A steady-state model for apical wall growth in fungi

The presence of cell walls makes plants immobile but fungi (defined as a separate kingdom, Whittaker 1969) have evolved as organisms which, despite the presence of cell walls, have a certain degree of mobility due to apical growth. The mycelial colony, consisting of a system of branched hyphae, may thus grow over and through substrates. Consequently, the actively growing part of the fungal mycelium constantly moves away from its original position while colonizing dead substrata (saprotrophs) or living organisms (biothrophs) as in parasitic and symbiotic associations. These activities are particularly prominent in relation to plants, as evidenced by the fact that fungi are the main decomposers of the lignocellulosic plant cell wall (Crawford 1981), they are also the main plant pathogens (Dickinson & Lucas 1982) and they form mycorrhizae with nearly all land plants (Harley & Smith 1983). Although the association of fungi with healthy animals (including man) is limited, their colonizing ability is now becoming a problem in immuno-compromised patients (Chandler 1986).