Changes in soluble sugar metabolism in loquat fruit during different cold storage.

To investigate soluble sugar metabolism and its relationship to chilling injury (CI), loquat fruits were stored at 0 and 5 °C for 5 weeks. CI symptoms were monitored during storage, and soluble sugar content and related enzyme activities were measured. Enzymes activities and substrate levels in the ascorbate-glutathione (AsA-GSH) cycle were also determined. Fruit at 0 °C had lower sucrose levels and higher levels of glucose and fructose than fruit maintained at 5 °C, and also manifested less severe CI symptoms. Fruit at 0 °C also exhibited increased activities of acid invertase, neutral invertase, sucrose phosphatesynthase and sucrose synthase. AsA-GSH cycle activity at 0 °C was much higher than that at 5 °C. Glucose levels correlated positively with levels of AsA and GSH and ascorbate peroxidase (APX) activity. The increased glucose levels are sufficient to account for the chilling tolerance of loquat fruit.