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• CGA reduces effects of methyl viologen (MV) stress in apple leaves. • CGA enhances the antioxidant capacity in apple leaves. • It is the first to confirm the in vivo antioxidant fuctions of CGA in plants. Considered to be an antioxidant, chlorogenic acid is involved in resistance to insects and pathogens, and beneficial effects on human health. However, little is known about the antioxidant functions of chlorogenic acid against oxidative stress in plants. In this study, we studied the potential role of exogenous chlorogenic acid in alleviating methyl viologen-mediated oxidative stress in detached leaves of apple (Malus domestica Borkh). The results showed that exogenous chlorogenic acid availably relieved the decreases in chlorophyll concentrations and maximum potential Photosystem II efficiency. Exogenous chlorogenic acid also effectively reduced membrane damage and lipid oxidation and stimulated activity of antioxidant enzymes, including peroxidase, catalase, and polyphenol oxidase. It is noteworthy that exogenous chlorogenic acid improves antioxidant activity of apple leaf under oxidative stress using DPPH, ABTS, and FRAP assays. In addition, the concentration of phenolics increased remarkably in response to chlorogenic acid application after methyl viologen exposure. Furthermore, exogenous chlorogenic acid also changed the transcription levels of related genes for antioxidant enzymes and phenolic metabolism. These results suggest that chlorogenic acid can be effective antioxidants protecting the plants against oxidative stress by enhancing antioxidant capacity. [ABSTRACT FROM AUTHOR]