Foliar L-Ascorbic Acid (Vit-C) Application Enhances Antioxidant Defense and Alleviates Heat- Induced Oxidative Stress in Wheat (Triticum aestivum L.) Genotypes

Abstract

High temperature stress disrupts cellular metabolism in plants by increasing the accumulation of reactive oxygen species (ROS) resulting in oxidative injury and impaired physiological function. This study investigated the mitigative role of foliar-applied L-ascorbic acid (Vit-C) in two contrasting wheat genotypes HUW-510 (heat-tolerant) and HUW-468 (heat-susceptible) subjected to normal and late-sown heat stress conditions. Heat stress significantly elevated ROS levels by 35–55%, while reducing chlorophyll content (20–30%), nitrate reductase activity (18–28%), total protein (25–35%), membrane stability index (MSI) and relative water content (RWC) indicating marked oxidative and metabolic impairment. Activities of key antioxidant enzymes catalase (CAT), superoxide dismutase (SOD) and ascorbate peroxidase (APX) also declined under heat stress suggesting suppression of the enzymatic defense system. Foliar application of L-ascorbic acid at 1.0, 5.0 and 10.0 mM substantially alleviated oxidative stress with 10.0 mM exhibiting the strongest mitigative effect. Ascorbic acid reduced ROS accumulation by 25–35%, enhanced CAT, SOD and APX activities by 30–50%, improved chlorophyll and NR activity and increased osmolyte levels (proline and soluble sugars). The tolerant genotype HUW-510 consistently displayed superior antioxidant recovery compared to HUW-468 demonstrating genotype-specific responsiveness to AA. Overall L-ascorbic acid effectively strengthened antioxidant defense, stabilized cellular metabolism and mitigated heat-induced oxidative damage highlighting its potential as a practical strategy for improving thermotolerance in wheat.