Polyol Metabolism and Stress Tolerance in Horticultural Plants

Various horticultural plants synthesize polyols as major products of photosynthesis in addition to sucrose and starch and use polyols and sucrose as translocated sugars. The parallel presence of two translocated sugars and their metabolic pathway is specific and complicates the comprehension of their roles in physiology and response to stress. This review first describes the metabolism of sorbitol, focusing on sorbitol-specific metabolizing proteins and their physiological roles in Rosaceae fruit trees. In addition, research on sorbitol as a signal molecule and sorbitol-metabolizing proteins regulated by sugar is discussed. A series of studies regarding various Rosaceae fruit trees has revealed the relationship of sorbitol accumulation with abiotic stresses, including drought, salt, cold, and micronutrient deficiency stresses. On the basis of acknowledging the metabolism of sorbitol, the biochemical mechanism of sorbitol accumulation in response to abiotic stress has been investigated. Furthermore, recent molecular analyses are providing direct evidence of the correlation of the proteins.