Abstract: To study the physiological response characteristics of cotton seedlings with different salt tolerance under salt stress, the salt-tolerant variety Zhong 9806 and salt-sensitive variety Zhong S9612 were used as test materials, four different concentrations (0, 100, 150, 200 mmol·L^-1) of NaCl were set to simulate different conditions of salt stress by hydroponic method. The results showed that with the increase of salt concentration, soluble sugar content of each cotton variety increased, and the antioxidant enzyme activity increased first and then decreased. Under salt treatment, the soluble protein and proline content of salt-tolerant cultivar increased more than those of salt-sensitive cultivar; Under S1 treatment (100 mmol·L^-1 NaCl), the accumulation of malondialdehyde content was lower in salt-sensitive cultivar, but under S2 and S3 treatments (150, 200 mmol·L^-1 NaCl), the increase of malondialdehyde content of salt-tolerant cultivar (5.35%-6.83%) was lower than those of salt-sensitive cultivar (36.93%-77.34%), and the activities of superoxide dismutase and peroxidase increased greatly. Under low salt concentration stress, the above-ground part of the salt-sensitive cultivar could maintain less Na⁺, and under high salt concentration stress, the increase of Na⁺ in the root of salt-tolerant variety was less than that of the salt-sensitive cultivar, and K⁺, K⁺/Na⁺ in the stems were relatively high. In summary, it had been shown that under salt stress, salt-tolerant cultivars of cotton could increase the content of osmoregulation substance, increase the activity of antioxidant enzymes to relieve membrane lipid peroxidation, and maintain a higher K⁺/Na⁺ ratio, thereby improving salt tolerance of seedlings.

Key words: salt stress, cotton, soluble sugar, antioxidant enzyme, soluble protein