Cell wall hydrolases, their mRNAs, and ultrastructural details of cell wall digestion have been studied in peach abscission zones (AZ) located at the base of flower bud (AZ1) and the base of flower receptacle (AZ2), respectively.
Induction of abscission was obtained by treatment of explants with exogenous ethylene. Cell separation patterns of the two examined abscission zones have been compared with those of other already known AZs of peach, i.e. the AZs located between fruit and peduncle and the leaf AZ. Analyses have shown similarities in response to ethylene treatment between AZ1 and leaf AZ and between AZ2 and AZs, respectively. Results have been discussed considering the precise position of AZ1 and AZ2 on the flower bud. The timing of functional differentiation, evaluated as the cells’ability to respond to induction by ethylene treatments, showed that AZ1 and AZ2 became functional after bud breaking and bud scale shedding. Later on, they lost their functionality at about 6–7 wk from anthesis. AZ3 became functional very precociously and could be activated 1 wk after anthesis in the fertilized flowers. In the latter zone the cells could also undergo a morphological predifferentiation, even though it occurred a long time after the acquisition of the ethylene responsiveness. This finding shows that morphological differentiation is not necessarily a prerequisite for those cells to become competent to respond to the abscission inducing stimuli.