaseous free radical that is largely produced by the enzyme NO synthase (NOS) in cells. NO produced by upper epidermal cells contributes to the inactivation of viruses and bacteria contained in air or aerosols. In addition to enzymatic production, NO can be gener-ated by the chemical reduction of inorganic nitrite (NO2−), an alternative mechanism for NO production in living organisms. Dietary vitamin C, largely contained in fruits and vegetables, can reduce the nitrite in saliva to produce NO in the oral cavity when chewing foods. In the stomach, salivary nitrite can also be reduced to NO by vitamin C secreted from the epidermal cells of the stomach. The strong acidic pH of gastric juice facilitates the chemical reduction of salivary nitrite to produce NO. Vitamin C contributes in multiple ways to the host innate immune system as a first-line defense mechanism against pathogens. Highlighting chemical NO production by vitamin C, we suggest that controversies on the therapeutic effects of vitamin C in previous clinical trials may partly be due to less appreciation of the pleiotropic functions of vitamin C as a universal bioreductant.

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Phytochemical Antioxidants: Past, Present and Future

Yasuko Sakihama, Hideo Yamasaki

Antioxidants - Benefits, Sources, Mechanisms of Action ( IntechOpen ) 2021年01月 [ 査読有り ]

掲載種別: 研究論文（その他学術会議資料等）

Most diseases that are difficult to prevent and cure are “syndromes” that are governed by multiple components with complicated interactions. Whatever the cause of such diseases, overproduction of harmful reactive oxygen species (ROS) can often be observed in progression of the disease. Under such conditions, the cells may be challenged by “oxidative stress” due to excessively generated oxidants. Antioxidants can be defined as chemical compounds that scavenge ROS or free radicals over-produced in the cells under oxidative stress conditions. The plant pigments flavonoids and betalains, rich in fruits and vegetables, are reactive not only with ROS but also with reactive nitrogen species (RNS) and possibly with reactive sulfur species (RSS). Here, we provide an overview of updates on the antioxidative functions of the plant pigments along with some prospects for future research on phytochemical antioxidants.

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Blood nitrate and nitrite modulating nitric oxide bioavailability: Potential therapeutic functions in COVID-19.

Yamasaki H

Nitric oxide : biology and chemistry ( Elsevier BV ) 103 29 - 30 2020年10月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Most outcomes of COVID-19 are associated with dysfunction of the vascular system, particularly in the lung. Inhalation of nitric oxide (NO) gas is currently being investigated as a treatment for patients with moderate to severe COVID-19. In addition to the expected vasodilation effect, it has been also suggested that NO potentially prevents infection by SARS-CoV-2. Since NO is an unstable radical molecule that is easily oxidized by multiple mechanisms in the human body, it is practically difficult to control its concentration at lesions that need NO. Inorganic nitrate and/or nitrite are known as precursors of NO that can be produced through chemical as well enzymatic reduction. It appears that this NO synthase (NOS)-independent mechanism has been overlooked in the current developing of clinical treatments. Here, I suggest the missing link between nitrate and COVID-19 in terms of hypoxic NO generation.

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D-Cysteine-Induced Rapid Root Abscission in the Water Fern Azolla Pinnata: Implications for the Linkage between D-Amino Acid and Reactive Sulfur Species (RSS) in Plant Environmental Responses.

Yamasaki H, Ogura MP, Kingjoe KA, Cohen MF

Antioxidants ( Antioxidants ) 8 ( 9 ) 2019年09月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Reactive Oxygen Species (ROS) and Reactive Nitrogen Species (RNS) have been proposed as universal signaling molecules in plant stress responses. There are a growing number of studies suggesting that hydrogen sulfide (H#D2#DRS) or Reactive Sulfur Species (RSS) are also involved in plant abiotic as well as biotic stress responses. However, it is still a matter of debate as to how plants utilize those RSS in their signaling cascades. Here, we demonstrate that d-cysteine is a novel candidate for bridging our gap in understanding. In the genus of the tiny water-floating fern #IAzolla#IR, a rapid root abscission occurs in response to a wide variety of environmental stimuli as well as chemical inducers. We tested five H#D2#DRS chemical donors, Na#D2#DRS, GYY4137, 5a, 8l, and 8o, and found that 5a showed a significant abscission activity. Root abscission also occurred with the polysulfides Na#D2#DRS#D2#DR, Na#D2#DRS#D3#DR, and Na#D2#DRS#D4#DR. Rapid root abscission comparable to other known chemical inducers was observed in the presence of d-cysteine, whereasLl-cysteine showed no effect. We suggest that D-cysteine is a physiologically relevant substrate to induce root abscission in the water fern #IAzolla#IR.

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Dynamics of nitrite content in fresh spinach leaves: evidence for nitrite formation caused by microbial nitrate reductase activity

Naoko S Watanabe, Hideo Yamasaki

Journal of Nutrition & Food Sciences 7 1 - 7 2017年02月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Nitrite (NO#D2#DR#U-#UR) contained in dietary foods has long been recognized for its toxicity as the causative agent of methemoglobinemia and also as a source of mutagenic nitrosamines. Because of these potential toxicities, nitrite as well as nitrate contained in foods and drinks are strictly limited by regulations in many countries. Recent studies have offered us to update our recognition of nitrite; nitrite is an important precursor for nitric oxide (NO) that is required for fundamental physiological activities including vasorelaxation. Although it is well established that green vegetables contain high amounts of nitrate, there has been controversy regarding the source of nitrite accumulation in fresh green vegetables. In this study, we investigated the dynamics of nitrite and nitrate contents in spinach leaf extracts to verify the mechanisms of nitrite formation. The time course of nitrite production in leaf extracts showed a reciprocal relationship with nitrate degradation, suggesting a conversion from nitrate to nitrite. The reaction strongly depended on temperature and it was suppressed at a low temperature. Sodium tungstate, a nitrate reductase enzyme inhibitor, was effective to suppress the conversion. Pre-sterilization by autoclaving or filter sterilization completely prevented the formation of nitrite as well as degradation of nitrate. We suggest that previous reports of nitrite accumulation can be attributed to microbial nitrate reductase activities that occur during the degradation spinach leaves.

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Biological consilience of hydrogen sulfide and nitric oxide in plants: Gases of primordial earth linking plant, microbial and animal physiologies.

Yamasaki H, Cohen MF

Nitric oxide: biology and chemistry 55-56 91 - 100 2016年05月

掲載種別: 研究論文（学術雑誌）

Hydrogen sulfide (H#D2#DRS) is produced in the mammalian body through the enzymatic activities of cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3MST). A growing number of studies have revealed that biogenic H#D2#DRS produced in tissues is involved in a variety of physiological responses in mammals including vasorelaxation and neurotransmission. It is now evident that mammals utilize H#D2#DRS to regulate multiple signaling systems, echoing the research history of the gaseous signaling molecules nitric oxide (NO) and carbon monoxide (CO) that had previously only been recognized for their cytotoxicity. In the human diet, meats (mammals, birds and fishes) and vegetables (plants) containing cysteine and other sulfur compounds are the major dietary sources for endogenous production of H#D2#DRS. Plants are primary producers in ecosystems on the earth and they synthesize organic sulfur compounds through the activity of sulfur assimilation. Although plant H#D2#DRS-producing activities have been known for a long time, our knowledge of H#D2#DRS biology in plant systems has not been updated to the extent of mammalian studies. Here we review recent progress on H#D2#DRS studies, highlighting plants and bacteria. Scoping the future integration of H#D2#DRS, NO and O#D2#DR biology, we discuss a possible linkage between physiology, ecology and evolutional biology of gas metabolisms that may reflect the historical changes of the Earth's atmospheric composition.

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An Overview of Methods in Plant Nitric Oxide (NO) Research: Why Do We Always Need to Use Multiple Methods?

Yamasaki H, Watanabe NS, Sakihama Y, Cohen MF

Methods in molecular biology 1424 1 - 14 2016年 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Bimodal effect of hydrogen peroxide and oxidative events in nitrite-induced rapid root abscission by the water fern Azolla pinnata.

Cohen MF, Gurung S, Birarda G, Holman HY, Yamasaki H

Frontiers in plant science 6 ( 518 ) 1 - 8 2015年07月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

In the genus #IAzolla#IR rapid abscission of roots from floating fronds occurs within minutes in response to a variety of stresses, including exposure to nitrite. We found that hydrogen peroxide, though itself not an inducer of root abscission, modulates nitrite-induced root abscission by #IAzolla pinnata#IR in a dose-dependent manner, with 2 mM H#D2#DRO#D2#DR significantly diminishing the responsiveness to 2 mM NaNO#D2#DR, and 10 mM H#D2#DRO#D2#DR slightly enhancing it. Hypoxia, which has been found in other plants to result in autogenic production of H#D2#DRO#D2#DR, dramatically stimulated root abscission of #IA. pinnata#IR in response to nitrite, especially for plants previously cultivated in medium containing 5 mM KNO#D3#DR compared to plants cultivated under N#D2#DR-fixing conditions without combined nitrogen. Plants, including #IAzolla#IR, produce the small signaling molecule nitric oxide (NO) from nitrite using nitrate reductase. We found #IAzolla#IR plants to display dose-dependent root abscission in response to the NO donor spermine NONOate. Treatment of plants with the thiol-modifying agents #IS#IR-methyl methanethiosulfonate or glutathione inhibited the nitrite-induced root abscission response. Synchrotron radiation-based Fourier transform infrared spectromicroscopy revealed higher levels of carbonylation in the abscission zone of dropped roots, indicative of reaction products of polysaccharides with potent free radical oxidants. We hypothesize that metabolic products of nitrite and NO react with H#D2#DRO#D2#DR in the apoplast leading to free-radical-mediated cleavage of structural polysaccharides and consequent rapid root abscission.

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Azide-dependent NO emission from the water fern Azolla pinnata

Sushma Gurung, Michael F Cohen, Hideo Yamasaki

Russian Journal of Plant Physiology 61 543 - 547 2014年07月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Nitric oxide (NO) is involved in versatile functions in plant growth and development as a signaling molecule. To date, plants have been reported to produce NO following exposure to nitrite (NO#D2#DR#U-#UR) the amino acid L-arginine, hydroxylamine, or polyamines. Here we demonstrate azide-dependent NO production in plants. The water fern #IAzolla pinnata#IR emitted NO into air upon exposure to sodium azide (NaN#D3#DR). The NO production was dependent on azide concentration and was strongly inhibited by potassium cyanide (KCN). Incubation of #IA. pinnata#IR with the catalase inhibitor 3-aminotriazole (3-AT) abolished the azide-dependent NO production. Although nitrite-dependent NO production was inhibited by sodium azide, azide-dependent NO production was not affected by nitrite. These results indicate that #IA. pinnata#IR enzymatically produces NO using azide as a substrate. We suggest that plants are also capable of producing NO from azide by the action of catalase as previously reported in animals.

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Controlled free radical attack in the apoplast: A hypothesis for roles of O, N and S species in regulatory and polysaccharide cleavage events during rapid abscission by Azolla

Michael F Cohen, Sushma Gurung, Jon M. Fukuto, Hideo Yamasaki

Plant Science 217-218 120 - 126 2014年03月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Shedding of organs by abscission is a key terminal step in plant development and stress responses. Cell wall (CW) loosening at the abscission zone can occur through a combination chain breakage of apoplastic polysaccharides and tension release of cellulose microfibrils. Two distinctly regulated abscission cleavage events are amenable to study in small water ferns of the genus Azolla; one is a rapid abscission induced by environmental stimuli such as heat or chemicals, and the other is an ethylene-induced process occurring more slowly through the action of hydrolytic enzymes. Although free radicals are suggested to be involved in the induction of rapid root abscission, its mechanism is not fully understood. The apoplast contains peroxidases, metal-binding proteins and phenolic compounds that potentially generate free radicals from H#D2#DRO#D2#DR to cleave polysaccharides in the CW and middle lamella. Effects of various thiol-reactive agents implicate the action of apoplastic peroxidases having accessible cysteine thiols in rapid abscission. The Ca#D2#DR#U+ #UR dependency of rapid abscission may reflect the stabilization Ca#D2#DR#U+#UR confers to peroxidase structure and binding to pectin. To spur further investigation, we present a hypothetical model for small signaling molecules H#D2#DRO#D2#DR and NO and their derivatives in regulating, via modification of putative protein thiols, free radical attack of apoplastic polysaccharides.

