Low-Temperature Storage Delays Sucrose Degradation in Postharvest Longan Fruit

Low-temperature (LT) storage effectively mitigates postharvest deterioration in longan fruit. To investigate the changes in sucrose metabolism underlying this effect, we compared the dynamic changes in sugar metabolism indicators under LT and room-temperature (RT) conditions. This sugar conversion was associated with the increased activities of acid invertase (AI), neutral invertase (NI), sucrose synthase (SS), fructokinase (FRK) and hexokinase (HXK) and the inhibited activity of sucrose phosphate synthase (SPS). Consistently, the transcription levels of DlAI, DlNI, DlSS, DlFRK and DlHXK were upregulated, while the transcriptional level of DlSPS was suppressed. In contrast, LT storage maintained higher sucrose levels with gradual declines in glucose and fructose. Meanwhile, the activities of AI, NI, SS, FRK and HXK were inhibited while SPS activity was promoted, accompanied by transcriptional downregulation of DlAI, DlNI, DlSS, DlSPS, and DlFRK. Pearson correlation and principal component analyses further revealed distinct sugar-metabolite networks between the two storage regimes. Collectively, LT storage preserves sucrose, coinciding with the transcriptional repression of catabolic pathways while maintaining biosynthetic capacity, which may contribute to restraining sugar depletion. These findings advance our understanding of LT-regulated sugar metabolism and offer theoretical support for optimizing postharvest cold-storage strategies.