Abstract
The preprophase band (PPB) is an array of microtubules (MTs) that forms during G2 and prophase, and which marks the site on the plasma membrane where the cell plate will fuse. How MTs assemble at the future division site and how the PPB MTs mark the future division site are of central importance for understanding the function of PPBs. We have quantitatively analyzed the MT and membrane architecture of PPBs in epidermal cells of high pressure frozen onion cotyledons visualized by dual-axis high voltage EM tomography (7 nm 3-D resolution). Together these modern electron microscopic techniques have enabled us to analyze MT dynamics in terms of the MT end structures. Our samples also show that forming PPB regions contain increased numbers of clathrin coated pits and vesicles, suggesting that formation of the PPB involves enhanced rates of endocytosis in the PPB region.