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Sulfate-reducing bacteria in the skeleton of the massive coral Goniastrea aspera from the great barrier reef.

Yeong Shyan Yuen, Seitaro S Yamazaki, Andrew H Baird, Takashi Nakamura, Hideo Yamasaki

Galaxea, Journal of Coral Reef Studies Special issue 160 - 165 2013年 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Differential influence of water-flow on photoinhibition of photosynthesis in endosymbiotic algae among shallow-inhabiting scleractinian corals

Takashi Nakamura, Hideo Yamasaki

Galaxea, Journal of Coral Reef Studies Special issue 366 - 372 2013年 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Evolution of thermal thresholds: Can corals adapt to projected rates of change in sea surface temperature?

Andrew BAIRD, Takashi NAKAMURA, Hideo YAMASAKI

Galaxea, Journal of Coral Reef Studies Special issue 160 - 165 2013年 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Polyamine-Induced Rapid Root Abscission in Azolla pinnata.

Sushma Gurung, Michael F Cohen, Jon Fukuto, Hideo Yamasaki

Journal of Amino Acids 493209 1 - 9 2012年07月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Floating ferns of the genus #IAzolla#IR detach their roots under stress conditions, a unique adaptive response termed rapid root abscission. We found that #IAzolla pinnata#IR plants exhibited dose-dependent rapid root abscission in response to the polyamines spermidine and spermine after a substantial time lag (>20 min). The duration of the time lag decreased in response to high pH and high temperature whereas high light intensity increased the time lag and markedly lowered the rate of abscission. The oxidation products of polyamines, 1,3-diaminopropane, β-alanine and hydrogen peroxide all failed to initiate root abscission, and hydroxyethyl hydrazine, an inhibitor of polyamine oxidase, did not inhibit spermine-induced root abscission. Exposure of #IA. pinnata#IR to the polyamines did not result in detectable release of NO and did not affect nitrite-dependent NO production. The finding of polyamine-induced rapid root abscission provides a facile assay for further study of the mode of action of polyamines in plant stress responses.

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Ontogenetic change in the lipid and fatty acid composition of scleractinian coral larvae.

. Figueiredo, A H Baird, M F Cohen, J-F Flot, . Kamiki, T Meziane, M Tsuchiya, H Yamasaki

Coral Reefs 31 613 - 619 2012年06月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Some scleractinian coral larvae have an extraordinary capacity to delay metamorphosis, and this is reflected in the large geographic range of many species. Coral eggs typically contain a high proportion of wax esters, which have been hypothesized to provide a source of energy for long-distance dispersal. To better understand the role of lipids in the dispersal of broadcast spawning coral larvae, ontogenetic changes in the lipid and fatty acid composition of #IGoniastrea retiformis#IR were measured from the eggs until larvae were 30 days old. Egg biomass was 78.8 ± 0.5% lipids, 86.3 ± 0.2% of which were wax esters, 9.3 ± 0.0% polar lipids, 4.1 ± 0.2% sterols, and 0.3 ± 0.1% triacylglycerols. The biomass of wax esters declined significantly through time, while polar lipids, sterols and triacylglycerols remained relatively constant, suggesting that wax esters are the prime source of energy for development. The most prevalent fatty acid in the eggs was palmitic acid, a marker of the dinoflagellate #ISymbiodinium#IR, highlighting the importance of symbiosis in coral reproductive ecology. The proportion of polyunsaturated fatty acids declined through time, suggesting that they are essential for larval development. Interestingly, triacylglycerols are only abundant in the propagules that contain #ISymbiodinium#IR, suggesting important differences in the energetic of dispersal among species with vertical and horizontal transmission of symbionts.

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Phenotypic Variations in Croton Codiaeum variegatum (L.) Blume Characterized by Digital Image-Based Procedure

AS Mollick, H Yamasaki

Acta Horticulturae 937 393 - 400 2012年 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Phenotypic Variations in Croton Codiaeum variegatum (L.) Blume Characterized by Digital Image-Based Procedure

Mollick, AS; Yamasaki, H

XXVIII INTERNATIONAL HORTICULTURAL CONGRESS ON SCIENCE AND HORTICULTURE FOR PEOPLE (IHC2010): INTERNATIONAL SYMPOSIUM ON ADVANCES IN ORNAMENTALS, LANDSCAPE AND URBAN HORTICULTURE 937 393 - 400 2012年 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Nitric oxide-dependent hypotensive effects of wax gourd juice

Nakashima M, Shigekuni Y, Obi T, Shiraishi M, MIyamoto A, Yamasaki H, Etoh T, Iwai S

Journal of Ethnopharmacoloy 138 404 - 407 2011年11月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Croton Codiaeum variegatum (L.) Blume cultivars characterized by leaf phenotypic parameters

20111105

Scientia Horticulturae 132 71 - 79 2011年11月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Croton #ICodiaeum variegatum#IR (L.) Blume is a popular ornamental foliage plant that displays an anomalous range of variations in its leaf size, shape and color pattern. By fixing such leaf variations, more than 300 cultivars have been produced in the world. Until now, however, only a limited number of studies have been made to describe the leaf phenotypic diversity. Here we investigated the diversity of leaf phenotype in croton cultivars with a numerical taxonomic approach. One-way analysis of variance confirmed significant phenotypic variations in the croton cultivars for 12 quantitative leaf parameters. Among the numerical parameter tested, the leaf index that is the ratio of leaf length to leaf width showed the highest variability. High coefficient of variation values were observed in petiole length, leaf area and leaf down quarter width. In contrast with leaf morphology, the composition of leaf pigments that contribute to leaf coloration did not show diversity. Based on the analyses of the leaf parameters, we clustered the croton cultivars into four major groups. The results of this study provide a numerical basis for classification of croton cultivars. A possible involvement of transposon is discussed in terms of somatic mutation that results in the leaf phenotypic diversity.

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Heat-shock-induced color-pattern changes of the blue pansy butterfly Junonia orithya: Physiological and evolutionary implications

Mahdi, SHA, Yamasaki, H, Otaki, JM

Journal of Thermal Biology 36 312 - 321 2011年08月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Temperature shock to early pupae causes wing color-pattern changes in butterflies. These plastic changes are ascribed to the hemolymph level of the cold-shock hormone (CSH) in pupae as well as to other mechanisms. Here, we characterized heat-shock-induced color-pattern changes using the blue pansy butterfly #IJunonia orithya#IR (Lepidoptera: Nymphalidae). In response to the 38–42 °C heat-shock treatments, parafocal elements (PFEs) were thinned and dislocated away from eyespots; this was the reverse of the direction of the cold-shock-induced changes. Somewhat surprisingly, in response to the lethal 44 °C heat shock, PFEs were modified as in the case of a cold-shock. These modifications were not affected by the removal of the head-prothorax portion of pupae. While the hemolymph-mediated transfer of the possible PFE-modification property induced by the 42 °C treatment was unsuccessful in the parabiosis experiment, the transfer of the factor induced by the 44 °C treatment was successful. In contrast, reduction of the blue background area was obtained not only by the 42 and 44 °C treatments but also by the injection of thapsigargin, a plant-derived stress inducer, in males. The result of this treatment was similar to the natural color patterns of other closely related #IJunonia#IR species. We also observed an increase in orange coloration by the 42 °C treatment in females, and this change was similar to ecdysteroid-induced modifications. Taken together, the heat-shock-induced PFE modifications in #IJ. orithya#IR can be explained by the levels of CSH, and other modifications are likely to be caused by general stress responses and ecdysteroid effects. We conclude that phenotypic plasticity of the wing color patterns to heat shock results from a combined effect of at least a few different mechanisms. These mechanisms might have been exploited in the color-pattern evolution of some #IJunonia#IR species.

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Effect of nitric oxide on leaf non photochemical quenching under heat-stress conditions,

KK Hossain, T Nakamura, H Yamasaki

Russian Journal of Plant Physiology 58 629 - 633 2011年07月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Non-photochemical quenching (NPQ) is a photoprotection mechanism in photosynthesis that can be monitored by NPQ of chlorophyll #Ia#IR fluorescence. Comparing NPQ response of #IArabidopsis thaliana#IR intact leaves between the wild type and ΔGLB3, which lacks truncated hemoglobin gene, we report here the effects of nitric oxide (NO) on NPQ under stress conditions. Heat stress was found to severely decline NPQ of ΔGLB3. The effect was mimicked by chemical NO donors, and it was completely prevented by the NO scavenger cPTIO. These results suggest that NO is involved in the decline of NPQ which is pronounced under heat stress conditions.

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NITRIC OXIDE SYNTHASE-LIKE ACTIVITIES IN PLANTS

Yamasaki, H; Itoh, RD; Bouchard, JN; Dghim, AA; Hossain, KK; Gurung, S; Cohen, MF

NITROGEN METABOLISM IN PLANTS IN THE POST-GENOMIC ERA 42 103 - 125 2011年 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Physiological characterization of the cold-shock-induced humoral factor for wing color-pattern changes in butterflies

Shah HA Mahdi , Yuya Tomita , Hideo Yamasaki, Joji M. Otaki

JOURNAL OF INSECT PHYSIOLOGY 56 1022 - 1031 2010年09月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Butterfly wing color patterns can be modified by the application of temperature shock to pupae immediately after pupation, which has been attributed to a cold-shock-induced humoral factor called cold-shock hormone (CSH). Here, we physiologically characterized CSH and pharmacological action of tungstate, using a nymphalid butterfly #IJunonia orithya#IR. We first showed that the precise patterns of modification were dependent on the time-point of the cold-shock treatment after pupation, and confirmed that the modification properties induced in a cold-shocked pupa were able to be transferred to another pupa in a parabiosis experiment. Cold-shock application after removal of the head and prothorax together still produced modified wings, excluding major involvement of the brain–retrocerebral neuroendocrine complex. Furthermore, tungstate injection induced modifications even in individuals whose head and prothorax were removed. Importantly, transplantation of tracheae isolated from cold-shocked pupae induced modifications in the recipient wings. We identified a chemical peak in hemolymph of the cold-shocked individuals using HPLC, which corresponded to dopamine, and demonstrated that dopamine and its related biogenic amines have ability to induce small color-pattern changes. Taken together, the present study suggests that CSH is likely to be secreted from trachea-associated endocrine cells upon cold-shock treatment and that tungstate may change color patterns via its direct action on wings.

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Chemical induction of rapid and reversible plastid filamentation in Arabidopsis thaliana roots

Ryuuichi D Itoh, Hideo Yamasaki, Andi Septiana, Shigeo Yoshida, Makoto T Fujiwara

PHYSIOLOGIA PLANTARUM 139 144 - 158 2010年06月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Effects of nitric oxide scavengers on thermoinhibition of seed germination in Arabidopsis thaliana

Hossain KK, Itoh RD, Yoshimura G, Tokuda G, Oku H, Cohen MF, Yamasaki H

RUSSIAN JOURNAL OF PLANT PHYSIOLOGY 57 222 - 232 2010年05月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Plant seeds sometimes do not germinate at elevated temperature. The thermoinhibition mechanisms of seed germination have yet not revealed. Here we describe a chemical approach to improve seed germination at high temperature. We compared the temperature response of germination between wild-type #IArabidopsis thaliana#IR and its T-DNA insertion mutant ΔAtGLB3 that lacks a functional gene encoding GLB3, a homologue of bacterial truncated Hb (trHb). Under optimal temperature conditions (e.g. 22°C), the seeds of ΔAtGLB3 and the wild type germinated at a frequency near 100%. In contrast, at 32°C the seeds of ΔAtGLB3 did not germinate while wild-type seeds retained the same high germination frequency. The germination of ΔAtGLB3 at 32°C was partially restored by supplementation with the nitric oxide-specific scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO; cPTIO), 3-(3,4-dihydroxycinnamoyl)quinic acid, bovine serum Hb, or isoprene. The results presented in this study suggest that chemical scavengers for reactive nitrogen species potentially improve seed germination at high temperature.

