A Role of Hydrogen Peroxide in the Metabolism of Phenolics in Mesophyll Cells of Vicia faba L.

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3,4-Dihydroxyphenylalanine (DOPA) and flavonols were oxidized by externally added H_2O_2 and the oxidation was inhibited by KCN (5 mM) in protoplasts of mesophyll cells of Vicia faba. DOPA was also oxidized by light in the presence of methyl viologen (MV), which can stimulate formation of O_2^- and H_2O_2 in vivo, both in the light and in the dark, in isolated mesophyll cells. The light-dependent oxidation of DOPA was partially inhibited by removal of MV or addition of NaN_3 (10 mM), an inhibitor of peroxidases, suggesting the participation of H_2O_2, generated in vivo, in the oxidation. The effects of light on the level of flavonols in isolated mesophyll cells were rather complicated. Level of flavonols increased by about 10-20% in the dark in the presence of MV. The levels in the light in the presence of MV were lower than those in the dark. The data suggest that flavonols can be oxidized by O_2^- and/or H_2O_2 generated in cells. Based on the data, the role of H_2O_2 in the metabolism of phenolics in mesophyll cells is discussed.
日本植物生理学会の論文