Abstract
Polyamines (PAs) have long been recognized to be linked with growth, differentiation, plant senescence and defense reactions of plants to various environmental stresses. However, little is known about their physiological relevance in plants subjected to hypoxia stress. In the present experiment, the effects of exogenous spermidine on polyamine content and antioxidant enzyme activities in seedlings of two cucumber cultivars (Cucumis sativus cv. Zhongnong No.8 and cv. Lubachun No.4) with different resistances to hypoxia stress were investigated. The results showed that under hypoxia treatment, the contents of putrescine (Put), spermidine (Spd), and spermine (Spm) in roots of seedlings of two cucumber cultivars increased significantly in the early period of treatment and then decreased in the later period. Over the entire treatment period, concentrations of PAs were significantly higher than those in the control. Activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) over the treatment period followed the same pattern as PAs. The fresh weight and dry weight of the two cucumber cultivar seedlings were significantly lower than the controls. Exogenous Spd treatment increased the contents of Spd and Spm in roots while decreased the Put content when compared to the hypoxia treatment, enhanced the activities of the antioxidant enzymes, and the fresh and dry weight of seedlings were similar to the controls. Under the same treatment, the activities of the antioxidant enzymes in the roots of the hypoxia-resistant cultivar (cv. Lubachun No.4) were higher than in the hypoxia-sensitive cultivar (cv. Zhongnong No.8). These results indicated that exogenous Spd can change the contents of PAs in the roots of both cucumber cultivars under hypoxia stress, and higher levels of Spd and Spm in roots can enhance both the activities of antioxidant enzymes and the growth of cucumber cultivar seedlings.
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