Hydrogen sulfide alleviates chromium toxicity by promoting chromium sequestration and re-establishing redox homeostasis in Zea mays L.

Hydrogen sulfide (H2S) is a multifunctional gaseous signaling molecule involved in the regulation of Cr stress responses. In the present study, we combined transcriptomic and physiological analyses to elucidate the mechanism underlying the mitigation of Cr toxicity by H2S in maize (Zea mays L.). We showed that treatment with sodium hydrosulfide (NaHS, a donor of H2S) partially alleviated Cr-induced growth inhibition. However, Cr uptake was not affected. RNA sequencing suggested that H2S regulates the expression of many genes involved in pectin biosynthesis, glutathione metabolism, and redox homeostasis. Under Cr stress, NaHS treatment significantly increased pectin content and pectin methylesterase activity; thus, more Cr was retained in the cell wall. NaHS application also increased the content of glutathione and phytochelatin, which chelate Cr and transport it into vacuoles for sequestration. Furthermore, NaHS treatment mitigated Cr-induced oxidative stress by enhancing the capacity of enzymatic and non-enzymatic antioxidants. Overall, our results strongly support that H2S alleviates Cr toxicity in maize by promoting Cr sequestration and re-establishing redox homeostasis rather than by reducing Cr uptake from the environment.