Localization of Persisting Agrobacteria in Transgenic Tobacco Plants. Anja Matzk. Institute for Biochemistry and Plant Virology, Federal Biological Research Centre for Agriculture and Forestry, Messeweg 11/12, 38104 Braunschweig, Germany. Sinclair Mantell (2), and Joachim Schiemann(1). (1) Institute for Biochemistry and Plant Virology, Federal Biological Research Centre for Agriculture and Forestry, Messeweg 11/12, 38104 Braunschweig, Germany; (2) Unit for Advanced Propagation Systems, Horticulture Section, Wye College, University of London, Wye, Ashford, Kent, TN25 5AH, UK. MPMI 9:373-381. Accepted 11 March 1996. Copyright 1996 The American Phytopathological Society.

The persistence of Agrobacterium tumefaciens cells of strain C58C1 in transformed tobacco plants {Nicotiana tabacum) was assessed over a period of 12 months post-transformation in vitro, and 3 to 6 months thereafter ex vitro. Three main approaches, i.e., enrichment culture followed by identification methods, tissue-print imimino-blotting, and scanning electron microscopy, were combined to investigate the persistence of the agrobacteria used for transformation. Agrobacteria cells were present on the surface and within the tissues of in vitro shoot cultures at 12 months post-transformation. Moreover, persisting agrobacteria were detectable in these transgenic tobacco plants grown ex vitro in soil for at least 3 to 6 months. Results of both tissue-print immunoblotting and enrichment culture experiments showed that agrobacteria were unevenly distributed in weaned transgenic tobacco, with the majority of agrobacteria cells being located at the stem base and in the roots of the plants. There was no evidence of agrobacteria being present in either flowers or mature seeds. The implications of these results are discussed in the context of the potential risks of inadvertent introduction of persisting transgenic agrobacteria into the environment during the release of transgenic plants.