Role of Exogenous Application of Auxin on Antioxidant Enzyme Activities in Rice Under Salt Stress

Phytohormones such as auxin are known to be involved in alleviating the detrimental effects of salinity by modulating the activity of enzymatic antioxidants and improving antioxidant system, which help in sustaining plant growth. The present study envisaged revealing the role of exogenous application of indole-3-acetic acid (IAA) in improving defense mechanisms in two genotypes (FL485 and IR29, salt tolerant and salt susceptible, respectively) of rice against NaCl stress. The results showed that salt stress led to an increase in the ascorbic acid (AsA) content of the tolerant cultivar suggesting that oxidative defense system was very operative in this cultivar. Exogenous application of IAA further increased the activities of AsA and ascorbate oxidase in the salt stressed FL485, whereas such effect was not observed in the susceptible cultivar (IR29). IAA was found to be more effective in enhancing the activities of α-tocopherol in salt stressed rice plants with more efficiently in the salt tolerant cultivar. In addition, IAA markedly increased hydrogen peroxide (H2O2) concentration in both cultivars as compared to untreated plants. Lipid peroxidation levels of both cultivars under salt treatment showed no change with foliar applications of IAA.