中文摘要：

以‘津春4号’黄瓜为试验材料,采用灌根的方法研究了外源褪黑素（MT）对硝酸盐胁迫下幼苗抗氧化系统的影响,为MT在设施蔬菜生产中的应用提供参考。结果表明：硝酸盐胁迫处理后,黄瓜幼苗叶片中超氧阴离子（O_2）产生速率、过氧化氢（H_2O_2）和丙二醛（MDA）含量显著增加;抗坏血酸（AsA）和谷胱甘肽（GSH）含量及活性均下降;超氧化物歧化酶（SOD）、过氧化物酶（POD）、抗坏血酸过氧化物酶（APX）、谷胱甘肽还原酶（GR）活性在硝酸盐胁迫3 d时,过氧化氢酶（CAT）活性在胁迫6 d时,脱氢抗坏血酸还原酶（DHAR）活性在胁迫9 d时均达最高,之后又逐渐下降;单脱氢抗坏血酸还原酶（MDHAR）活性则持续降低。MT处理可有效抑制硝酸盐胁迫条件下黄瓜幼苗中O_2的产生速率及H_2O_2和MDA的积累,提高AsA和GSH含量及活性,增强SOD、POD、CAT、APX、MDHAR、DHAR、GR活性,提高叶片的光合速率及干物质积累。这些结果说明,MT可减缓硝酸盐胁迫的危害,提高黄瓜幼苗对硝酸盐的耐性,且100μmol·L-1MT处理效果最佳。

英文摘要：

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（O_2~ ）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 （O5） production rate, hydrogen peroxide （H2O2） content and malonaldehyde （MDA） content, but increase ascorbic acid （AsA） and glutatbione （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.