Garden with Insight v1.0 Help: apical dominance

Apical dominance is a mechanism plants use to control their growth habit (shape) by communicating between different parts of the plant. An apical meristem (bud) at the end of a plant branch puts out a plant hormone, which diffuses down the stem and communicates with all the other meristems on the branch. Every branch has one or more axillary (side) meristems along its length that are just waiting to branch out. The hormone tells them to sit still because the branch needs to grow longer. Thus the apex (tip) of the branch is dominating the rest of the branch.

If the bud at the tip is cut off, or if a response to some environmental cue changes the tip's growth (according to the genetic program), the apical dominance hormone gradient decreases. When this happens some of the side buds jump into action and begin to create new branches. As they grow, they turn into apical meristems and themselves put out an apical dominance hormone so they can lengthen their new branch.

Since the hormone is in a gradient, which means it decreases as you move away from its source (like food coloring in water), axillary meristems furthest away from the apical meristem are inhibited least. This means the plant can finely regulate how much branching goes on by reducing the hormone concentration only slightly to allow just the lowest axillary buds to branch.

This fascinating mechanism of control by some modular parts over others enables the plant to concentrate its resources on what is needed at the moment: extra height to reach above the shade, or more leaves to make good use of a sunny spot (or both, in different parts of the plant).

The simulation of apical dominance in this version of the program is simple. If an axillary meristem is within a node distance smaller than that of a parameter (representing the strength of apical dominance), it will not branch. Axillary meristems far enough away from the apex to contemplate branching will branch with a probability determined by another parameter. So this is like apical dominance with a stepped gradient (all or nothing).

How it works:
branching