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Implication of nitric oxide in the heat-stress-induced cell death of the symbiotic alga Symbiodinium microadriaticum

Josee Nina Bouchard, Hideo Yamasaki

MARINE BIOLOGY 156 2209 - 2220 2009年10月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

One of the major consequences of global warming is a rise in sea surface temperature which may affect the survival of marine organisms including phytoplankton. Here, we provide experimental evidence for heat-induced cell death in a symbiotic microalga. Shifting #ISymbiodinium microadriaticum#IR from 27 to 32°C resulted in an increase in mortality, an increase in caspase 3-like activity, and an increase in nitric oxide (NO) production. The caspase-like activity was strongly correlated with the production of NO in thermally challenged microalgae. For this experiment, the application of Ac-DEVD-CHO, a mammalian caspase 3-specific inhibitor, partly prevented (by 65%) the increase in caspase-like activity. To verify the relationship between NO and the caspase-like activity, S. microadriaticum were subsequently incubated with 1.0 mM of the following chemical NO donors: sodium nitroprusside (SNP), S-nitrosoglutathione (GSNO), S-nitroso-N-acetylpenicillamine (SNAP) and 3,3bis(Aminoethyl)-1-hydroxy-2-oxo-1-triazene (NOC-18). The supplementation of both SNP and NOC-18 caused a significant increase in caspase-like activity compared to the control treatment. Pre-treatment of the microalgae with the inhibitor Ac-DEVD-CHO before the supplementation of the different NO donors completely prevented the increase in caspase-like activity. These results suggest that NO could play a role in the induction of cell death in heat-stressed #IS. microadriaticum#IR by mediating an increase in caspase-like activity.

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Effects of live rock on the reef-building coral Acropora digitifera cultured with high levels of nitrogenous compounds

Yuen YS, Yamazaki SS, Nakamura T, Tokuda G, Yamasaki H

AQUACULTURAL ENGINEERING 41 35 - 43 2009年07月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Reef-building corals are sensitive to excessive nitrogenous (N) compounds. To maintain levels of inorganic nitrogenous compounds low in coral aquaria, various technologies, mechanical, chemical and biological, have been applied. As one of the biological techniques, “live rock,” which can be defined as a dead coral skeleton covered with crustose coralline algae (CCA), has long been applied for coral aquaria. Until recently, however, there has been little evidence for the effectiveness of live rock in removal of N compounds from coral aquaria. Demonstrating comparative experiments with live rocks, here we report that the live rock is capable of removing N compounds and reduces the mortality of reef-building coral. We cultured the reef-building coral #IAcropora digitifera#IR with the sea cucumber #IHolothuria atra#IR as a natural nitrogen producer.#I H. atra#IR increased the concentration of the inorganic N compounds (NH#D4#DR#U+#UR, NO#D3#DR#U−#UR and NO#D2#DR#U−#UR) that resulted in high coral mortality. The presence of the live rock remarkably reduced the concentrations and sustained a high coral photosynthetic activity. We detected the functional genes #IamoA#IR and #InirS#IR within the live rock, suggesting the occurrence of both nitrifying and denitrifying bacteria. These results support the idea that “live rock” is an effective biofilter that can maintain water quality suitable for reef-building corals.

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Purification and Molecular Cloning of Xylanases from the Wood-Feeding Termite, Coptotermes formosanus Shiraki

Arawaka G, Watanabe H, Yamasaki H, Maekawa H, Tokuda G

BIOSCIENCE BIOTECHNOLOGY AND BIOCHEMISTRY 73 710 - 718 2009年03月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

#ICoptotermes formosanus#IR is one of the most destructive termites in the southern part of Japan as well as in the United States. Hemicellulose is a noncellulosic polysaccharide found in plant cell walls, and xylan is the major constituent of hemicellulose. Since hemicellulose prevents access of cellulolytic enzymes to cellulose, enzymatic hydrolysis of hemicellulose is beneficial for cellulose digestion. We purified three functional xylanases to homogeneity from #IC. formosanus#IR for the first time. Elution profiles from the whole termite extract suggest that these three xylanases play major roles in xylan digestion in the gut of the termites. The corresponding cDNAs were successfully cloned based on the N-terminal amino acid sequences, encoding GHF11 xylanases. Reverse transcription-PCR using manipulated protozoan cells in the hindgut revealed that the corresponding genes were expressed in the symbiotic flagellate Holomastigotoides mirabile. These results suggest that the GHF11 xylanases that are produced by the symbiotic flagellates play a primary role in xylan degradation in #IC. formosanus#IR.

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Latitudinal variation in reproductive synchrony in Acropora assemblages: Japan vs. Australia

Andrew H Baird, Chico L Birrel, Terence P Hughes, Abbi Mcdonald, Satoshi Nojima, Cathie A Page, Morgan S Prachett, Hideo Yamasaki

Galaxea, Journal of Coral Reef Studies 11 101 - 108 2009年 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

The annual mass spawning of scleractinian corals on the Great Barrier Reef (GBR), Australia, is purported to be unprecedented in terms of the taxonomic and geographical scale of spawning synchrony. Here, we compare spawning synchrony both within and among coral species in four regions spanning 10°of latitude on the GBR and compare this with four regions separated by a similar latitudinal range within the Japanese tropical and sub-tropical Archipelago. On the GBR, peak reproductive activity at all latitudes occurred in November whereas there was a clear disjunction in the period of peak reproductive activity among the four regions in Japan, with tropical locations spawning up to 3 months earlier. In Sekesei Lagoon (22°N), a high proportion of #IAcropora#IR colonies were mature following the full moon in April; at Akajima Island (26°N) peak reproductive activity occurred in May; at Oku (28°N) peak reproductive activity occurred in June and in Amakusa (31°N), reproductive activity likely peaked in July. However, mature colonies of #IAcropora#IR were found prior to every full moon for at least 5 months at two regions examined in detail (The Whitsundays Islands on the GBR and Akajima Island). While these regions on GBR appear to act more homogeneously than regions over a similar latitudinal range in Japan with respect to the timing of peak reproductive activity, and the proportion of colonies mature was often higher during these peaks, the reproductive season on the GBR is much longer (5 months) than is typically appreciated.

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Flicker light effects on photosynthesis of symbiotic algae in the reef-building coral Acropora digitifera (Cnidaria : Anthozoa : Scleractinia)

Takashi Nakamura, Hideo Yamasaki

PACIFIC SCIENCE 62 314 - 350 2008年08月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Reef-building corals inhabit a variety of aquatic habitats with a range of light conditions. Because the coral host depends on photosynthetic products assimilated from endosymbiotic algae, reef-building corals have to cope with irradiance fluctuations on instantaneous to seasonal time scales. Underwater high-frequency light fluctuations resulting from the lens effect on the water surface are prominent in oligotrophic coral reef environments, a phenomenon known as flicker light. Effects of flicker light on endosymbiont photosynthesis of the reef-building coral #IAcropora digitifera#IR (Dana, 1846) were evaluated with pulse amplitude modulation chlorophyll fluorometry. At supersaturating light intensities, photosynthesis was less inhibited by flicker light than by constant light. Reduction in photoinhibition by flicker light was pronounced at high water temperatures. Flicker light may strongly influence endosymbiont photosynthesis of corals inhabiting shallow reef habitats, especially during periods of strong solar irradiance and high water temperature.

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Heat stress stimulates nitric oxide production in Symbiodinium microadriaticum: A possible linkage between nitric oxide and the coral bleaching phenomenon

Josee Nina Bouchard, Hideo Yamasaki

PLANT AND CELL PHYSIOLOGY 49 641 - 652 2008年04月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Nitric oxide (NO) is a gas displaying multiple physiological functions in plants, animals and bacteria. The enzymes nitrate reductase and NO synthase have been suggested to be involved in the production of NO in plants and algae, but the implication of those enzymes in NO production under physiological conditions remains obscure. #ISymbiodinium microadriaticum#IR, commonly referred to as zooxanthellae, is a marine microalga commonly found in symbiotic association with a cnidarian host including reef-building corals. Here we demonstrate NO production in zooxanthellae upon supplementation of either sodium nitrite or L-arginine as a substrate. The nitrite-dependent NO production was detected electrochemically and confirmed by the application of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), a specific NO scavenger. Cells stained with the diaminofluorescein, DAF-2 DA, an NO fluorescent probe, showed an increase in fluorescence intensity upon supplementation of both sodium nitrite and L-arginine. Microscopic observations of DAF-stained cells verified that NO was produced inside the cells. NO production in S. microadriaticum was found to increase upon exposure of cells to an acute heat stress which also caused a decline in the photosynthetic efficiency of PSII (Fv/Fm). This study provides substantial evidence to confirm that zooxanthellae can synthesize NO even when they are not in a symbiotic association with a coral host. The increase in NO production at high temperatures suggests that heat stress stimulates the microalgal NO production in a temperature-dependent manner. The implications of these findings are discussed in the light of the coral bleaching phenomenon which is associated with elevated sea surface temperature due to global warming.

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Influence of water flow on skeletal isotopic composition in the coral Pocillopora damicornis

Atsushi Suzuki, Takashi Nakamura, Hideo Yamasaki, Kayo Minoshima, Hodaka Kawahata

CORAL REEFS 27 209 - 218 2008年03月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Fragments of branching #IPocillopora damicornis#IR coral colonies were grown in experimental flumes under two water flow regimes. Colony size and buoyant weight increased most rapidly in the fast-flow regime. Branch tips from the upper and outer parts of the colonies showed the lowest and most consistent skeletal oxygen isotope ratios. Flow regime had little influence on the lowest oxygen isotope ratios, which were at least 3.5‰ lighter than the calculated oxygen isotopic equilibrium. These “kinetic” isotope effects are comparable to those observed in #IPorites#IR corals. Relatively more branch tips showed extreme #U18#URO depletions under low-flow conditions, and among small coral colonies. Isotopic variability was greater among branch tips from the lower and inner parts of the colonies and at high flow. Skeletal oxygen and carbon isotope ratios generally showed positive correlations. Despite the particularly large offsets from isotopic equilibrium, the isotopically lightest branches showed the greatest isotopic consistency and therefore would make the best isotopic thermometers. Isotopic variability within the colony may provide an indication of flow regime.

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Colonization of Sulfurovum sp on the gill surfaces of Alvinocaris longirostris, a deep-sea hydrothermal vent shrimp

Gaku Tokuda, Akinori Yamada, Kazuma Nakano, Nao Arita O, Hideo Yamasaki

MARINE ECOLOGY-AN EVOLUTIONARY PERSPECTIVE 29 106 - 114 2008年03月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Deep‐sea hydrothermal vents are unique light‐independent ecosystems that are sustained by chemosynthetic bacteria. For many of the invertebrates inhabiting in such environments, bacteria play essential roles in both energy acquisition and detoxification of potentially toxic gases such as H#D2#DRS. In this study, the bacterial flora present on the gills of #IAlvinocaris longirostris#IR (Bresiliidae: Caridea), a shrimp inhabiting hydrothermal vents (1532 m depth) at the Hatoma Knoll of the Okinawa Trough, was investigated. Bacterial 16S rDNA fragments were successfully amplified from the gills and 70% of these fragments showed an identical pattern in the restriction fragment length polymorphism analysis. These fragments were assigned to the ribotype AL‐1. Phylogenetic analyses suggest that AL‐1 forms a monophyletic clade with #ISulfurovum#IR spp. (ε‐Proteobacteria). Fluorescence in situ hybridization for AL‐1 and electron microscopy showed the presence of short‐rod bacteria lining up on the cuticular layer of the surface of the gill filaments. These results suggest that bacterial association with gills also occurs in bresiliid shrimps.

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Isoprene emission from tropical trees in Okinawa Island, Japan

Tambuan T, Baba S, Kuniyoshi A, Iwasaki H, Nakamura T, Yamasaki H, Oku H

CHEMOSPHERE 65 2138 - 2144 2006年11月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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NO signal at the crossroads: polyamine-induced nitric oxide synthesis in plants?

