Evaluating Physiological and Hormonal Responses of Two Distinct Rice Genotypes Under High Temperatures

Climate change poses a major threat to rice productivity, particularly due to high-temperature stress during anthesis, which severely impacts the grain yield. Understanding the physiological and biochemical responses of different rice genotypes to high-temperature stress is critical for breeding resilient varieties. In this study, we assessed two contrasting rice genotypes, high-temperature-tolerant-1 (HTR-1) and high-temperature-sensitive (HTS-5), to confirm previously established physiological and hormonal mechanisms associated with high-temperature tolerance. The study evaluated morphological, physiological, and biochemical markers at the anthesis stage under control (29/24 °C) and high-temperature stress (38 °C for six hours) conditions. Our results confirmed that HTR-1 exhibits superior tolerance through better antioxidant enzyme activity, higher anther dehiscence, and lower oxidative damage. The genotype HTS-5 exhibited a substantial rise in hydrogen peroxide (1.9-fold) and malondialdehyde (1.74-fold) levels, accompanied by the reduced activity of antioxidant enzymes. Furthermore, the high transcript level of cytosolic APX (<i>OsAPX1</i>, <i>OsAPX2</i>), peroxisomal APX (<i>OsAPX3</i> and <i>OsAPX4</i>), <i>OsCATA</i>, and <i>OsCATB</i> confirmed high antioxidant activity in HTR-1. Moreover, the GA and IAA levels were reduced in both genotypes, while the ABA concentration was increased significantly in the anthers of HTS-5 as compared to those of HTR-1. This suggests that higher ABA production, along with higher reactive oxygen species (ROS) in the anthers, could lead to sterility in rice under high-temperature scenarios. These findings confirmed HTR-1 as a promising genetic resource for breeding heat-tolerant rice, by validating physiological and biochemical mechanisms of high-temperature resilience. This study also provides practical insights for selecting suitable genotypes to improve rice production under the challenges of climate change.