Heat Stress‐Induced Reduction in Bioactive <scp>GA</scp> Content Decreases Rice Thermotolerance by Causing Membrane Damage Through Accumulated <scp>ROS</scp>

ABSTRACT Rice ( Oryza sativa L.) is a staple crop, but heat stress adversely impacts rice production and poses serious threats to global food security. Gibberellin (GA) is widely recognized as a critical regulator of rice growth and development; however, the mechanisms by which GA homeostasis responds to heat stress and its role in rice thermotolerance remain to be fully elucidated. This study reveals that heat stress disrupts GA homeostasis by suppressing biosynthesis and enhancing inactivation, leading to reduced bioactive GA content and impaired rice thermotolerance. The GA‐deficient mutant d18 exhibited lower thermotolerance than wild‐type (WT) plants, which was restored by exogenous GA 3 application. In contrast, the GA biosynthesis inhibitor paclobutrazol (PBZ) reduced thermotolerance in WT plants. Mechanistically, heat stress‐reduced bioactive GA content triggered excessive reactive oxygen species (ROS) accumulation by promoting ROS generation and inhibiting ROS scavenging. The d18 mutant accumulated higher ROS and displayed greater membrane damage under heat stress compared to WT. Both GA 3 and the ROS scavenger glutathione alleviated ROS accumulation and membrane damage, enhancing thermotolerance in d18 , while PBZ exacerbated ROS accumulation and membrane damage, further impairing thermotolerance in WT. Importantly, exogenous GA 3 application or genetic enhancement of GA signaling, such as knocking out the GA signaling repressor gene SLR1 , improved rice yield under heat stress. These findings demonstrate that GA‐mediated regulation of ROS homeostasis is critical for rice thermotolerance, providing strategies for developing heat‐resilient rice varieties by regulating GA‐ROS homeostasis.