S-nitrosylation of GSNOR and LCD facilitates cadmium-induced programmed cell death in tomato seedlings

Nitric oxide (NO) and hydrogen sulphide (H₂S) perform multiple regulatory functions in plants; however, the molecular mechanisms underlying NO and H₂S interaction remain poorly understood. In this study, we aim to analyse the function of S-nitrosoglutathione reductase (GSNOR) and L-cysteine desulfhydrase (LCD) in the programmed cell death (PCD) response to cadmium (Cd²⁺) stress using GSNOR and LCD knockout and overexpressing transgenic tomato (Solanum lycopersicum). Our results confirmed that GSNOR, an enzyme that mediates NO dynamic equilibrium, and LCD, an enzyme involved in H₂S generation, inhibit Cd²⁺ stress-induced PCD in tomato plants. GSNOR and LCD knockout plants were sensitive to Cd²⁺ and exhibited increased cell death compared to the controls. S-nitrosylation of GSNOR at Cys47 and LCD at Cys225 changed their subcellular localisation and decreased GSNOR and LCD activity, thereby increasing Cd²⁺ uptake and promoting PCD. Thus, S-nitrosylation attenuates the interaction between GSNOR and LCD during PCD. In conclusion, GSNOR and LCD are involved in the response to Cd²⁺ stress, and their interactions and S-nitrosylation play critical roles in NO- and H₂S-induced Cd²⁺ stress responses.