Abstract: Effects of different exogenous Spermidine (Spd) concentration on Polyamines contents , antioxidant enzyme activities, O₂^ˉ production rate, H₂O₂ and MDA contents in roots and leaves of cucumber (Cucumis sativus L.) cultivar 'zhongnong 8' in hydroponics were investigated. The results showed that exogenous Spd at 0.05 mmol·L^-1 significantly enhanced growth of cucumber seedlings and alleviated the damage of hypoxia stress efficiently. Under hypoxia stress, activities of antioxidant enzymes were associated closely with polyamines contents. The addition of 0.05 mmol·L^-1 exogenous Spd obviously increased endogenous leaves of Spd, Spermine (Spm), and (Spd+Spm)/Put ratio, while decreased putrescine (Put) content, enhanced the activities of antioxidant enzymes, While decreased the O₂^ˉ production rate, H₂O₂ and MDA contents. Therefore, exogenous Spd at a suitable concentration promoted the growth of cucumber seedlings under hypoxia stress, and improved tolerance of cucumber seedlings to hypoxia stress.

Key words: Cucumber, Hypoxia stress, Polyamines, Antioxidant enzyme