Both sorbitol and sucrose are synthesized in source leaves and transported to fruit for supporting fruit growth in tree fruit species of the Rosaceae family. In apple (Malus domestica), antisense suppression of aldose-6-phosphate reductase, the key enzyme for sorbitol synthesis, significantly decreased the sorbitol concentration but increased the sucrose concentration in leaves, leading to a lower sorbitol but a higher sucrose supply to fruit in these plants. In response to this altered carbon supply, the transgenic fruit had lower concentration of sorbitol and much higher concentration of glucose but similar levels of fructose, sucrose, and starch throughout fruit development relative to the untransformed control. Activities of sorbitol dehydrogenase, fructokinase, and sucrose phosphate synthase were lower, whereas activities of neutral invertase, sucrose synthase, and hexokinase were higher in the transgenic fruit during fruit development. Transcript levels of MdSOT1, MdSDHs, MdFK2, and MdSPS3/6 were downregulated, whereas transcript levels of MdSUC1/4, MdSUSY1-3, MdNIV1/3, MdHKs, and MdTMT1 were upregulated in the transgenic fruit. These findings suggest that the Sucrose cycle and the sugar transport system are very effective in maintaining the level of fructose and provide insights into the roles of sorbitol and sucrose in regulating sugar metabolism and accumulation in sorbitol-synthesizing species.

中文翻译：

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山梨糖醇合成减少的转基因苹果树上糖的代谢和积累。

山梨糖醇和蔗糖都在源叶中合成，并运输到果实中，以支持蔷薇科家族树果实中的果实生长。在苹果（苹果属家蝇），反义抑制醛糖-6-磷酸还原酶山梨醇合成的关键酶，显着降低了山梨醇的浓度，但增加了叶片中的蔗糖浓度，导致这些植物中山梨醇的含量降低，但水果的蔗糖供应量增加。响应于这种碳供应的变化，相对于未转化的对照，转基因果实在整个果实发育中具有较低的山梨糖醇浓度和较高的葡萄糖浓度，但是果糖，蔗糖和淀粉的水平相似。在果实发育期间，转基因果实中的山梨糖醇脱氢酶，果糖激酶和蔗糖磷酸合酶的活性较低，而中性转化酶，蔗糖合酶和己糖激酶的活性较高。的转录水平MdSOT1，MdSDHs，MdFK2和MdSPS3 / 6被下调，而MdSUC1 / 4，MdSUSY1-3，MdNIV1 / 3，MdHK s和MdTMT1的转录水平在转基因果实中被上调。这些发现表明，蔗糖循环和糖转运系统在维持果糖水平方面非常有效，并提供了山梨糖醇和蔗糖在调节山梨糖醇合成物种的糖代谢和积累中的作用的见解。