Hydrogen Sulfide Alleviates Cadmium Toxicity in Chrysanthemum indicum L. by Modulating Photosynthesis, Mineral Homeostasis and Antioxidant Capacity

Abstract Hydrogen sulfide (H₂S), recognized as a third gaseous signaling molecule, plays a role in resistance to abiotic stress. However, the role of H₂S during cadmium (Cd) resistance in Chrysanthemum (Chrysanthemum indicum L.) remains uncharacterized. In this study, we aimed to investigate the regulatory role of H₂S in Chrysanthemum under Cd toxicity. Our objective is to provide a theoretical foundation for utilizing H₂S in combination with ornamental plants for the remediation of Cd pollution. We conducted hydroponic experiments to examine the effects of foliar H₂S spraying on the growth, photosynthesis, chloroplast ultrastructure, and physiological attributes of various C. indicum seedlings under Cd stress. The results demonstrated that Cd toxicity had a substantial impact on photosynthetic parameters and the structural integrity of chloroplasts, when compared to non-cadmium conditions. It also elevated the content of reactive oxygen species (ROS), causing disturbances in element uptake. However, the addition of H₂S played a pivotal role in preserving chloroplast integrity, consequently improving photosynthetic performance and avoiding cadmium-induced ultrastructural damage. Additionally, H₂S also positively promoted uptake of elements and regulated antioxidant enzyme activities on the one hand, and mitigated oxidative stress and reduced the accumulation of ROS on the other. In summary, our findings suggest that exogenously applied H₂S can effectively alleviate the detrimental effects of Cd toxicity.