Enzymatic and non-enzymatic systems play an important role in the survival of plants, especially under moisture stress. Therefore, responses of four cucumber (Cucumis sativus L.) cultivars, i.e., Esfahani, Super pretty, Superps and Bonanza, subjected to different moisture stress levels, viz., 100 (control), 75, 50 and 25% field capacity, were investigated in the greenhouse to evaluate their antioxidant enzyme activities. Contents of proline, hydrogen peroxide, a-tocopherol, electrolyte leakage, activities of catalase (CAT), and peroxidase (POX), lipid peroxidation in terms of malondialdehyde (MDA) content and 2,2- diphenyl-1-picrylhydrazyl (DPPH) scavenging activity were measured. The experiment was arranged in complete factorial design with five replications. The activities of antioxidant enzymes CAT and POX and DPPH scavenging activity, contents of a-tocopherol, proline, electrolyte leakage as well as lipid peroxidation significantly increased in all the cultivars under increasing moisture stress levels as compared with their controls. Percent increase in antioxidant enzymes activity, a-tocopherol and proline accumulation were highest, while MDA content and electrolyte leakage were lowest in the moisture stress tolerant cultivar Bonanza under moisture stress. Hence, it may be concluded that the moisture stress tolerance of the cucumber cultivars is due to the activity of enzymatic antioxidants and contents of non-enzymatic antioxidants, and proline accumulation.
