EXPRESSION OF THE HYGROMYCIN-B PHOSPHOTRANSFERASE GENE CONFERS TOLERANCE TO THE HERBICIDE GLYPHOSATE

Escherichia coli cells and tobacco (cv. Xanthi) plants transformed wit h the hygromycin B phosphotransferase gene were able to grow in cultur e medium containing glyphosate at 2.0 mM. The growth of tobacco calli in media containing increasing glyphosate concentrations was measured. The ID50 for glyphosate was 1.70+/-0.03 mM for hygromycin-B resistant plants, and 0.45+/-0.02 mM for control plants. Regenerated plants and progeny selected for resistance to hygromycin B were tested for glyph osate tolerance by spraying them with Faena herbicide (formulated glyp hosate with surfactant) at a dose equal to 0.24 kg/ha. This was two ti mes the dose required to kill 100 percent of the control plants. Phosp hotransferase activity was measured in the extracts of the transformed leaves by the incorporation of P-32 from [gamma(32)P]ATP and it was o bserved that hygromycin B phosphotransferase was able to recognize the molecule of glyphosate as substrate.