Sucrose-metabolizing enzymes and their genes in the arils of two Dimocarpus longan cultivars

This study aimed to investigate sucrose-metabolizing enzymes and their genes in fruits of two longan (Dimocarpus longan Lour) cultivars Cihezhong (CHZ) and Lidongben (LDB). Content of sucrose, glucose, and fructose were measured by high-performance liquid chromatography. The genes of sucrose-metabolizing enzymes were cloned by combining reverse transcription polymerase chain reaction and rapid amplification of cDNA ends, and enzyme activities were analyzed at various points in the fruiting cycle. The total soluble solid (TSS) content of longan arils rose and was positively correlated with sucrose content during maturation and then declined as the fruit senesced. Cihezhong showed a more rapid decrease in sucrose content than LDB. The activities of both sucrose phosphate synthase (SPS) and sucrose synthase (SS) were lower in CHZ, whereas the activities of soluble acid invertase (SAI) and neutral invertase (NI) were higher. The full-length cDNA of the genes of the sucrose-metabolizing enzymes were cloned successfully. The patterns of changes of sucrose synthase-2 (DlSS-2), sucrose synthase-3 (DlSS-3), and neutral invertase-3 (DlNI-3) gene expressions corresponded to those of SS and NI activities. The rate of sucrose decline in the longan fruits was related to sugar receding, sucrose metabolizing enzyme activities, and corresponding gene expressions.