Abstract

This study analyzes the effects of soil salinity on photosynthetic character, osmoregulation, content of pigment, K⁺/Na+ ratio, lipoxygenase and antioxidants activities in functional leaves during the flowering and boll-forming stages of two cotton cultivars, namely, CCRI-44 (salt-tolerant) and Sumian12 (salt-sensitive), grown under different soil salinity conditions. In the control plants, non-significant differences were found in gas exchange, saturation irradiance (SI) and carotenoid (Car) content between the two cultivars. However, it showed higher K⁺/Na⁺ ratio, antioxidant enzyme activities, soluble sugar and protein contents, and lower chlorophyll (Chl) content and yield in CCRI-44. Salinity stresses remarkably increased soluble sugar and protein contents, lipoxygenase and the antioxidant activities, but decreased K⁺/Na⁺ ratio, Chl and Car contents, SI, photosynthetic capacities and yield, the extent being considerably larger in Sumian12 than CCRI-44. Although the soluble sugar, protein contents and the antioxidant activities of Sumian12 elevated more evidently under salt stresses, those variables never reached the levels of CCRI-44. Thus, CCRI-44 could maintain higher seed cotton yield than Sumian12 by sustaining higher osmoregulation and antioxidative abilities, which led to higher photosynthetic capacity. Hence, the salt-tolerant cotton cultivars could harmonize the relationship between CO₂ assimilation (source) and the seed cotton yield (sink) under the experimental conditions.

Key words: Cotton (Gossypium hirsutum L.), mixed salt stress, salt tolerance, photosynthesis, ion accumulation, antioxidant enzyme activity, seed cotton yield.