Nitric oxide donor CySNO promotes plant growth and alleviates drought stress in soybean via antioxidant defense and transcriptional regulation

Drought, or consistent shortage of water supply, can have a variety of detrimental effects on the physiology of soybean [Glycine max (L.) Merr.] such as reduced growth, wilting, and abnormal cellular biochemistry. Nitric oxide (NO) is a crucial signaling molecule that regulates a wide range of physiological processes in plants. In this study, we investigated the role of NO in regulating soybean plant responses to drought stress. Exogenous application of different concentrations of the NO donor CySNO significantly promoted plant growth and development under both normal and drought conditions induced by withholding water for eight days. CySNO, when used at a concentration of 0.1 mM, significantly increased plant height, chlorophyll content, relative water content, and fresh and dry weight of soybean plants grown under normal and drought stress conditions. CySNO application had a similar effect on the below-ground parts of the plants, significantly increasing the length, surface area, volume, tips, and forks of roots, along with an increase in the number, size, and weight of nodules. Further antioxidant tests indicated that CySNO protected against drought-induced oxidative damage by activating the antioxidant machinery, as we recorded significantly lower electrolyte leakage and superoxide anion production with a concomitant increase in the concentration of reduced glutathione and activity of the catalase enzymes. Further analysis indicated that NO provided protection against drought stress by mediating the expression of related marker genes. A significant increase in the expression of soybean MYB84, WRKY12, and DREB1 was observed following CySNO application under drought stress conditions. Furthermore, the CySNO application resulted in a general decrease in the expression of GmNOX1 but an increase in the expression of GmNR which are nitric oxide-related marker genes. These results indicate the significant utility of nitric oxide in protecting crop plants against the negative effects of drought stress.