Observations on the fine structure of two species of Platymonas with special reference to flagellar scales and the mode of origin of the theca
Manton, I. and Parke, M. (1965) Observations on the fine structure of two species of Platymonas with special reference to flagellar scales and the mode of origin of the theca. Journal of the Marine Biological Association of the United Kingdom, 45 (3). pp. 743-754.
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The morphology and microanatomy of two species of Platymonas have been investigated and certain stages of cell division studied. The anatomical features closely resemble those recently described for the motile phase of Prasinocladus except for characteristic differences in pyrenoid structure (cf. Parke & Manton, 1965). The flagella of Platymonas are indistinguishable from those of Prasinocladus, being covered with two layers of scales beneath a layer of structureless mucus which obscures their presence except in sections. Caducous hairs resembling those of Prasinocladus and related genera are also borne on the flagella. An observation of exceptional importance concerns the production of the new theca round each of the two daughter-cells at the end of a cell division. This occurs within the theca of the mother-cell by coalescence of many small stellate particles liberated into the space surrounding each protoplast from vesicles derived from the Golgi bodies. These particles, and hence the theca derived from them, are thus homolgous with scales. Coalescence of the particles to form the theca begins at a predetermined place on the surface of each protoplast irrespective of the mutual positions of the two sister-cells, this place being related to the position of the pyrenoid. It is suggested that an enzyme capable of agglutinating stellate particles is elaborated or liberated at the site of the pyrenoid and secreted thence to the cell exterior. This investigation is being continued.
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