Hydrogen peroxide is involved in methyl jasmonate-induced senescence of rice leaves

The role of H2O2 in the senescence of detached rice leaves induced by methyl jasmonate (MJ) was investigated. MJ treatment resulted in H2O2 production in detached rice leaves, which was prior to the occurrence of leaf senescence. Dimethylthiourea, a chemical trap of H2O2, was observed to be effective in inhibiting MJ-induced senescence and MJ-increased malondialdehyde (MDA) content in detached rice leaves. Diphenyleneiodonium chloride (DPI) and imidazole (IMD), inhibitors of NADPH oxidase, prevented MJ-induced H2O2 production, suggesting that NADPH oxidase is a H2O2-generating enzyme in MJ-treated detached rice leaves. DPI and IMD also inhibited MJ-promoted senescence and MJ-increased MDA content in detached rice leaves. Phosphatidylinositol 3-kinase inhibitors wortmannin (WM) or LY 294002 (LY) inhibited MJ-induced H2O2 production and senescence of detached rice leaves. Exogenous H2O2 reversed the inhibitory effect of WM or LY. In terms of leaf senescence, it was observed that rice seedlings of cultivar Taichung Native 1 (TN1) are jasmonic acid (JA)-sensitive and those of cultivar Tainung 67 (TNG67) are JA-insensitive. On treatment with JA, H2O2 accumulated in the leaves of TN1 seedlings but not in the leaves of TNG67. Evidence was also provided to show that MJ-induced H2O2 production in detached rice leaves is abscisic acid (ABA)-independent. Ethylene action inhibitor, silver thiosulfate, was observed to inhibit MJ- and ABA-induced H2O2 production and senescence of detached rice leaves, suggesting that the action of MJ and ABA is ethylene-dependent.