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 degrees 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 degrees C had lower sucrose levels and higher levels of glucose and fructose than fruit maintained at 5 degrees C, and also manifested less severe CI symptoms. Fruit at 0 degrees C also exhibited increased activities of acid invertase, neutral invertase, sucrose phosphatesynthase and sucrose synthase. AsA-GSH cycle activity at 0 degrees C was much higher than that at 5 degrees 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.