P. Olesen Larsen

Meta-carboxy-substituted aromatic amino acids in plant metabolism. III

Abstract 1. 1. Investigations have been performed on the mignonette species Reseda odorata L. and Reseda lutea L. with the purpose of obtaining information about the biosynthesis and metabolism of four meta -carboxy-substituted aromatic amino acids encountered in higher plants, namely d -(3-carboxyphenyl)glycine , l -3-(3-carboxyphenyl)alanine, d -(3-carboxy-4-hydroxyphenyl)glycine, and l 3-(3-carboxy-4-hydroxyphenyl)alanine. 2. 2. The concentration of d -(3-carboxy-4-hydroxyphenyl)glycine + l -3-(3-carboxyphenyl)alanine was measured at intervals during the whole growth period of R. odorata L. The two amino acids occurred in all parts of the plant throughout the life cycle, the highest concentrations being observed in roots, flowers, and seeds. 3. 3. Precursors labelled with 14 C were fed to R. odorata L. and R. lutea L. A high incorporation of shikimic acid into l -3-(3-carboxyphenyl)alanine, and l -3-(3-carboxy-4-hydroxyphenyl)alanine, a slight incorporation of carbon from glucose into l -3-(3-carboxyphenyl)alanine and l -3-(3-carboxy-4-hydroxyphenyl)alanine, and a slight incorporation of tyrosine into l -3-(3-carboxy-4-hydroxyphenyl)alanine have been demonstrated, whereas virtually no incorporations of carbon atoms from phenylalanine, methionine, and acetate into the meta -carboxy-substituted aromatic amino ac ds occurred. 4. 4. Degradation methods permitting the detection of the radioactivity in the aromatic and alipathic carboxyl groups of l -3-(3-carboxyphenyl)alanine, d -(3-carboxy-4-hydroxyphenyl)glycine and l -3-(3-carboxy-4-hydroxyphenyl)alanine are described. 5. 5. Degradation of these three amino acids labelled by feeding uniformly-labelled [ 14 C]shikimic acid to the plant demonstrates that 1 7 of the radioactive carbon atoms are positioned in the aromatic carboxyl group, the residual 6 7 in the rest of the molecule. This indicates that the aromatic ring of the three amino acids can be derived from the ring of shikimic acid, and that the aromatic carboxyl group of the three amino acids is derivable from the carboxyl group of shikimic acid. 6. 6. Degradation of l -3-(3-carboxy-4-hydroxyphenyl)alanine labelled by feeding dl -[ carboxy - 14 C]tyrosine to the plants shows that all the radioactive carbon atoms are present in the aliphatic carboxyl group. This indicates that tyrosine can function as a precursor for this amino acid without fission of the C 6 C 3 skeleton. 7. 7. The presence of two unidentified compounds, possibly with a biosynthetic relationship to the meta -carboxy-substituted aromatic acids, is briefly discussed. 8. 8. The biosynthetic pathways derived from the above observations and the implications for knowledge of the biosynthesis of tyrosine and phenylalanine in higher plants are discussed.