Carbohydrate Metabolism and Source-Sink Relationships in Peach

Abstract

A growing plant can be viewed as a collection of carbohydrate sinks competing with each other for the available photosynthate supplied by the exporting leaves. Differences in sink strength often result in changes in the ability of various organs to compete for the available food determining final tree growth. A series of experiments have been conducted in peach to study changes and regulation of carbohydrate metabolism in growing organs and get a better understanding of the link between carbohydrate metabolism, sink strength, carbon partitioning and overall tree growth. Along with sucrose, sorbitol represents the major photosynthetic product and the main form of translocated carbon in peach. In sink tissues, sorbitol is converted primarily to fructose via the NAD+-dependent sorbitol dehydrogenase (SDH). The SDH reaction precedes all other steps involved in sorbitol-derived carbon metabolism and may play a significant role in regulating sink strength and growth in peach. Sorbitol and sucrose accumulation and metabolism have been studied in various organs of peach trees, at various developmental stages, and under various stress conditions. Regulation of carbohydrate metabolism along with changes associated to different tissues, developmental stages and stress responses suggest that the ability of peach trees to produce and translocate large amounts of sorbitol (in addition to sucrose) allows for better adaptation to varying environmental conditions. Specifically, the sorbitol metabolic pathway may provide an additional and efficient mechanism to shift carbon (and energy) allocation toward growth or protection from abiotic/biotic stress, and ultimately improve plant performance.