Hydrogen peroxide is required for abscisic acid-induced NH4+ accumulation in rice leaves

The role of H2O2 in abscisic acid (ABA)-induced NH4+ accumulation in rice leaves was investigated. ABA treatment resulted in an accumulation of NH4+ in 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 seem to be the enzymes responsible for the accumulation of NH4+ in ABA-treated rice leaves. Dimethylthiourea (DMTU), a chemical trap for H2O2, was observed to be effective in inhibiting ABA-induced accumulation of NH4+ in rice leaves. Inhibitors of NADPH oxidase, diphenyleneiodonium chloride (DPI) and imidazole (IMD), and nitric oxide donor (N-tert-butyl-α-phenylnitrone, PBN), which have previously been shown to prevent ABA-induced increase in H2O2 contents in rice leaves, inhibited ABA-induced increase in the content of NH4+. Similarly, the changes of enzymes responsible for NH4+ accumulation induced by ABA were observed to be inhibited by DMTU, DPI, IMD, and PBN. Exogenous application of H2O2 was found to increase NH4+ content, decrease GS activity, and increase protease and PAL-specific activities in rice leaves. Our results suggest that H2O2 is involved in ABA-induced NH4+ accumulation in rice leaves.