Hydrogen sulfide alleviates thiocyanate stress in rice seedlings via tissue-specific carbon and nitrogen metabolic reprogramming.

Thiocyanate (SCN-), an industrially pervasive chemical, has pronounced phytotoxicity, resulting in compromised root development, photosynthetic inhibition, and stunted growth in crops. Hydrogen sulfide (H2S) is recognized as a gaseous signaling molecule crucial for plant stress responses; however, the precise mechanisms by which H2S enhances rice tolerance to SCN- stress through metabolic network reconfiguration remain elusive. By utilizing an integrated approach combining biochemical analysis, widely-targeted metabolomics, and weighted gene coexpression network analysis (WGCNA), this study systematically deciphered the regulatory role of exogenous H2S in reshaping the metabolic network of rice seedlings under SCN- stress. Our findings reveal that H2S alleviates SCN- toxicity via tissue-specific reprogramming of carbon (C) and nitrogen (N) metabolism. In roots, H2S stabilizes carbon accumulation (CA) and nitrogen accumulation (NA), with purine metabolism and riboflavin metabolism serving as core metabolic hubs that cooperatively ensure energy supply and membrane integrity, thereby establishing the foundation for systemic stress resistance in the root system. While in shoots, H2S maintains high levels of CA and NA, triggering extensive metabolic remodelling by driving the synthesis of flavonoids, phenolic acids and terpenoids. This increased antioxidant and detoxification capacities confirmed that shoots are the key site for H2S-mediated stress alleviation. H2S enhances rice seedling tolerance to SCN- stress through systematic reconfiguration of C and N metabolism, providing a vital theoretical foundation for the ecological restoration of contaminated farmlands and the development of stress-resistant crop varieties.