A NEW VERSION OF THE AG-NOR TECHNIQUE - A COMBINATION WITH DAPI STAINING

The Ag-NOR staining technique is widely used for visualizing nucleolar organizer regions (NORs) in various plant and animal tissues. We desc ribe a simple and time-saving combination of Ag-NOR staining with DNA detection by fluorescence microscopy. This modification was tested on cultured cells and semi-thin sections of plastic-embedded tissues. Of the different fixatives and embedding media used in our studies, the b est results (i.e., high selectivity of staining, and lack of or very l ow background precipitation) were obtained with fixation in methanol-a cetone at -20 degrees C for cultured cells, and fixation in 4% formald ehyde followed by embedding in Histocryl resin for tissue sections. Th e optimal time of Ag-NOR staining was determined experimentally for al l materials tested. The specificity of the staining was checked at the electron microscopical level. Especially good results were obtained b y mixing epifluorescence with standard bright-field illumination. In s uch a combination, Ag-NOR-positive nucleoli, or their fibrillar centre s and dense fibrillar components, were clearly visible against a brigh t background of nuclear DNA.