A cloned tobacco crown gall teratoma induced by A. tumefaciens strain T37 was found to contain part of the Ti plasmid (T-DNA) of the causative bacterium. The tumor line contained transcripts of the ends of the T-DNA; transcripts of the intervening T-DNA were not detected. When grafted to a healthy tobacco plant, the cloned tumor line produced a plant that flowered and set seed. Tissues from leaves and flower petals when placed in tissue culture resumed a malignant growth pattern and grew in the absence of phytohormones. Both leaf and flower petal tissues were found to contain T-DNA, but in smaller quantity than observed in the parental line. Haploid tissue derived from anther and tissue from F1 progeny plants, which morphologically appear to be completely normal and require phytohormones for growth in vitro, were found to be free from T-DNA. Thus, meiosis acts either to cause or select for loss of the foreign DNA. The correlation between the presence of foreign DNA and the tumor phenotype indicates that the continued presence of T-DNA is required for the maintenance of the tumorous state.
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