| To explore the regulative mechanism of hydrogen peroxide (H2O2), a signaling molecule for the physiological response of Avena nuda L. (naked oats) seedlings under drought stress. In this study, a sand culture experiment was conducted to investigate the effect of spraying 0.01 mmol·L-1 H2O2 on leaves photosynthesis, active oxygen metabolism, osmotic regulation substances accumulation, and growth of ‘Baiyan 7’ Avena nuda L. seedlings under drought stress simulated by 17.8% polyethylene glycol 6000. The results showed that chlorophyll a, chlorophyll b, total chlorophyll, carotenoid contents, and chlorophyll a/b in leaves of naked oats seedlings under drought stress after spraying with H2O2 increased by 20.0%, 12.9%, 18.5%, 8.1%, and 24.3%, respectively, over the control (drought stress spraying distilled water). In addition，the net photosynthetic rate, stomatal conductance, intercellular CO2 concentration, and water use efficiency in leaves increased by 20.6%, 25.9%, 12.0%, and 33.8%, respectively, whereas the transpiration rate decreased by 9.7%. Moreover, the catalase, ascorbate peroxidase activities, and ascorbic acid content in the leaves under drought stress after spraying with H2O2 increased by 113.5%, 102.9%, and 13.8%, respectively, and the activities of superoxide dismutase, peroxidase, the contents of O—[KG-1][JX*3]·[JX-*3]2, H2O2, malondialdehyde (MDA), and relative plasma membrane permeability in leaves decreased by 21.5%, 60.4%, 29.3%, 38.4%, 19.7%, and 14.2%, respectively. The contents of soluble protein, soluble sugar, free amino acid, and proline in leaves increased by 10.5%, 40.3%, 13.8%, and 17.2%, respectively, and plant height, root length, fresh weight, dry weight, and relative water content of naked oats seedlings increased by 14.8%, 25.0%, 20.1%, 11.0%, and 5.93%, respectively, but there were no significant changes in glutathione content. These results indicated that exogenous H2O2 reduced the inhibition of drought stress on growth of naked oats seedlings, enhanced the drought resistance by reducing the membrane lipid peroxidation, promoted osmotica accumulation, and improved the photosynthesis and plant water condition. |