Fig. 5. CUC::GUS expression in embryos. (A) Top view of the embryo apex. The cotyledon boundary is indicated in turquoise: C, cotyledon; EM, embryonic meristem. (B-O) Siliques of cuc2-1/cuc2-1 atbrm-1/+ (B-I) and cuc1-1/cuc1-1 syd-2/+ (J-O) plants were examined. Genotypes are indicated to the right. cuc2 comprises cuc2-1/cuc2-1+/+ and cuc2-1/cuc2-1 atbrm-1/+; whereas cuc1 comprises cuc1-1/cuc1-1+/+ and cuc1-1/cuc1-1 syd-2/+. Representative embryos expressing CUC1::GUS (B-D,G,J,M), CUC2::GUS (E,H,K,N) and CUC3::GUS (F,I,L,O) are shown. When viewed from the front (f), CUC::GUS expression in the cotyledon boundary will appear as a small circle of expression (C-F,J-L). When viewed from the side (s) a line of expression will be observed (B). Embryos were at the torpedo stage (B,C) or at the bent cotyledon stage (D-O). Bent cotyledon stage embryos with fused cotyledons present a side view (s), whereas non-fused embryos usually present a front (f) view. Orientation (s,f) is indicated in each panel. In C, the same cuc2-1 atbrm-1 embryo is shown from two sides: nonfused (left) and fused (right). (G-I) CUC::GUS expression missing in the presumptive cotyledon boundary in the double mutants is indicated by a yellow arrow. (N) CUC2::GUS expression in the boundary between the cotyledons is severely reduced in cuc1-1 syd-2. Faint residual CUC2::GUS expression was observed in the presumptive boundary between each cotyledon and the shoot apical meristem, consistent with the observed lack of shoot apical meristem defects in cuc1-1 syd-2 (Fig. 2C). Where applicable, red arrowheads indicate the end points of cotyledon fusions (C,G-I,M-O). Scale bars: 100 µm.