Abstract
In plant syncytial cells the position of the new cell walls is determined by microtubule systems radiating from the nuclear envelopes. Using a combination of high-pressure freezing/freeze substitution and dual-axis electron tomography we have studied the organization of cytoskeletal elements and membranous cell plate intermediates in two syncytial systems, the cellularizing endosperm and the post-meiotic microsporocytes of Arabidopsis. In both systems, cytokinesis involves the assembly of clusters of microtubules called mini-phragmoplasts and specific types of cell plates. However, whereas endosperm cell plates assemble first in the central part of the division plane, post-meiotic microsporocyte cell plates assemble across the entire division plane simultaneously. This fact, together with a particular pattern of callose synthesis, determines that post-meiotic cell plates mature centripetally, and not centrifugally. In conclusion, cytokinesis in different tissues of higher plant cells involves the formation of different types of cell plates but never cleavage furrows.
