Shoot branching is a key determinant of aboveground plant form. The timing of bud break and the number of branches formed subsequently determine the amount of light absorbed by the plant, and the plant’s competitive strength in relation to neighbouring plants in terms of light capture. Bud break and branch growth are known to be regulated by internal factors which are influenced by environmental signals. These internal and environmental factors do not operate independently but are part of a complex regulatory system that operates at the levels of the cell, the organ and the whole plant, up to the level of populations.

One of the main internal factors affecting bud break is hormonal regulation, with pivotal roles for plant hormones auxin, cytokinin and strigolactone. These hormones have signalling properties in various compartments of the plant. The hormone signalling network is a delicate, finely tuned network in which the actors keep each other in balance. The exact state of this balance can be modified by environmental cues. A key environmental signal known to result in bud break suppression is a low red / far-red intensity ratio (R:FR) of the light reflected by neighbouring plants. A low R:FR is indicative of surrounding vegetation, since red light is mainly absorbed by green plant parts, in contrast to far-red light which is mainly scattered. Reduced branching is an important aspect of the "shade avoidance syndrome". Shade avoidance enables plants to anticipate future competition by preventing being shaded, rather than to react to prevailing shade conditions.

A modelling approach will be presented that integrates hormone synthesis, transport and signalling, bud break, branch formation, plant development, light signalling and shade avoidance in Arabidopsis thaliana. It will be demonstrated that phenomena such as acropetal branching, bud break upon decapitation, and shade avoidance responses can be simulated as emerging behaviour, controlled by hormone and light signalling. Opportunities will be presented to study branching behaviour in other plants, plant competition and crop management.