Yamasaki H, Cohen MF

TRENDS IN PLANT SCIENCE 11 522 - 524 2006年11月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Currently, the most confounding issue in plant NO biology is the mechanism(s) for NO production. Until only a few years ago, the source of arginine-dependent NO production in plants had been presumed to be a mammalian-type NOS. However, to date, no such homologue has been found in plant genomes. In 2003, two types of NOS (iNOS and AtNOS1) were reported that do not share sequence similarity to mammalian-type NOS but were thought to have unique mechanisms for arginine-dependent NO synthesis. One year later, two papers describing iNOS were retracted, and now the NOS activity of AtNOS1 seems to be in doubt. Although it is still possible that a unique plant NOS might exist, the loss of two strong candidates for catalysis of an arginine-dependent NO pathway in plants has left a gaping hole in the field. Problems with NO detection methodologies could account for some of the present confusion. As an enzymatic source of NO in plants, nitrate reductase (NR) is now the only protein whose NO-producing activity has been confirmed. Although it seems unlikely that cytosolic assimilatory NR functions as the sole source of NO signals, PAs can down-regulate nitrate assimilation, and probably also NO production from nitrite, by interacting with the binding protein 14-3-3. Although further onfirmation of PA-induced NO production is necessary, the bservations reported by Tun et al. could imply the presence of an unknown enzyme responsible for direct conversion of PAs to NO.

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Influence of Tithonia diversifolia and triple superphosphate on dissolution and effectiveness of phosphate rock in acidic soil

Isaac Savini, Paul C. Smithson, Nancy K. Karanja, Hideo Yamasaki

JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE 169 539 - 604 2006年10月

掲載種別: 研究論文（学術雑誌）

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Acroporid corals growing over a methane-bubbling hydrothermal vent, Southern Ryukyu Archipelago

Nakamura T, Yamazak SS, Sakai K, Yamasaki H, Furushima Y, Yamamoto H

CORAL REEFS 25 382 - 382 2006年08月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Hydrothermal vents have been reported from the areas of coral reef in Papua New Guinea, Baja California and Taketomi-jima in the southern Ryukyu Archipelago. The high temperature and chemical composition of hydrothermal fluids are normally lethal to many marine animals. In 2005 an investigation was conducted of a submarine hot spring field 1 km off Taketomi Island, Okinawa, Japan in depths of 13–22 m. The main hydrothermal vent discharged water at 50–60 ºC, at a pH of 6.56, DO 1 gl#U-1#UR, and salinity 3.3%. There was a barren zone surrounding the vent out to 5–10 m. At a distance of 20 m small aggregations of live Acroporid corals were found. Live branching corals were also found in an area of vigorous methane release, where coral and sediment are covered with a white microbial mat, notwithstanding temperatures of 41 ºC, salinity 3.3%, pH 6.67, and DO 0.4 gl#U-1#UR,. It is notable that no massive, encrusting, or tabular colonies grow in this area. The lower parts of colonies appear to be inhibited by the microbial mats; however, upper parts (20 cm above the substrate) are well pigmented. Reduced pigmentation at the axial tips is indicative of active growth.

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Occurrence and recent long-distance dispersal of deep-sea hydrothermal vent shrimps

Gaku Tokuda, Akinori Yamada,, Kazuma Nakano, Nao Arita, Hideo Yamasak

BIOLOGY LETTERS 2 257 - 260 2006年06月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Deep-sea hydrothermal vents and methane seeps are extreme environments that have a high concentration of hydrogen sulphide. However, abundant unique invertebrates including shrimps of the family Bresiliidae have been found in such environments. The bresiliid shrimps are believed to have radiated in the Miocene (less than 20 Myr); however, the period when and the mechanisms by which they dispersed across the hydrothermal vents and cold seeps in oceans worldwide have not been clarified. In the present study, we collected the deep-sea blind shrimp #IAlvinocaris longirostris#IR from the hydrothermal vent site in the Okinawa Trough and carried out the first investigation of the 18S rRNA gene of a bresiliid shrimp. The phylogenetic analysis revealed that the bresiliid shrimp is situated at an intermediate lineage within the infraorder Caridea and shows monophyly with palaemonid shrimps, which live in shallow sea and freshwater. Furthermore, the mitochondrial cytochrome oxidase I (#ICOI#IR) gene sequences were analysed to determine the phylogenetic relationship with known bresiliid shrimps. #IA. longirostris#IR of the Okinawa Trough had two haplotypes of the #ICOI#IR gene, one of which was identical to the #IAlvinocaris#IR sp. of the cold seeps in Sagami Bay. These results indicate that a long-distance dispersal of A. longirostris occurred possibly within the last 100 000 years.

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一酸化窒素（ＮＯ）発生の蛍光試薬による生体観察法

徳田岳, 有田奈央, 山崎秀雄

沖縄生物学会誌 44 2138 - 2144 2006年03月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Nitric oxide (NO) has been known as one of the toxic air pollutants NOx. Recent studies have evaluated that NO is endogenously produced through enzymatic activities in vertebrate animals. NO production similar to vertebrates has also been found in bacteria, fungi, algae, plants, and invertebrates, suggesting that NO is actually an essential molecule for living organisms. It is thus expected that NO also plays important roles in physiology of diverse living organisms in Ryukyu archipelago. However, our understanding on NO biology is yet too premature to account for diverse actions of this molecule. For studies of NO biology, technique(s) for detecting in vivo NO production is essential. In this paper we have reviewed a fluorometric method that has been recently developed for NO detection in vivo..

A simple method for two-dimensional color analyses of plant leaves

Shimoji H, Tokuda G, Tanaka Y, Moshiri B, Yamasaki H

RUSSIAN JOURNAL OF PLANT PHYSIOLOGY ( その他の出版社 ) 53 ( 1 ) 126 - 133 2006年01月

掲載種別: 研究論文（学術雑誌）

Coloration and color pattern are basic information for plant physiology, ecology, and taxonomy. Until recently, such color analysis of biological materials required expensive equipment. Here we report a convenient method for analyzing color of plant leaves with ImageJ, free software. Color digital images of croton leaves were divided with ImageJ into Red, Green, and Blue images, and then exported as two-dimensional numeric data. After processing images with Adobe Photoshop Elements and Microsoft Excel, color patterns were obtained as histograms. A comparison of the histograms evaluated characteristics of croton leaf variegation. The method successfully quantified color information of the plant leaves with an inexpensive PC set. Apart from taxonomic applications, the simple algorithms allow application of the present methodology to various types of color and color pattern analyses.

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Nitrogen oxidation in bacterium-plant interactions

Cohen MF, Mazzola M, Yamasaki H

Microbe 8 347 - 347 2006年 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Requirement of water-flow for sustainable growth of Pocilloporid corals during high temperature periods

Nakamura T, Yamasaki H

MARINE POLLUTION BULLETIN ( その他の出版社 ) 50 ( 10 ) 1115 - 1120 2005年10月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Reef-building corals are threatened worldwide by mass-scale coral bleaching episodes that are pronounced in high sea surface temperature (SST) conditions. Although water-flow has been suggested to be a mitigating factor for bleaching, long-term effects of flow-mediated bleaching suppression are as yet not fully understood. In order to investigate flow effects, we monitored the corals #IPocillopora damicornis#IR and #IStylophora pistillata#IR grown for 20 months in experimental outdoor flumes with the flow rates of 20 cm s#U−1#UR (flow) and <3 cm s#U−1#UR (still). Although bleaching was observed under high SST conditions, both species showed a shorter period or entirely no visible bleaching under the flow conditions. Better colony growth was found in the flow conditions whereas significant growth suppression and higher mortality were observed in still conditions. We conclude that water-flow is an essential environmental factor for the corals #IP. damicornis#IR and #IS. pistillata#IR, especially under high SST conditions.

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Brassica napus seed meal soil amendment modifies microbial community structure, nitric oxide production and incidence of Rhizoctonia root rot

Michael F Cohen, Hideo Yamasaki, Mark Mozzola

SOIL BIOLOGY & BIOCHEMISTRY ( その他の出版社 ) 37 ( 7 ) 1215 - 1227 2005年07月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

A low glucosinolate content (21.8 μmol g#U−1#UR) #IBrassica napus#IR seed meal (RSM) applied to orchard soils altered communities of both pathogenic and saprophytic soil micro-organisms. RSM amendment reduced infection by native and introduced isolates of #IRhizoctonia#IR spp. and recovery of #IPratylenchus#IR spp. from apple roots. Root infection by #IRhizoctonia solan#IRi AG-5 was also suppressed in split-root assays where a portion of the root system was cultivated in RSM-amended soils and the remainder grown in the presence of the pathogen but lacking RSM. #IR. solani#IR hyphal growth was not inhibited by RSM amendment. Suppression of #IPratylenchus#IR was attained to an equivalent extent by amending soils with either RSM or soybean meal (SM) when applied to provide a similar N content. Thus, glucosinolate hydrolysis products did not appear to have a significant role in the suppression of #IRhizoctonia#IR spp. or #IPratylenchus#IR spp. obtained via RSM amendment. RSM amendment elevated populations of #IPythium#IR spp. and of ammonia-oxidizing bacteria that release nitric oxide but suppressed fluorescent pseudomonad numbers. #IStreptomyces#IR spp. soil populations increased significantly in response to RSM but not SM amendment. The vast majority of #IStreptomyces#IR spp. recovered from the apple rhizosphere produced nitric oxide and possessed a nitric oxide synthase homolog. We propose that transformations in the bacterial community structure are associated with the observed control of #IRhizoctonia#IR root rot, with NO production by soil bacteria potentially having a role in the induction of plant systemic resistance

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Photoinhibition of photosynthesis is reduced by water flow in the reef-building coral Acropora digitifera

Nakamura T, van Woesik R, Yamasaki H

MARINE ECOLOGY-PROGRESS SERIES ( その他の出版社 ) ( 301 ) 109 - 118 2005年03月 [ 査読有り ]

掲載種別: 研究論文（その他学術会議資料等）

While photosynthesis of symbiotic algae is essential for reef-building corals, excess irradiance inhibits photosynthesis through photoinhibition, which can lead to coral bleaching under elevated temperature conditions. Here we show that water flow reduces photoinhibition of in hospite endosymbionts in the coral #IAcropora digitifera#IR. Diurnal monitoring of chlorophyll fluorescence, under 2 different flow regimes (<3 and 20 cm s#U–1#UR flow rates) in an outdoor aquarium, showed reduced photoinhibition, but only under moderate flow conditions (20 cm s#U–1#UR). Experimental (laboratory) measurements, on time scales ranging from minutes to hours, showed that flow-mediated reductions in photoinhibition occurred not by enhancing recovery of the damaged photosystem, but rather through inducing differential photodamage. Moreover, experiments involving sequential light oscillations (500/20 and 1000/20 µmol photons m#U–2#UR s#U–1#UR) at 3 flow regimes, <3, 10, and 20 cm s#U–1#UR, on a time scale ranging from hours to days, revealed water-velocity-dependent reductions of dynamic photoinhibition. These results, on time scales ranging from minutes to weeks, confirm that reduced water flow amplifies photodamage of algal photosynthesis under strong irradiance, which in turn affects coral tolerance to strong irradiance and temperature.

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Inhibitory effects of flavonoids on alternative respiration of plant mitochondria

Shimoji H, Yamasaki H

BIOLOGIA PLANTARUM ( その他の出版社 ) 49 ( 1 ) 117 - 119 2005年03月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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The NO world for plants: achieving balance in an open system

Hideo Yamasaki

PLANT CELL AND ENVIRONMENT ( その他の出版社 ) 28 ( 1 ) 78 - 84 2005年01月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Nitric oxide (NO) is a free radical that had been known for many years simply as a toxic air pollutant. The discovery of enzymatic NO production in many living organisms has established a new paradigm: NO being an essential molecule endogenously produced in the cells. In plant science it has been suggested that NO acts as a plant hormone equivalent to ethylene; that is, as a gaseous signal transmitter. Even after experiencing such a scientific breakthrough, however, researchers may still feel difficulty in exploring plant NO signalling systems with conventional approaches. A major difference between plants and animals is that the growth and development of plants is closely linked to the surrounding environment where NO levels vary according to biotic and abiotic activities. This fundamental difference may make the NO‐signalling network system of plants larger and more complicated than that of vertebrates. This review intends to show prospects for the future of NO signalling research in plants by introducing a holistic concept to aid in the exploration of complicated systems such as the plant‐environment system. Furthermore, the novel ONS hypothesis is proposed to encompass the complexity and simplicity of NO in chemistry, biochemistry and physiology.

