Abstract
Although preprophase band (PPB) disappears in prometaphase, the newly formed cell plate attaches to the former PPB site at the end of cytokinesis. To understand how the memory of the PPB site is generated, we have analyzed the structural changes in membrane architecture associated with PPB formation using epidermal cells of high-pressure frozen onion cotyledons. Our micrographs demonstrate that the forming PPB regions contain large numbers of vesicles with densely-staining contents. A detailed morphological analysis of the vesicles by means of high-voltage electron microscopy combined with dual-axis tomography has enabled us to distinguish two types of vesicles, one with a typical clathrin coat, and the other without any clear coat. The latter had larger diameter and distributed even slightly further from the plasma membrane and was observed to fuse to multivesicular bodies. Based on these observations, possible involvement of endocytosis in the PPB memory will be discussed.
