Abstract
Recent studies using GFP-labeled plant cortical microtubules showed that the microtubule nucleation occurs at dispersed sites in the cell cortex. Once nucleated, microtubules do not remain anchored to their site of initiation, and exhibit dynamics at both ends. However, we know little about the structure of microtubule end. To investigate the microtubule dynamics at ultrastructural level, we quantitatively analyzed the structure of cortical microtubule ends in epidermal cells of high pressure frozen onion cotyledons visualized by dual-axis electron tomography. Most microtubule ends were open and can be classified according to their architecture into coiled end, open sheet and blunt end. Capped ends exist but their frequency was low. Some capped ends were seen in regions of the cortical cytoplasm that were free of other structures, but others abutted against other microtubules. These results have structural implications for models of microtubule initiation and dynamics in plants.
