Amino Acid Uptake by Amino Acid Analog Resistant Tobacco Cell Lines

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Abstract
Two tobacco [Nicotiana tabacum] cell lines resistant to p-fluorophenylalanine (PFP) and one resistant to 5-methyltryptophan (5-MT) are compared with wild type cells in their ability to absorb amino acids from the medium. One p-fluorophenylalanine-resistant cell line shows greatly reduced uptake of all amino acids so it is resistant to growth inhibition by other amino acid analogs. The impaired absorption is noted with amino acids, amino acid analogs and shikimate, but not with cinnamate, salicylate, nicotine, glucose, 3-O-methylglucose and palmitate. The phenylalanine transport system of the PFP-resistant cell line and the wild type both have Km values of 90 .mu.M, but have different Vmax values. Several analogs of phenylalanine and several neutral L-amino acids inhibit the phenylalanine transport system, while L-aspartic acid, L-arginine, D-phenylalanine or chlorogenic acid do not interfere with the L-phenylalanine uptake. The results indicate the presence of more than 1 transport system for amino acid uptake. The lessened uptake of all amino acids, the specificity of the uptake systems and the unchanged binding indicate that a pleiotropic mutation or some inhibitor causes the reduced uptake of all amino acids by the PFP-resistant cell line.