| Budget Amount *help |
¥3,720,000 (Direct Cost: ¥3,300,000、Indirect Cost: ¥420,000)
Fiscal Year 2007: ¥1,820,000 (Direct Cost: ¥1,400,000、Indirect Cost: ¥420,000)
Fiscal Year 2006: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Research Abstract |
Environmental stresses such as heat, drought and UV-B commonly lead to oxidative damage in leaf cells due to enhanced production of reactive oxygen species in chloroplasts. Recently, lipid peroxide-derived aldehydes have been recognized to mediate cell injury, but their metabolism and toxicology in plants are poorly investigated. In this study we investigated (i) the metabolism of lipid peroxide-derived aldehydes in the chloroplast and (ii) the physiological roles of those aldehydes in the plant responses to environmental stresses. We have obtained the following results : (1) Various species of aldehydes inactivated the CO2-fixation in isolated chloroplasts in vitro. The toxicity was higher for 2-alkenals than n-alkanals. Acrolein and 4-hydroxynonenal showed the greatest toxicity. Several enzymes in the Calvin cycle by 2-alkenals, but the thylakoid electron transport chain was much less affected. (2) Glutathione supplemented to chloroplasts retarded the aldehyde-induced loss of CO_2-fi
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xation, but ascorbate did not, showing the specific role of glutathione to scavenge aldehydes. Aldehydes were extracted from distinct compartments in the chloroplast, derivatized with 2,4-dinitrophenylhydrazine and determined with HPLC. Lipoxygenase pathway-dependent C6 aldehydes were major components found in envelopes and stroma. Thylakoids contained greater variety of aldehydes, including highly toxic 2-alkenals and 4-hydroxy-2-alkenals, suggesting non-enzymatic(reactive oxygen species-mediated)production of aldehydes in thylakoids. (3) Aldehyde composition in the linolenic acid-deficient Arabidopsis mutant was compared with that in wild type. Acrolein, propionaldehyde malondialdehyde and 2E-pentenal were derived from linolenic acid. (4) When Arabidopsis plants were heat stressed or tobacco leaves were strongly illuminated, aldehyde-modification of several chloroplast enzymes in them were increased. One of the malondialdehyde-modified proteins was OEC33 protein, suggesting the production of malondialdehyde in the lumen. Thus heat- or light-stress induces the production highly toxic aldehydes from lipid peroxides in chloroplasts, leading to inactivation of the Calvin cycle. Glutathione is a critically important detoxicant against aldehydes. Less
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