Role of sulfur in pyrroline-5-carboxylate synthase (P5CS) gene expression, proline accumulation, and antioxidant enzyme activity of wheat under water deficit conditions

Sulfur (S) plays a crucial role in plant growth and development and serves numerous biological functions in plants. To investigate the role of sulfur in drought stress protection, two experiments were conducted under greenhouse and growth ‎chamber conditions in 2021 Also, to evaluate ‎the influence of foliar application of sulfur on the expression of Pyrroline-5-carboxylate synthase, )P5CS)‎, proline concentration, and antioxidant enzyme activities‎, the plants of wheat Sardari and Ivan cultivars were exposed to two levels of water regimes. Plants under well-watered irrigation and drought stress conditions showed different P5CS expression levels and accumulated proline. The P5CS expression level in the Ivan cultivar was significantly increased by foliar application of S, while the same application had no significant effect on P5CS expression in the Sardari cultivar. Plants exposed to drought stress and foliar-sprayed with S showed a higher proline accumulation The activities of antioxidant enzymes, including peroxidase (POD), catalase, ‎glutathione peroxidase (GP), and glutathione reductase , were increased by 134 %, 40.4 %,  45.4 %, and 77.4 %, respectively, in plants exposed to drought stress. POD and GR ‎were ‎significantly increased‎ by 19.6 % and 51.8 %, respectively, ‎due to S application. Drought-induced plants that were foliar-sprayed with S exhibited a significantly lower rate of ion leakage and higher leaf-relative water content than those of control plants. Based on the results of the present research, it was revealed that S substantially enhances the expression rate of the P5CS gene, leading to proline accumulation, and activates defense reactions in water-stressed wheat.