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Comment on 'Effects of geography, taxa, water flow, and temperature variation on coral bleaching intensity in Mauritius' (McClanahan et al. 2005)

van Woesik R, Nakamura T, Yamasaki H, Sheppard C

MARINE ECOLOGY-PROGRESS SERIES ( その他の出版社 ) ( 305 ) 297 - 299 2005年 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Bioremediation of soils by plant-microbe systems

Michael F Cohen, Hideo Yamasaki, Mark Mozzola

INTERNATIONAL JOURNAL OF GREEN ENERGY ( その他の出版社 ) 1 ( 3 ) 301 - 312 2004年08月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Sustainable ecosystems can be designed to eliminate environmental toxins and reduce pathogen loads through the direct and indirect consequences of plant and microbial activities. We present an approach to the bioremediation of disturbed environments, focusing on petroleum hydrocarbon (PHC) contaminants. Treatment consists of incorporating a plant-based amendment to enhance ecosystem productivity and physiochemical degradation followed by the establishment of plants to serve as oxidizers and foundations for microbial communities. Promising amendments for widespread use are entire plants of the water fern Azolla and seed meal of Brassica napus (rapeseed). An inexpensive byproduct from the manufacture of biodiesel and lubricants, rapeseed meal is high in nitrogen (6% wt/wt), stimulates >100-fold increases in populations of resident Streptomyces species, and suppresses fungal infection of roots subsequently cultivated in the amended soil. Synergistic enzymatic and chemical activities of plant and microbial metabolism in root zones transform and degrade soil contaminants. Emphasis is given to mechanisms that enable PHC functionalization via reactive molecular species.

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Repair machinery of symbiotic photosynthesis as the primary target of heat stress for reef-building corals

Takahashi S, Sakamizu M, Nakamura T, van Woesik R, Yamasaki H

PLANT AND CELL PHYSIOLOGY ( その他の出版社 ) 45 ( 2 ) 251 - 255 2004年02月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

In a coral-algae symbiotic system, heat-dependent photoinhibition of photosystem II (PSII) leads to coral bleaching. When the reef-building coral #IAcropora digitifera#IR was exposed to light, a moderate increase of temperature induced coral bleaching through photobleaching of algal pigments, but not through expulsion of symbiotic algae. Monitoring of PSII photoinhibition revealed that heat-dependent photoinhibition was ascribed to inhibition of the repair of photodamaged PSII, and heat susceptibility of the repair machinery varied among coral species. We conclude that the efficiency of the photosynthesis repair machinery determines the bleaching susceptibility of coral species under elevated seawater temperatures.

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A photocarotenogenic Rhodococcus sp. isolated from the symbiotic fern Azolla

Cohen MF, Meziane T, Yamasaki H

Endocytobiosis and Cell Research 15 350 - 355 2004年 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

An aerobic, heterotrophic bacterium, termed strain APG1, was isolated from surfacesterilized fronds of #IAzolla pinnata#IR, a water fern having symbiotic leaf cavities. Based on its fatty acid profile, morphology and biochemical characteristics, strain APG1 was assigned to the genus #IRhodococcus#IR. Exposure to light caused colonies to yellow due to accumulation of a ß-carotene-like pigment. We suggest that photocarotenogenesis and other traits of strain APG1 could facilitate the survival of the bacterium in planta.

Enzymatic nitration of phytophenolics: evidence for peroxynitrite-independent nitration of plant secondary metabolites

Sakihama Y, Tamaki R, Shimoji H, Ichiba T, Dukushi Y, Tahara S, Yamasaki H

FEBS LETTERS ( その他の出版社 ) 553 ( 3 ) 377 - 380 2003年10月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Peroxynitrite (ONOO#U−#UR), a reactive nitrogen species, is capable of nitrating tyrosine residue of proteins. Here we show in vitro evidence that plant phenolic compounds can also be nitrated by an ONOO#U−#UR‐independent mechanism. In the presence of NaNO#D2#DR, H#D2#DRO#D2#DR, and horseradish peroxidase (HRP), monophenolic #Ip#IR‐coumaric acid (#Ip#IR‐CA, 4‐hydroxycinnamic acid) was nitrated to form 4‐hydroxy‐3‐nitrocinnamic acid. The reaction was completely inhibited by KCN, an inhibitor for HRP. The antioxidant ascorbate suppressed #Ip#IR‐CA nitration and its suppression time depended strongly on ascorbate concentration. We conclude that nitrogen dioxide radical (NO#D2#DR#U #UR• ), but not ONOO#U−#UR, produced by a guaiacol peroxidase is the intermediate for phytophenolic nitration.

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Involvement of nitric oxide synthase in sucrose-enhanced hydrogen peroxide tolerance of Rhodococcus sp strain APG1, a plant-colonizing bacterium

Cohen MF, Yamasaki H

NITRIC OXIDE-BIOLOGY AND CHEMISTRY ( その他の出版社 ) 9 ( 1 ) 1 - 9 2003年08月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Hydrogen peroxide (H#D2#DRO#D2#DR) tolerance of #IRhodococcus#IR sp. strain APG1, previously isolated from the aquatic fern #IAzolla pinnata#IR, was examined in relation to nitric oxide (NO) production by cells cultured on a variety of C sources. Cells inoculated onto #IA. pinnata#IR fronds established a surface-sterilant resistant density of 2–4 × 107 cells g#U−1#UR without causing disease. Compared to cultures containing glucose, fructose, mannitol, or glycerol, those provided only with sucrose displayed, on a per C basis, substantially lower (<10%) growth yields and higher resistance to H#D2#DRO#D2#DR. NO, a positive regulator of catalase synthesis in bacteria, was produced in larger amounts in sucrose-grown cells as evidence by eightfold greater per cell accumulations in the medium of nitrite (NO#D2#DR#U−#UR), a stable oxidation product of NO. Addition to cells of L-arginine, the substrate for nitric oxide synthase (NOS), stimulated production of NO, detected both by fluorometric reaction with diaminofluorescein-FM diacetate (DAF-FM DA) and by increased levels of NO#D2#DR#U−#UR in the culture medium. These results suggest that sucrose may enhance H#D2#DRO#D2#DR tolerance of #IRhodococcus#IR APG1 by increasing cellular NO producing capacity. We propose a regulatory role for NOS in promoting tolerance of #IRhodococcus#IR APG1 to oxidative stress in the phyllosphere.

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Simultaneous time resolution of the emission spectra of fluorescent proteins and zooxanthellar chlorophyll in reef-building coral

Gilmore AM, Larkum AWD, Salih A, Itoh S, Shibata Y, Bena C, Yamasaki H, Papina M, Van Woesik R

PHOTOCHEMISTRY AND PHOTOBIOLOGY ( その他の出版社 ) 77 ( 5 ) 515 - 523 2003年05月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Light is absorbed by photosynthetic algal symbionts (i.e. zooxanthellae) and by chromophoric fluorescent proteins (FP) in reef-building coral tissue. We used a streak-camera spectrograph equipped with a pulsed, blue laser diode (50 ps, 405 nm) to simultaneously resolve the fluorescence spectra and kinetics for both the FP and the zooxanthellae. Shallow water (<9 m)–dwelling #IAcropora#IR spp. and #IPlesiastrea versipora#IR specimens were collected from Okinawa, Japan, and Sydney, Australia, respectively. The main FP emitted light in the blue, blue-green and green emission regions with each species exhibiting distinct color morphs and spectra. All corals showed rapidly decaying species and reciprocal rises in greener emission components indicating Förster resonance energy transfer (FRET) between FP populations. The energy transfer modes were around 250 ps, and the main decay modes of the acceptor FP were typically 1900–2800 ps. All zooxanthellae emitted similar spectra and kinetics with peak emission (∼683 nm) mainly from photosystem II (PSII) chlorophyll (chl)#I #IRa. Compared with the FP, the PSII emission exhibited similar rise times but much faster decay times, typically around 640–760 ps. The fluorescence kinetics and excitation versus emission mapping indicated that the FP emission played only a minor role, if any, in chl excitation. We thus suggest the FP could only indirectly act to absorb, screen and scatter light to protect PSII and underlying and surrounding animal tissue from excess visible and UV light. We conclude that our time-resolved spectral analysis and simulation revealed new FP emission components that would not be easily resolved at steady state because of their relatively rapid decays due to efficient FRET. We believe the methods show promise for future studies of coral bleaching and for potentially identifying FP species for use as genetic markers and FRET partners, like the related green FP from #IAequorea#IR spp.

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Water flow facilitates recovery from bleaching in the coral Stylophora pistillata

Nakamura T, Yamasaki H. van Woesik R

MARINE ECOLOGY-PROGRESS SERIES ( その他の出版社 ) ( 256 ) 287 - 291 2003年03月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Exposing partially bleached samples of #IStylophora pistillata#IR coral colonies to controlled water-flow treatments revealed differential recovery rates that varied in accordance with flow rate. Recovery of the number of zooxanthellae per unit area and chlorophyll #Ia#IR concentrations increased rapidly in moderate-flow treatments (of 20 cm s#U-1#UR), after an initial 3 wk of stasis. Colonies in low-flow treatments (≤3 cm s#U-1#UR) remained pale for the entire 7 wk experimental period and showed only slight increases in zooxanthellae per unit area. In an earlier study, we showed that when corals were subjected to high temperature and high irradiance, coral bleaching occurred in low-flow but not in moderate-flow treatments; the present study shows that recovery from bleaching is facilitated by flow treatment. In combination, prevention of and rapid recovery from bleaching by enhanced water flow suggest that the mechanisms that lead to dysfunction of the algae-coral symbiosis are driven by mass-transfer-limited processes.

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Involvement of nitric oxide in the mechanism for stomatal opening in Vicia faba leaves

Sakihama Y, Murakami S, Yamasaki H

Biologia Plantarum ( その他の出版社 ) 46 117 - 119 2003年 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Feeding deterrence of the aquatic fern Azolla in relation to anthocyanin and fatty acid composition

Cohen MF, Mezine T, Tsuchiya M, Yamasaki H

Aquatic Botany ( その他の出版社 ) ( 74 ) 181 - 187 2002年10月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Higher levels of deoxyanthocyanins in #IAzolla#IR fronds correlated with feeding deterrence against adult #ILymnea swinhoei#IR snails and #IPolypedates leucomystax#IR tadpoles. After 7 days in co-culture, the growth yield of #IAzolla filiculoides#IR was almost twice that of #IAzolla pinnata#IR, which contained approximately 20-fold higher levels of deoxyanthocyanins. Inclusion of snails upon initiating a plant co-culture resulted in an A. pinnata growth yield that was 1.5-fold higher than that of #IA. filiculoides#IR. The two plant species did not differ significantly in fatty acid composition. However, snails incubated for 1 week solely with #IA. pinnata#IR showed a characteristic starvation-like fatty acid profile, with a two-fold lower proportion of polyunsaturated fatty acids (PUFAs) compared to snails that had access to #IA. filiculoides#IR, either as a sole food source or in co-culture with #IA. pinnata#IR. A 3-month cultivation of #IA. pinnata#IR with tadpoles resulted in fronds having a 260% higher concentration of deoxyanthocyanins and a 10-fold lower proportion of PUFAs in comparison to plants unexposed to tadpoles, indicating that prolonged feeding reduces the desirability of the surviving plants as a food source.

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Synergistic Effect of Deoxyanthocyanins from the Symbiotic Fern Azolla on hrmA Gene Induction in the Cyanobacterium Nostoc punctiforme.

Cohen MF, Sakihama Y, Takagi YC, Ichiba T, Yamasaki H

Molecular Plant Microbe Interactions ( その他の出版社 ) ( 15 ) 875 - 882 2002年09月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

The #IhrmA#IR gene of the N#D2#DR-fixing cyanobacterium #INostoc punctiforme#IR functions in repressing the formation of transitory motile filaments, termed hormogonia, by plant-associated vegetative filaments. Here, we report that anthocyanins can contribute to induction of #IhrmA#IR expression. Aqueous extract from fronds of the fern #IAzolla pinnata#IR, a host of symbiotic #INostoc#IR spp., was found to be a potent inducer of #IhrmA-luxAB#IR in #IN. punctiforme#IR strain UCD 328. The#I hrmA-luxAB#IR inducing activities of #IA. pinnat#IRa, as well as #IAzolla filiculoides#IR, were positively correlated with levels of frond deoxyanthocyanins. Analyses of the deoxyanthocyanins in frond extracts revealed, in order of predominance, an acetylated glycoside derivative of luteolinidin (m/z 475) and of apigeninidin (m/z 459) and minor amounts of a second luteolinidin derivative. At up to 150 μM, a purified preparation of deoxyanthocyanins only weakly induced #IhrmA-luxAB#IR on its own, but mixtures with #IhrmA-luxAB#IR inducers (#IA. filiculoides#IR extract or the flavonoid naringin) synergistically doubled to tripled their inducing activities. These results suggest that appropriately localized deoxyanthocyanins could function in plant-mediated mechanisms for repressing #INostoc#IR spp. hormogonium formation.

