Fig. 5. Phenotypes associated with the brassinosteroid, ethylene, cytokinin and abscisic acid receptor mutants. All images are shown against wild type for comparison. (A) The brassinosteroid receptor mutant bri1-301 (bottom) shows a dwarf phenotype. (B) The dark-grown ethylene receptor mutant ein4 (right) lacks the triple response (left; see main text). (C) The triple cytokinin receptor mutant cre1 ahk2 ahk3 (right) shows reduced growth. (D) The root vascular bundle normally consists of xylem, phloem and procambium cell files, whereas in wol (bottom), or in cre1 ahk2 ahk3 (not shown), there are fewer vascular cell lineages, all of which differentiate as protoxylem. The vascular bundle is encircled by a layer of pericycle cells (asterisks) (E) The abscisic acid receptor mutant fca (right) flowers later than wild type, as demonstrated by increased leaf number at flowering. Scale bars: in C, 2 mm; in D, 10 µm. [A is reprinted, with permission, from Cano-Delgado et al. (Cano-Delgado et al., 2004); B is reprinted, with permission, from Hua et al. (Hua et al., 1998); E is reprinted, with permission, from Amasino (Amasino, 2003).]