Figure 1. Model of wall structure at apex, lateral walls and branch points. Different kinds of microvesicles are produced by the Golgi bodies and transported to the apex (a) and branch sites (b) on cytoskeletal elements: microfilaments (beaded lines) and microtubules (parallel lines). The vesicles accumulate at the apex to form the Spitzenkörper. Enzymes, such as chitin and glucan synthases, contained in the vesicles (solid circles) become incorporated in the cell plasma membrane or released into the wall area by fusion of the vesicles with the plasma membrane. Other vesicles (open circles) may contain matrix components and other materials needed for wall biosynthesis and structure. In the apical dome the chitin and -(1-3)-glucans become more crystalline by hydrogen bonding and become progressively more crosslinked by the formation of covalent bonds (black dots) as the wall matures. Branch formation requires the redirection or localized accumulation of vesicles containing both wall softening (lytic) enzymes and synthases. Turgor pressure is assumed to push out the weakened wall, but cytoskeletal elements may also play an important role in branch formation. Modified with permission from Gooday GW (1995) Cell walls. In: Gow NAR and Gadd GM (eds) The Growing Fungus, pp. 43–62. London: Chapman and Hall. Copyright © 1995 Plenum Publishers.

Figure 2. Major cell wall structural components. Cellulose and chitin are straight-chain polymers, able to form parallel strands that become almost crystalline. -glucans (a -(1,3) chain with -(1,6) branches) can form complex interlinked structures with other glucans and glycoproteins.