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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. [ABSTRACT FROM AUTHOR]

Rice (Oryza sativa L.) seeds were soaked for 18 h in distilled water in the absence (–PBZ) or presence (+PBZ, a triazole) of 100 mg l−1 paclobutrazol and then air dried. These air-dried seeds were germinated in the dark and then cultivated in a Phytotron. Twelve-day-old–PBZ and +PBZ seedlings were treated or not with CdCl2. Cd toxicity was judged by the decrease in biomass production, decrease in chlorophyll and protein content, increase in NH4+ content and induction of oxidative stress. The results indicated that PBZ applied to seeds was able to protect rice seedlings from Cd toxicity. On treatment with CdCl2, the abscisic acid (ABA) content increased in +PBZ leaves, but not in –PBZ leaves. The decrease in the transpiration rate of –PBZ seedlings by CdCl2 was less than that of +PBZ seedlings. Exogenous application of the ABA biosynthesis inhibitor, fluridone (Flu), reduced ABA accumulation, increased the transpiration rate and Cd content, and decreased the Cd tolerance of +PBZ seedlings. The effects of Flu on the Cd toxicity, transpiration rate and Cd content were reversed by the application of ABA. It seems that the PBZ-induced Cd tolerance of rice seedlings is mediated through an accumulation of ABA. [ABSTRACT FROM AUTHOR]