Abstract: 503 strains of endophytic bacteria were isolated from four cotton varieties after a strict surface-sterilization among which, 102 strains were subordinate to Pseudomonas, Erwinia, Xanthomoas and Bacillus genera. The concentration of soluble proteins and the activities of superoxide dismutases (SOD) and peroxidases(POD) in the four cotton varieties were measured at three different growth stages, and the results show that the SOD activities tended to decrease from seeds, sprouts to seedlings. A significant difference of eigher soluble protein concentration or SOD activity was found among different varieties and different growth stages, and there was an interaction between cotton variety and growth stage.

Key words: Cotton, Microecology, Endophyte, Superoxide dismutase, Peroxidase