Asymmetric cytokinesis guide the development of pseudomonads in Rhynchospora pubera (Cyperaceae).

The late stages of microsporogenesis in the family Cyperaceae are marked by the formation of an asymmetrical tetrad, degeneration of three of the four nuclei resulting from meiosis and the formation of pseudomonads. In order to understand the cytological changes involved in the development of pseudomonads, a combination of 11 different techniques (conventional staining, cytochemistry procedures, immunofluorescence, FISH and transmission electron microscopy: TEM) were used to study the later stages of microsporogenesis in Rhynchospora pubera. The results demonstrated the occurrence of two cytoplasmic domains in the pseudomonads, one functional and the other degenerative, which are physically and asymmetrically separated by cell plate with an endomembrane system rich in polysaccharides. Other changes associated with endomembrane behaviour were observed, such as a large number of lipid droplets, vacuoles containing electron-dense material and concentric layers of endoplasmic reticulum. Concomitant with the isolation of degenerative nuclei, the tapetal cells also showed evidence of degeneration, indicating that both tissues under programmed cell death (PCD), as indicated by immunofluorescence and TEM procedures. The results are significant because they associate cellular polarisation and asymmetry with different cytoplasmic domains, and hence open new possibilities for studying cellular compartmentalisation and PCD.