Abstract:Osmotic stress of root system of maize seedling was induced by treatment with different concentrations of polyethyleneglycol solution. After 1--3 h of treatment, obvious physiological changes were observed in leaves. The leaf water potential decreased with the increase of PEG concentration and time of stress. An increase of malondialdehyde content was associated with the higher electrolyte leakage through cell membrane. Osmotic stress of root system caused degradation of chlorophyll, reduction of photosysthetic rates and photosynthetic electron transport, as well as the increase of respiration/photosynthesis ratio. The inhibition of electron transport was more severs in PS Ⅱ than in PS Ⅰ . Pretreatment by leaf spraying with 6-BA and the three kinds of antioxidants (propyl gallate, dibutyl hydroxytoluene and ascorbic acid) before the roots were submited to osmotic stress in -0. 41 MPa PEG solution for 3 h improved all of the above parameters significantly. The results indicated that antioxidant possessed definite protective regulative and adaptative effects on photosysthetic membrane under water stress of root. As the damage of water stress to plant may volve the free radical mechanism.