Mutations in AS1 alter the proximal domains of the medial sepals. Medial (A-D, I-L) and lateral (E-H) views of wild-type and as1 mutant flowers (stage 17). A/E: Wild-type flowers. B-D: Detachment of the medial sepals of as1-20 (B) and as1-1 (C) flowers usually occurs at inverted V-shaped abscission zones (AZ). The triangular-shaped regions of proximal zone (PZ) tissue that remain behind do not senesce. In some as1 flowers (D), the sides of the sepals abscise along the edges of larger proximal-distal zones (PDZ) that remain green. F-H: Shedding of the lateral sepals and petals of as1-20 (F/G) and as1-1 (H) flowers leaves behind tissue stubs that remain green. I/J: The altered PZs of as1-20 (I) and as1-1 (J) medial sepals can be visualized during the extended senescence that occurs prior to organ abscission. The constriction of growth associated with the sepal-receptacle boundary in wild-type flowers is located at the base of the altered PZs (see arrowhead, I). K/L: Substantially larger, hourglass-shaped PDZs are observed in some as1-20 (K) and as1-1 (L) medial sepals. Scale bars, 200 μm.