Tracer studies with 13C-labeled carbohydrates in cultured plant cells. Retrobiosynthetic analysis of chelidonic acid biosynthesis.

The biosynthesis of chelidonic acid was studied in cell suspension cultures of Leucojum aestivum. Cell cultures were supplied with [U-13C]glucose, [l-13C]glucose or [U-13Cs]ribose/ribulose in standard medium containing unlabeled glucose. 13C labeling patterns of amino acids obtained by hydrolysis of biomass were determined by NMR spectroscopy and compared to the labeling pattern of chelidonic acid. The data document the incorporation of a contiguous 4-carbon fragment derived from the pentose phosphate pool into chelidonic acid. This suggests a biosynthetic pathway involving the condensation of phosphoenolpyruvate with a pentose phosphate followed by dehydration, dehydrogenation, ring closure and decarboxylation conducive to the loss of C-5 of the pentose precursor.