Fig. 5. Initiation of shoot meristem stem cells in the Arabidopsis embryo. An OC precursor cell lineage expressing WUS (red) is established in the four subepidermal cells of the 16-cell embryo. As judged from CLV3 expression (blue), stem cells are induced in heart stage embryos. The thick line indicates the clonal boundary between apical and basal derivatives of the 8-cell embryo (figure adapted from Schrick and Laux, 2000).