Exogenous hydrogen peroxide influences antioxidant enzyme activity and lipid peroxidation in cucumber leaves at low light

In order to investigate whether exogenous hydrogen peroxide (H2O2) is involved in regulation of antioxidant enzymes and lipid peroxidation at low light, and thereby to elucidate the physiological mechanism of low light stress mitigated by H2O2 pretreatment, seedlings of Cucumis sativus cv. Jinchun no. 4 were pretreated with 1.5 mM H2O2 for 12 h and then were cultivated at low light intensity of 100 μmol m−2 s−1 for 144 h. Low light alone increased the levels of superoxide radical (O2−), endogenous H2O2 and malonaldehyde (MDA) in cucumber leaves, accompanying with increases in activities of some antioxidants such as superoxide dismutase (SOD, EC 1.15.1.1), glutathione peroxidase (GSH-Px, EC 1.11.1.9), ascorbate peroxidase (APX, EC 1.11.1.11), monodehydroascorbate reducatase (MDHAR, EC 1.6.5.4), glutathione reductase (GR, EC 1.6.4.2), reduced glutathione (GSH) and ascorbate (AsA). On the other hand, 12 h of H2O2 application caused moderate stress and induced APX activity in leaves. When H2O2-pretreated seedlings were exposed to low light intensity for 144 h, we obtained the higher activities of SOD, catalase (CAT, EC 1.11.1.6), GSH-Px, APX, dehydrateascorbate reductase (DHAR, EC 1.8.5.1), MDHAR and GR and as well got the enhanced levels of AsA and GSH in comparison to low light treatment alone. The combination of exogenous H2O2 and low light also resulted in the decreased levels of O2−, endogenous H2O2 and MDA in cucumber leaves. So exogenous H2O2 is able to moderate activities of antioxidant enzymes and decrease lipid peroxidation, thus reducing stress intensity at low light.

► In this study H2O2-pretreated cucumber seedlings are exposed to low light stress. ► H2O2 pretreatment increases antioxidant activities in low light-stressed leaves. ► H2O2 also decreases MDA levels in leaves and reduces stress intensity at low light. ► Exogenous H2O2 mitigates low light stress through regulating antioxidant activities.