Abstract: In order to approach the effect of nitric oxide (NO) on the plant antioxidant system under the stress of UV-B radiation, a pot experiment with 5-year old Taxus chinensis var. mairei seedlings was conducted to study the effect of sodium nitroprusside (SNP) as an exogenous NO donor on the seedlings leaf antioxidant system under elevated UV-B radiation. Four treatments, i.e., CK (control), SNP (+ 0.1 mmol·L^-1 of SNP), UV-B (+4.22 kJ·m^-2·d^-1 UV-B), and UV-B+SNP (+ 0.1 mmol·L^-1 of SNP + 4.22 kJ·m^-2·d^-1 UV-B), were installed, and the leaf hydrogen peroxide (H₂O₂),  malondialdehyde (MDA),
 and  antioxidant concentrations were measured. Elevated UV-B radiation increased the leaf H₂O₂ and MDA concentrations significantly (P<0.05), while exogenous NO addition decreased the H₂O₂ and MDA concentrations and increased the taxol, flavonoids, carotenoids and soluble protein concentrations significantly (P<0.05). Different treatments had different effects on the leaf antioxidase activities. SNP increased the CAT and POD activities significantly (P<0.05), while UV-B and SNP+UV-B increased the POD activity and decreased the CAT and APX activities significantly (P<0.05), as compared with CK. It was suggested that exogenous NO could increase the plant antioxidase activities and antioxidant concentrations and decrease the plant H₂O₂ concentrations and lipid peroxidation, and thereby, could relieve the impact of UV-B stress on plant to a certain extent.

Key words: apple, blooming period, orchard, temperature, prediction.