Algal morphogenesis: modelling interspecific variation in Micrasterias with reaction-diffusion patterned catalysis of cell surface growth

Semi-cell morphogenesis in unicellular desmid algae of the genus Micrasteri as generates a stellar shape by repeated dichotomous branching of growing t ips of the cell surface. The numerous species of the genus display variatio ns of the branching pattern that differ markedly in number of branchings, l obe width and lobe length. We have modelled this morphogenesis, following p revious work by D. M. Harrison and M. Kolar on the assumptions that pattern ing occurs by chemical reaction-diffusion activity within the plasma membra ne, leading to morphological expression by patterned catalysis of the exten sion of the cell surface. The latter has been simulated in simplified form by two-dimensional computations. Our results indicate that for generation o f repeated branchings and for the control of diverse species-specific shape s, the loss of patterning activity and of rapid growth in regions separatin g the active growing tips is an essential feature. We believe this conclusi on to be much more general than the specific details of our model. We discu ss the limitations of the model especially in terms of what extra features might be addressed in three-dimensional computation.