Figure 2.

Conceptual model of tissue and substrate (i.e. assimilate) fluxes among functionally distinct zones of a regrowing tiller of perennial ryegrass. Leaf expansion is confined to the basal region of the IM-AE and gives rise to a flux of tissue to the EX-AE. As leaves stop to expand, they are ”displaced” to the expanded leaves category (EX-AE → EX-FE, IM-AE → EN-FE). Tissue flux is mainly in the form of structural biomass. Substrate flux is mainly directed toward the immature zone, where cell production, expansion, and maturation (including synthesis of proteins and secondary cell walls) take place. Substrate fluxes to and from other plant parts are not shown.