Abstract: Hydrogen sulfide (H₂S), as a gas signal, plays an important role in plant resistance to salinealkali stress. We explored the regulation of H₂S on osmotic stress of naked oat (Avena nuda) seedlings under salinealkali stress. The leaves of seedlings were sprayed with H₂S donor NaHS and the roots were irrigated with saline-alkali mixture solution (NaCl∶Na₂SO₄∶NaHCO₃∶Na₂CO₃=12∶8∶9∶1). The effects of H₂S on cell membrane permeability and osmoticum in leaves under salinealkali mixed stress were investigated. The results showed that the contents of malondialdehyde (MDA), a membrane lipid peroxidation product, and the relative permeability of cell membrane increased with a stressed duration and concentrationdependent manner under 25, 50, and 75 mmol·L^-1 salinealkali mixed stress. The MDA content and relative permeability of cell membrane under 50 mmol·L^-1 mixed salinealkali stress significantly decreased when sprayed with 10, 25 and 50 μmol·L^-1 NaHS, with the strongest effect under 25 μmol·L^-1 NaHS. Spraying 25 μmol·L^-1 NaHS could reduce the increase of Na⁺ content and the decrease of K⁺ content in naked oat leaves under 50 mmol·L^-1 saline-alkali mixed stress, and increased K⁺/Na⁺. Furthermore, it significantly promoted the accumulation of soluble sugar in early salinealkali stress (12-48 h), soluble protein in late salinealkali stress (60-72 h), and betaine in the whole stress period (12-72 h). However, the contents of free amino acids, proline and organic acids showed no change or decrease trend. Our results indicated that exogenous H₂S can alleviate oxidative damage induced by salinealkali stress through increasing K⁺/Na⁺ ratio and promoting the accumulation of osmotic substances in leaves (soluble sugar, soluble protein and betaine), thus enhance the tolerance of naked oats to saltalkali stress.

Key words: H₂S, naked oat, saline-alkali mixed stress, osmoticum.