A persulfidation-based reversible post-translational modification of Cys desulfhydrase and NADPH oxidase RBOHD fine-tunes guard cell ABA signaling.

Hydrogen gas (H₂) was recently proposed as a novel antioxidant and signalling molecule in animals. However, the physiological roles of H₂ in plants are less clear. Here, we showed that exposure of alfalfa seedlings to paraquat stress increased endogenous H₂ production. When supplied with exogenous H₂ or the heme oxygenase‐1 (HO‐1)‐inducer hemin, alfalfa plants displayed enhanced tolerance to oxidative stress induced by paraquat. This was evidenced by alleviation of the inhibition of root growth, reduced lipid peroxidation and the decreased hydrogen peroxide and superoxide anion radical levels. The activities and transcripts of representative antioxidant enzymes were induced after exposure to either H₂ or hemin. Further results showed that H₂ pretreatment could dramatically increase levels of the MsHO‐1 transcript, levels of the protein it encodes and HO‐1 activity. The previously mentioned H₂‐mediated responses were specific for HO‐1, given that the potent HO‐1‐inhibitor counteracted the effects of H₂. The effects of H₂ were reversed after the addition of an aqueous solution of 50% carbon monoxide (CO). We also discovered enhanced tolerance of multiple environmental stresses after plants were pretreated with H₂. Together, these results suggested that H₂ might function as an important gaseous molecule that alleviates oxidative stress via HO‐1 signalling.