Heme oxygenase is involved in H2O2-induced lateral root formation in apocynin-treated rice

Apocynin is a natural organic compound structurally related to vanillin. We demonstrated that hydrogen peroxide and heme oxygenase participated in apocynin-induced lateral root formation in rice. Apocynin, also known as acetovanillone, is a natural organic compound structurally related to vanillin. Information concerning the effect of apocynin on plants is limited. In this study, we examined the effect of apocynin on lateral root (LR) formation in rice. Treatment with apocynin induced LR formation and increased H2O2 production, but had no effect on nitric oxide production. Diphenyleneiodonium chloride, an inhibitor of H2O2 generating NADPH oxidase, was effective in reducing apocynin-induced H2O2 production and LR formation. Apocynin treatment also increased superoxide dismutase activity and decreased catalase activity. H2O2 application was able to increase the number of LRs. Moreover, H2O2 production caused by H2O2 and apocynin was localized in the root area corresponding to the LR emergence. Treatment with H2O2 and apocynin also increased heme oxygenase (HO) activity and induced OsHO1 mRNA expression. Lateral root formation and HO activity induced by H2O2 and apocynin were reduced by Zn protoporphyrin IX (the specific inhibitor of HO). Our data suggest that both H2O2 and HO are required for apocynin-induced LR formation in rice.