CN-Wheat, a functional-structural model of carbon and nitrogen metabolism in wheat culms after anthesis. I. Model description

Abstract

Background and Aims Improving crops requires better linking of traits and metabolic processes to whole plant performance. In this paper, we present CN-Wheat, a comprehensive and mechanistic model of carbon (C) and nitrogen (N) metabolism within wheat culms after anthesis. Methods The culm is described by modules that represent the roots, photosynthetic organs and grains. Each of them includes structural, storage and mobile materials. Fluxes of C and N among modules occur through a common pool and through transpiration flow. Metabolite variations are represented by differential equations that depend on the physiological processes occurring in each module. A challenging aspect of CN-Wheat lies in the regulation of these processes by metabolite concentrations and the environment perceived by organs. Key Results CN-Wheat simulates the distribution of C and N into wheat culms in relation to photosynthesis, N uptake, metabolite turnover, root exudation and tissue death. Regulation of physiological activities by local concentrations of metabolites appears to be a valuable feature for understanding how the behaviour of the whole plant can emerge from local rules. Conclusions The originality of CN-Wheat is that it proposes an integrated view of plant functioning based on a mechanistic approach. The formalization of each process can be further refined in the future as knowledge progresses. This approach is expected to strengthen our capacity to understand plant responses to their environment and investigate plant traits adapted to changes in agronomical practices or environmental conditions. A companion paper will evaluate the model.

Keywords: Triticum aestivum; Amino acids; carbon; cytokinins; fructans; nitrogen; plant metabolism and physiology; process-based functional–structural plant model; proteins; sink–source relations; sucrose; wheat.

Fig. 1.

Botanical description of the culm structure of wheat as implemented in the model. Culm structure is defined as a single root compartment and photosynthetic organs are organized in phytomers, chaff and grains. Phytomers are numbered acropetally according to their rank (n being the uppermost phytomer) and are composed of a lamina (Lam), a sheath (She) and an internode (Int) or a peduncle (Ped). Parts of the internode n and peduncle are either exposed (exp) or enclosed (enc), i.e. surrounded by the previous sheath.

Fig. 2.

Overview of the model of C and N distribution within wheat architecture for post-anthesis stages. The model consists in a culm described as a root compartment (A), a set of photosynthetic organs (B) and the whole grains (C); each organ includes different metabolites. Inter-organ fluxes occur through transpiration flow [export of nitrates, amino acids and cytokinins from roots to photosynthetic organs (blue arrows)] and through a common pool called phloem (D, red arrows) containing sucrose and amino acids. Definitions and equations of fluxes are detailed in the main text. Regulation is denoted by dotted lines.