Carbohydrate metabolism and its possible roles in endodormancy transition in Japanese pear

In order to elucidate the possible roles of carbohydrate in Japanese pear (Pyrus pyrifolia, 'Kosui') during endodormancy, seasonal changes of carbohydrate concentrations and the activities of sorbitol- and sucrose-metabolizing enzymes were investigated in the lateral flower buds and current shoots. 'Kosui' flower buds were released from endodormancy between mid- and late December. During this period, a decrease in the shoot starch concentration and an increase of soluble sugars in both the flower buds and shoots were observed, concomitant with the onset of acid invertase and sucrose synthase activity in flower buds. Following these changes, a notable accumulation of sorbitol was recorded in xylem sap in late-December, accompanied by considerable expression of the sorbitol transporter gene (PpSOT2) in shoots. After that, in mid- to late January, flower buds exhibited increased activity of NAD-dependent sorbitol dehydrogenase simultaneous to an increase of sorbitol transporter gene (PpSOT3) expression. We, thus, assume that pear flower buds regulate endodormancy by modulating the systems for sorbitol- and sucrose-catabolism depending on the dormancy stage. We also discuss the possible inhibitory effect of sorbitol on flower bud growth during endodormancy.

► We have examined carbohydrate dynamics during the endodormancy period of Japanese pear. ► As endodormancy release approaches, starch stored in shoots was largely degraded. ► At the time of endodormancy release, much sorbitol had accumulated in xylem sap. ► After sorbitol accumulation, buds' activity to uptake/catabolize sorbitol increased.