Effect of oxidative stress caused by hydrogen peroxide on senescence of rice leaves

Lipid peroxidation is considered to be an important mechanism of leaf senescence. The peroxidation of lipids can be initiated by free radicals. H 2 O 2 itself is active oxygen species and can react with superoxide radicals to form more reactive hydroxyl radicals in the presence of trace amounts of Fe or Cu. Thus, it is of interest to investigate the relationship between lipid peroxidation and H 2 O 2 -promoted senescence in detached rice leaves. H 2 O 2 effectively promoted senescence and increased malondialdehyde levels in detached rice leaves under both light and dark conditions. However, the promotion of senescence by the exogenous level of H 2 O 2 is not associated with an increase in its endogenous level. Thiourea (a scavenger of hydroxyl radical) almost completely prevented H 2 O 2 promoted senescence and the H 2 O 2 -induced decrease in superoxide dismutase and ascorbate peroxidase activities in light and darkness. It seems that promoted senescence by H 2 O 2 in detached rice leaves is associated free radicalinduced lipid peroxidation.