Methane control of cadmium tolerance in alfalfa roots requires hydrogen sulfide

ABSTRACT Hydrogen sulfide (H2S) is well known as a gaseous signal in response to heavy metal stress, while methane (CH4), the most prevalent greenhouse gas, confers cadmium (Cd) tolerance. In this report, the causal link between CH4 and H2S controlling Cd tolerance in alfalfa (Medicago sativa) plants was assessed. Our results observed that the administration of CH4 not only intensifies H2S 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 H2S, either in the presence of either hypotaurine (HT; a H2S scavenger) or DL-propargylglycine (PAG; a H2S biosynthesis inhibitor). Using in situ noninvasive microtest technology (NMT) and inductively coupled plasma mass spectroscopy (ICP-MS), subsequent results confirmed the participation of H2S in CH4-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 H2S operates downstream of CH4 enhancing tolerance against Cd stress, which are significant for both fundamental and applied plant biology.