NaCl-induced heme oxygenase in roots of rice seedlings is mediated through hydrogen peroxide

Recent findings have suggested that H2O2 is an important signaling molecule for regulating plant responses to abiotic stress. H2O2 plays a critical role in NaCl stress. Heme oxygenase (HO) is known to play a protective role against oxidative stress. In this study, we examined the possible involvement of H2O2 in regulating NaCl-promoted HO activity in rice roots. Treatment with NaCl increased HO activity and H2O2 content in rice roots. As well, NaCl could induce OsHO1 mRNA expression. NaCl (150 mM) and NaNO3 (150 mM) were equally effective in inducing HO activity. However, mannitol at the concentration (276 mM) iso-osmotic with 150 mM NaCl had no effect on HO activity. NaCl-promoted HO activity and OsHO1 expression in rice roots was reduced by NADPH oxidase inhibitors i.e. dipehnyleneiodonium and imidazole. Moreover, exogenous application of H2O2 enhanced the activity of HO and the mRNA level of OsHO1. Our data suggest that H2O2 production plays a positive role in NaCl- induced HO activity by enhancing its mRNA level in rice roots.