Poster: Cell division
Abs #
671: Temporal and spatial regulation of cyclins in developing maize endosperm
Three types of cell cycle occur successively in developing maize endosperm. During the first three days after pollination (DAP), nuclei divide without cytokinesis, forming a syncytium. This is followed by a mitotic stage which occurs after cellularization of the syncytium and persists until 8-10 DAP. Finally, there is a period of endoreduplication that coincides with the terminal differentiation of starchy endosperm cells. The mitotic stage comprises the four classic cell cycle phases (G1, S, G2, M), while the endoreduplication stage consists of alternating G and S phases resulting in polyploid cells. Progress through the cell cycle phases is controlled by cyclin-dependent kinases, which are regulated by association with variable cyclin subunits. Among these, D- and B-type cyclins regulate the G1-S transition and M-phase progression, respectively. The nature and role of these cyclins during the mitotic and endoreduplication periods of developing endosperm are unknown. To investigate these questions, we characterized cyclins B1;3, D1;1, and D2;1 in developing endosperm. Polyclonal antibodies that recognize these cyclins were generated and used to determine their accumulation, activity and spatial localization in endosperm cells. Cyclin B1;3, D1;1, and D2;1 protein levels were nearly constant throughout development. Kinase activity associated with cyclin B1;3 decreased dramatically at 15 DAP compared to 7 DAP, while that of cyclins D1;1 and D2;1 decreased slightly. Cyclin B1;3 formed aggregates in the cytoplasm and punctate foci in nuclei of interphase cells and localized to the spindle at metaphase and the phragmoplast at telophase. Cyclin D2;1 localized to nuclei, while cyclin D1;1 localized the cytoplasm of the aleurone and two subaleurone layers at 15 DAP.
