Exogenous cysteine and hydrogen sulfide stimulate cyanide assimilation in rice plants through different assimilation strategies

Cysteine (Cys) functions as an essential substrate for β-cyanoalanine synthase (β-CAS)-mediated cyanide (CN − ) assimilation in plants, with the metabolic coordination between hydrogen sulfide (H 2 S) and Cys cycling becoming physiologically critical under stress conditions. Our results demonstrated that exogenous application of Cys and/or H 2 S significantly enhanced CN − assimilation efficiency in rice plants compared to additive-free controls. CN − exposure significantly reduced endogenous Cys levels in both roots and shoots relative to untreated plants. Conversely, supplementation with these compounds (singly or combined) restored tissue Cys concentrations across all CN − treatments, with root Cys pools consistently exceeding shoot levels. Correlation analyses revealed rice plants strategically modulated Cys allocation between glutathione (GSH) biosynthesis and CN − detoxification pathways, effectively limiting tissue CN − accumulation during additive supplementation. While shoot expression patterns of β-CAS and sulfurtransferase (ST) genes remained unaltered across CN − treatments regardless of additives, the application of additives significantly influenced gene expression in roots, which differed among the CN − treatments. In summary, Cys and H 2 S synergistically enhance CN − detoxification by modulating the expression of relevant genes activated in the β-CAS and ST pathways, as well as optimizing mitochondrial Cys trafficking. This regulatory mechanism sustains rice growth under CN − stress by improving CN − conversion efficiency. • Growth improvement of CN − -treated rice plants was evident due to application of either Cys or H 2 S alone or combined. • Application of either Cys or H 2 S alone or combined significantly improved the CN − assimilation in rice plants. • Rice plants modulated Cys flux between GSH synthesis and CN − assimilation in the presence of different additives. • Different regulatory mechanisms exist in the roots of rice plants during CN − assimilation in the presence of different additives.