Measuring the Changes in the Oxidant Compounds and Antioxidant Capacity of Alfalfa (Medicago sativa L.) in Response to Drought Stress

To explore the impact of drought stress on the amount of oxidant compounds and antioxidant capacity of alfalfa, a factorial experiment in completely randomized block design with three replications was carried out using Yazdi and Hamedani cultivars in four drought levels including 100 (as control), 75, 50 and 25% field capacities. Drought stress effects on superoxide (O2 •–), peroxide (H2O2), α-tochopherol, ascorbic acid contents, and antioxidant power were investigated. The results indicated that the drought stress increased the amount of peroxide content in both cultivars, while the increase in Yazdi cultivar was more than the Hamedani one. The amount of superoxide content increased in both cultivars with Hamedani cultivar showing more increase at P≤0.05. The results of drought effects on antioxidant compounds indicated that α-tochopherol content significantly increased in Yazdi cultivar at 75% FC, but reduced in all drought levels in the Hamedani one. In both cultivars, drought stress caused an increase in ascorbic acid content and antioxidant capacity. In Yazdi cultivar, the ascorbic content and antioxidant capacity significantly increased only at 50% FC, but in Hamedani cultivar, these factors were significantly higher at P≤0.05 in all drought stress levels compared with control. It can be concluded that alfalfa increases its oxidant capacity in response to drought stress and against the oxidant ions resulting from such a stress. Since the antioxidant capacity was increased more in Hamedani cultivar compared to the Yazdi one, Hamedani cultivar can be considered as a more resistant cultivar. This, however, requires further research.