Abstract: 【Objective】The purpose of this paper is to clarify the protective effects of nitric oxide (NO) on seedling growth and leaf oxidative damage in NaCl stressed tomato (Lycopersicon esculentum Mill.). 【Method】Under 100 mmol·L-1 NaCl stress condition, the effects of sodium nitropprusside (SNP, an exogenous nitric oxide donor) at the concentrations of 0.05-0.8 mmol·L-1 on the growth, leaf protective enzymatic activities and oxidative damage in tomato seedlings were investigated.【Result】The best effect on the alleviation of NaCl stress damage was observed in the treatment of 0.1 mmol·L-1 SNP. At this concentration, the seedling growth, chlorophyll content, activities of protective enzymes (including SOD, POD, CAT and APX) in leaves, and contents of proline and soluble sugar in leaves were significantly increased, while malondialdehyde (MDA) content and O2- producing rate in leaves were significantly decreased.【Conclusion】The above results indicated that dosage effect of exogenous nitric oxide donor (SNP) existed on the alleviation of NaCl stress in tomato seedlings, and the best alleviating effect on NaCl stress damage was 0.1 mmol·L-1 SNP, which elevated the salt tolerance of plants.

Key words: Nitric oxide, NaCl stress, Activities of protective enzymes, Oxidative damage, Tomato