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Selection and Characterization of Amino Acid Analog Resistant Plant Cell Cultures¹

A method is outlined which may be useful for increasing the levels of specific free amino acids in plants.

Carrot (Daucus carota L.) and tobacco (Nicotiana tabacum L.) cell culture lines have been selected which are resistant to growth inhibition caused by tryptophan, phenylalanine, lysine, methionine, and proline analogs. Most of these lines accumulate six to 30 times the normal levels of the corresponding natural free amino acid and these increases apparently cause the resistance to the analog, since exogenous amino acids will reverse the inhibition. At least in the case of lines .resistant to 5.methyltryptophan and p-fluorophenylalanine, the control enzymes in the tryptophan and phenylalanine biosynthetic pathways, respectively, have altered feedback control properties which apparently allow the oversynthesis of the endproduct amino acids. Studies of the enzymes in the lysine, methionine, and proline pathways have not been carried out.

Increases in the free amino acid content can cause very marked increases in the total content of a particular amino acid. Regeneration of plants from such altered lines may give plants with increased levels of certain amino acids. With species where plant regeneration is not possible from established cultures, seedlings can also be screened by growing them in nutrient solution containing inhibitory amino acid analogs. Some evidence suggests that these approaches may be successful in increasing the levels of certain amino acids in plants, but only continued study can provide a definite conclusion.

Key Words: Daucus carota L. • Nicotiana tabacum L. • Amino acids analogs • Tissue culture • Feedback inhibition

² Associate professor of plant physiology, Dep. of Agronomy, Univ. of Illinois, Urbana, IL 61801.

Received for publication November 10, 1976.