Early meiosis in Rhynchospora pubera L. (Cyperaceae) is marked by uncommon ultrastructural features

The family Cyperaceae has an unusual microsporogenesis in which tetrad formation does not occur. In addition, other cytological features are important, such as the occurrence of holokinetic chromosomes and post-reductional meiosis. We have examined the ultrastructural features of the pollen mother cell (PMC) of Rhynchospora pubera. Anthers of several sizes were analyzed using light and transmission electron microscopy. The PMC before meiosis presented a central nucleus and a regular profile of the nuclear envelope. During prophase I, the nucleus was in the abaxial region of the cell. This cellular polarization was accompanied by other marked ultrastructural features in the nuclear envelope. Morphological changes involved dilations of perinuclear cisterns and polarization of the nuclear pore complexes. The results show that polarization occurs in the initial phases of microsporogenesis in R. pubera, unlike other plant species.