Figure 9.1.

Ground tissue formation in the root. (A) Schematic of a longitudinal section of the Arabidopsis root tip. Individual or groups of cell types are depicted in different colors. (B) Cut away of the ground tissue cell types from (A) with an emphasis on the asymmetric divisions and cellular defects in short root (shr) and scarecrow (scr) mutants. (B, upper panel) Ground tissue formation in wild type. (B upper panel, left to right) The CEI (dark green) divides transversely (white arrowheads) to regenerate itself and produce the CEID (light green). The CEID then divides longitudinally (black arrowhead) to generate the cells of the endodermis (blue) and cortex (yellow). (B, center panel) Ground tissue formation in short root. In the absence of the longitudinal asymmetric cell division, a single layer of ground tissue with cortical cell features (yellow with white stripes) forms. (B, lower panel) Ground tissue formation in scarecrow. The longitudinal asymmetric cell division also does not occur; however, the single layer of ground tissue exhibits both endodermal and cortical cell features (yellow with blue stripes). (C) Schematic of a portion of the Arabidopsis root tip, focusing on the localization of SHR mRNA, SHR protein and SCR mRNA and protein. Yellow arrows depict SHR protein movement from the stele into the adjacent cell layer. Note that SHR and SCR proteins are colocalized in the nuclei (small circles within the cells) of the adjacent cell layer. This figure was adapted from Petricka et al. (2009).