Selection of promising salt tolerant rice mutants derived from cultivar 'Drew' and their antioxidant enzymes activity under salt stress

Four salt tolerant rice mutant lines were identified by screening 400 M-2 families derived from the tropical japonica cultivar 'Drew' after Gamma irradiation. The selected lines had significantly higher number of filled grains, lower grain sterility, and higher grain yield as compared with their parent 'Drew' when grown under the NaCl stress of 10dSm(-1) EC. The mutant lines gave 8-9 times as much grain yield as the parent under salt stress and yielded 45-60% of the grain yield of the parent without salt stress. The activity of anti-oxidant enzymes was determined in the salt tolerant lines as well as their parent under 200mM NaCl stress. Salt stress enhanced the activities of the ascorbate peroxidase (APX), glutathione reductase (GR), and superoxide dismulase (SOD) in the selected mutants; whereas, there was a decrease in the catalase (CAT) activity. The induction of APX, GR, and SOD was higher in the rice mutants indicating that they have the ability to up-regulate their antioxidative system in order to cope with the salt-induced stress. Increased antioxidant enzyme activity was one of the NaCl-stress tolerance mechanisms of the salt tolerant rice mutants obtained in this study.