Figure 10.

Model of the development of apple fruitlets and their respective AZs. This model was developed from the analyses of X3177 corymbs, pedicel vascular tissue, and AZ development. Data presented from analyses in this article are schematically summarized in relation to the relative positions of the fruitlets within the corymb. In this model, additional bundles develop early in the central fruit pedicel and may provide it with additional resources such as sorbitol, allowing it to develop a strong dominance over the lateral ones. Global gene expression data indicate a general trend toward an up-regulation of genes involved in vascular tissue differentiation in central pedicels together with a down-regulation of genes involved in sugar transport in L1 pedicels. AZ activation is triggered 4 to 5 d following lateral fruit growth arrest and is initiated with a cycle of cell divisions. Following the formation of layers of isodiametrically flattened cells, we observe a degradation of cell walls and middle lamella at the separation zone by multiple cell wall-modifying enzymes. Cells located on the pedicel side become impregnated with lignin, while cells located on the bourse side accumulate suberin depositions. C, Central fruitlet; L1, small lateral fruitlet; L2, medium lateral fruitlet; L3, big lateral fruitlet.