A role of endocytosis in plant cytokinesis.

The preprophase band (PPB) of microtubules (MTs) marks the site of the future division plane irrespective of the orientation of the equatorial plane. Because the PPB MTs disappear during prometaphase, some positional information is thought to remain in the cortical cytoplasm after the disappearance of the PPB MTs. Cytoskeletal proteins are known to be excluded from the PPB site during mitosis. These depleted zones of cytoskeletal proteins are potential candidates for a "negative memory" system. However, how these depleted zones of the cytoskeletal proteins are produced remains unknown. In a recent paper, we have quantified the distribution of clathrin-coated pits and vesicles as well as of secretory structures during PPB formation using a combination of high-pressure freezing and electron tomography techniques. Our results demonstrated that the rate of endocytosis is enhanced in PPB regions. We postulate that the removal of membrane proteins by endocytosis plays a role in the creation of PPB "memory" structures.