Fig. 4. Prolonged expression of PIN1 at the margin accompanies leaflet initiation in FIL>>BP leaves. (A-D) Young rosette leaves stained for GUS expression of (A,B) PIN1::GUS in wild type (A) and 35S::BP (B), and (C,D) DR5::GUS in wild type (C) and 35S::BP (D). (E-J) Confocal micrographs of GFP expression (green) in developing leaf margins, 7 (E,H), 10 (F,I) and 12 (G,J) days after germination. (E-G) PIN1:GFP in (E) wild-type (arrow indicates GFP expression in initiating serration), (F) wild-type (arrow indicates a basal shift in GFP expression as a second serration initiates), and (G) FIL>>BP (arrows indicate prolonged GFP expression in developing lobes; inset shows a magnification of one of these lobes). (H-J) ANT::GFP is expressed in a similar manner in (H) wild type (arrows indicate GFP expression in initiating serrations), (I) wild-type (arrow indicates a basal shift in GFP expression as a second serration initiates), and (J) FIL>>BP (arrows indicate prolonged GFP expression in developing lobes). (K,L) Rosette leaves of FIL>>BP plants grown on (K) MS medium and (L) MS medium supplemented with 10 µM NPA. (M) Confocal micrograph of PIN1:GFP expression in a developing leaf margin of FIL>>BP plants grown on MS medium supplemented with 5 µM NPA. (N) Proposed role of auxin in regulating BP activity and leaf shape. AS1 acts in overlapping pathways with PIN1 and AXR1 to repress BP expression in Arabidopsis leaves (solid barred lines), thus contributing to definition of the leaf-meristem boundary and control of leaf development. PIN1 is also required to elaborate margin outgrowths (arrow) in wild-type leaves and in leaves in which BP is ectopically expressed. Such BP-mediated changes in leaf shape may involve restriction of the PIN1 expression domain by BP (dotted barred line). Arrows and barred lines denote genetic and not physical interactions. Red indicates chlorophyll autofluorescence. Scale bars: 200 µm in A-D; 20 µm in E-J; 0.5 cm in K,L; 10 µm in M.