Figure 1.

Developmental Stages during Lateral Root Formation in Arabidopsis.

(A) Radial organization of the Arabidopsis primary root showing the cortical (C), endodermal (E), epidermal (EP), and pericycle (P) cell layers.

(B) Radial section of the primary root showing a lateral root primordium (LR) developing opposite the xylem pole.

(C) Longitudinal section of the primary root, with arrows indicating the cell walls of a founder pericycle cell before the first anticlinal division, initiating the formation of a lateral root primordium (stage 0).

(D) Two founder pericycle cells, each having undergone a single asymmetric anticlinal division (stage Ib primordium). Arrowheads indicate the positions of the newly formed cell walls.

(E) One founder cell has undergone three asymmetric anticlinal divisions, whereas the other has formed a single anticlinal division (stage Id).

(F) A stage II primordium that had previously undergone three asymmetric anticlinal divisions, with the newly formed inner layer (IL) and outer layer (OL) indicated.

(G) A stage II primordium that underwent six asymmetric anticlinal divisions before the first periclinal division.

(H) A newly emerged lateral root primordium.

. Asterisks indicate xylem poles.