Cell division in the pennate diatom pinnularia observations on live cells

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Pickett-Heaps, J. D.; Tippit, D. H.; Andreozzi, J. A., 1979: Cell division in the pennate diatom pinnularia observations on live cells. Biologie Cellulaire (Ivry Sur Seine) 35(3): 295-304

All stages of mitosis and cytokinesis were observed in vivo with Nomarski and birefringence optics. The chloroplasts rotate in the cell during preprophase to give a clear window through which the spindle can be observed in girdle view. Pinnularia is sensitive to handling and has not yet proceeded through prophase-metaphase under observation or time-lapse filming; however, all stages are easily found. These correlate well with the ultrastructural images obtained previously, including the presence of prominent polar plates during prophase and their disappearance by metaphase; the subsequent openness of the spindle is attested to by the frequent entry of granules (and sometimes mitochondria) into its lumen. During prometaphase, pairs of chromosomes soon attach to the central spindle, displaying at first rapid, irregular oscillations interspersed with more positive motions directed along invisible tracks emanating from either pole. Soon, each pair independently appears to attach to the other pole as well, whereupon they immediately stretch across the spindle, stabilize and merge laterally with the mass of chromatin already attached. The metaphase spindle appears stable and relatively quiescent. Anaphase commences suddenly, and chromosomes soon reach the poles. The central spindle elongates as its overlap decreases; measurements confirm that the half spindles stay the same length from late metaphase to telophase, and that spindle elongation is likely due to the half spindles sliding apart. The rigid, elongated central spindle is finally broken at late telophase by the ingrowing cleavage furrow.

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