Unravelling the physiological and antioxidant mechanisms of wheat tolerance to individual and combined ozone and water deficit stress

Abstract

Tropospheric ozone (O₃) and water deficit stress (WS) are major abiotic constraints on wheat growth, physiology, and yield. Elevated O₃ induces oxidative stress by generating reactive oxygen species (ROS), impairing photosynthesis and cellular integrity, while water deficit stress limits CO₂ uptake via stomatal closure, diminishing photosynthetic efficiency. However, the combined effects of O₃ and WS, particularly cultivar-specific responses and the roles of stomatal and apoplastic antioxidants remain poorly understood. This study investigated physiological and biochemical responses of four wheat cultivars, RAJ-3077, RAJ-4079, RAJ-4120, and RAJ-4037, under elevated O₃ and WS, individually and in combination. These environmental stresses modulated ROS accumulation, antioxidant enzyme activities, stomatal behavior, membrane integrity, and photosynthetic pigment stability. Cultivars RAJ-4037 and RAJ-4120 demonstrated higher resilience to both individual and combined stresses, maintaining antioxidant defenses, stable carotenoid and phenolic contents, and delayed senescence, whereas RAJ-3077 and RAJ-4079 were more susceptible to both individual and combined stresses, exhibiting enhanced oxidative damage and reduced antioxidative capacity. While WS induced stomatal closure that limited O₃ uptake, this protective mechanism showed variability depending on cultivar traits and stress intensity. Notably, under combined stress conditions, O3 and WS exerted a synergistic effect that exacerbated lipid peroxidation and cellular injury, often rendering the ascorbic acid and broader antioxidant network insufficient for full detoxification. These findings highlight biochemical and physiological differences among cultivars, emphasizing the need to incorporate such traits into breeding and management strategies to improve wheat tolerance to multiple environmental stresses, thereby ensuring sustainable production amid the escalating climate variability and pollution.