Effects of exogenous abscisic acid on the content of osmotic adjustment substances and antioxidant enzyme activity in the leaves of Reaumuria soongorica

An outdoor experiment was conducted to investigate the effects of exogenous abscisic acid (ABA) on the contents of osmotic adjustment substances and antioxidant enzymatic activity on the leaves of the perennial, Reaumuria soongorica. Concentrations of abscisic acid (ABA) at 2, 4, 6, and 8 mg·L^–1 were utilized, all under natural field environmental drought conditions. The results revealed that the content of soluble sugar (SS), free proline (Pro), and soluble protein (SP) in the leaves of R. soongorica were reduced by exogenous ABA application, and the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) were increased with sprayed ABA. With increasing ABA concentration, it was observed that the above functions initially increased, but then tapered off at higher ABA concentrations. When comparing concentrations to function, the function of exogenous ABA at 6 mg·L^–1 was the greatest. Before spraying osmotic adjustment substances as well as antioxidant enzymes with exogenous ABA, the content of SS, Pro, and SP in the leaves of R. soongorica significantly decreased by 35.75%, 90.08%, and 16.66% at 6 mg·L^–1 of exogenous ABA. Additionally, the activity of SOD significantly increased by 28.94%, with the activity of POD being 1.35 times higher. The resultant activity of CAT significantly increased by 84.46%. In conclusion, damage to R. soongorica caused by drought stress was alleviated by the application of exogenous ABA on the leaves. Spraying at a concentration of 6 mg·L^–1 of exogenous ABA obtained the most optimal results. These results show that spraying exogenous ABA at 6 mg·L^–1 could alleviate the damage of drought stress on plants for the conservation of the R. soongorica population in desert areas.