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Plant phenolic antioxidant and prooxidant activities: implications for involvement of phenoxyl radicals in oxidative damage of plants

Sakihama Y, Cohen MF, Grace SC, Yamasaki H

Toxicology ( その他の出版社 ) 177 ( 1 ) 67 - 80 2002年08月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Plant phenolic compounds such as flavonoids and lignin precursors are important constituents of the human diet. These dietary phytophenolics have been recognized largely as beneficial antioxidants that can scavenge harmful active oxygen species including O#D2#DR#U−#UR, H#D2#DRO#D2#DR, OH, and #U1#URO#D2#DR. Here we review our current understanding of the antioxidant and prooxidant actions of phenolics in plant cells. In plant systems, phytophenolics can act as antioxidants by donating electrons to guaiacol-type peroxidases (GuPXs) for the detoxification of H#D2#DRO#D2#DR produced under stress conditions. As a result of such enzymatic as well as non-enzymatic antioxidant reactions, phenoxyl radicals are formed as the primary oxidized products. Until recently, phenoxyl radicals had been difficult to detect by static electron spin resonance (ESR) because they rapidly change to non-radical products. Application of Zn exerts spin-stabilizing effects on phenoxyl radicals that enables us to analyze the formation and decay kinetics of the radicals. The ESR signals of phenoxyl radicals are eliminated by monodehydroascorbate radical (MDA) reductase, suggesting that phenoxyl radicals, like the ascorbate radical, are enzymatically recycled to parent phenolics. Thus, phenolics in plant cells can form an antioxidant system equivalent to that of ascorbate. In contrast to their antioxidant activity, phytophenolics also have the potential to act as prooxidants under certain conditions. For example, flavonoids and dihydroxycinnamic acids can nick DNA via the production of radicals in the presence of Cu and O#D2#DR. Phenoxyl radicals can also initiate lipid peroxidation. Recently, Al, Zn, Ca, Mg and Cd have been found to stimulate phenoxyl radical-induced lipid peroxidation. We discuss the mechanism of phenoxyl radical prooxidant activity in terms of lifetime prolongation by spin-stabilizing agents.

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High susceptibility of photoinhibition of photosynthesis in the tropical fig tree Ficus microcarpa L. cv. Golden Leaves

Takahashi S, Tamashiro A, Sakihama Y, Yamamoto Y, Kawamitsu Y, Yamasaki H

BMC Plant Biology ( その他の出版社 ) 2 ( 2 ) 1471 - 2229 2002年04月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

The tropical plant #IFicus microcarpa#IR L. f. cv. Golden Leaves (GL) is a high-light sensitive tropical fig tree in which sun-leaves are yellow and shade-leaves are green. We compared the response of photosynthetic activities to strong light between GL and its wild-type (WT, #IFicus microcarpa#IR L. f.). Field measurements of maximum photosystem II (PSII) efficiency (Fv/Fm) of intact sun-leaves in GL showed that photo synthetic activity was severely photoinhibited during the daytime (Fv/Fm = 0.46) and subsequently recovered in the evening (Fv/Fm = 0.76). In contrast, WT did not show any substantial changes of Fv/Fm values throughout the day (between 0.82 and 0.78). Light dependency of the CO#D2#DR assimilation rate in detached shade-leaves of GL showed a response similar to that in WT, suggesting no substantial difference in photosynthetic performance between them. Several indicators of photoinhibition, including declines in PSII reaction center protein (D1) content, Fv/Fm value, and O#D2#DR evolution and CO#D2#DR assimilation rates, all indicated that GL is much more susceptible to photoinhibition than WT. Kinetics of PAM chlorophyll a fluorescence revealed that nonphotochemical quenching (NPQ) capacity of GL was lower than that of WT. We conclude that the photosynthetic apparatus of GL is more highly susceptible to photoinhibition than that of WT.

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Separation of highly fluorescent proteins of Aquropola corals by SDS-PAGE

Papina M, Sakihama Y, Bena C, van Woesik R, Yamasaki H

Comparative Physiology and Biochemistry ( その他の出版社 ) ( 13 ) 767 - 774 2002年04月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

This study characterized the spectral properties of #IAcropora tenuis, A. nasuta, A. secale#IR, and #IA. aspera#IR, all of which showed strong colorful fluorescence under ultraviolet light-A (black light). The emission maxima of fluorescence from the intact corals were 517, 482, 484, and 514 nm in #IA. tenuis, A. nasuta, A. secale#IR, and #IA. aspera#IR, respectively. Using a soluble fraction of cell-free extract of the corals, we applied a method of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) to separate each fluorescent protein component contained in the corals. Green fluorescent bands were detected in all #IAcropora#IR examined, although their apparent molecular mass and relative content were different. #IA. aspera#IR had two orange bands in addition to the green one. The major excitation and emission peaks of the orange fluorescence bands were almost identical (476 and 478 nm), however, they were discernible by their spectral profiles and molecular masses. Some biochemical properties of the highly fluorescent proteins of #IAcropora#IR are described and implications of the results are discussed.

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Nitric oxide production mediated by nitrate reductase in the green alga Chlamydomonas reinhardtii: an alternative NO production pathway in photosynthetic organisms

Sakihama Y, Nakamura S, Yamasaki H

Plant and Cell Physiology ( その他の出版社 ) 43 290 - 297 2002年03月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Biological activity of nitric oxide (NO) production was investigated in the unicellular green alga #IChlamydomonas reinhardtii#IR. An NO specific electrode detected a rapid increase in signal when nitrite (NO#D2#DR#U–#UR) was added into a suspension of #IC. reinhardtii#IR intact cells in the dark. The addition of KCN or the NO quencher bovine hemoglobin completely abolished the signal, verifying that the nitrite-dependent increase in signal is due to enzymatic NO production. L-arginine, the substrate for NO synthase, did not induce detectable NO production and the NOS inhibitor Nω-nitro-L-arginine showed no inhibitory effect on the nitrite-dependent production of NO. Illuminating cells showed a significant suppressive effect on NO production. When the photosynthetic electron transport inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea was present in the suspension, "IC. reinhardtii#IR cells produced NO after the addition of nitrite even under illumination. Kinetic and microscopic observations, using the intracellular fluorescent NO probe 4,5-diaminofluorescein-2 diacetate, both demonstrated that NO was produced within the cells in response to the addition of nitrite. The Chlamydomonas mutant cc-2929, which lacks nitrate reductase (NR) activity, did not display any of the responses observed in the wild-type cells. The results presented here provide direct in vivo evidence to confirm that NR is involved in the nitrite-dependent NO production in the green alga

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Reversible inhibition of photophosphorylation in chloroplasts by nitric oxide

Takanashi S, Yamasaki H

FEBS Letters ( その他の出版社 ) 512 145 - 148 2002年02月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Nitric oxide (NO) is a bioactive molecule involved in diverse physiological functions in plants. Here we demonstrate that NO is capable of regulating the activity of photophosphorylation in chloroplasts. The electron transport activity in photosystem II determined from chlorophyll a fluorescence was inhibited by NO. NO also inhibited light‐induced ΔpH formation across the thylakoid membrane. High concentrations of nitrite and nitrate did not show such inhibitory effects, suggesting that the inhibition is not due to uncoupling effects of the oxidized products of NO. ATP synthesis activity upon illumination was severely inhibited by NO (IC#D50#DR=0.7 μM). The inhibition was found to be temporary and the activity was completely recovered by removing NO. Bovine hemoglobin and bicarbonate were effective in preventing NO‐dependent inhibition of photophosphorylation. These results indicate that NO is a reversible inhibitor of photosynthetic ATP synthesis.

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Biodegradation of diesel fuel by an Azolla-derived bacterial consortium.

Cohen MF, Williams J, Yamasaki H

Journal of Environmental Science and Health, Part A Toxic/Hazardous Substances ( その他の出版社 ) ( 9 ) 1593 - 1606 2002年 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

The widely distributed water fern #IAzolla#IR was investigated for use as an amendment in the bioremediation of fuel-contaminated environments. In a field experiment #IAzolla#IR pinnata as well as #IPistia stratiotes#IR and #ISalvinia molesta#IR were applied to plots containing soil that had been surface-contaminated with diesel fuel (2.4 L m#U−2#UR) and flooded with water. The plants quickly died and bacterial flocs developed around the dead #IA. pinnata#IR fronds. After 16 weeks, diesel concentrations (as determined by levels of gas chromatography-detectable hydrocarbons) in the plant-added plots were less than half that of the control plot, and concentrations of xylenes and ethylbenzene were 50–100 times lower. In laboratory experiments, a consortium composed of #IA. pinnata#IR-derived bacteria displayed dense growth in a 4% diesel-containing mineral salts medium and was found to lower the fluorescence from aromatic compounds by approximately 50% after 19 d. It is concluded that the observed enhancement of diesel degradation in the plant-added plots was due to the release of bacteria (bioaugmentation) and physiochemical improvement of the plot conditions (biostimulation).

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Lipid peroxidation induced by phenolics in conjunction with aluminum ion

Sakihama, Yamasaki H

BIOLOGIA PLANTARUM 45 249 - 254 2002年 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Using the whole plant and model systems, we demonstrate that the aluminum ions (Al#U3+#UR) stimulate phenolic-dependent lipid peroxidation. Lipid peroxidation in barley (#IHordeum vulgare#IR L. cv. Donor) roots was 30 % higher under AlCl#D3#DR treatment than without Al. Major decomposition product of lipid peroxidation was 4-hydroxynonenal (4-HNE) but not thiobarbituric acid reactive substances (TBARS), a widely used markers for lipid peroxidation. Similarly, AlCl#D3#DR stimulated lipid peroxidation of soybean liposomes in the presence of chlorogenic acid (CGA) and H#D2#DRO#D2#DR/horseradish peroxidase system which can oxidize phenolics. Al#U3+#UR was found to enhance lipid peroxidation induced by oxidized CGA. Intermediates of lignin biosynthesis in plants, including p-coumaric acid, ferulic acid, sinapic acid and coniferyl alcohol, also showed similar effects. These results suggest that Al#D3#DR+#U #URhas a potential to induce oxidative stress in plants by stimulating the prooxidant nature of endogenous phenolic compounds.

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Inhibitory effects of nitric oxide on oxidative phosphorylation in plant mitochondria

Yamasaki H, Shimoji H, Ohshiro Y, Sakihama Y

NITRIC OXIDE-BIOLOGY AND CHEMISTRY 5 261 - 270 2001年06月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Plant nitrate reductase (NR) produces nitric oxide (NO) when nitrite is provided as the substrate in the presence of NADH [H. Yamasaki and Y. Sakihama (2000) FEBS Lett. 468, 89–92]. Using a NR-dependent NO producing system, we investigated the effects of NO on the energy transduction system in plant mitochondria isolated from mung bean (#IVigna radiata#IR). Plant mitochondria are known to possess two respiratory electron transport pathways—the cytochrome and alternative pathways. When the alternative pathway was inhibited by n-propyl gallate, the addition of NR strongly suppressed respiratory O2 consumption driven by the cytochrome pathway. In contrast, the alternative pathway measured in the presence of antimycin A was not affected by NO. The extent of the steady-state membrane potential (Δψ) generated by respiratory electron transport rapidly declined in response to NO production. The addition of bovine hemoglobin, a quencher of NO, resulted in the recovery of Δψ to the uninhibited level. Consistent with its inhibition of Δψ, NO produced by NR strongly suppressed ATP synthesis in the mitochondria. These results provide substantial evidence to confirm that the plant alternative pathway is resistant to NO and support the idea that the alternative pathway may lower respiration-dependent production of active oxygens under conditions where NO is overproduced.

