title: Morphogenesis in Micrasterias. I. Tip growth.
abstract: Observations on lobe growth in the lateral wings of the developing primary cell wall in the desmid Micrasterias rotata are reported and discussed. Patterns of incorporation of methyl-[3H]-methionine and C-1[3H] glucose into the primary wall as revealed in autoradiograms indicate that formation of the new wall is concentrated at the tips of lobes. Patterns follow the predictions of Robertson's model for tip growth in fungal hyphae; thus they link growth in M. rotata lobes with mechanisms of cell elongation found in other cells. Damage done to selected regions of the cell surface with a laser microbeam demonstrates that only certain regions are required for continued growth and morphogenesis while much of the surface plays only a passive role. In growth stages at which lobes are already well defined (stage 4 and later) continued growth of each lobe requires the participation of an area no more than 4-5 mum in diameter, here termed a singularity, at its tip. At early stages (prior to stage 3) singularities per se cannot be demonstrated. At these stages the capacity to intitiate lobes and hence to form singularities is not fixed at specific points, but is distributed over an area of the surface no less than 10 mum in diameter. Singularities, by their persistence and repeated duplication, are directly responsible for the spatial form of the two lateral wings.
mesh_terms: D001345:Autoradiography; D002473:Cell Wall; D056890:Eukaryota / Q000254:growth & development* / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D007834:Lasers; D008715:Methionine / Q000378:metabolism; D009024:Morphogenesis; D013194:Staining and Labeling
chemical_list: D008715:Methionine; D005947:Glucose