Abstract:Saline-alkali stress interferes with cell metabolism, and inhibits plant growth and development. Proline metabolism is closely related with plant salt-alkali resistance. As signaling molecules, hydrogen peroxide(H2O2) plays vital roles in the regulation of plant cell metabolism, as well as in adaptation to the environmental stress. In order to understand the regulatory mechanism of exogenous H2O2 on proline metabolism in oat(Avena nuda) under salinity-alkalinity stresses, the ‘Dingyou No.6‘(a new oat cultivar) seedlings with two leaves were used to investigate the effects of exogenous H2O2 on proline accumulation in leaves of the seedlings under complex saline-alkali stress by the method of solution culture. The results showed that 75 mmol·L-1 complex saline-alkali stress(molar ratio of NaCl:Na2SO4:NaHCO3:Na2CO3=12:8:9:1) led to a significant accumulation of proline in leaves, and induced a rapid increase of activities of the key enzymes ornithine-δ-aminotransferase(δ-OAT) of proline biosynthesis, and a decrease of activities of the key enzymes Δ1-pyrroline-5-carboxylate synthetase(P5CS) of proline biosynthesis, as well as the key enzyme proline dehydrogenase(ProDH) of proline degradation. Moreover, treatments with 0.01-1 000 μmol·L-1, especially, 10 μmol·L-1 H2O2 could enhance the accumulation of proline in oat seedling leaves under complex saline-alkali stress. H2O2 of 10 μmol·L-1 also increased the activities of P5CS and δ-OAT, and decreased the activity of ProDH in leaves under complex saline-alkali stress. In addition, 10 μmol·L-1 H2O2 treatments could rapidly increase the endogenous H2O2 levels in oat seedling leaves under complex saline-alkali stress. The exogenous H2O2 treatment resulted in the increase of endogenous H2O2 content in oat seedlings under complex saline-alkali stress. H2O2 induced proline accumulation might be a combined result of the activation of glutamate and ornithine pathways of proline biosynthesis and inhibition of proline degradation pathway.