Comparative metabolism of L-tyrosine and L-phenylalanine in tobacco plants in relation to the biosynthesis of phenylacetic acids

Abstract

The biosynthesis of phenyl and p-hydroxyphenyl substances in tobacco plants (Nicotiana tabacum var. Mammoth) was investigated by feeding solutions of L-[U-14C]phenylalanine or L-[U-14C]tyrosine to excised shoots for 24 h. Radioactive metabolites were extracted into acetone, fractionated into acidic and basic ether fractions, and then analysed by gas–liquid chromatography or by TLC followed by liquid scintillation spectrometry and gas–liquid chromatography. Results show that the 14C label was incorporated into several p-hydroxyphenyl substances in shoots supplied with [14C]tyrosine and into both phenyl and p-hydroxyphenyl substances in shoots supplied with [14C]phenylalanine. The radioactive metabolites identified from each 14C-labelled amino acid are homologous to many of the indole substances postulated to be intermediates in the conversion of L-tryptophan to the growth hormone indole-3-acetic acid, in tobacco and other higher plants. The present data suggest that in tobacco plants similar metabolic pathways exist for the conversion of all three aromatic amino acids to their corresponding arylacetic acids.