Evaluation of proline content and enzymatic defense mechanism in response to drought stress in rice

To study proline content and enzyme defense system in response to drought stress in rice, a randomized complete block design with three replications was conducted in two separate environments (drought stress and non-stress). The rice cultivars used included two commercial cultivars, i.e., Ahlemi Tarom (low-yield and drought tolerant) and Sepidrood (high-yield and sensitive to drought) and three promising lines of fourth generation mutants (high-yield and drought tolerant), namely, No. 4, 94 and 95 tested on a research farm at Gonbad Kavous University in the 2018 crop year. Plant roots were separately sampled in each block at the reproductive stage. The proline content and activity of the enzymes involved in the defense system, including superoxide dismutase, catalase, ascorbate peroxidase and glutathione peroxidase were measured by extracting the enzymes from each root sample. Results indicated that the drought-tolerant mutant lines had lower proline contents. The mutant lines and Ahlemi Tarom and Sepidrood cultivars had the highest to lowest levels of defense enzymes in the oxidative pathway, respectively. Correlation was found between the decrease in proline contents and increase in levels of defense enzymes of the oxidative stress pathway. The mutants possessed reliable genetic storages for tolerance to drought stress and had a significant superiority over the commercial cultivars at P≤0.05.