Abstract: In order to clarify the alleviating effects of exogenous nitric oxide (NO) on tomato seedlings under salt stress, using tomato variety Qinfengbaoguan as research object, and sodium nitroprusside (SNP) as donor of NO, the effects of different SNP concentration (50, 100, 200, 400, 800 μmol·L^-1) on the growth, photosynthetic pigment contents, gas exchange and chlorophyll fluorescence parameters, membrane peroxidation and antioxidase activity under stress of 100 mmol·L^-1 NaCl were studied in this paper. The results showed that, under salt stress, the growth inhibition of tomato seedlings treated with different concentrations of SNP could be effectively alleviated. At the same time, chlorophyll content, photosynthetic rate (P_n), stomatal conductance (G_s), maximal fluorescence (F_m), PSⅡ maximal photochemistry efficiency (F_v/F_m), practical photochemical efficiency (Φ_PSⅡ) and photochemical fluorescence quenching coefficient (qP) of leaves increased significantly, while original fluorescence (F_o) and non-photochemical quenching coefficient (qN) decreased significantly, and when the SNP concentration was 100 μmol·L^-1, the variation range of each index reached the maximum. The activity of catalase (CAT) in tomato leaves was not significantly changed under salt stress, and the activity of superoxide dismutase (SOD) and peroxidase (POD) were significantly increased. Except that the activity of POD was inhibited by 400 and 800 μmol·L^-1 SNP treatment, the SNP treatment at all concentrations could promote the increase of the above three enzyme activities, and significantly reduced the malondialdehyde content and electrolyte leakage rate in leaves, with the most significant change at 100 μmol·L^-1. These results suggested that exogenous NO donor SNP alleviated the oxidative damage caused by salt stress by enhancing the photosynthetic ability of seedling leaves, and thus improved the salt tolerance of tomato plants.

Key words: nitric oxide, NaCl stress, tomato, photosynthetic characteristics, chlorophyll fluorescence, antioxidase