Difference in Energy Metabolism between the Peel and Juice Sac of Red-Fleshed Pomelo Fruit

In order to study the difference in energy metabolism between the peel and juice sac of red-flesh sweet pomelo fruit during postharvest storage, the water contents, malondialdehyde (MDA) contents, energy-related matter contents, energy metabolism-related enzyme activities and energy charge (EC) in three fruit tissues (juice sac, white cortex and peel) as well as the contents of total soluble solid (TSS) and lignin in juice sac were measured during storage at room (25 ℃ as a control) or cold temperatures (8 ℃). The results showed that after 80 days of storage, the contents of TSS and lignin in juice sac increased, whereas water and MDA contents decreased compared to those at harvest. The energy metabolism-related enzyme activities varied significantly among fruit tissues. For all three tissues, a decrease in the levels of adenosine triphosphate (ATP), adenosine diphosphate (ADP) and EC was observed, together with an increase the level of adenosine monophosphate (AMP), indicating that juice sac granulation may be related to energy metabolism. Compared to the control group, cold storage maintained the activities of succinate dehydrogenase (SDH), cytochrome oxidase (CCO), H⁺-ATPase and Ca²⁺-ATPase in the late storage period as well as the levels of ATP, ADP and EC, inhibited the increase in AMP content, maintained the water content of juice sac and white cortex, and repressed the increase in lignin and TSS contents, thereby maintaining the fruit quality and prolonging the storage period of pomelo.