Exogenous Hydrogen sulfide attenuates cadmium toxicity to Chrysanthemum (Chrysanthemum indicum) by modulating glutathione synthesis and cadmium adsorption capacity in the cell wall.

Soil cadmium (Cd) contamination leads to plant toxicity and poses a risk to human health both directly and indirectly through the food chain. Hydrogen sulfide (H2S), a novel gaseous signaling molecule, has been shown to enhance plant tolerance to various abiotic stresses. In this study, the potential of H2S in mitigating Cd toxicity in chrysanthemum (Chrysanthemum indicum) was investigated through physiological, biochemical and transcriptomic analyses. Results showed that the application of exogenous H2S resulted Cd accumulation in the roots by 21.15 %, while reducing Cd in the aboveground parts by 13.21 %. It was further found that H2S increased the pectin and hemicellulose content by 50.09 % and 49.79 %, respectively, through the regulation of cell wall polysaccharide synthesis-related genes, leading to changes in root functional group content and cell wall adsorption capacity for cadmium ions (Cd2+). Additionally, H2S also promoted the synthesis of GSH and PCs by regulating the expression of genes related to sulfur metabolism, chelating free Cd2+ in the cytoplasm, and reducing their harmful effects on the organelles. It was also found that exogenous H2S may have regulated the expression of transporter proteins by modulating the expression of transcription factors (MYB, AP2/ERF, and WRKY), thereby affecting the uptake, transport, and accumulation of Cd2+. In conclusion, exogenous H2S reduced the free Cd2+ content in the cytoplasm by promoting the adsorption of Cd2+ in the root cell walls and facilitating the synthesis of GSH and PCs in the cells, which in turn alleviated the toxic effects of Cd2+ on chrysanthemum.