Exogenous ascorbic acid improved tolerance in maize (Zea mays L.) by increasing antioxidant activity under salinity stress

Salinity causes additional manufacture of reactive oxygen species (ROS) in plants, and ascorbate plays important role in maintaining of ROS scavenging antioxidant enzymes. In this study, the role of exogenous ascorbic acid (AsA) was examined on growth, chlorophyll and oxidative stress related enzymatic and non-enzymatic antioxidants in three maize hybrids under NaCl mediated salt stress. In hydroponic culture, AsA was applied at 0.5 and 1.0 mM with and without 12 dSm-1 NaCl, each treatment comprised two independent experiments with three replications. After four weeks, plants were harvested for recording growth and biochemical parameters. Root length, shoot length, dry matter accumulation, chlorophyll (Chl a and Chl b), AsA, reduced glutathione (GSH) and activity of ascorbate peroxidase (APX) were markedly reduced by salt stress, while H2O2 and Malondialdehyde (MDA) content were increased significantly. Exogenous application of AsA in saline treatment significantly improved root length, shoot length, dry matter accumulation, chlorophyll, AsA, GSH and APX activity while it decreased the contents of oxidized glutathione (GSSG) significantly in all the hybrids. However, content of dehydroascorbate (DHA) was reduced only in 900M Gold and PS-999. On the other hand, activity of monodehydroascorbatereductase (MDHAR) was increased only in Super gold and 900M gold (by 0.5 mM AsA) while dehydroascorbatereductase (DHAR) activity increased in Super gold only. The results of the present study evidently concluded that exogenous AsA application responded differentially in maize genotypes under salt stress and mitigated the negative effects of salinity.   Key words: Maize, salinity, reactive oxygen species, antioxidant, ascorbic acid.