Microtubule and actin filament organization during acentral divisions in potato suspension culture cells

Microtubule and filamentous(F)-actin organization in the potato suspension culture line HH260 was studied by fluorescence microscopy in double-labelled cells. During interphase, microtubules and F-actin were randomly arrayed in isodiametric cells but were aligned transversely to the direction of growth in elongated cells. Microtubules and F-actin coaligned in preprophase bands which were, however, comparatively rare and diffuse. Interestingly, more than half of the cells in telophase contained phragmoplasts that were either horseshoe-shaped or straight, instead of being round. We traced the cause of this difference to preprophase, where misplaced nuclear localization away from the central axis of cells may give rise to acentrally placed spindles and, subsequently, to acentrally placed phragmoplasts and cell plates. Further, we hypothesize that it is the uneven fusion of the expanding cell plates with the parent plasma membrane, and the accompanying depolymerization of those parts of the phragmoplasts, that gives the incomplete phragmoplasts observed.