Cytological localization of fast renaturing and satellite DNA sequences in Vicia faba

DNA sequences reassociating within a Cot value of 1.8 x 10 -1 and those producing a light satellite in a CsC1 density gradient were isolated from Viciafaba DNA and hybridized in situ on squashes of roots of the same species. Silver grains were seen to be scattered over both the interphase nuclei and the metaphase chromosomes after hybridization with fast renaturing DNA sequences, indicating these are fairly regularly interspersed in the V. faba genome. Clustered labeling occurred after hybridization with satellite DNA sequences, indicating these are clustered in the genome. The localization of satellite DNA in chromosomes appeared to correspond closely to the position of the bright bands detectable after staining with quinacrine mustard. After hybridization with both DNA probes, labeling intensity over the nuclei of meristematic cells was higher than that over the nuclei of differentiating and/or differentiated cells. These results are discussed in relation to the structure of the cell nucleus, the mechanism of quinacrine banding and to previous data suggesting underrepresentation of nuclear repeated DNA sequences in differentiating V. faba root cells.