Résumé
Context: Leaves are the main interface between plants and their above ground environment. Thus, leaf size and properties such as specific C and N masses are essential components of plant adaptation to their growing conditions. In the present work, we propose a model of leaf growth that integrates the current knowledge in order to account for leaf plasticity. The model is applied to wheat but is thought to be representative of the functioning of a wide panel of monocotyledon leaves. Model: Growth - cell division and expansion - takes place at the basis of monocotyledon leaves, where young tissues are hidden by the sheaths of older leaves. Thus, two zones are considered in the model: a hidden growing zone, and a mature, exposed zone. Each zone is constituted of structural matter, sucrose, fructan, starch, amino-acid and protein pools. Syntheses, degradations and transports among pools are formalized by differential equations. Structural matter synthesis takes place in the hidden zone, while photosynthesis takes place in the mature zone. The two zones are linked by mass flows: the structural material synthetized in the hidden growing zone is exported to the mature zone, while sucrose and amino acids flow from the mature zone to the hidden growing zone. Besides, the hidden zone is linked to a common pool of sucrose and amino-acids, corresponding to the rest of the plant. Material fluxes and activities of both zones are modelled according to following frame: the activity of the hidden zone activity follows successive developmental stages corresponding to (i) the establishment of the hidden zone, (ii) a steady state functioning resulting in the production of mature tissues and (iii) the end of leaf elongation. The transitions between the phases are related to the emergence of the successive leaves on the tiller. During the first period of leaf growth, the extension rate of the leaf is regulated by amino-acid and sucrose concentrations in the hidden zone. Then, leaf extension is assumed to follow a determined kinetic. Leaf width and specific structural mass are regulated by empirical functions of substrate concentration, which allows computing the structural matter synthesis associated with the growth in dimensions. Sucrose and amino-acids fluxes among compartments are passively driven by concentration gradients. Results: Parameters were estimated from literature on wheat and monocotyledons. Mass and length kinetics, as well as sucrose, amino-acid and fructan concentrations in both hidden and mature zone are realistically simulated. The time at which occurred the sink-source transition of the leaf is consistent with the literature. Conclusion: This is the first model that simultaneously takes account of carbon and nitrogen metabolism, leaf extension, and its coordination with the rest of the plant. At this time the model works for an isolated leaf. It is currently being integrated in a whole plant model and paves the way for mechanistic modelling of plant plasticity depending on carbon and nitrogen resources.