Plant growth modelling and the integration of shoot and root activities without communicating messengers: Opinion

In this paper, we consider the use of compartmental modelling to examine the integration of root and shoot resource allocation without the use of partitioning functions or communicating messengers. Emphasing overall growth and the partitioning of biomass and resources between shoots and roots, we discuss the use of modelling to explore mechanisms of control, to direct experimentation and to test physiological hypotheses concerning their regulation. We discuss how the interrelationships of allocation processes and growth might be considered by generating ''mutants'' of a basic model, and we suggest this approach as one general way to increase interactions between modellers and experimentalists. Recognizing that the meristematic origin of plant organs inherently limits the usefulness of two compartment (root and shoot) models, we consider three problems to be solved (both computationally and experimentally) in extending modelling to more complex simulations: the incorporation of direct root/shoot signaling for regulation of the shoot-shoot ratio (S/R), the modelling of growth of individual leaves, and the definition of shoots based on component leaves and internodes. Finally, we briefly consider the problem of nitrogen and the regulation of S/R as an example of experimentation directed by modelling.