Methyl jasmonate improves pulp flavor by modulating sugar metabolism in postharvest longan fruit

Flavor deterioration reduces the postharvest quality of longan fruit. As an important plant endogenous environmental responsive hormone, the effects of methyl jasmonate (MeJA) treatment on the sugar metabolism of postharvest longan fruit remains to be elucidated. In present study, fruit treated with 100 μmol L⁻¹ MeJA exhibited higher levels of total soluble solids (TSS), sucrose, and total sugar, while lower levels of glucose and fructose. These results are attributed to the inhibited of activities of acid invertase (AI), neutral invertase (NI), and sucrose synthase-cleavage direction (SS-c) in MeJA-treated longan fruit which promote the decomposition of sucrose into glucose and fructose. Additionally, there was an increase in sucrose synthase-synthesis direction (SS-s) and sucrose phosphate synthase (SPS) activities, facilitating sucrose accumulation. Elevated fructokinase (FRK) and hexokinase (HXK) activities in MeJA-treated longan fruit led to a better utilization of glucose and fructose in the glycolysis pathway, thus providing energy for postharvest longan fruit. Compared to the control fruit, the MeJA treatment up-regulated the transcript levels of SS (DlSS-1, DlSS-2, and DlSS-3), DlSPS, DlFRK, and DlHXK, while down-regulating the transcript levels of AI (Cell wall acid invertase (DlCWAI) and soluble acid invertase (DlSAI)), and NI (DlNI-2 and DlNI-3). In the SS gene, correlation analysis showed that DlSS-1 mainly contributes to promote the sucrose synthesis. These findings suggest that MeJA treatment could improve the status of sugar by modulating the enzyme activities and the expression of genes associated with sugar metabolism, thereby preserving the flavor quality of longan fruit.