Hydrogen sulfide (H₂S) is a cell signal molecule produced endogenously and involved in regulation of tolerance to biotic and abiotic stress in plants. In this work, we used molecular biology, physiology, and histochemical methods to investigate the effects of H₂S on cadmium- (Cd-) induced cell death in Chinese cabbage roots. Cd stress stimulated a rapid increase of endogenous H₂S in roots. Additionally, root length was closely related to the cell death rate. Pretreatment with sodium hydrosulfide (NaHS), a H₂S donor, alleviated the growth inhibition caused by Cd in roots—this effect was more pronounced at 5 μM NaHS. Cd-induced cell death in roots was significantly reduced by 5 μM NaHS treatment. Under Cd stress, activities of the antioxidant enzymes were significantly enhanced in roots. NaHS + Cd treatment made their activities increase further compared with Cd exposure alone. Enhanced antioxidant enzyme activity led to a decline in reactive oxygen species accumulation and lipid peroxidation. In contrast, these effects were reversed by hydroxylamine, a H₂S inhibitor. These results suggested that H₂S alleviated the cell death caused by Cd via upregulation of antioxidant enzyme activities to remove excessive reactive oxygen species and reduce cell oxidative damage.

Arabidopsis (Arabidopsis thaliana) PROTEIN ARGININE METHYLTRANSFERASE5 (PRMT5), a highly conserved arginine (Arg) methyltransferase protein, regulates multiple aspects of the growth, development, and environmental stress responses by methylating Arg in histones and some mRNA splicing-related proteins in plants. Hydrogen sulfide (H₂S) is a recently characterized gasotransmitter that also regulates various important physiological processes. l-cysteine desulfhydrase (LCD) is a key enzyme of endogenous H₂S production. However, our understanding of the upstream regulatory mechanisms of endogenous H₂S production is limited in plant cells. Here, we confirmed that AtPRMT5 increases the enzymatic activity of AtLCD through methylation modifications during stress responses. Both atprmt5 and atlcd mutants were sensitive to cadmium (Cd²⁺), whereas the overexpression (OE) of AtPRMT5 or AtLCD enhanced the Cd²⁺ tolerance of plants. AtPRMT5 methylated AtLCD at Arg-83, leading to a significant increase in AtLCD enzymatic activity. The Cd²⁺ sensitivity of atprmt5-2 atlcd double mutants was consistent with that of atlcd plants. When AtPRMT5 was overexpressed in the atlcd mutant, the Cd²⁺ tolerance of plants was significantly lower than that of AtPRMT5-OE plants in the wild-type background. These results were confirmed in pharmacological experiments. Thus, AtPRMT5 methylation of AtLCD increases its enzymatic activity, thereby strengthening the endogenous H₂S signal and ultimately improving plant tolerance to Cd²⁺ stress. These findings provide further insights into the substrates of AtPRMT5 and increase our understanding of the regulatory mechanism upstream of H₂S signals.