Plasma membrane ghosts form differently when produced from microtubule-free tobacco BY-2 cells

When lysed in an actin stabilizing buffer, protoplasts made from tobacco BY -2 suspension culture cells formed plasma membrane ghosts that retained bot h cortical actin and microtubules. Distinct cytoskeletal arrays occurred: t he most common ghost array (type I) derived from protoplasts in interphase and had random actin and microtubules, although the alignment of the actin was dependent, at least partially, on microtubule organization. Type II gho sts were larger and more irregular in shape than type I ghosts, and were ch aracterized by a lack of microtubules and the presence of distinctive array s of actin bundles in concentric arcs. These ghosts derived from protoplast s lacking cortical microtubules produced when wall digestion occurred while the cells were in cell division, or from protoplasts isolated in the prese nce of 100 mu M propyzamide. Because type II ghosts derived from protoplast s of similar size to those that give rise to type I ghosts, and because typ e II ghosts retained ordered actin arrays while the parent protoplasts had random cortical actin, type II ghosts apparently form differently to type I ghosts. We speculate that instead of the protoplast being sheared off to p roduce a round ghost, the plasma membrane tears and collapses onto the slid e, ordering the actin bundles in the process. One implication of this model would be that cortical microtubules provide structural support to the plas ma membrane of the protoplast so that only in their absence do the type II ghosts form.