Effects of Spermidine and Its Inhibitors on the Storage Quality and Reactive Oxygen Species Metabolism of Sweet Cherry Fruits during Refrigerated Storage

To investigate the effect of spermidine (SPD) on postharvest fruit pitting, storage quality and reactive oxygen (ROS) metabolism in sweet cherry, ‘Summit’ sweet cherry fruits were treated with one of SPD and two polyamine synthesis inhibitors: methylglyoxal-bis(guanylylhydrazone) (MGBG) and dicyclohexylamine (DCHA) before storage. Physicochemical indices were determined periodically during storage. The results showed that SPD treatment significantly inhibited the increase in pitting rate, pitting index and decay rate during storage, while maintaining high fruit firmness, soluble solid content and titratable acidity. At the end of storage, the pitting rate, pitting index and decay rate of SPD-treated fruits were 28.69%, 27.28% and 19.97% lower than those of the control group, respectively. The fruit firmness, soluble solid content and titratable acidity were 38.74%, 9.23% and 11.20% higher than those of the control group, respectively. Furthermore, SPD treatment promoted the accumulation of the endogenous SPD, putrescine (PUT) and spermine (SPM), significantly enhanced the activities of superoxide dismutase (SOD), glutathione reductase (GR), catalase (CAT) and peroxidase (POD), promoted the accumulation of total phenolics and reduced glutathione, and maintained high free radical scavenging capacity, thereby effectively inhibiting the accumulation of superoxide anion, hydrogen peroxide and malondialdehyde (MDA). In addition, it slowed down the increase in relative conductivity. On the contrary, MGBG and DCHA treatments inhibited the accumulation of endogenous SPD, PUT, and SPM in sweet cherry fruits, reduced the activity of antioxidant enzymes and the contents of antioxidants, and inhibited free radical scavenging capacity, thereby resulting in the accumulation of large amounts of ROS, causing cell membrane damage, and leading to a significant increase in the rate of fruit pitting and decay and consequently a significant decline in fruit quality. In conclusion, SPD treatment could significantly improve the antioxidant capacity of sweet cherry fruits during cold storage and reduce the damage caused by ROS to the cellular membrane, thereby inhibiting the occurrence of fruit pitting and consequently maintaining high fruit quality during storage.