[Effects of exogenous NO on the growth and antioxidant enzyme activities of cucumber seedlings under NO3- stress].

In this study, cucumber seedlings were cultivated in nutrient solution added with different concentration (0.05, 0.1, 0.2, and 0.3 mmol x L(-1)) sodium nitroprusside (SNP) as nitric oxide (NO) donor to study the effects of exogenous NO on the growth of cucumber seedlings and the activities of antioxidant enzymes in cucumber leaves under NO3- stress. Under the stress of 140 mmol x L(-1) NO3-, treating with 0.1 mmol x L(-1) of SNP for 1 d or 7 d increased the leaf soluble protein content and superoxidase (SOD), catalase (CAT), and ascorbic acid peroxidase (APX) activities, and decreased the leaf malondialdehyde (MDA) content significantly, suggesting that exogenous NO could enhance the capacity of cucumber seedlings in scavenging active oxygen species, protect the seedlings from the peroxidation of membrane lipids, and promote the seedlings growth and increase their resistance to high concentration NO3- stress. After the cucumber seedlings grew in 0.3 mmol x L(-1) of SNP for 7 d, the activities of leaf SOD, POD, and CAT decreased, and the MDA content increased, resulting in the injury of cucumber seedlings. It was indicated that certain concentration (0.1-0.2 mmol x L(-1)) exogenous NO could alleviate the NO3- stress to cucumber seedlings.