Study of antioxidant defense genes expression in rice (Oryza sativa L.) cultivars in response to drought stress

Drought stress is one of the important factors that restrict crop production in the world. This studywas conducted to investigate defense gene expression in response to drought stress, and also to evaluate the drought tolerance and its mechanism in rice cultivars based on randomized complete block design in two separate environments (drought stress and non-stress). The rice cultivars used included two commercial cultivars, i.e., Ahlemi-Tarom, Sepidrood, and three promising lines of fourth mutant generation called 4, 94 and 95 tested on the research farm at Gonbad Kavous University in 2018. For carrying out the drought stress-related experiment, irrigation was completely cut off 40 days after the transplantation (a stage with maximum tillering) until the end of the growth period. In seeding stage, each plant leaf was separately sampled in each block (under the stress and non-stress conditions). TBARM, superoxide andhydrogen peroxide contents and oxidative-stress related gene expression including superoxide dismutase, catalase, ascorbate peroxidase and glutathione peroxidase were measured. Results indicated that the drought-tolerant mutant lines had lower TBARM, superoxide andhydrogen peroxide contents compared to the studied cultivars. The mutant lines 94, 4 and 95 and Ahlemi-Tarom and Sepidrood had the highest to lowest levels of gene expression and yield in drought stress condition, sequentially. Accordingly, there was a complete correlation between the decreases in TBARM, superoxide andhydrogen peroxide and an increase in the level of gene expression. Mutant 94 had the highest yield and probably a suitable genetic potential in relation to drought tolerance. Therefore, the mentioned mutant is recommended for carrying out further studies.