Hydrogen sulfide modulates cadmium-induced physiological and biochemical responses to alleviate cadmium toxicity in rice

We investigated the physiological and biochemical mechanisms by which H₂S mitigates the cadmium stress in rice. Results revealed that cadmium exposure resulted in growth inhibition and biomass reduction, which is correlated with the increased uptake of cadmium and depletion of the photosynthetic pigments, leaf water contents, essential minerals, water-soluble proteins, and enzymatic and non-enzymatic antioxidants. Excessive cadmium also potentiated its toxicity by inducing oxidative stress, as evidenced by increased levels of superoxide, hydrogen peroxide, methylglyoxal and malondialdehyde. However, elevating endogenous H₂S level improved physiological and biochemical attributes, which was clearly observed in the growth and phenotypes of H₂S-treated rice plants under cadmium stress. H₂S reduced cadmium-induced oxidative stress, particularly by enhancing redox status and the activities of reactive oxygen species and methylglyoxal detoxifying enzymes. Notably, H₂S maintained cadmium and mineral homeostases in roots and leaves of cadmium-stressed plants. By contrast, adding H₂S-scavenger hypotaurine abolished the beneficial effect of H₂S, further strengthening the clear role of H₂S in alleviating cadmium toxicity in rice. Collectively, our findings provide an insight into H₂S-induced protective mechanisms of rice exposed to cadmium stress, thus proposing H₂S as a potential candidate for managing toxicity of cadmium, and perhaps other heavy metals, in rice and other crops.