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Cytokinesis in plant cells and the role of the cytoskeleton
Cytokinesis in plant cells involves the formation and insertion of a new cell wall that separates daughter nuclei after mitosis. The deposition of the new wall is regulated by a structure called the phragmoplast which contains microtubules, actin filaments and membranes. The experiments described in this thesis, emphasize the participation of the actin filaments in the cytokinetic process. Caffeine inhibition of cytokinesis shows that two distinct phases cell plate development can be distinguished; an early initiation phase and a late lateral expansion phase. Caffeine completely inhibits the latter stage. I have looked at the dynamics of actin filaments, as well the microtubules, during the inhibition of cytokinesis by caffeine. I found that formation of the cytoskeletal torus, associated with the later stages of cell plate formation, is completely inhibited in the presence of caffeine. The functional role of actin filaments was probed by microinjection of the actin monomer binding protein profilin. The results show a dose-dependent effect on cytokinesis, in which the effects range from delayed cell plate formation to complete inhibition. To asses the localization of profilin, I microinjected a fluorescent profilin probe into living cells and analyzed the localization throughout mitosis. Profilin is accumulated in the nucleus during interphase and prophase and is released in the accessible volume after nuclear envelope break down at the onset of metaphase. It remains in the accessible volume during the subsequent mitotic stages until it re-accumulates in the telophase nuclei. No specific localization of profilin in the phragmoplast was observed. Also, the role of actomyosin in plant cytokinesis was studied by using the myosin ATPase inhibitor, 2,3-butanedione monoxime (BDM). Cytokinetic cells, treated with BDM, displayed buckled and thin cell plates that were often tilted at a significant angle. In addition, late lateral cell plate expansion was inhibited and actin filaments in the phragmoplast lost their proper orientation. These results show that actomyosin plays a crucial role in cell plate alignment and late lateral expansion of the cell plate. Finally, a new cell plate formation model is presented that combines some of the results of this thesis with existing models and previous findings. ^
Aline Hendrika Valster,
"Cytokinesis in plant cells and the role of the cytoskeleton"
(January 1, 2000).
Doctoral Dissertations Available from Proquest.