Hyphal tip growth and absorptive nutrition.

(a) TEM (transmission electron micrograph) showing the hyphal tip of Aspergillus nidulans, a fungus commonly used as a genetic model system. (b) Diagram of a hyphal tip, showing vesicles of two types: those containing cell-wall materials, and those bearing digestive enzymes. On fusion of these vesicles with the plasma membrane, both types of vesicle contents are released to the cell exterior. Digestive enzymes degrade extracellular organic polymers into smaller components that can be taken into hyphae by means of plasma membrane transporter proteins. The uptake of minerals and organic molecules causes osmotic water uptake, with the result that cells enlarge and hyphal tips extend. New cell-wall materials are added to the hyphal tip as it extends.