Comparison of free amino acid profiles in carrot cell suspension cultures resistant to stress conditions.

Abstract

Plant cells resistant to specific amino acid analogs have been reported to accumulate the corresponding free amino acids. The purpose of this study was to determine the concentrations of fifteen free amino acids: alanine, valine, leucine, isoleucine, glutamate, proline, arginine, aspartate, threonine, methionine, lysine, serine, glycine, tryptophan and phenylalanine in Daucus carota cell lines, resistant either to the proline analog azetidine-2 carboxylic acid (A2C), or to the tryptophan analog 5-methyltryptophan (5-MT), or to both the analogs combined. This study also intended to determine if these analogs influence the biosynthesis of the above-mentioned fifteen amino acids in the cell line resistant to A2C and 5-MT. Carrot cell lines resistant to 5-MT, to A2C, or to both the analogs were selected by incubating carrot cells in liquid growth media containing either 0.3 mM 5-MT, or 0.5 mM A2C for 6 to 16 weeks. Free amino acid concentrations were then determined in the extracts of the cells. Resistance to 5-MT resulted in significant increases in the intracellular concentrations of tryptophan, phenylalanine, leucine, valine, isoleucine, and proline. Resistance to A2C resulted in significant increase in proline only. Resistance to both the analogs caused increases in proline, lysine, phenylalanine, and tryptophan concentrations. In the cell line resistant to both the analogs, the treatment with 5-MT caused increases in leucine, proline, aspartate, threonine, lysine, and tryptophan. The treatment with A2C caused increases in isoleucine, arginine, threonine, methionine, lysine, and glycine, whereas treatment with both the analogs caused increases in threonine, lysine, phenylalanine, and tryptophan. These results indicate the possibility of a common biosynthetic control of a number of amino acids in carrot cells, resembling that found in microorganisms. It is also evident from the results that the analogs play an active role in the biosynthesis of amino acids in the resistant cell lines.