Microtubular fir-trees in mitotic spindles of onion roots

Summary The organization of kinetochore fibers was examined inAllium root cells processed for tubulin immunocytochemistry. Metaphase fibers consist of a core or trunk of Mts to which are attached numerous branches, yielding a bottle-brush of fir-tree pattern similar to that reported inHaemanthus endosperm cells. Many of the branches cross the midzone and extend into the opposite half-spindle. In addition, branch Mts associate with more than one kinetochore fiber. During anaphase, branch Mts elongate while the trunks shorten and fuse into polar caps. Our results are discussed in terms of spindle fiber organization and Mt polarity.Abbreviations K Kinetochore - Mt microtubule