研究者詳細 - 山崎　秀雄

論文 - 山崎　秀雄

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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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