The Roles of Actin in Tip Growth of Fungi

This chapter discusses the multiple features of tip growth and examines the organization of actin in the growth zones. A synthesis of these data provides models for the possible roles of actin in the diverse processes. The process of tip growth is the hallmark of the fungal kingdom. The process occurs in other walled cells, such as pollen tubes and root hairs, but in the other kingdoms it is restricted to a few specialized cell types, whereas, among the fungi, it is the mode of growth that generates the dominant vegetative structure, the hypha. The fundamental basis of tip growth is that it results from the balance between highly localized cell extensibility and osmotically generated turgor pressure. The extensibility is likely to be regulated by many factors, and equally, turgor pressure is the result of multiple inputs, such as membrane-located transport channels, membrane and cell wall permeability, and intracellular and extracellular solute concentrations—all of which are regulated by many systems. The disposition, properties, and functioning of actin arrays are known to be influenced by three general intracellular features: ion composition and concentration, actin-binding proteins (ABP), and other cytoskeletal elements.