Involvement of abscisic acid and H2O2 in antioxidant enzyme activities mediated by nitric oxide synthase-like activity in maize

Abstract

In recent years, nitric oxide (NO) has emerged as an important endogenous plant signalling molecule that mediates many developmental and physiological processes. NO regulates the activity of antioxidant enzymes in response to droughtinduced stress by controlling the expression of the genes that encode these enzymes. Antioxidant enzymes function in scavenging reactive oxygen species like superoxide ion (O2 -) and hydrogen peroxide (H2O2) that are generated in response to drought-induced stress and other abiotic stresses. Abscisic acid, a phytohormone that acts as a stress-related hormone in plants, also stimulates production of H2O2, thus further triggering the antioxidant enzyme activity in order to scavenge the excess H2O2. Accumulated data indicate that NO interacts with reactive oxygen species, notably hydrogen peroxide and superoxide. This study was aimed at clarifying the role of NO derived from nitric oxide synthase-like (NOS-like) enzymatic activity in scavenging of H2O2 and to establish if this is dependent or independent of ABA signaling. This was achieved by using Nω-Nitro-L-Arginine methyl ester (L-NAME), an inhibitor of NOS to control the amount of NO in maize tissue. The study investigated the effect of L-NAME on the accumulation of superoxide, which is scavenged by superoxide dismutase. Furthermore, the study determined the role of NOS-like activity in ABA-mediated production of H2O2. Lastly, the effect of L-NAME on H2O2 accumulation and antioxidant enzyme activity was also investigated. Application of L-NAME altered the enzymatic activity of superoxide dismutase, ascorbate peroxidase and catalase. These changes in enzymatic activity were coupled with altered levels of O2 - and H2O2 in leaves and roots. Treatments with ABA in combination with L-NAME resulted in reversal of H2O2 content to basal levels. These results suggest that nitric oxide, produced by nitric oxide synthase-like activity, is important in regulation of antioxidant enzyme activity and cross-talks with ABA.