Redistribution of Golgi stacks and other organelles during mitosis and cytokinesis in plant cells

We have followed the redistribution of Golgi stacks during mitosis and cyto kinesis in living tobacco BY-2 suspension culture cells by means of a green fluorescent protein-tagged soybean alpha-1,2 mannosidase, and correlated t he findings to cytoskeletal rearrangements and to the redistribution of end oplasmic reticulum, mitochondria, and plastids. In preparation for cell div ision, when the general streaming of Golgi stacks stops, about one-third of the peripheral Golgi stacks redistributes to the perinuclear cytoplasm, th e phragmosome, thereby reversing the ratio of interior to cortical Golgi fr om 2:3 to 3:2. During metaphase, approximately 20% of all Golgi stacks aggr egate in the immediate vicinity of the mitotic spindle and a similar number becomes concentrated in an equatorial region under the plasma membrane. Th is latter localization, the "Golgi belt," accurately predicts the future si te of cell division, and thus forms a novel marker for this region after th e disassembly of the preprophase hand. During telophase and cytokinesis, ma ny Golgi stacks redistribute around the phragmoplast where the cell plate i s formed. At the end of cytokinesis, the daughter cells have very similar G olgi stack densities. The sites of preferential Golgi stack localization ar e specific for this organelle and largely exclude mitochondria and plastids , although some mitochondria can approach the phragmoplast. This segregatio n of organelles is first observed in metaphase and persists until completio n of cytokinesis. Maintenance of the distinct localizations does not depend on intact actin filaments or microtubules, although the mitotic spindle ap pears to play a major role in organizing the organelle distribution pattern s. The redistribution of Golgi stacks during mitosis and cytokinesis is con sistent with the hypothesis that Golgi stacks are repositioned to ensure eq ual partitioning between daughter cells as well as rapid cell plate assembl y.