Modeling translocation and metabolism in plants

A whole-plant model of movement of water and nutrients will predict growth. In this model, a plant consists of tissues; root, stem, and leaf, and each tissue has cells with compartments; apoplast, cytoplast, phloem, and xylem. Diffusion leads to rapid short-distance transport of water among compartments within cells. All metabolism of nutrients, such as sugar, nitrate, amino acid, protein, and structure, occurs in cytoplast, and follows the same Michaelis-Menten kinetics in each tissue. All transfers of water to and from cytoplast, phloem, or xylem, are through apoplast. Compartment volume and water content define water potential, and in combination with solute content, define turgor and osmotic pressure. Volume increases according to structure. Long-distance transport between tissues is in xylem and phloem. Nitrate is moved from roots to leaves in xylem by transpiration. Sugar is moved from leaves to roots in phloem by translocation. Nitrate is transformed into ammonium and amino acids. Protein and structure are synthesized in the cytoplast, and cannot move between tissues. Linear relations describe water potential, and short-distance movement among compartments within one tissue, and long-distance transport in xylem and phloem between tissues, and metabolism with each tissue. These relations were programmed in VENSIM (Ventana Systems) to examine the effect of external nitrate, and sunlight, on movement of water and nutrients in xylem and phloem, and on water content and metabolites in organs of an idealized plant.