Configuration of nucleolar DNA in situ in nucleolus of Allium cepa cells

The location and configuration of nucleolar DNA have notbeen determined for a long time. In this paper, we have observed the nucleolar ultrastructure and the character of nucleolar DNA in Allium cepa cells by conventional ele ctron microscopy and the cytochemical NAMA-Ur DNA specific staining method. Furthermore, we have property improved the NAMA-Ur method so as to analyze the location and configuration of nucleolar DNA in situ. Our results indic ated that the nucleolar DNA in Allium cepa: cells is mainly located at the border between fibrillar centers and dense fibrillar component, especially distributed in the configuration of encircling the fibrillar centers.