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Exogenous paraquat changes antioxidant enzyme activities and lipid peroxidation in drought-stressed cucumber leaves

Liu, Zhong-Jing, Zhang, Xiao-Long, Bai, Ji-Gang, Suo, Bang-Xia, Xu, Pei-Lei, Wang, Lin
Scientia horticulturae 2009 v.121 no.2 pp. 138-143
Cucumis sativus, cucumbers, lipid peroxidation, drought, water stress, leaves, paraquat, antioxidant activity, cultivars, hydroponics, malondialdehyde, superoxide dismutase, catalase, peroxidase, ascorbate peroxidase, glutathione dehydrogenase (ascorbate)
In order to examine whether paraquat modifies the functioning of antioxidants and oxidative stress levels in drought-stressed plants, a cucumber cultivar (Cucumis sativus cv. Yuexiu no. 3) was grown hydroponically for 2 days. Drought stress, which was induced by polyethylene glycol (PEG), increased the contents of malonaldehyde (MDA), superoxide radical (O₂ ⁻) and hydrogen peroxide (H₂O₂) in cucumber leaves, while pretreatment of paraquat decreased them. Under drought stress induced by PEG, we observed the decreased contents of MDA, H₂O₂ and O₂ ⁻ in paraquat-pretreated plants in comparison to unpretreated stressed plants. Drought stress and paraquat both increased the activities of antioxidants such as superoxide dismutase (SOD, EC, catalase (CAT, EC, guaiacol peroxidase (GPX, EC, ascorbate peroxidase (APX, EC, dehydroascorbate reductase (DHAR, EC, monodehydroascorbate reducatase (MDHAR, EC, glutathione reductase (GR, EC, reduced glutathione (GSH) and reduced ascorbate (AsA). But the combined effect of paraquat application and drought stress resulted in the highest activities of antioxidants. So paraquat is able to moderate the activities of scavenging system enzymes and to influence oxidative stress intensity under drought stress induced by PEG.