Integrated regulation of antioxidant defence, photosystem II stability, and carbon metabolism drives drought tolerance in contrasting Sorghum bicolor genotypes

Drought stress severely limits crop productivity by disrupting plant water status, redox balance and photosynthetic efficiency. This study aimed to identify key adaptive traits by comparing a drought-tolerant genotype (CSV 15) with a drought-sensitive genotype (PC 1080) under progressive drought and recovery conditions. In the present study, a controlled pot experiment was conducted, and plants were subjected to graded water deficit followed by rehydration. Physiological (relative water content, chlorophyll a fluorescence OJIP kinetics) and biochemical parameters, including antioxidant enzymes (SOD, CAT, GPOD, GR), carbohydrate-metabolizing enzymes (invertase, α-amylase), proline, and starch content, were systematically evaluated. Results highlighted that CSV 15 maintained higher relative water content, exhibited sustained antioxidant enzyme activities, and showed efficient glutathione-mediated redox regulation under drought stress. In contrast, PC 1080 displayed erratic antioxidant responses, reduced metabolic adaptability, and poor recovery. Further, Chlorophyll a fluorescence analysis revealed that CSV 15 preserved PSII functionality, stable OJIP transients, and higher performance indices, whereas PC 1080 exhibited early photoinhibition and disrupted energy flux dynamics. These findings indicate that drought tolerance is governed by the coordinated regulation of antioxidant defence, metabolic flexibility, and photosynthetic efficiency rather than isolated mechanisms. The superior resilience of CSV 15 highlights the importance of integrated stress responses in maintaining cellular and photochemical stability under water deficit. Overall, this study identifies key physiological and fluorescence-based markers that can be utilized for screening and breeding drought-resilient sorghum genotypes, contributing to sustainable crop improvement under changing climatic conditions.