Melatonin Enhances the Waterlogging Tolerance of Prunus persica by Modulating Antioxidant Metabolism and Anaerobic Respiration

Prunus persica is considered one of the most hypoxia-intolerant stone fruits. However, waterlogging, which causes hypoxia, occurs frequently in southern China where peaches are commercially important. As useful waterlogging-tolerant rootstock for peaches is limited, effective emergency strategies are urgent to identify solutions for this problem. In this study, we assessed the effect of exogenous melatonin application at different concentrations on the physiological, metabolic, and molecular properties of peach seedlings during waterlogging. The results revealed that melatonin markedly enhanced the waterlogging tolerance of peach seedlings, especially using a 200-μM solution of melatonin, as evidenced by the tolerant phenotype including new leaves and root activity, as well as by the higher levels of relative chlorophyll content and stomatal aperture, compared with waterlogging-stressed plants. In addition, higher levels of superoxide dismutase (SOD, EC 1.15.1.1) and peroxidase (POD, EC 1.11.1.7) activity and lower levels of lipid peroxidation, hydrogen peroxide (H 2 O 2 ), as well as ethylene content in melatonin-treated plants suggest that melatonin acts as an antioxidant in the context of waterlogging stress. Anaerobic respiration was controlled by melatonin through the enhanced aerenchyma and the suppressed regulation of metabolic enzymes (ADH: EC 1.1.1.1, PDC: EC 4.1.1.1, and LDH: EC 1.1.1.27) and the enzymatic and/or transcript level. Moreover, the expression levels of Ca 2+ signalling and hypoxia-related ERF VII transcription factor genes were elevated by melatonin against waterlogging stress. Taken together, these results highlight that melatonin was an effective molecule for enhancement of hypoxia tolerance, particularly in peach plants, through the regulation of antioxidant enzymes and anaerobic respiration.