Fig. 3. Morphology of vestigial AZs in wild type (Col-0) and bop1 bop2. (A-F) Scanning electron micrographs of stem fracture planes in Arabidopsis following removal of cauline leaves. (A) Fracture plane in wild type shows ruptured cells following removal of green leaves. (B) Removal of 50% yellow leaves reveals a few rounded AZ cells. (C) Fracture planes from yellow leaves often show many rounded AZ cells. Stipules always flank the fracture plane (A, arrow). (D-F) Corresponding fracture planes of bop1 bop2 from green (D), 50% yellow (E) and yellow (F) cauline leaves show no development of rounded AZ cells or evidence of flanking stipules. (G,H) A furrow of narrowed cells (arrows) flanked by stipules (H, arrowhead) is observed between the abaxial surface of the cauline leaf and the stem in wild type. (I) Toluidine Blue-stained longitudinal sections show darkened files of cells that mark the vestigial AZ (arrow) at the adaxial boundary between the cauline leaf and stem in wild type and at the branching point with the primary inflorescence stem (arrowhead). The leaf-steam boundary furrow is also apparent (asterisk). (J,K) bop1 bop2 cauline leaves lack stipules and leaf-stem boundary furrow. (L) No vestigial AZs are visible in bop1 bop2 sections. as, axillary shoot; cl, cauline leaf; st, primary inflorescence stem. Scale bars: 600 µm in A-H,J,K; 35 µm in I,L.