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Reduction of phenoxyl radicals mediated by monodehydroascorbate reductase

Sakihama Y, Mano J, Sano S, Asada K, Yamasaki H

BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS 279 949 - 954 2000年11月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Monodehydroascorbate (MDA) reductase catalyzes the reduction of MDA, the only organic radical substrate for the enzyme reported so far. Here, we show that cucumber MDA reductase is also capable of reducing phenoxyl radicals which are generated by horseradish peroxidase (HRP) with H#D2#DRO#D2#DR. The addition of MDA reductase plus NADH suppressed the HRP/H#D2#DRO#D2#DR-dependent oxidation of quercetin, accompanied by the oxidation of NADH. The quenching of the quercetin radical by MDA reductase plus NADH was confirmed by ESR. MDA reductase with NADH also suppressed the HRP/H#D2#DRO#D2#DR-dependent oxidation of hydroxycinnamates, including ferulic acid, coniferyl alcohol, and chlorogenic acid. Thus, the phenoxyl radicals of plant phenols can be reduced to their respective parent phenols by MDA reductase via a mechanism similar to the reduction of MDA.

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Nitrite-dependent nitric oxide production pathway: implications for involvement of active nitrogen species in photoinhibition in vivo

Hideo Yamasakl

PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES ( The Royal Society, London ) 355 1477 - 1488 2000年10月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Air pollution studies have shown that nitric oxide (NO), a gaseous free radical, is a potent photosynthetic inhibitor that reduces CO#D2#DR uptake activity in leaves. It is now recognized that NO is not only an air pollutant hut also an endogenously produced metabolite, which may play a role in regulating plant cell functions. Although many studies have suggested the presence of mammalian-type NO synthase (NOS) in plants, the source of NO is still not clear. There has been a number of studies indicating that plant cells possess a nitrite-dependent NO production pathway which can be distinguished from the NOS-mediated reaction. Nitrate reductase (NR) has been recently found to be capable of producing NO through one-electron reduction of nitrite using NAD(P)H as an electron donor. This review focuses on current understanding of the mechanism for the nitrite-dependent NO production in plants. Impacts of NO produced by NR on photosynthesis are discussed in association with photo-oxidative stress in leaves.

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Flavonoid-induced expression of a symbiosis-related gene in the cyanobacterium Nostoc punctiforme

Cohen MF, Yamasaki H

JOURNAL OF BACTERIOLOGY 182 4644 - 4646 2000年08月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Simultaneous production of nitric oxide and peroxynitrite by plant nitrate reductase: in vitro evidence for the NR-dependent formation of active nitrogen species

Yamaasaki H, Sakihama Y

FEBS LETTERS ( その他の出版社 ) 468 ( 1 ) 89 - 92 2000年02月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

We examined the ability of plant nitrate reductase (NR) to produce nitric oxide (NO) using in vitro assays. Electrochemical and fluorometric measurements both showed that NO is produced by corn NR in the presence of nitrite and NADH at pH 7. The NO production was inhibited by sodium azide, a known inhibitor for NR. During the reaction, absorbance of 2',7'-dichlorodihydrofluorescein increased markedly. This change was completely suppressed by sodium azide, glutathione or depletion of oxygen. We conclude that plant NR produces both NO and its toxic derivative, peroxynitrite, under aerobic conditions when nitrite is provided as the substrate for N

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Effects of oxygen stress on ¹H-NMR relaxation time (T₁) of Vigna radiata seedling

Iwaya-Inoue M, Yoshimura K, Otubo M, Yamasaki H

JOURNAL OF THE FACULTY OF AGRICULTURE KYUSHU UNIVERSITY 44 249 - 256 2000年02月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Effects of the oxygen exposure on plants were investigated in intact hypocotyl tissues of etiolated seedlings from mung bean (#IVigna radiata#IR L.). We report here that spin-lattice NMR relaxation time (#IT#D1#DR#IR) of water proton of intact tissues, which can be measured with a 180° - r - 90° pulse sequence at 20 MHz, is responsible to the oxygen exposure. When the tissues placed, in the NMR tube were exposed to 95% oxygen for 5 s, a rapid decrease in the #IT#D1#DR#IR, values and a subsequent relaxation process were observed. The value was fully recovered to the initial one during a 40 min incubation. Heat-denatured tissues did not show such recovery response, suggesting that the #IT#D1#DR#IR, recovery requires heat-sensitive components contained in the tissues. To examine a possibility that scavenging activities of oxygen radicals is involved in the mechanism for the #IT#D1#DR#IR, response, effects of supplemental scavengers were tested. We have found that the shortening of #IT#D1#DR#IR, induced by oxygen exposure to membrane fractions was strongly suppressed by the radical scavenger superoxide dismutase (SOD), Tiron and ascorbate. These results suggest that activities of O#D2#DR#U-#UR production in the tissues are involved in the mechanism for abrupt shortening of #IT#D1#DR#IR.

The tropical fig Ficus microcarpa L. f. cv. golden leaves lacks heat-stable dehydroascorbate reductase activity

Yamasaki H, Takahashi S, Heshiki R

PLANT AND CELL PHYSIOLOGY 40 640 - 646 1999年06月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Dehydroascorbate reductase (DHAR) is an enzyme which mediates a regeneration of ascorbate from dehydroascorbate using GSH as the electron donor. Here we report a tropical fig lacking a heat-stable DHAR activity in leaves. The leaves of #IFicus microcarpa#IR L. f. cv. Golden Leaves are normally green under dim light but are yellow under full sunlight in the field. We compared DHAR activity from the leaves of Golden Leaves to that of the wild type using two distinct assay methods. Total leaf DHAR activity of Golden Leaves, determined in the presence of 2-mercaptoethanol and EDTA, was 0.3 μmol min#U−1#UR (mg protein)#U−1#UR which was comparable to that of the wild type or spinach leaves. This activity was completely eliminated by heat treatment at 80°C, whereas 40% of the activity was resistant to this treatment in the wild type leaves. Similar results were obtained with another assay method employing dithiothreitol and gel filtration. We conclude that the absence of heat-stable DHAR activity is a significant biochemical marker that distinguishes Golden Leaves from the wild type. A physiological role for DHAR in adaptation to high light stress is proposed.

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An alternative pathway for nitric oxide production in plants: new features of an old enzyme

Yamasaki H, Sakihama Y, Takanashi S

TRENDS IN PLANT SCIENCE ( その他の出版社 ) 4 ( 4 ) 128 - 129 1999年04月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

An earlier study reported that NO production was unique to the #IPhaseolus#IR tribe of the family leguminosae, which possesses constitutive nitrate reductase. The results shown here indicate that plant species other than leguminosae potentially produce NO in a reaction catalyzed by nitrate reductase. In plant cells, all nitrite, nitrate, nitrate reductase and NADH are present in the same compartment (i.e. in the cytosol). Under optimal conditions, nitrite is translocated into the chloroplasts and it is reduced to NH#D4#DR#U+#UR by nitrite reductase. However, nitrite could be present in the cytosol at a significant concentration when photosynthetic electron transport is not operational. Indeed, high NO emissions from plants were observed when they were treated with herbicide, or when a nitrate-rich nutrient solution was applied at night. These observations suggest that plants are capable of producing NO as a byproduct of nitrogen metabolism. Because NO is a reactive free radical that can produce the toxic compound peroxynitrite, high NO concentrations exert deleterious effects on lipids, DNA and proteins, similar to that observed with oxygen-derived species such as hydroxyl radicals. This nitrate reductase-dependent NO production could participate in oxidative damage, which is pronounced in conditions of abiotic and biotic stress. Although nitrate reductase has been studied extensively as a key enzyme of nitrogen metabolism, its NO-producing ability has been almost overlooked. To date, neither the gene nor the protein responsible for NOS activity has been isolated from plants. In addition to identifying putative NOS, we feel that the focus of our research should also be directed towards exploring this novel feature of the old enzyme, nitrate reductase.

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9-aminoacridine and dibucaine exhibit competitive interactions and complicated inhibitory effects that interfere with measurements of Delta pH and xanthophyll cycle-dependent photosystem II energy dissipation

Gilmore AM, Yamasaki H

PHOTOSYNTHESIS RESEARCH 57 159 - 174 1998年08月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

This study concerns measurements and interpretations of the trans-thylakoid membrane pH gradient, delta pH, and xanthophyll cycle-dependent energy dissipation in Photosystem II (PS II). Compared and contrasted are the concentration-dependent inhibitory effects and interactions between two lipophilic tertiary amines, namely, 9-aminoacridine the delta pH indicator and dibucaine a local anesthetic reported to inhibit both the delta pH and xanthophyll cycle deepoxidation. Chlorophyll a fluorescence monitored both electron transport efficiency and xanthophyll cycle-dependent energy dissipation, high-performance liquid chromatography monitored deepoxidase and chloroplast ATPase activities and steady-state fluorescence monitored various activities of the amines in solution. Low concentrations (up to 2 µM) of both 9-aminoacridine and dibucaine showed similar fluorescence properties and delta pH-dependent uptake into thylakoids. Importantly both amines exhibited mutually competitive inhibitory effects with respect to this delta pH-dependent uptake and fluorescence quenching. The fluorescence yields of both compounds in aqueous solution were strongly quenched by sodium ascorbate, a necessary cofactor for in vitro deepoxidation. Both compounds similarly inhibited several light induced activities including deepoxidation, photosynthetic electron transport and PS II energy dissipation. However, for all these activities 9-aminoacridine was 2 to 5 times more potent. Importantly, 9-aminoacridine inhibited deepoxidation with an I#D50#DR ≈ 1µM, a concentration far below that which inhibits the delta pH, ATP synthesis/hydrolysis or electron transport. The inhibitory effects of both compounds on PS II energy dissipation were exerted at 3 to 5 times lower concentration if added before as opposed to after a saturating level of deepoxidation. This result confirms the important role for deepoxidation in mediating PS II energy dissipation. Compared to 9-aminoacridine and in contrast to similar effects on the light induced activities, dibucaine exhibited significantly different inhibitory effects on ATPase activity and ATPase mediated PS II energy dissipation. However, we conclude from the more potent inhibition by 9-aminoacridine and the similar inhibitory patterns of all the light-induced activities that neither 9-aminoacridine nor dibucaine possess unique capacities to neutralize the light-mediated delta pH.

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EPR detection of phytophenoxyl radicals stabilized by zinc ions: evidence for the redox coupling of plant phenolics with ascorbate in the H₂O₂-peroxidase system

Yamasaki H, Grace SC

FEBS LETTERS 422 377 - 380 1998年02月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Chlorogenic acid (CGA; 3‐#Io#IR‐caffeoylquinic acid), a phenylpropanoid metabolite of plants, was oxidized by H#D2#DRO#D2#DR in the presence of horseradish peroxidase. The primary and secondary oxidized products both were free radicals which gave EPR multiline signals at g=2.0044 and 2.0042 in the presence of zinc as a spin stabilizing agent. The EPR kinetics showed that ascorbate functioned as a cooperative reductant by regenerating CGA from its corresponding radicals. These results provide evidence to support the idea that the ascorbate‐phenolic redox couple in conjunction with guaiacol peroxidase is an efficient H#D2#DRO#D2#DR scavenging mechanism in higher plants.

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Flavonoid-peroxidase reaction as a detoxification mechanism of plant cells against H₂O₂

Yamasaki H, Sakihama Y, Ikehara N

PLANT PHYSIOLOGY ( その他の出版社 ) 115 ( 4 ) 1405 - 1412 1997年12月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Recent studies have revealed that dietary flavonoids are potent radical scavengers, acting in a manner similar to ascorbate and [alpha]-tocopherol. However, it is still not clear whether flavonoids have a similar antioxidative function in plants. We examined the possibility that flavonoids could function as stress protectants in plant cells by scavenging H#D2#DRO#D2#DR. Two major flavonoids, quercetin and kaempferol glycosides, were isolated from leaves of the tropical tree #ISchefflera arboricola#IR Hayata. Both glycosides and aglycones of isolated flavonols were oxidized by H#D2#DRO#D2#DR in the presence of horse-radish peroxidase and/or in a soluble fraction of #IS. arboricola#IR leaf extract. The rates of oxidation were in the order quercetin > kaempferol > quercetin glycoside >> kaempferol glycoside. Judging from the effects of inhibitors such as KCN, #Ip#IR-chloromercuribenzoate, and 3-amino-1H-1,2,4-triazole, we conclude that guaiacol peroxidase in the soluble fraction catalyzes H#D2#DRO#D2#DR -dependent oxidation of flavonols. In the flavonol-guaiacol peroxidase reaction, ascorbate had the potential to regenerate flavonols by reducing the oxidized product. These results provide further evidence that the flavonoid-peroxidase reaction can function as a mechanism for H#D2#DRO#D2#DR scavenging in plants.

