Melatonin Enhances Cold Resistance in Apricot Fruits by Regulating the Energy Metabolism and Antioxidant Capacity

In order to explore the effects of melatonin (MT) treatment on cold resistance in apricot fruits, Xinjiang-grown ‘Saimaiti’ apricot fruits were treated with MT or distilled water as a control at 0.05 MPa for 2 min followed by atmospheric pressure for 8 min. During 49 days of storage at (0 ± 0.5) ℃ and relative humidity of 90%–95%, chilling injury index, incidence of chilling injury, cell membrane permeability, malondialdehyde (MDA) content, superoxide anion (O2-·) production rate, hydrogen peroxide (H2O2) content, antioxidant content, energy substance content and related enzyme activity were measured every 7 days, and mitochondrial structure was observed by transmission electron microscopy (TEM). The results showed that MT treatment effectively inhibited the increase of cell membrane permeability and the accumulation of MDA during storage, significantly reduced the incidence and index of chilling injury, and delayed the occurrence of chilling injury symptoms. In addition, compared with the control group, MT treatment enhanced the activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), aseorbate peroxidase (APX) and glutathione reductase (GR), inhibited the increase of O2-· production rate and the accumulation of H2O2, increased glutathione (GSH) content, delayed the decrease of ascorbic acid (ASA) content, and effectively maintained the balance of intracellular ROS. MT treatment could also effectively delay the decrease of succinic dehydrogenase (SDH), cytochrome c oxidase (CCO) and H+-ATPase and Ca2+-ATPase during storage, maintain high levels of adenosine triphosphate (ATP), adenosine diphosphate (ADP) and energy state, and preserve the integrity of mitochondrial structure and function. In conclusion, MT treatment could enhance the cold resistance of apricot fruits by regulating the energy metabolism and antioxidant capacity. This provides a new theoretical basis for chilling injury control of apricot fruits.