A three-dimensional model of fungal morphogenesis based on the vesicle supply center concept

We developed a three-dimensional model of hyphal morphogenesis under the sa me basic assumption used for the construction of a two-dimensional model. N amely, that the polarized growth of tubular cells (hyphoids) arises from a gradient of wall-building vesicles generated by a vesicle supply center (VS C). Contrary to the 2-D mathematical formulation, the three-dimensional der ivation led to an indetermination whose solution required defining a priori the pattern of expansion of the wall, i.e. defining the overall spatial mo vement of the wall as the newly inserted wall elements displace the existin g wall fabric. The patterns of wall expansion can be described by tracing t he movement of marker points on the cell surface (point trajectories). Poin t trajectories were computed for three different modes of wall expansion of the VSC-generated hyphoids: orthogonal, isometric, and rotational. The 3-D VSC models allowed us to either stipulate or calculate the degree of aniso tropy for each type of wall expansion. Wireframe models were built to visua lize growth anisotropy in each model. Although the overall shape of the thr ee hyphoid models is similar, they differ substantially in point trajectori es and anisotropy. Point trajectories are experimentally testable and were the basis for the conclusion that hyphae grow in orthogonal fashion. (Bartn icki-Garcia et al., 2000. Biophys. J. 79, 2382-2390.) (C) 2001 Academic Pre ss.