Nitric oxide induced by hydrogen peroxide mediates abscisic acid-induced activation of the mitogen-activated protein kinase cascade involved in antioxidant defense in maize leaves

The role of nitric oxide (NO) and the relationship between NO, hydrogen peroxide (H2O2) and mitogen-activated protein kinase (MAPK) in abscisic acid (ABA)-induced antioxidant defense in leaves of maize (Zea mays) plants were investigated. Both ABA and H2O2 induced increases in the generation of NO in mesophyll cells of maize leaves, and H2O2 was required for the ABA-induced generation of NO. Pretreatment with NO scavenger and nitric oxide synthase (NOS) inhibitor substantially reduced the ABA-induced production of NO, and partly blocked the activation of a 46 kDa MAPK and the expression and the activities of several antioxidant enzymes induced by ABA. Treatment with the NO donor sodium nitroprusside (SNP) also induced the activation of the MAPK, and enhanced the antioxidant defense systems. Conversely, SNP treatment did not induce the production of H2O2, and pretreatments with NO scavenger and NOS inhibitor did not affect ABA-induced H2O2 production. Our results suggest that ABA-induced H2O2 production mediates NO generation, which, in turn, activates MAPK and results in the upregulation in the expression and the activities of antioxidant enzymes in ABA signaling.