Hydrogen peroxide alleviates salinity-induced damage through enhancing proline accumulation in wheat seedlings.

NADPH oxidase-mediated HO maintains proline concentration under NaCl stress through regulating its biosynthesis and degradation, conferring salt tolerance to wheat plants. Considerable attention has been paid to the specific role of hydrogen peroxide (HO) in plant stress responses. Here, using microscopic, pharmacological and biochemical approaches, we explored HO production and its roles in redox control under salt stress in wheat roots. Exogenous HO pretreatment decreased salt-induced lipid peroxidation, while increased proline content in wheat roots. Salt stress led to a transient increase in NADPH oxidase activity accompanied by accumulation of HO and proline in roots. The elevated proline accumulation in the presence of NaCl was significantly suppressed by diphenyleneiodonium, an inhibitor of NADPH oxidase, and dimethylthiourea, a scavenger of HO. The rate-limiting enzyme involved in proline biosynthesis, Δ-pyrroline-5-carboxylate synthetase (P5CS), was induced by NaCl, whereas the house-keeping enzyme in proline degradation, proline dehydrogenase (ProDH), was inhibited. After 6 h, the activity of P5CS increased by 1.5-fold, whereas ProDH decreased by 13.9%. The levels of these enzymes, however, were restored by NADPH oxidase inhibitor or HO scavenger. After treatment with HO, the effects of diphenyleneiodonium and or dimethylthiourea on proline content and activities of P5CS and ProDH were reversed. These results suggested that NADPH oxidase-mediated HO alleviates oxidative damage induced by salt stress through regulating proline biosynthesis and degradation.