XVI International Botanical Congess

Most of the angiosperms form four pollen grains from one pollen mother cell after meiotic division, while in the Cyperaceae only one pollen grain develops from one pollen mother cell. DNA content in degenerative and functional nuclei of Carex ciliato-marginata were investigated during meiotic and primary pollen division. It is concluded that DNA replication was carried out in only one nucleus of the tetrad and that the other three nuclei were composed of unreplicated chromosomes at the primary pollen nuclear division. Chromosomal locations of 18S rDNA genes were investigated by in situ hybridization. At meiotic metaphase I, the 18S rDNA loci were detected at both ends of two bivalent chromosomes. T anaphase I, the chromosomes divide longitudinally into half-configurations and the 18S rDNA sites were detected at both ends. This result shows the first meiotic division of Carex is equational, and the second one is reductional.