H2S improves salt‐stress recovery via organic acid turn‐over in apple seedlings

Signalling roles of hydrogen sulphide (H2S) in stress biology are widely reported but not sufficiently established to urge its use in agronomic practice. Our lack of quantitative understanding of the metabolic rewiring in H2S signalling makes it difficult to elucidate its functions in stress tolerance on the biochemical level. Here, Malus hupehensis Rehd. var. pingyiensis seedlings were first treated with salt stress for 2 weeks and then treated with four different concentrations of NaHS. Through vigorous investigations, including phenotypic analysis, 13C transient labelling and targeted metabolic and transcriptomic analysis, for the first time in the seedlings of a woody fruit crop, we found out that H2S recycles fixed carbons through glycolysis and tricarboxylic acid cycle to inhibit the futile accumulation of carbohydrates, to maintain an efficient CO2 assimilation, to keep a balanced starch metabolism, to produce sufficient H2O2, to maintain malate/γ‐aminobutyric acid homeostasis via an H2O2‐induced anion channel (aluminium‐activated malate transporter) and eventually to improve salt‐stress recovery. Our results systematically demonstrate the vital roles of central carbon metabolism in H2S signalling and clarify the mode of action of H2S in apple seedlings. We conclude that H2S signalling interacts with central carbon metabolism in a bottom‐up manner to recover plant growth after salt stress.