l‐cysteine desulfhydrase‐related H2S production is involved in OsSE5‐promoted ammonium tolerance in roots of Oryza sativa

Previous studies revealed that rice heme oxygenase PHOTOPERIOD SENSITIVITY 5 (OsSE5) is involved in the regulation of tolerance to excess ammonium by enhancing antioxidant defence. In this study, the relationship between OsSE5 and hydrogen sulfide (H₂S), a well‐known signalling molecule, was investigated. Results showed that NH₄Cl triggered the induction of l ‐cysteine desulfhydrase (l ‐DES)‐related H₂S production in rice seedling roots. A H₂S donor not only alleviated the excess ammonium‐triggered inhibition of root growth but also reduced endogenous ammonium, both of which were aggravated by hypotaurine (HT, a H₂S scavenger) or dl ‐propargylglycine (PAG, a l ‐DES inhibitor). Nitrogen metabolism‐related enzymes were activated by H₂S, thus resulting in the induction of amino acid synthesis and total nitrogen content. Interestingly, the activity of l ‐DES, as well as the enzymes involved in nitrogen metabolism, was significantly increased in the OsSE5‐overexpression line (35S:OsSE5), whereas it impaired in the OsSE5‐knockdown mutant (OsSE5‐RNAi). The application of the HT/PAG or H₂S donor could differentially block or rescue NH₄Cl‐hyposensitivity or hypersensitivity phenotypes in 35S:OsSE5‐1 or OsSE5‐RNAi‐1 plants, with a concomitant modulation of nitrogen assimilation. Taken together, these results illustrated that H₂S function as an indispensable positive regulator participated in OsSE5‐promoted ammonium tolerance, in which nitrogen metabolism was facilitated.