XVI International Botanical Congess

Mechanism of cortical microtubule (MT) assembly in plant cells is mostly unknown. We examined structure of MT ends at electron microscopic level. Onion cotyledons were cryofixed with Balzers high pressure-freezer, freeze substituted and analysed by reconstruction of extra thin (40-50 nm) sections and by computer-aided tomography of a semi-thin (150-200 nm) section. Coiled ends, which were observed during MT depolymerization in vitro, was detected for the first time in plant cells. Both ends of a single MT were coiled in some cases. A MT cap was detected by tomography but the frequency was low. These results strongly suggest that cortical MTs can elongate and shrink in both ends.