Integrated physiological, biochemical, and gene expression responses of tomato (Solanum lycopersicum L.) to time-dependent salinity stress

BACKGROUND: Salinity is a major abiotic stress factor limiting tomato production by affecting plant growth, physiology, and metabolism. This study investigated the time-dependent physiological, biochemical, and gene expression responses of tomato (Solanum lycopersicum L.) cultivar H2274 under different salinity levels (control, 1.5, 3.0, and 4.5 dS m⁻¹). Plants were sampled on the 15th and 45th days of stress exposure. Physiological parameters, including chlorophyll content and leaf color, biochemical responses associated with antioxidant activity and lipid peroxidation, and the expression of salt stress-related genes were evaluated. RESULTS: Increasing salinity levels significantly altered chlorophyll content, leaf color parameters, antioxidant enzyme activities, and malondialdehyde (MDA) accumulation, with responses varying depending on stress intensity and duration. Gene expression analyses revealed differential regulation of genes involved in antioxidant defense, osmotic regulation, ion homeostasis, stress signaling, chlorophyll catabolism, and DNA repair mechanisms under salinity stress. Hierarchical clustering and heatmap analyses further demonstrated distinct expression patterns among the investigated genes under different salinity conditions and sampling times. CONCLUSIONS: The findings provide an integrated overview of the physiological, biochemical, and molecular responses of tomato plants under salinity stress. Overall, prolonged and high-intensity salinity stress appeared to weaken several physiological, biochemical, and transcriptional responses in H2274 tomato plants. These findings may contribute to future studies on salinity stress physiology and stress-response regulation in tomato plants.