Abstract: For exploring the internal mechanism of exogenous NO in improving the cold resistance of bitter melon， in this experiment， the variety of Bilv was taken as test material， different concentrations of sodium nitroprusside （SNP） （0， 01， 05， 10， 15 and 20 mmol·L-1） was employed as exogenous nitric oxide （NO） donor to study the effects of different concentrations of exogenous nitric oxide （NO） on the plant growth， relative electrical conductivity， MDA content， proline content and the activities of POD， SOD， CAT of bitter melon seedlings under 8 ℃ lowtemperature stress. The results showed that the treatment of SNP could improve plant height/stem diameter and leaf area/root volume; reduce the relative electrical conductivity and content of MDA; increase proline content and the activities of POD， SOD and CAT of the bitter melon seedlings under lowtemperature stress to reduce the damage caused by lowtemperature. It was also found that the cold resistance effect of treatment with low concentration of SNP was better than that with high concentration， especially the treatment with 05 mmol·L-1 SNP was the best. It indicated that the exogenous NO with proper concentration could promote the plant growth and enhance the bitter melon seedlings adaptability for low temperature stress through improving the activities of defensive enzymes， increasing the osmotic adjustment substance contents， reducing membrane lipid peroxidation and protecting the stability of cell membrane structure.

Key words:  bitter melon, exogenous NO （SNP）, low temperature stress, defensive enzyme