Kinetochore fiber formation in dividing generative cells of Tradescantia Kinetochore reorientation associated with the transition between lateral microtubule interactions and end-on kinetochore fibers

Division of the generative cell of Tradescantia virginiana is unusual in that a typical bipolar spindle is not present Instead, the cell contains an axial system of microtubule (Mt) bundles, with kineto-chores distributed along the length and depth of the cell. Kinetochore fibers appear to be derived from and remain attached to the Mt bundles. Localizations with both anti-tubulin and CREST serum were performed in order to probe this relationship further. Pairs of CREST-positive, fluorescent dots presumed to be kinetochores are initially oriented transverse to the cell axis and appear to be associated with the Mt bundles via latéral interactions. Adjacent pairs are often joined to the same bundles, like rungs on a ladder. Lateral interactions are then converted intoor replaced by end-on kinetochore fibers similar in morphology to those seen in other cells. This conversion is accompanied by a realignment of the kinetochore pairs along the long axis of the cell. In addition, the center-to-center spacing between filial kinetochores doubles. Interconnections between kinetochore fibers and surrounding Mts appear to be maintained during the transition. These results may provide a general insight into the manner in which kinetochores interact with the division apparatus in eukaryotes.