<P> The cytokinetic furrow ingresses until a so - called midbody structure (composed of electron - dense, proteinaceous material) is formed, where the actin - myosin ring has reached a diameter of about 1--2 μm . Most animal cell types remain connected by an intercellular bridge for up to several hours until they are split by an actin - independent process termed abscission, the last step of cytokinesis . The process of abscission physically cleaves the aforementioned midbody into two . Abscission proceeds by removal of cytoskeletal structures from the intercellular bridge, constriction of the cell cortex, and plasma membrane fission . The intercellular bridge is filled with dense bundles of antiparallel microtubules that derive from the central spindle . These microtubules overlap at the midbody, which is generally thought as a targeting platform for the abscission machinery . Microtubule severing protein spastin is largely responsible for the disassembly of microtubule bundles inside the intercellular bridge . Complete cortical constriction also requires removal of the underlying cytoskeletal structures . Actin filament disassembly during late cytokinesis depends on the PKCε--14 - 3 - 3 complex, which inactivates RhoA after furrow ingression . Actin disassembly is further controlled by the GTPase Rab35 and its effector, the phosphatidylinositol - 4, 5 - bisphosphate 5 - phosphatase OCRL . Understanding the mechanism by which the plasma membrane ultimately splits requires further investigation . </P> <P> Cytokinesis must be temporally controlled to ensure that it occurs only after sister chromatids separate during the anaphase portion of normal proliferative cell divisions . To achieve this, many components of the cytokinesis machinery are highly regulated to ensure that they are able to perform a particular function at only a particular stage of the cell cycle . Cytokinesis happens only after APC binds with CDC20 . This allows for the separation of chromosomes and myosin to work simultaneously . </P> <P> After cytokinesis, non-kinetochore microtubules reorganize and disappear into a new cytoskeleton as the cell cycle returns to interphase (see also cell cycle). </P> <P> Due to the presence of a cell wall, cytokinesis in plant cells is significantly different from that in animal cells, Rather than forming a contractile ring, plant cells construct a cell plate in the middle of the cell . The stages of cell plate formation include (1) creation of the phragmoplast, an array of microtubules that guides and supports the formation of the cell plate; (2) trafficking of vesicles to the division plane and their fusion to generate a tubular - vesicular network; (3) continued fusion of membrane tubules and their transformation into membrane sheets upon the deposition of callose, followed by deposition of cellulose and other cell wall components; (4) recycling of excess membrane and other material from the cell plate; and (5) fusion with the parental cell wall </P>

Where does the cellulose wall form in the mother cell of the onion root tip