Hydrogen sulfide (H 2 S) is well known as a gaseous signal in response to heavy metal stress, while methane (CH 4), the most prevalent greenhouse gas, confers cadmium (Cd) tolerance. In this report, the causal link between CH 4 and H 2 S controlling Cd tolerance in alfalfa (Medicago sativa) plants was assessed. Our results observed that the administration of CH 4 not only intensifies H 2 S metabolism, but also attenuates Cd-triggered growth inhibition in alfalfa seedlings, which were parallel to the alleviated roles in the redox imbalance and cell death in root tissues. Above results were not observed in roots after the removal of endogenous H 2 S, either in the presence of either hypotaurine (HT; a H 2 S scavenger) or DL -propargylglycine (PAG; a H 2 S biosynthesis inhibitor). Using in situ noninvasive microtest technology (NMT) and inductively coupled plasma mass spectroscopy (ICP-MS), subsequent results confirmed the participation of H 2 S in CH 4 -inhibited Cd influx and accumulation in roots, which could be explained by reestablishing glutathione (GSH) pool (reduced/oxidized GSH and homoglutathione) homeostasis and promoting antioxidant defence. Overall, our results clearly revealed that H 2 S operates downstream of CH 4 enhancing tolerance against Cd stress, which are significant for both fundamental and applied plant biology. [Display omitted] • Methane mitigation of cadmium toxicity in alfalfa requires the involvement of hydrogen sulfide. • Methane and hydrogen sulfide can debase the influx rate of cadmium ions into alfalfa. • The reestablishment of glutathione and redox homeostasis in alfalfa by methane requires hydrogen sulfide. [ABSTRACT FROM AUTHOR]
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