Exogenous nitric oxide improves chilling tolerance of Chinese cabbage seedlings by affecting antioxidant enzymes in leaves

The effects of exogenous sodium nitroprusside (SNP), a nitric oxide (NO) donor, on growth of Chinese cabbage seedlings and antioxidant enzyme activity in leaves were studied under chilling stress. The results showed that the growth of Chinese cabbage seedlings was strongly inhibited when plants were exposed to chilling, whereas spraying SNP in shoots significantly alleviated the inhibition of growth from chilling stress. The plant height, root length, fresh and dry weight of chilling plants all increased. Chilling caused increases of membrane permeability and antioxidant enzymes activity with the exception of catalase after 8 days of treatment. Meanwhile, chilling also resulted in the decrease of chlorophyll content, accumulation of malondialdehyde (MDA) and protein in leaves. Interestingly, application SNP further enhanced the antioxidant enzyme activities, the chlorophyll and protein content, on the contrary, reduced the member permeability and MDA content. Therefore, it was concluded that NO protected plants from oxidative damage and promoted the growth by enhancing activity of antioxidant enzymes in leaves sufficiently to lower membrane injury. However, exogenous NO had no significant effects on seedling in normal conditions.