Naphthylacetamide-induced growth suppression of transformed carrot tissue and its adaptation to this compound

Naphthylacetamide (NAAm, 50-100 mg/l) almost completely suppressed the grow th of carrot (Daucus carota L.) tissues transformed by a wild type strain o f Agrobacterium tumefaciens. Resistant carrot lines which were selected wer e able to grow at 50 and 100 mg/l NAAm, at growth rates similar to or even higher than that of the initial culture on the medium without NAAm. On the inhibitor-free medium, these lines grew much faster than the initial cultur e. In the adapted lines, activity of amidohydrolase (EC 3.5.1.17) did not d ecrease; thus, resistance to NAAm could not be related to poor NAAm hydroly sis. NAA (50 mg/l) suppressed the growth of the adapted line threefold, but its rate was still similar to that of the initial culture on the medium wi thout NAA. This NAA concentration completely suppressed the growth of the i nitial culture. After incubating for 6 h with IAA, only the adapted, but no t the initial line produced indoleacetylaspartate. We suggested that NAAm r esistance of the adapted lines was determined by their enhanced capacity fo r conjugating aspartate and the NAA released during NAAm hydrolysis.