Hydrogen sulfide in coordination with sulfur mediates thermotolerance and improves photosynthetic responses through regulating membrane integrity, redox homeostasis and metabolite remodelling in rice.

Heat stress causes detrimental changes in the plant system, resulting in decreased photosynthesis, growth and crop productivity. In this study, we demonstrated that the combined application of hydrogen sulfide (H2S) and sulfur (S) under heat stress conditions improved photosynthetic functions and the overall plant performance in rice (Oryza sativa L.). The treatment facilitated lipid remodelling, thereby strengthening membrane integrity and function. Plants treated with H2S and S exhibited elevated levels of saturated acids, namely palmitic acid, steric acid, myristic acid, tridecanoic acid and butyric acid, alongside increased concentration of phytol and other phytosterols. This shift towards saturated lipids contributed to maintaining membrane fluidity and structural integrity under heat stress. Phytosterols like sitosterol and stigmasterol helped enhance plant resistance against heat stress. Similarly, the combined application of H2S and S robusted the antioxidant defense system. The quantitative and histochemical staining indicated higher activity of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) and reduced hydrogen peroxide (H2O2) and thiobarbituric acid reactive substances (TBARS) content in the combined treatment under heat stress. Moreover, the microscopic examination revealed that the treatment also preserved the structural integrity of chloroplast and thylakoid membranes. Thereby, preserving the photosynthetic efficiency under heat stress. Thus, the synergistic application of H2S and S regulated lipid remodelling, improved antioxidant defence and chloroplast structure, and collectively augmented tolerance in rice plants against heat stress. The study suggests the improved influence of H2S in thermotolerance in the presence of S through remodelling lipids and the antioxidant system in rice.