Fig. 6. The CLV1 promoter was transiently activated during ectopic organogenesis. (A,B) Optical sections through the apex of 3-day old control seedlings. (A) Seedling lacking CLV1::GFP. The red chlorophyll fluorescence marks the base of the cotyledon petioles; the space in the centre is occupied by the meristem and the first two leaf primordia. (B) CLV1::GFP seedling. GFP signal is visible in the meristem (arrow); the dark areas adjacent to the meristem is occupied by leaf primordia. (C-F) Longitudinal optical sections through the hypocotyls of seedlings with ectopic organs (35S::lox-uidA-lox-WUS; hsp18.2::Cre; 35S::STM-GR, heat shocked and plated on medium with 1 µM dexamethasone; equivalent to the seedlings shown in Figs 4C,D and 5B). (C-E) CLV1::GFP seedlings, (C) 2 days, (D) 7 days and (E) 10 days after heat shock. The arrows in C indicate the division of epidermal cells seen in early stages of outgrowth formation. (F) Control seedling lacking CLV1::GFP, 10 days after heat shock. (G,H) Longitudinal optical sections through the hypocotyls of control seedlings (35S::lox-uidA-lox-WUS; hsp18.2::Cre; 35S::STM-GR, CLV1::GFP) with activation of STM-GR or WUS alone. (G) seedling that was not heat shocked, after growth for 7 days in medium with 1 µM dexamethasone (STM-GR activation alone); (H) seedling that was heat shocked and grown for 7 days on medium without dexamethasone (WUS activation alone). The green/yellow signal seen along part of the walls of the large cells in H is an artefact of light refraction, also seen in seedlings that lacked CLV1::GFP. Bar: 100 µm.