The cytoskeleton and polarization during pollen development in Carex blanda (Cyperaceae)

Patterns of cytoskeletal organization during distinct polarizations that ch aracterize pollen development in the sedge Carer blanda (Cyperaceae) were s tudied by correlated methods of immunohistochemistry and confocal and trans mission electron microscopy. As is typical of the family Cyperaceae, Carer produces a unique pollen type known as a pseudomonad in which all four micr ospores of the tetrad are enclosed within the wall of a single pollen grain . Only one member of the tetrad is functional and the other three abort. Th e pseudomonads are precisely oriented in the locule with the functional mic rospore in the wide abaxial portion of the wedge-shaped cytoplasm adjacent to the tapetum, and the degenerative microspores are packed tightly in the pointed adaxial portion. A unique sequence of post-meiotic developmental ev ents reflects bath intracellular and intercellular polarity. Development in cludes: (1) random placement of tetrad nuclei in the coenocytic sporocyte a fter meiosis, (2) interrupted cytokinesis resulting in a tetrad of nuclei t hat migrates as a unit into the narrow adaxial tip, (3) completion of unequ al cytokinesis and centering of the functional nucleus in the wide abaxial portion of the microsporocyte via a radial array of microtubules and microf ilaments, (4) unequal mitosis resulting in a small generative cell at the p roximal surface of the functional microspore (adjacent to the abortive micr ospores), and (5) recentering of the vegetative nucleus in the abaxial cyto plasm via a radial cytoskeletal array.