Cytokinesis: The Art of Partitioning

In higher plants, cytokinesis partitions the cytoplasm of a dividing cell by forming a new cell wall between the two sets of daughter chromosomes. Although conceptually simple, this process involves a sequence of wellorchestrated events, starting with the determination of the division plane before the onset of mitosis (reviewed in Staehelin and Hepler, 1996; Heese et al., 1998; Smith, 1999). A transient preprophase band of microtubules and actin microfilaments marks a cortical division site which is in the same plane as the dividing nucleus. Following disintegration of the nuclear envelope and formation of the mitotic spindle, the chromosomes condense, align, and separate before the spindle moves the daughter chromosomes away from the division plane. Remnants of the spindle are incorporated into the phragmoplast, which appears in the interzone in late anaphase. The phragmoplast consists of two opposing sets of microtubules and actin microfilaments with their plus ends toward the plane of division. The phragmoplast mediates the translocation of Golgi-derived vesicles to the division plane where the vesicles fuse with one another to form the cell plate, a transient membrane compartment. The disc-shaped cell plate expands from the center of the division plane to the periphery and eventually fuses with the lateral cell wall at the cortical division site. During cell plate expansion, the phragmoplast microtubules depolymerize in the center and repolymerize along the edge such that additional Golgi-derived vesicles are targeted to the margin of the cell plate. While expanding, the cell plate undergoes a complex transformation from an initial network of thin fusion tubes to a solid plate, with polysaccharides secreted into its lumen (Samuels et al., 1995). In Cytokinesis: The Art of Partitioning