Fig. 5. Ectopic organogenesis was a non cell-autonomous response to WUS. (A,B) Whole seedlings stained for GUS activity after induction of ectopic organogenesis. 35S::lox-uidA-lox-WUS; hsp18.2::Cre; 35S::STM-GR seedlings were grown on medium with 1 µM dexamethasone for 10 days (A) or 7 days (B) after heat shock. Arrows indicate GUS-expressing outgrowths. (C) Transverse section through the hypocotyl of a seedling treated as described in B, showing an outgrowth with GUS-expressing cells. Bar: 100 µm. (D-G) Detection of WUS mRNA by in situ hybridisation. (D) Control showing endogenous WUS expression (arrow) below the centre of the meristem, in a transverse section through the apical meristem (m) and leaf primordia (p) of a 35S::STM-GR seedling (equivalent to the seedlings in Figs 1B and 2B). (E-G) Patches of ectopic WUS mRNA in sections through a leaf primordium (p) and cotyledons (c) in seedlings with mosaic WUS expression combined with STM-GR activation (equivalent to the seedlings shown in Fig. 4C,D). The arrow indicates outgrowths on cotyledons, consisting of cells that did not express WUS. Bar: 100 µm.