Abstract: In this experiment, 4-year-old Taxus chinensis var. mairei seedlings were used as test material and treated with different concentrations (0, 0.01, 0.1, 0.5 and 1 mmol·L^-1) of sodium nitroprusside (SNP), a donor for exogenous nitric oxide (NO) to study the effect of exogenous nitric oxide on photosynthetic pigment and antioxidant enzymes in T.chinensis seedlings. The contents of photosynthetic pigment, malondialdehyde (MDA) and hydrogen peroxide (H₂O₂), and the activities of antioxidant enzymes in T.chinensis seedlings were determined. Spraying low concentrations (0.01, 0.1 mmol·L^-1) of SNP would significantly increased chlorophyll a/b ratio and the contents of chlorophyll a, chlorophyll b, carotenoids and the total chlorophyll, while the treatment of high concentrations (0.5, 1 mmol·L^-1) of SNP would reduce the chlorophyll contents. The activity of catalase(CAT) significantly increased with the increasing of the concentration of exogenous NO donor, while the activity of peroxidase(POD) was first increased, and then decreased. Moreover, at the early stage of treatment, low concentrations of SNP treatment obviously increased the ascorbate peroxide(APX) activity, while high concentrations of SNP treatment significantly decreased the APX activity, and at the later stage of treatment, the activity of APX significantly decreased with the increasing of SNP concentration. Spraying low concentrations of SNP would effectively improve the superoxide dismutase(SOD) activity and increase the soluble protein concentrations, reduced MDA and H₂O₂ contents, while the treatment of high concentrations of SNP significantly increase the MDA and H₂O₂ contents. Therefore, treatment of low concentrations of SNP (<0.5 mmol·L^-1) would increase chlorophyll contents, the activity of antioxidant enzymes, and reduce the MDA and H₂O₂ contents in T.chinensis seedlings, while the treatment of high concentrations of SNP (≥0.5 mmol·L^-1) would reduce the chlorophyll contents, increase the H₂O₂ contents and membrane lipid peroxidation, and might cause a certain injuries on T.chinensis seedlings.

Key words: Taxus chinensis var. marei, nitric oxide, photosynthetic pigment, antioxidant enzymes