Catabolic ring-cleavage of tyrosine in plant cell cultures

Ten species of plants from 8 families, grown as sterile cell cultures, were examined for their ability to degrade the aromatic ring of L-tyrosine and two of its metabolites, homogentisic acid and 3,4-dihydroxyphenylalanine (DOPA). All cultures showed low levels of tyrosine degradation (0.3-2.6% in 24 h) and high levels of homogentisic acid degradation (9.3-31.0% in 24 h). Cultures of Amaranthus caudatus L. resembled the other nine species in possessing a moderate capacity for DOPA degradation (0.3-11.1% in 24 h).

TOBACCO POLYPHENOLS: III. THE ROLE OF FERULIC ACID IN THE BIOSYNTHESIS OF CHLOROGENIC ACID

C14-labelled ferulic acid (3-methoxy-4-hydroxycinnamic acid) is actively metabolized by leaf tissues of Nicotiana tabacum with the formation of its glucoside and glucose ester, and the coumarin glucoside, scopolin (6-methoxy-7-O-β-D-glucosido-coumarin). There is considerably less utilization in quinic acid ester formation. The only quinic acid esters which become labelled following the administration of labelled ferulic acid in the light yield ferulic acid on hydrolysis. One of these is 3-O-feruloyl-quinic acid. In the dark, the principal quinic acid esters synthesized again contain ferulic acid, but a low incorporation of activity into chlorogenic acid (3-O-caffeoyl-quinic acid) can be demonstrated. These findings are discussed in relation to reports of the utilization of ferulic acid in chlorogenic acid biosynthesis in other higher plant tissues.

TOBACCO POLYPHENOLS: II. ON THE BIOSYNTHESIS OF CHLOROGENIC ACID

Leaf disks of Nicotiana tabacum var. Delcrest were supplied with α-C14-labelled cinnamic, p-coumaric, and caffeic acids, p-coumaroyl-quinic acid, and the 1-glucose esters of cinnamic and p-coumaric acids. Considerable incorporation of radioactivity into chlorogenic acid occurred in 40 hours from all substrates except caffeic acid. In particular, p-coumaric acid was found to be a good precursor of chlorogenic acid in contrast to the findings of other workers with potato tuber tissue. More p-coumaric acid than cinnamic acid is converted to chlorogenic acid, although the reverse holds for conversion to p-coumaroyl-quinic acid. Chlorogenic acid synthesis from caffeic acid involves breakdown and resynthesis of the acid supplied, leading to the incorporation of radioactivity into other positions in the caffeic acid molecule and into the quinic acid moiety. Cinnamic and p-coumaric acids, on the other hand, are incorporated essentially intact into both p-coumaroyl-quinic and chlorogenic acids. These findings are discussed in relation to the pathway of chlorogenic acid biosynthesis postulated for potato tuber tissue.

TOBACCO POLYPHENOLS: III. THE ROLE OF FERULIC ACID IN THE BIOSYNTHESIS OF CHLOROGENIC ACID

C14-labelled ferulic acid (3-methoxy-4-hydroxycinnamic acid) is actively metabolized by leaf tissues of Nicotiana tabacum with the formation of its glucoside and glucose ester, and the coumarin glucoside, scopolin (6-methoxy-7-O-β-D-glucosido-coumarin). There is considerably less utilization in quinic acid ester formation. The only quinic acid esters which become labelled following the administration of labelled ferulic acid in the light yield ferulic acid on hydrolysis. One of these is 3-O-feruloyl-quinic acid. In the dark, the principal quinic acid esters synthesized again contain ferulic acid, but a low incorporation of activity into chlorogenic acid (3-O-caffeoyl-quinic acid) can be demonstrated. These findings are discussed in relation to reports of the utilization of ferulic acid in chlorogenic acid biosynthesis in other higher plant tissues.

TOBACCO POLYPHENOLS: II. ON THE BIOSYNTHESIS OF CHLOROGENIC ACID

Leaf disks of Nicotiana tabacum var. Delcrest were supplied with α-C14-labelled cinnamic, p-coumaric, and caffeic acids, p-coumaroyl-quinic acid, and the 1-glucose esters of cinnamic and p-coumaric acids. Considerable incorporation of radioactivity into chlorogenic acid occurred in 40 hours from all substrates except caffeic acid. In particular, p-coumaric acid was found to be a good precursor of chlorogenic acid in contrast to the findings of other workers with potato tuber tissue. More p-coumaric acid than cinnamic acid is converted to chlorogenic acid, although the reverse holds for conversion to p-coumaroyl-quinic acid. Chlorogenic acid synthesis from caffeic acid involves breakdown and resynthesis of the acid supplied, leading to the incorporation of radioactivity into other positions in the caffeic acid molecule and into the quinic acid moiety. Cinnamic and p-coumaric acids, on the other hand, are incorporated essentially intact into both p-coumaroyl-quinic and chlorogenic acids. These findings are discussed in relation to the pathway of chlorogenic acid biosynthesis postulated for potato tuber tissue.