SPATIAL LIMITATIONS INDUCE SPINDLE TILTING AND RESULT IN OBLIQUE PHRAGMOPLASTS IN VICIA-FABA L. ROOT-TIP CELLS, BUT DO NOT RESULT IN OBLIQUE CELL-WALLS

Chromosome and phragmoplast positioning proceed differently during mit osis and cytokinesis in short and long root tip cells of Vicia faba L. and has been studied previously (Oud & Nanninga 1992, 1994). No corre lations, however, were made with the microtubular cytoskeleton. Here t his correlation is investigated using longitudinal sections of hydroxy -urea synchronized root tip cells, Microtubules were labelled with ant i alpha-tubulin, chromosomes were stained with propidium iodide, and b oth were visualized using confocal scanning laser microscopy, Preproph ase bands of microtubules were always positioned in the midplane of bo th short and long cells, and they were perpendicular to the length axi s of the files of cells in the root. Also spindle formation started in a similar way in short and long cells, but from meta-to anaphase, the spindle axis in short cells increasingly tilted, due to spatial const raints, While chromosomes separated, the spindle axis acquired a posit ion inclining to a diagonal of the cell, thus giving rise to the earli er observed oblique chromosome positions in anaphase plates, In short cells oblique phragmoplasts/cell plates expanded in oblique division p lanes. However, after karyokinesis, oblique cell plates rotated toward s the transversal plane and the final site of wall connection was not eccentric, but at the site of the earlier preprophase band, We conclud e that the suggestion that, in Vicia faba L., oblique walls are due to oblique anaphase plates (Oud & Nanninga 1992), has to be corrected, E ven when chromosomal alignment is offset and oblique cell plates are f ormed in cramped cells, transverse preprophase bands still predict tra nsverse division planes.