Gene Expression and Activity of Enzymes Involved in Sugar Metabolism and Accumulation During “Huangguan” and “Yali” Pear Fruit Development

Abstract

Since the carbohydrate content affects pear flavor during the process of growth, it is necessary to determine the sugar components that accumulate in the fruit. We analyzed the fruit carbohydrate content, and the gene expression and activity of acid invertase (AI), neutral invertase (NI), sucrose synthase (SS), and sucrose phosphate synthase (SPS) during the development of “Huangguan” and “Yali” pears. The results demonstrate that during development, the fruit sugar metabolism of the “Huangguan” pear follows a typical sorbitol–starch-soluble sugars middle model, whereas the “Yali” pear fruit follows a typical sorbitol–sucrose–starch-soluble sugars middle model. In the “Huangguan” pear, we found the AI and NI gene expressions, as well as AI (P < 0.05) and NI (P < 0.01) enzyme activities, to be positively correlated, whereas we found the NI gene expression and NI enzyme activity of “Yali” pear to be negatively correlated (P < 0.01). We observed the high levels of late-stage AI and early-stage SS during development to roughly correspond with the gene expression found in the late and early stages, respectively, suggesting their potential regulatory roles in “Huangguan” pear fruit development. Our results indicate that the primary function of SPS during the early developmental stage is to accumulate sucrose, whereas the primary function of AI is to promote hexose accumulation during the late developmental stage of mature “Yali” pear fruit.