Behavior of Free Aromatic Amino Acid Pools in Rosmarinic Acid-Producing Cell Cultures of Anchusa officinalis L.

The pool sizes of free l-phenylalanine and l-tyrosine, the precursors of rosmarinic acid in Anchusa officinalis L. cell suspension cultures, fluctuated during the culture cycle. The major increase in pool sizes was preceded by a peak of prephenate aminotransferase activity, while the subsequent decrease coincided with the presence of high activities of phenylalanine ammonia-lyase and tyrosine aminotransferase, the two entrypoint enzymes of the rosmarinic acid biosynthesis pathway. Timecourse feeding studies with linear growth stage cells revealed that the tyrosine pool turned over rapidly, consistent with direct participation in rosmarinic acid synthesis. Since externally applied l-tyrosine was rapidly incorporated into rosmarinic acid with little evidence of radioactively labeled intermediates, it is suggested that there exists a close coupling between the l-tyrosine pool and the rosmarinic acid biosynthetic pathway, which may involve the channelling of intermediates both into and within the pathway.