Localization of the T-DNA on marker chromosomes in transformed tobacco cells by in situ hybridization

Summary Chromosome and molecular analyses were conducted on tobacco cells which had been transformed by the T-DNA of the Ti-plasmid. These analyses showed that there were specific chromosome rearrangements in the transformed cells (marker chromosomes). There was a positive correlation between the number of marker chromosomes per cell and the oncogenic potential of the transformed cells. However, we show, using the Southern hybridization method, that the T_L fragment of T-DNA, but not the T_R, clearly hybridizes with nuclear DNA. In situ hybridization was used to locate the insertion site of T-DNA: the hybridization signal was found on a small metacentric chromosome. This chromosome may occur single or translocated onto other chromosomes, to make marker chromosomes. Thus, by locating the T-DNA, we have confirmed the correlation between the marker chromosomes and the oncogenic potential.