Abstract: 【Objective】Loquat (Eriobotrya japonica Lindl.) fruit is a famous southern fruit in China with its special texture and high metabolism. High metabolism rates reflect fast consumption of energy and rapid depletion of reserves such as carbohydrates and organic acids, so that its senescence is quick after harvest, and they are very liable to spoilage under improper storage conditions (such as room temperature). The cold storage can effectively prolong the shelf life and reduce the decay of loquat fruits, but the phenomenon of the peeling difficulty, flesh lignification, browning and hardening will occur in cold-stored loquat fruits. The quality deterioration of cold-stored loquat fruit is a main reason causing postharvest losses, and has become a limiting factor in market distribution of loquat fruits. The objectives of present study were to investigate the effect of nitric oxide (NO) treatment on the flesh lignification of loquat fruits and the relationship between flesh lignification and energy metabolism, to provide a better foundation for further researches on molecular biological mechanism of regulation on quality deterioration in cold-stored loquat fruits and storage technology of postharvest loquat fruits.【Method】Loquat fruits（E. japonica Lindl.cv. Jiefangzhong）were fumigated with 0(control group), 15 and 25 μL•L-1 NO gas for 2 h in a sealed container and then ventilated for 20 min. The fruits were stored at 5℃ and 85% RH. The changes of membrane permeability, firmness, juice percentage, lignin content, adenosine triphosphate (ATP) content, adenosine diphosphate (ADP) content, adenosine monophosphate (AMP) content, energy charge and the activities of succinate dehydrogenase (SDH), cytochrome oxidase（CCO）, H+-ATPase and Ca2+-ATPase were determined during cold storage, and the correlation between lignin content and energy charge was analyzed after NO treatments. 【Result】 Membrane permeability and firmness of loquat fruits increased gradually and the juice percentage decreased during the storage. Lignin content increased rapidly 10 days later and the chilling injury symptoms of loquat fruits were obvious. As compared with the control group, NO treatments delayed the increase of membrane permeability and fruit firmness, postponed the decrease of juice percentage, and significantly inhibited the formation of lignin content, kept the integrity of the cell membrane, thereby reducing the chilling injury of loquat fruits. ATP content decreased during cold storage. ADP content dropped rapidly in the first 10 days and stayed lower level eventually. The activities of SDH, CCO, H+-ATPase, and Ca2+-ATPase dropped sharply at the middle and later storage (15-30 d). These results showed that mitochondrial function was impaired which lead to energy charge level of loquat fruits drop rapidly. As compared with the control group, NO treatments delayed the decline of ATP and ADP content, inhibited the decrease of the activities of SDH, CCO, H+-ATPase, and Ca2+-ATPase significantly at the middle and later storage, which maintained better mitochondrial function. After 30 days of storage later, energy charge of loquat fruits by 15 and 25 μL•L-1 NO treatments were 11.8% and 12.9%, respectively, higher than control group. Correlation analysis showed that energy charge was very significantly negatively related with lignin content of loquat fruits and the correlation indexes were -0.715** and -0.598**, respectively, in 15 and 25 μL•L-1 NO treatments.【Conclusion】Energy deficit had a closely relationship with lignification of loquat fruits during cold storage. All the results indicated that NO treatments maintained high energy level by regulating the activities of SDH, CCO, H+-ATPase, and Ca2+-ATPase of mitochondria metabolism-related enzymes, thereby enhanced the chilling tolerance and delayed the development of loquat fruits’ lignification, the treatment with 25 μL•L-1 NO was better.

Key words: loquat , fruit , lignification , energy metabolism , nitric oxide