Is plant growth driven by sink regulation?

There is a new interest in plant morphogenesis and architecture because molecular genetics is providing new information on their genetic and physiological control. From a crop modeller¿s point of view, this requires particular attention paid to the regulation of sinks associated with organ development, as well as their interactions with assimilate sources. Existing agronomic and architectural crop models are not capable of simulating such interactions. A conceptual framework is presented for the analysis and simulation of crop growth driven by either assimilate source or sink dynamics, building on the assumption that meristems are the main sites in the plant architecture where sinks are initiated and adjusted to resources. Among the numerous sink source feedbacks to be considered are sensing of the plant¿s resource and stress status by meristems (enabling adjustment of morphogenesis), as well as transitory reserves, organ senescence and end-product inhibition of photosynthesis (necessary for the plant to cope with acute imbalances). These feedbacks are to a large extent related to sugar metabolism and can be explained with recent molecular findings on the prominent place in plant development of sugar sensing and the regulation of sucrose cleavage at sink sites. A model integrating these phenomena in a simplified manner, called EcoMeristem, was developed and is being applied in phenotyping for functional-genomics studies on rice. Theoretical evidence and model sensitivity analyses suggested that sink regulation during vegetative growth has a strong effect on plant vigour and growth rate, even at given levels of leaf photosynthetic capacity. However, the usefulness of complex, whole-plant models such as EcoMeristem for heuristic phenotyping approaches remains to be demonstrated. Specific problems are related to the stability of process-based crop parameters across environments, as well as the measurement of such crop parameters that are inaccessible to direct observation. But it is argued that integrated, structural-functional models may be the only means to quantify complex traits, such as those governing adaptive morphology (phenotypic plasticity). Furthermore, such models may be well suited to develop improved plant type concepts in silico. (Résumé d'auteur