HS Alleviates Salinity Stress in Cucumber by Maintaining the Na/K Balance and Regulating HS Metabolism and Oxidative Stress Response.

Salinity stress from soil or irrigation water can significantly limit the growth and development of plants. Emerging evidence suggests that hydrogen sulfide (HS), as a versatile signal molecule, can ameliorate salt stress-induced adverse effects. However, the possible physiological mechanism underlying HS-alleviated salt stress in cucumber remains unclear. Here, a pot experiment was conducted with an aim to examine the possible mechanism of HS in enhancement of cucumber salt stress tolerance. The results showed that HS ameliorated salt-induced growth inhibition and alleviated the reduction in photosynthetic attributes, chlorophyll fluorescence and stomatal parameters. Meanwhile HS increased the endogenous HS 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, HS maintained Na and K homeostasis via regulation of the expression of , and at the transcriptional level under excess NaCl. Moreover, HS 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 HS could protect cucumber seedlings against salinity stress, likely by keeping the Na/K balance, controlling the endogenous HS level by regulating the HS synthetic and decomposition enzymes, and preventing oxidative stress by enhancing the antioxidant system under salinity stress.