The participation of hydrogen peroxide in methyl jasmonate-induced NH4+ accumulation in rice leaves

Ammonium is a central intermediate in the nitrogen metabolism of plants. We have previously shown that methyl. jasmonate (MJ) not only increases the content of H2O2, but also causes NH4+ accumulation in rice leaves. More recently, H2O2 is thought to constitute a general signal molecule participating in the recognition of and the response to stress factors. In this study, we examined the rote of H2O2 as a link between MJ and subsequent NH4+ accumulation in detached rice leaves. MJ treatment resulted in an accumulation of NH4+ in detached rice leaves, which was preceded by a decrease in the activity of glutamine synthetase (GS) and an increase in the specific activities of protease and phenylalanine ammonia-lyase (PAL). GS, PAL, and protease appear to be the enzymes responsible for the accumulation of NH in MJ-treated detached rice leaves. Dimethylthiourea (DMTU), a chemical trap for H2O2, was observed to be effective in inhibiting MJ-induced NH4+ accumulation in detached rice leaves. Scavengers of free radicals (sodium benzoate, SB, and glutathione, GSH), nitric oxide donor (N-tert-butyl-alpha-phenylnitrone, PBN), the inhibitors of NADPH oxidase (diphenyleneiodonium chloride, DPI, and imidazole, IMD), and inhibitors of phosphatidylinositol 3-kinase (wortmannin, WM, and LY 294002, LY), which have previously been shown to prevent MJ-induced H2O2 production in detached rice leaves, inhibited MJ-induced NH4+ accumulation. Similarly, changes in enzymes responsible for NH4+ accumulation induced by MJ were observed to be inhibited by DMTU, SB, GSH, PBN DPI, IMD, WM, or LY. Seedlings of rice 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. Ethylene action inhibitor, silver thiosulfate, was observed to inhibit MJ- and abscisic acid-induced accumulation of NH4+ and changes in enzymes responsible for NH4+ accumulation in detached rice leaves, suggesting that the action of MJ and ABA is ethylene dependent. (C) 2006 Elsevier GrnbH. All rights reserved.