Abstract:The time course of reactive oxygen generation in plants under stress and the corresponding mechanisms of alleviation in plants are often used as an important indicator for evaluating stress tolerance. However, the quantification of the reactive agents and enzymes is complicated by genetic variations in experimental materials. Clones of ‘texoka’ buffalograss (Buchloe dactyloides (Nutt.) Engelm) were cultured in a hydroponic system to investigate the efficts of reactive oxygen, lipid peroxidation, and antioxidase activities in leaves under physiological drought stress induced by high PEG-6000 concentration in the cultural solution. Superoxide radical (O-?2), hydrogen peroxide (H2O2), and malondlaldehyde (MDA) in the leaves were quantitatively regressive to the concentration of PEG-6000 over the time course. On the other hand, the activities of superoxide dismutase (SOD EC 1.15.1.1), guaiacol peroxidase (G\|POD EC1.11. 1.7), and catalase (CAT EC 1.11. 1.6) in the leaves showed pulses, increasing at the early stage and then decreasing gradually to the level of the control. The occurrence of peak activities of SOD, G\|POD and CAT in the leaves was earlier with increased stress intensity. These results indicated that both the time course and quantities of the antioxidase in buffalograss are important for evaluating the defense response against oxidation damage induced by water stress. Therefore, sampling time as well as the quantification of the antioxidase has to be considered for better understanding the stress response system in buffalograss.