A mutagenic procedure of carrot cell suspension by means of UV-light has been established. The application of this procedure to the selection of cell lines resistant to 5-methyltryptophan (5MT) increased 11 times the spontaneous mutation rate. Eighteen colonies selected in the course of one experiment have been analyzed for quantitative resistance to the analogue. Four of the most 5MT-resistant lines selected (one spontaneous and three induced) were also tested for their resistance to azetidine-2-carboxylic acid (A2C) to which all of them proved to be resistant even though this was an unselected trait. The four lines were tested for the intracellular content of some free amino acids. Results of such determination showed that the content of tryptophan and proline was roughly proportional to the degree of resistance of the lines to the two analogues. The fact that all the lines resistant to 5MT over-produced proline suggests that the latter feature may be a direct consequence of the increased pool of free tryptophan. The four cell lines tested showed a rate of tryptophan uptake similar to that of the parental line. On the contrary the rate of proline and A2C by the 5MT-l1 cell line was reduced to 23% and 10% of that of the parental line, respectively.
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