Duplication of the flagellar apparatus and cytoskeletal microtubule system in the alga Polytomella

We have used immunofluorescence staining with monoclonal antibodies to tubulin and to components of the flagellar basal apparatus to examine duplication of the basal apparatus and the microtubule system assembled from it during cell division in the quadriflagellate alga Polytomella . The monoclonal antitubulin, prepared against Polytomella flagellar axonemes, detects Polytomella and mammalian tubulin by immunoblotting. By immunofluorescence and immunogold electron microscopy, it detects all microtubular structures that have been described in Polytomella . One of the antibodies generated using the isolated basal apparatus as immunogen appears to stain four of the eight basal body rootlets and is used in this study to detect early stages in the duplication of the flagellar apparatus. A cytoplasmic microtubule system is present, the elongate morphology of the cell is maintained, and the cells are motile throughout mitosis. The closed mitotic spindle forms perpendicular to the long axis of the cell. During mitosis, the newly formed basal bodies mature and four additional elongating flagella appear. Following mitosis, the eight flagella segregate into two groups, which begin to separate towards opposite poles of the cell. Concomitant with this separation, the rootlets of the parental basal apparatus separate and new rootlets are detected. We suggest that the components of the parental flagellar apparatus are segregated equally to the daughter cells. An interphase cytoskeletal microtubule array is assembled from each basal apparatus, and the morphology of the two cells is progressively established during cytokinesis.