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A function of colour

Hideo Yamasaki

TRENDS IN PLANT SCIENCE ( その他の出版社 ) 2 ( 1 ) 7 - 8 1997年01月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

In leaves, flavonols have been proposed to act as a filter for ultraviolet light, and it has been suggested that anthocyanins act as screens to reduce the light intensity．High light intensity can induce reactive oxygen intermediates (ROI) production in chloroplasts and cause oxidative damage to cells. Flavonoids may thus protect leaves from light damage by indirect means such as H#D2#DRO#D2#DR scavenging. Also, even under favourable conditions, plant tissues sometimes show red or purple colouration caused by anthocyanins (e.g. in rapidly developing shoots). Since rapid cell wall elongation is accompanied by the active production of H#D2#DRO#D2#DR during lignification, this phenomenon may also be attributable to the antioxidative characteristics of anthocyanins. These results suggest that anthocyanins and flavonols may have a primary role in protecting against active oxygen species during growth and stress.

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Bleaching of the red anthocyanin induced by superoxide radical

Yamasaki H, Uefuji H, Sakihama Y

ARCHIVES OF BIOCHEMISTRY AND BIOPHYSICS ( その他の出版社 ) 322 ( 1 ) 183 - 186 1996年08月 [ 査読有り ]

掲載種別: 研究論文（その他学術会議資料等）

Red anthocyanin prepared from petals of #IHibiscus rosa-sinensis#IR L. was photobleached in the EDTA-riboflavin system. The rate of bleaching monitored at 565 nm depended on the light intensity and EDTA concentrations. Anaerobic conditions and/or addition of superoxide dismutase prevented the bleaching of anthocyanin, whereas mannitol and catalase did not, A similar bleaching was observed under dark conditions in the xanthine-xanthine oxidase system. The results indicate that anthocyanin is bleached by the nonenzymatic reaction with the superoxide radical and suggest that the pigment can function as an antioxidant. The antioxidative efficiency of cyanidin to superoxide was 10-fold higher than that of cyanidin-3-sophoroside as a #IHibiscus#IR anthocyanin.

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Leaf-goldenning induced by high-light in Ficus microcarpa L.f., a tropical fig

Yamasaki H, Heshiki R, Ikehara N

JOURNAL OF PLANT RESEARCH 108 171 - 180 1995年06月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

A novel yellow-leaved cultivar of tropical tree was characterized with morphological, histochemical and biochemical analysis. #IFicus microcarpa#IR L. f. cv. Golden Leaf shows characteristic golden (yellow) leaves as well as normal green leaves under the subtropical field condition. Except the appearance of the yellow leaves, morphological characteristics of Golden Leaf agreed to those of wild-type. The yellow leaves of Golden Leaf contained low amount of chlorophyll (8%) and carotenoid (26%), whereas flavonoid level was 5-fold higher than that of wild-type. TLC of hydrolysate of the methanol-extract showed the increase of two flavonols in the yellow leaves. Fluorescence from leaf transverse section indicated that those changes in pigment contents took place in mesophyll cells. Despite low content of photosynthetic pigments the yellow leaves involved the comparable amount of Rubisco subunits to wild-type. The reduced chlorophyll content of the yellow leaves was restored by shading them from high-light but the UV shading did not alter the pigment content. Those characteristics of the yellow leaves were not observed in the green leaves of Golden Leaf. Results suggest that Golden Leaf is attributed to a chloroplast mutant of #IF. microcarpa#IR that is sensitive to continuous high-light irradiation. The mechanism of the leaf-goldenning (yellowing) is discussed in relation to high-light stress and to leaf-senescence.

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熱帯植物ガジュマルFicus microcarpa L. f. の生葉中スーパーオキシドジスムターゼ（SOD）

平敷りか, 池原規勝, 山崎秀雄

沖縄生物学会誌 33 49 - 54 1995年03月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Superoxide dismutase (SOD) activity of leaf-extract was investigated in the tropical fig tree #IFicus microcarpa#IR L. f. The leaf-extract contained a large amount of components that showed SOD-like activity on polyacrylamide gel after electrophoresis. Characteristics of their absorption spectrum agreed with those of flavonoids. Improving the sample preparation with polyvinyl polypyrrolidone treatment and gel filtration chromatography, we determined the total SOD activity of the leaf-extract to be 364 units/mg protein and identified the major SOD isozymes to be Fe-SOD and Cu/Zn-SOD. Significance of SODs involved in leaves was discussed in relation to environmental stress on tropical plants.

ヤドリフカノキSchefflera arboricola Hayata の生葉中フラボノール

崎浜靖子, 池原規勝, 山崎秀雄

沖縄生物学会誌 33 43 - 48 1995年03月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Two flavonol gylcosides were isolated from the fresh leaves of the tropical tree #ISchefflera arboricola#IR Hayata. The major flavonol glycosides of #IS. arboricola#IR were identified to be quercetin and kaempferol glycosides on the basis of thin layer chromatogram and absorption spectral data. The absorption coefficients of these glycosides were estimated to be 14.7 mM#U-1#URcm#U-1#UR at A#D358#DR (the quercetin glycoside) and 16.0 mM#U-1#URcm#U-1#UR at A#D346#DR (the kaempferol glycoside).

Characteristic Changes in Relaxation Times of Water Protons in Vigna radiata Seedlings Exposed to Temperature Stress

Iwaya-Inoue M, Yoshimura K, Yamasaki H, Kaku S

Plant & Cell Physiology 34 705 - 711 1993年07月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

Water protons in hypocotyl tissues from etiolated seedlings of #IVigna radiata#IR that were exposed to temperature stress showed characteristic relaxation behaviors for #U1#URH#D-#DRNMR. Cold stress treatment (0°C) caused gradual prolongation of NMR relaxation times (T#D1#DR). After exposure of tissues to cold stress for 24 h, T#D1#DR returned to the initial value as a result of subsequent incubation at normal temperature (20°C). By contrast, heat stress treatment (40°C) induced a time-dependent decrease in T#D1#DR, which did not return completely to the initial value upon subsequent incubation at 20°C after exposure to heat stress for 4 h. We examined changes in various physical factors that influence the response of T#D1#DR to temperature stress, namely, water content and the concentrations of protein, diamagnetic (K#U+#UR, Na#U+#UR, Ca#D2#DR#U+#UR and Mg#D2#DR#U+#UR) and paramagnetic (Mn#D2#DR+#U #URand Fe#D2#DR#U+#UR) ions in the tissues. From the relationships between T#D1#DR and these factors in vitro, we could not interpret the responses of T1 to the temperature stress only in terms of a change in water content. A synergistic effect of an Mn#D2#DR#U+#UR -protein complex and pH might be essential for the mechanism of changes in T#D1#DR that are due to cold stress. The influence of heat stress on structural water in tissues is discussed in terms of water-protein interactions.

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Interaction of amino acid-substituted partial extension peptides of adrenodoxin precursor with artificial membranes and isolated mitochondria

Aoyagi H, Waki K, Kato T, Lee S, Yamasaki H, Furuya S

Peptide Research 5 91 - 96 1992年03月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

The N-terminal fragment Met-Ala-Ala-Arg-Leu-Leu-Arg-Val-Ala-Ser-Ala-Ala-Leu-Gly (PA1-14) of the adrenodoxin precursor was previously found to inhibit the import of the precursor into mitochondria. In order to obtain further information on the structure-function relationship, five analogs of PA1-14 ([Leu1]PA1-14 (1), [Leu1,Ala10]PA1-14 (2), [Leu1,Ser4]PA1-14 (3), [Leu1,Arg11]PA1-14 (4) and [Leu1,Ser7,Arg10]PA1-14 (5) were synthesized. The CD study showed that PA1-14 and all analogs were random in an aqueous solution and formed an alpha-helical structure in the solution containing acidic liposomes. Peptides 1 and 2 were found to cause dye leakage from lipid vesicles more strongly than other analogs and PA1-14. All analogs completely inhibited the import of the precursor into mitochondria at a concentration of 30 microM. However, 1 and 2 destroyed the mitochondrial membrane potential. These results indicate that an increase in hydrophobicity by replacement of the Met and Ser residues by Leu and Ala, respectively, participates in the perturbation of the membranes. Furthermore, the requirement for the number and position of the Arg residue was found to be not very strict, although its presence in the extension peptide is essential for the precursor to import into mitochondria.

Inhibition of the light-induced H⁺ release from uncoupled thylakoid membranes by N-ethylmaleimide

Yamasaki H, Okayama S, Shibata M, Nishimura M

Biochemical and Biophysical Research Communications 182 1277 - 1281 1992年02月

掲載種別: 研究論文（学術雑誌）

The light-induced H#U+#UR release from thylakoids, which can be observed under completely uncoupled conditions, was inhibited by the SH reagent #IN#IR-ethylmaleimide (NEM) and its analogs, while the conventional H#U+#UR uptake and electron transfer were not affected. The half-inhibiting concentration of NEM for the H#U+#UR release was 10 mM and 4 mM in thylakoids in the presence of nigericin and in CF#D1#DR-depleted thylakoids, respectively. The inhibitory effect increased with the increase in hydrophobicity of the NEM analogs: #IN#IR-methylmaleimide <#IN#IR-ethylmaleimide <#IN#IR-phenylmaleimide. It is suggested that SH groups in hydrophobic interior within the membrane are essential to the release of protons.

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Induction of the H⁺ Release from Thylakoid Membranes by Illumination in the Presence of Protonophores at High Concentrations

Hideo Yamasaki, Shigeki Furuya, Akira Kawamura, Akio Ito, Shigeki Okayama, Mitsuo Nishimura

Plant & Cell Physiology 32 925 - 934 1991年10月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

The generally observed light-induced uptake of protons into the thylakoid lumen is diminished by adding protonophores. Instead of the H#U+#UR uptake, the release of protons was observed during illumination in the presence of various protonophores at high concentrations, namely, 1 μM nigericin, 10 μM carbonylcyanide m-chlorophenylhydrazone or 30 μM gramicidin. An uncoupler, NH#D4#DRC1 (4 mM), and a detergent, Triton X-100 (0.02%), also induced the H#U+#UR release but a K#U+#UR ionophore, valinomycin, did not. The amount of H#U+#UR released reached about 100 nmol H#U+#UR (mg Chl)−1 at pH 7.5 under continuous illumination. The rate of the H#U+#UR release was similar to that of the conventional H#U+#UR uptake but its dark relaxation was much slower than that of the H#U+#UR uptake. We compared the H#U+#UR release in protonophore-added thylakoids with the previously reported H#U+#UR release in coupling factor 1 (CF#D1#DR)-depleted thylakoids. The H#U+#UR release in thylakoids with nigericin showed similar characteristics to that in CF#D1#DR-depleted thylakoids in terms of their responses to pH, phenazine methosulfate and light intensity. Both types of H#U+#UR release were relatively insensitive to DCMU and were stimulated somewhat by DCMU at low concentrations (around 200 nM). Nigericin did not inhibit the superoxide dismutase activity of the membranes. These results indicate that the H#U+#UR release in protonophore-added thylakoids and that in CF#D1#DR depleted thylakoids involve the same mechanism and that water-derived protons from PS II that result from an impairment of the activity of superoxide dismutase, as previously proposed, are not involved. Judging from the rate of electron flow and the lumenal acidification under the illumination, we conclude that the H#U+#UR release is a light-dependent scalar process which can be observed in thylakoid membranes with high H+ permeability. The H#U+#UR release of this type was not observed in mitochondria from rat liver or in chromatophores from Rhodobacter sphaeroides.

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Non-Vectorial Light-Induced H⁺ Release from CF₁-Depleted Thylakoid Membranes. Absence of Correlation to Stoichiometric H⁺ Production and Consumption Coupled to Electron Transfer

Hideo Yamasaki, Mitsuo Nishimura

Plant & Cell Physiology 29 1081 - 1084 1988年09月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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