Differential expression of crown gall tumor markers in transformants obtained after in vitro Agrobacterium tumefaciens-induced transformation of cell wall regenerating protoplasts derived from Nicotiana tabacum.
To obtain transformation of plant cells, we incubated 3-day-old cell wall-regenerating protoplasts from tobacco with Agrobacterium tumefaciens harboring tumor-inducing plasmids. Putative transformed tobacco cells were selected by phytohormone autotrophic growth and were shown to be transformed by the detection of the tumor cell specific enzymes lysopine dehydrogenase or nopaline dehydrogenase. This was substantiated by the detection, in transformed tumor tissues, of DNA sequences homologous to sequences in the tumor-inducing plasmid. Segregation of tumor markers has been observed among the transformants and it is suggested that this happened during the initiation of the transformation. The stable character of the transformed state was shown by the retention of tumor markers in subcloning of primary transformants under nonselective conditions. Suppression of the neoplastic state of transformants could take place, resulting in the development of transformed shoots. Indications were obtained for the inheritance of tumor markers through meiosis from seedlings obtained from seeds of flowering transformed plants that still expressed nopaline synthesis.