Abstract

Hydrogen sulfide (H 2 S) is recognized as an important redox signaling molecule in plant stress responses, yet how it coordinates metabolic regulation across subcellular compartments remains poorly understood. Here, using rice as a model system, we investigated whether H 2 S functions as a spatial metabolic signal that integrates carbon flux reprogramming with NADPH-dependent redox homeostasis under salt stress. By combining subcellular H 2 S quantification, persulfidation profiling, enzyme activity assays, and targeted metabolite analyses, we identified fructose-1,6-bisphosphate aldolase (FBA) as a central regulatory node of compartment-specific H 2 S signaling. H 2 S preferentially accumulated in chloroplasts and directly modified both cytosolic and chloroplastic FBA isozymes via persulfidation, but with differential functional outcomes. In chloroplasts, persulfidation suppressed FBA activity, constrained Calvin-Benson cycle regeneration, and redirected NADPH from carbon assimilation toward glutathione-based antioxidant defense. In the cytosol, H 2 S modulated FBA activity and upstream metabolic enzymes, promoting glucose-6-phosphate flux into the oxidative pentose phosphate pathway and enhancing NADPH production to sustain redox buffering. Together, these findings reveal that H 2 S operates as a compartment-specific metabolic coordinator that integrates carbon metabolism with NADPH allocation, thereby enabling plants to prioritize redox stability over growth during salt stress.