Biosynthesis of Protein Amino Acids in Plant Tissue Culture IV Isotope Competition Experiments using Glucose-U-C and Potential Intermediates.

The isotope competition method with glucose-U-(14)C as a carbon source has been used to determine whether or not selected compounds contribute carbon to the biosynthesis of protein amino acids in cells derived from Paul's Scarlet Rose. Of 48 compounds tested, 15 contributed carbon to protein amino acids. The results show for the first time that homoserine is an intermediate in threonine biosynthesis; that homoserine, cystathionine and homocysteine are intermediates in methionine biosynthesis and that histidinol is an intermediate in histidine biosynthesis in plant cells.