Molecular biological approach to improve the sink and source function in Rosaceae fruit tree

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The purpose of this research is to make clear the sink-source relation of fruit by investigating the properties and gene expression of enzymes which play an important role for sugar metabolism and the vacuolar function to accumulate sugars.1. Sorbitol dehydrogenase was purified from Japanese pear fruit, and its cDNA was also cloned from fruits of apple, loquat and peach. The gene expression was investigated throughout the development of their fruits.2. The gene of sorbitol-6-phosphate dehydrogenase expressed on source leaves unfolded enough, but not on leaves folded yet.3. Sucrsoe synthase isoform appearing with sugar accumulation was purified and the reaction inclined to sucrose synthesis rather than sucrose cleavage. The direction of reaction changes easily by phosphorylation and non-phosphorylation.4. Two soluble acid invertases were purified from Japanese pear fruit, and there was no difference between properties of both isoforms.5. We isolated the cDNA clone of fructokinase which is closely relating to fructose accumulation and examined the relations between the gene expression and fructose metabolism.6. H^+-ATPase and H^+-pyrophosphatase which supply the energy needed to uptake sugars into vacuole were purified from pear fruit, and the gene expression throughout fruit development were investigated using cDNA clone of their subunits.7. We could prove the presence of sugar transporters across the tonoplast by sugar uptake experiment, although could not isolate their protein and cDNA.As described above, we could obtain the proteins and cDNA of some enzymes needed to accumulate sugars into fruit, analyzed their gene expressions and clarified partially the melecular mechanism of sugar accumulation.