Abstract:

Taking the seedlings of cucumber cultivar‘Jinchun 4’as experimental material and using irrigation root method，this paper studied the effect of exogenous melatonin（MT）on the antioxidant system of cucumber seedlings under nitrate stress，providing theoretical basis and reference for the application of MT in vegetable protected production. The results showed that under the nitrate stress the leaf superoxide radical（）production rate，hydrogen peroxide（H₂O₂）and malonadehyde（MDA）contents of the cucumber seedling increased significantly；the contents and the activities of ascorbic acid（AsA）and glutathione（GSH）had a decrease. The activities of superoxide radical（SOD），perxidase（POD），ascorbate peroxidase（APX）and glutathione（GR）in the seedling leaves under nitrate stress increaded markly，with the maximun after 3 d stress. The activities of catalase（CAT）had a maximum after 6d stress and the activities of dehydroascorbate reductase（DHAR）had a maximum after 9 d stress，while the activities of monodehydroascorbate reductase（MDHAR）decreased persistently under the nitrate stress. The exogenous melatonin could significantly decrease the leaf superoxide radical（）production rate，hydrogen peroxide（H₂O₂）content and malonaldehyde（MDA）content，but increase ascorbic acid（AsA）and glutathione（GSH）contents，improve the activities of superoxide radical（SOD），peroxidase（POD），catalase（CAT），ascorbate peroxidase（APX），monodehydroascorbate reductase（MDHAR），dehydroascorbate reductase（DHAR）and glutathione（GR）. In addtion，it added photosynthetic rate and maked accumulation of the leaf dry matter. These results suggest that exogenous melatonin can effectively alleviate the damage of cucumber seedlings and improve the resistance of cucumber seedling under the nitrate stress，and the exogenous melatonin which of concentration was 100 μmol · L^-1 is the most effecttive.

Key words: cucumber seedling, melatonin, nitrate stress, antioxidantion