PHYSIOLOGICAL RESPONSES OF TWO CUCUMBER CULTIVARS TO NITRATE STRESS

Effect of nitrate (NO3 −) on lipid peroxidation, activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX), soluble sugar, and proline accumulation were investigated in cucumber [Cucumis sativus L. cv. ‘Xintaimici’ (salt-tolerant) and ‘Shennongchunwu’ (salt-sensitive)] seedlings treated with 14 (control) and 140 mM NO3 − for seven days. The results showed that excess NO3 − increased malondialdehyde (MDA) content and electrolyte leakage in cucumber roots of both cultivars, and the degree of increase was higher in ‘Shennongchunwu’. The activities of SOD, CAT, POD, and APX increased in the roots of ‘Xintaimici’, but decreased in roots of ‘Shennongchunwu’, with respect to the control plants. Compared to the control, the soluble sugar and proline content increased in the cucumber roots of both cultivars, especially in ‘Xintaimici’. These results suggested that ‘Xintaimici’ tolerance to NO3 − stress may partly be due to higher activities of antioxidant enzymes an...