Roles of calcium gradients in hyphal tip growth: a mathematical model.

A tip-high Ca2+ gradient is observed in growing fungal hyphae, but so far its role remains unknown. A mathematical model is presented, which provides evidence for the functions of such a Ca2+ gradient, in terms of its non-linear effect on the visco-elastic properties of the hyphal cytoskeleton. The model explains how the Ca2+ status at the tip may be responsible for the apical accumulation of vesicles and for an increase in the cytogel osmotic pressure, accompanied by the contraction of the cytoskeleton. The experimentally observed retraction of the spitzenkörper preceding the initiation of a branch is also reproduced, by simulating a subapical transient release of Ca2+ from internal stores.