Schematic of the diel–multicell–FBA model of leaf tissue showing the inputs, outputs, and exchanges of metabolites, gases, and minerals between the 4 cell types considered. Each cell contains a core stoichiometric model of central metabolism, and fluxes are scaled to account for the different proportions of each cell type in the leaf. Each cell model is further replicated to account for the light phase (above) and the dark phase (below) with certain metabolites and minerals allowed to be passed between the phases as indicated. Since sieve elements do not have vacuoles, only starch is allowed to accumulate in them. The cells are all connected via the apoplast (this is also split into light phase apoplast and dark phase apoplast). However, only the companion cell, sieve element, and petiole sieve element cells are symplastically connected; sugars and amino acids must transit through the apoplast in order to move between the mesophyll and companion cells. CC, companion cell; MC, mesophyll cell; SE, sieve element (in the leaf); petiole SE, sieve element in the petiole, fru, fructose, glu, glucose.