Salinity stress from soil or irrigation water can significantly limit the growth and development of plants. Emerging evidence suggests that hydrogen sulfide (H₂S), as a versatile signal molecule, can ameliorate salt stress-induced adverse effects. However, the possible physiological mechanism underlying H₂S-alleviated salt stress in cucumber remains unclear. Here, a pot experiment was conducted with an aim to examine the possible mechanism of H₂S in enhancement of cucumber salt stress tolerance. The results showed that H₂S ameliorated salt-induced growth inhibition and alleviated the reduction in photosynthetic attributes, chlorophyll fluorescence and stomatal parameters. Meanwhile H₂S increased the endogenous H₂S level concomitant with increased activities of D/L-cysteine desulfhydrase and β-cyanoalanine synthase and decreased activities of O-acetyl-L-serine(thiol)lyase under excess NaCl. Notably, H₂S maintained Na⁺ and K⁺ homeostasis via regulation of the expression of PM H⁺-ATPase, SOS1 and SKOR at the transcriptional level under excess NaCl. Moreover, H₂S alleviated salt-induced oxidative stress as indicated by lowered lipid peroxidation and reactive oxygen species accumulation through an enhanced antioxidant system. Altogether, these results demonstrated that application of H₂S could protect cucumber seedlings against salinity stress, likely by keeping the Na⁺/K⁺ balance, controlling the endogenous H₂S level by regulating the H₂S synthetic and decomposition enzymes, and preventing oxidative stress by enhancing the antioxidant system under salinity stress.

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