Selection and characterization of cultured carrot and tobacco cells resistant to lysine, methionine, and proline analogs

Amino-acid-analog-resistant lines were selected from mutagen-treated suspension-cultured tobacco (Nicotiana tabacum L.) and carrot (Daucus carota L.) cells. Tobacco cell lines resistant to the lysine analogs aminoethyl-L-cysteine and delta-hydroxylysine and carrot lines resistant to a methionine analog and a proline analog, ethionine and hydroxyproline, respectively, were selected. The resistant lines were 10 to more than 1000 times less sensitive to the analogs than the parent strains. The resistant cells were selected with a low frequency, were generally stable during growth in the absence of the selective agent, and accumulated the corresponding natural free amino acid. The lysine-analog-resistant tobacco lines had more than 10 times the normal levels of free lysine while the methionine-analog-resistant carrot line had similar increases in free methionine. The hydroxyproline-resistant carrot line contained from 15 to 30 times the normal free proline levels and was cross resistant to certain other proline analogs.