Effects of Photosynthate Transport and Water Flow to Young Fruit on Fruit Drop via Ethylene Synthesis in Persimmon (Diospyros kaki Thunb.)

In this study, we aimed to characterize which factors control ethylene production and fruit drop in persimmon (Diospyros kaki Thunb.). We determined the effects of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU; a specific photosynthesis inhibitor) and defoliation treatments on the photosynthetic rate, transpiration rate, sap flow, fruit drop, and ethylene evolution. DCMU treatment, which prevented photosynthate transport but allowed water flow, promoted fruit drop by 67% 10 days after treatment. Defoliation treatment, which prevented both photosynthate and water transport, significantly hastened fruit drop. On average, fruit drop occurred 2 days earlier with defoliation treatment than DCMU treatment. Compared with the control, treated fruit attached to the tree showed an increasing trend in ethylene production, although at a low level (<= 0.8 nL.g(-1).h(-1) in the flesh; <= 20 nL.g(-1).h(-1) in the calyx). Fruit abscission is thought to be induced by a following ethylene burst, because fruit showing an abscission trend showed high rates of ethylene production (almost 200 nL.g(-1).h(-1)). Thus, blocking photosynthate transport and water flow induced initial and autocatalytic increases in the production of ethylene, which plays a crucial role in triggering fruit drop. Overall, our results suggest that the transport of photosynthates, or both photosynthates and water, to fruit inhibits fruit drop by preventing the induction of ethylene synthesis in young persimmon fruit.