The positions of the sepal and petal abscission zones are altered in as1 mutant flowers. Scanning electron micrographs of wild-type and mutant flowers (stage 17). Medial (A-D) and lateral (E-H) views are shown. A/E: After the outer organs are shed in wild-type flowers, the sepal (se) abscission zone (AZ) appears as a continuous ring adjacent to the pedicel. Individual petal (pe) and stamen (st) AZ regions can be distinguished. The remaining AZ cells have a rounded appearance. Nectary (ne) tissue is sandwiched between the stamen and petal AZs. B: Abscission of the medial (md) sepals is delayed in as1 flowers. Cell separation first occurs at the proximal edges of an inverted V-shaped region. Cell expansion is apparent in the sepal AZ cells that remain associated with this region (see arrowhead). C: Flower shown in (B) with medial sepal removed. Stubs of tissue are visible at the petal attachment sites. D: Inner view of an as1 medial sepal. Expansion of cells within an inverted V-shaped AZ is apparent (see arrowhead). F: Rounded cells are present at the tips of the stubs found at the petal attachment sites. Triangular-shaped regions of tissue are present at the lateral (lt) sepal attachment sites. G: Flower shown in (F) with the medial sepals removed. Positioning of the lateral stamen AZs in as1 flowers is not detectably altered; the medial stamen AZs appear to be slightly displaced. H: Inner view of an as1 lateral sepal (stage 16). An inverted V-shaped AZ is present. Scale bars, 100 μm.