Abstract
The preprophase band (PPB) of microtubules marks the site of the future division plane on the plant cell cortex where the cell plate will fuse during the final stage of cytokinesis. Although the PPB microtubules on the cell cortex disappear during prometaphase, some unknown positional information is considered to remain in the PPB site after the disappearance of the PPB microtubules. Recent studies have shown that cytoskeletal proteins are known to be excluded from the PPB site. These depleted zones of cytoskeletal proteins are potential candidates for a "negative memory" system formed in the PPB site. However, the processes that produce these depleted zones of the cytoskeletal proteins are still unknown. In our recent paper, we have quantified the distribution of clathrin-coated pits and vesicles as well as of secretory structures during PPB formation of epidermal cells of onion cotyledons using a combination of high-pressure freezing and dual-axis electron-tomography techniques. Our results demonstrated that the rate of clathrin-mediated endocytosis is higher in PPB regions. We postulate that the removal of some membrane proteins by endocytosis plays a role in the creation of PPB "negative memory" structures.
