Fig. 2.

Apical dominance. (A–C) Schematic representations of an apex in the vegetative state (A), in the flowering state (B), and of the root (C). Other aspects are represented as in Fig. 1A. (D–F) Selected stages of the simulation of acropetal bud activation. The simulated plant initially consists of a vegetative apex and root (D). As the plant grows, auxin from the apex is transported basipetally and inhibits lateral buds close to the apex (E). Auxin levels decrease with distance from the growing apex; this decrease eventually switches lateral buds to the active state, producing an acropetal activation sequence (F). (G–I) Simulation of decapitation experiments. After decapitation of a growing plant (G), the lateral apex closest to the decapitation site is activated and becomes dominant (H). Several buds close to the decapitation site are activated in the case of overcompensation (I). (J) GUS expression (red arrowheads) detected with the chromogenic substrate X-Gluc, driven by the DR5 auxin-responsive promoter in an Arabidopsis stem section immediately below a growing lateral shoot, prepared as in ref. 9. Lateral shoots vascularize into 2 adjacent vascular bundles in the main stem (avb) (19, 22) lt: leaf trace.