H 2 S improves salt-stress recovery via organic acid turn-over in apple seedlings.

Signalling roles of hydrogen sulphide (H 2 S) 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 H 2 S 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, 13 C transient labelling and targeted metabolic and transcriptomic analysis, for the first time in the seedlings of a woody fruit crop, we found out that H 2 S recycles fixed carbons through glycolysis and tricarboxylic acid cycle to inhibit the futile accumulation of carbohydrates, to maintain an efficient CO 2 assimilation, to keep a balanced starch metabolism, to produce sufficient H 2 O 2 , to maintain malate/γ-aminobutyric acid homeostasis via an H 2 O 2 -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 H 2 S signalling and clarify the mode of action of H 2 S in apple seedlings. We conclude that H 2 S signalling interacts with central carbon metabolism in a bottom-up manner to recover plant growth after salt stress.