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Characterization of Cultured Tobacco Cell Lines Resistant to Ethionine, a Methionine Analog ¹

Department of Agronomy, University of Illinois, Urbana, Illinois 61801

Two cultured tobacco cell lines (Nicotiana tabacum L. cv Xanthi) were selected for resistance to growth inhibition by the methionine analog ethionine. Comparison of the free amino acid pool levels in these lines with those of the ethionine-sensitive parental line showed substantial accumulation of methionine (110x), threonine (18x), and lysine (5x). In vitro enzymic analysis of lysine-sensitive aspartate kinase activity showed the resistant lines to contain 16 times that found in the sensitive line. The lysine-sensitive enzymes from both resistant and sensitive lines coeluted from DEAE-cellulose and exhibited similar K_m values. Both showed identical lysine plus S-adenosylmethionine inhibition profiles suggesting that the elevated activity in the resistant lines is not due to a structural change in the lysine-sensitive enzyme but possibly to the level of its expression.

¹ Supported by funds from the Illinois Agricultural Experiment Station and by Grant PCM 80-10927 from the National Science Foundation.

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