Integrated Evaluation of Osmotic and Antioxidant Defense Mechanisms in Cotton Genotypes Exposed to NaCl Stress

Salinity stress is one of the major abiotic factors limiting cotton productivity worldwide by inducing osmotic imbalance, oxidative stress, and metabolic disturbances in plant tissues. The present study aimed to evaluate the physiological and biochemical responses of different cotton (Gossypium hirsutum L.) genotypes under NaCl-induced salinity stress through analysis of proline accumulation, antioxidant enzyme activities, and lipid peroxidation intensity. The experiment was conducted under controlled conditions using several cotton genotypes exposed to different NaCl concentrations. Proline content, superoxide dismutase (SOD), catalase (CAT), and malondialdehyde (MDA) levels were analyzed as major biochemical indicators associated with salinity tolerance and oxidative stress responses. In addition, modern bubble heatmap visualization was applied for comparative assessment of genotype-specific stress response patterns under saline treatments. The obtained results demonstrated that increasing NaCl concentrations generally stimulated proline accumulation and enhanced antioxidant enzyme activities in most investigated cotton genotypes. Increased SOD and CAT activities indicated activation of enzymatic antioxidant defense mechanisms under salinity stress conditions. Simultaneously, elevated MDA accumulation reflected enhanced oxidative membrane damage caused by excessive reactive oxygen species (ROS) production under saline environments. Considerable genotype-dependent variability was observed among the investigated cotton varieties. Genotypes such as "Nasaf", "Gulbahor-2", "Ravnaq-1", "Buxoro-6", "Afsona", "Baraka", "Namangan-77", "Porloq-1", and "C-4727" demonstrated comparatively stronger physiological and antioxidant responses under salinity stress conditions, suggesting relatively higher adaptive capacity to NaCl-induced stress. The heatmap visualization additionally confirmed substantial heterogeneity among cotton genotypes in biochemical stress responses and allowed comprehensive comparative interpretation of salinity-induced physiological variability. Overall, the present findings suggest that proline accumulation, antioxidant enzyme activities (SOD and CAT), and MDA content may serve as important biochemical markers for evaluation of salinity tolerance in cotton. The identified stress-tolerant genotypes may therefore represent valuable genetic resources for future breeding programs aimed at improving cotton productivity under saline environmental conditions.