Cell Division in Nautilocalyx Explants I. Phragmosome, Preprophase Band and Plane of Division

Abstract

Summary Dedifferentiation and cell division in small explants of Nautilocalyx lynchii (Hook f.) Sprague are described. The sequence of events and their timing have been observed in living epidermis cells. A first indication of a coming division was found in the migration of the nucleus to the centre of the cell about 10-20 hours before mitosis. Phragmosome formation started some hours later, and resulted in the presence of a continuous very thin cytoplasmic layer traversing the cell two hours before prometaphase. Mitosis and cytokinesis took about 40 minutes and 1.5-6 hours, respectively. Adjustments of the equatorial plane of the spindle to the phragmosome were sometimes observed at the end of mitosis. The cell plate reached the cell wall exactly where the phragmosome was situated. Electron microscopy of selected cells confirmed the presence of a very thin pre-mitotic phragmosome. In some cells with a continuous phragmosome a band of microtubules (BMT) was found in the peripheral cytoplasm where the phragmosome reached the cell wall. The phragmosome seemed to play an important part in guiding the cell plate to the narrow zone of the cell wall opposite which the band of microtubules had been present some hours earlier.