Abscisic acid is an inducer of hydrogen peroxide production in leaves of rice seedlings grown under potassium deficiency

Potassium (K) is essential for many physiological processes. K deficiency is known to increase the production of reactive oxygen species including H2O2 in bean and Arabidopsis. Accumulating evidence indicates that the action of abscisic acid (ABA) is associated with H2O2 production. In this study, we examined the possible involvement of ABA in K deficiency-induced H2O2 production in the leaves of rice seedlings. The histochemical and colorimetrical methods were used to determine H2O2 production in the leaves of rice seedlings. It was observed that K deficiency resulted in an increase in H2O2 content in the leaves. H2O2 production in rice leaves induced by K deficiency was blocked by diphenyleneiodonium chloride and imidazole, NADPH oxidase inhibitors. In this study, ABA content was judged by the expression of OsRab16A (an ABA responsive gene) or was determined by the enzyme-linked immunosorbent assay. K deficiency also resulted in an increase in ABA content in rice leaves. However, ABA accumulation in the leaves under K deficiency is not induced by H2O2. Tungstate (Tu), an ABA biosynthesis inhibitor, was effective in reducing K deficiency-increased ABA content, as well as K deficiency-induced H2O2 production, indicating that K deficiency-induced H2O2 in rice leaves is mediated through ABA. This conclusion is supported further by the observation that exogenous ABA treatment increased H2O2 content in the leaves of rice seedlings grown under K-sufficient conditions.