Exogenous hydrogen sulphide alleviates nodule senescence in Glycine max-Sinorhizobium fredii symbiotic system

Aim: Hydrogen sulphide (H₂S), as a signalling molecule, regulates the process of plant growth and development. H₂S is involved in the establishment of the legume and rhizobial symbiotic relationship, but little is known about the role of H₂S during nodule senescence. Method: We studied the function of H₂S during nodule senescence in the Glycine max-Sinorhizobium fredii symbiotic system. Physiological and biochemical methods were used to modulate nitrogen fixation, nodule structure, senescence-related protein and gene expression. Results: Our results indicated that H₂S decreased the senescent nodule number, increased nitrogenase (Nase) activity and ureide content, and further promoted the accumulation of NO₃⁻-N, NH₄⁺-N, and total N, which caused the accumulation of biomass in the late steps of symbiosis. H₂S alleviated nodule senescence by maintaining the normal nitrogen fixation structure of nodules. Meanwhile, the expression levels of the NifH and NodGS proteins and the N metabolic enzyme activities were enhanced by H₂S during nodule senescence. Moreover, H₂S stimulated the expression of nitrogen metabolism-related genes in the nodules. Finally, senescence-related gene expression levels were regulated by H₂S during nodule senescence. Conclusion: These findings suggested that H₂S prolonged the lifespan of N₂ fixation by delaying nodule senescence, which will be important for increasing soybean yield and agricultural sustainability development.