Fig. 2. Hormone response and gene expression during callus induction. All samples were stained with propidium iodide (red) to stain cell walls. (A) In wild-type roots, the auxin-responsive reporter, pDR5rev::3XVENUS-N7 (green), was present in a subset of cells in the root vasculature, lateral root progenitors and columellar root cap cells. (B) Clusters of small cells marked by pDR5rev::3XVENUS-N7 reporter (green) proliferate to form callus, 5 days after induction on CIM. (C) After 8 days of CIM induction, the pDR5rev::3XVENUS-N7 reporter was weakly expressed in callus. (D) Pre-CIM cytokinin-responsive pARR5::GFP reporter expression (green) in the root stele, and lateral root progenitors. (E) pARR5::GFP reporter expression, 8 days and (F) 2 weeks after CIM induction, was visible in proliferating callus cells. (G) Pre-CIM pCUC2::3XVENUS-N7 reporter expression (green) in a subset of cells within the root stele and lateral root meristems. (H) pCUC2::3XVENUS-N7 reporter expression 8 days and (I) 2 weeks after CIM induction marked proliferating callus cells originating from sites of lateral root formation, root meristems and pericycle. (J,K) Two weeks induction on CIM without cytokinin, resulted in cell proliferation and expression of the pCUC2::3XVENUS-N7 (J) and pARR5::GFP reporters (K). (L) Two weeks after induction on CIM without 2,4-D, callus was not induced and expression of the pCUC2::3XVENUS-N7 reporter was faint and confined to the vasculature of the primary root. Scale bars: 50 µm (A,B,D,E,G,H); 100 µm (C,F,I-L). Arrowheads indicate lateral roots.