MICROTUBULE TRANSLOCATION IN THE CYTOKINETIC APPARATUS OF CULTURED TOBACCO CELLS

IN higher plant cells, cytokinesis is achieved by new cross-wall formation mediated by the phragmoplast 1, a double ring of microtubules of opposite polarity, in which the short microtubules are arranged perpendicular to the equatorial plane of the phragmoplast with their plus ends interdigitating at the plane 1,2. The phragmoplast and its enclosed cell plate move out centrifugally until the mother cell divides. We report here results of a newly developed method using glycerinated cultured tobacco cells, which show that the equatorial region of the phragmoplast can translocate microtubules toward their minus ends concomitantly with tubulin polymerization at their plus ends. The translocation is induced effectively by GTP and less effectively by ATP, and is inhibited by the unhydrolysable nucleotide analogues GMP-PNP and AMP-PNP. Thus, the equatorial region of the phragmoplast seems to be associated with a mechanochemical enzyme that generates the force for microtubule translocation by hydrolysing GTP.