Abstract
There are two kinds of translocating sugars in the Rosaceae; sorbitol and sucrose. It is important to understand the mechanism of sugar sensing and signaling in the Rosaceae because sorbitol and sucrose ratio synthesized in source leaves affects fruit quality and vegetative growth. Sorbitol-6-phosphate dehydrogenase (S6DPH) and sucrose-phosphate synthase (SPS) are key enzymes of sorbitol and sucrose synthesis, respectively. In this study, effects of sugars on their gene expression were investigated. Leaf-petiole cuttings of loquat were treated with sugar solution and an analysis of the transcript levels was performed using qRT-PCR. The S6PDH transcript levels were decreased by sorbitol, but increased by sucrose. Simultaneous treatments of sorbitol and sucrose revealed that that was not result from osmotic effects. Glucose and fructose decreased the level. The SPS transcript levels were decreased by any sugars tested. These results suggest the presence of the mechanisms to make sorbitol and sucrose ratio high in source organs of the Rosaceae and that sucrose could be associated with the mechanism as a signal molecule.
