24-Epibrassinolide (24-EBL) Enhances Antioxidant Defense to Mitigate Heat-induced Oxidative Stress in wheat (Triticum aestivum L.)

Abstract

Heat stress is a major abiotic constraint limiting wheat (Triticum aestivum L.) productivity, primarily by inducing excessive accumulation of reactive oxygen species (ROS) that disrupt cellular homeostasis. Brassinosteroids such as 24-epibrassinolide (24-EBL) are known to enhance plant stress tolerance through modulation of antioxidant defense systems. This field study evaluated the effect of foliar-applied 24-EBL (0.01, 0.02, and 0.03 mM) on antioxidant enzyme activities, ROS accumulation, and grain yield in two contrasting wheat genotypes HUW-510 (heat-tolerant) and HUW-468 (heat-susceptible) grown under normal and late-sown (heat-stressed) conditions. Foliar sprays were applied at pre-flowering (45 DAS) and post-flowering (65 DAS). Antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) and ROS levels were assayed at 65 and 85 DAS. Statistical analyses included ANOVA (LSD, p ≤ 0.05), stepwise multiple linear regression to examine the relationships between biochemical and yield traits. Application of 24-EBL significantly enhanced SOD, CAT, and APX activities by 25–35%, reduced ROS accumulation by 20–30%, and improved grain yield by 80–120% under heat stress, with the 0.02–0.03 mM concentration being most effective. The heat-tolerant genotype HUW-510 exhibited superior antioxidant capacity and yield stability compared with HUW-468. Regression analysis showed strong positive associations between antioxidant enzyme activities and grain yield (R² = 0.78–0.87; p < 0.01), indicating that biochemical fortification through 24-EBL plays a key role in thermotolerance. These findings demonstrate that foliar 24-EBL application can serve as a practical, eco-friendly strategy to mitigate terminal heat stress in wheat.