Enzymes of Flavone and Flavonol-Glycoside Biosynthesis. Coordinated and Selective Induction in Cell-Suspension Cultures of Petroselinum hortense

We have extended our previous studies, which had resulted in the classification of two groups of coordinately induced enzymes of phenylpropanoid metabolism in irradiated cell-suspension cultures of Petroselinum hortense Hoffm. The additional enzymes investigated were acetyl-CoA carboxylase, a methyltransferase, and a flavonol-specific glucosyltransferase. The results indicate that the second group (group II) includes the enzymes of both flavone and flavonol glycoside formation from 4-coumaroyl-CoA and acetyl-CoA (utilized via malonyl-CoA). The enzymes of this pathway, as opposed to those of the general phenylpropanoid metabolism (group I), met the following operational criteria for their common classification into group II. Under the experimental conditions employed, they increased in activity after a considerably longer, but uniform, lag period of about 4 h, as compared with about 2 h for group I; pronounced peaks of the individual enzyme activities in the range between about 25 and 40 h after the onset of induction occurred significantly later than in the case of group I; subsequent periods of exponential decline of the enzyme activities occurred with relatively long apparent half-lives of the order of 30–70 h. The induction of the two groups of enzymes was shown to be highly selective. Several enzymes involved in various pathways of intermediary metabolism were not affected by irradiation of the cell cultures. Even those enzymes, which are assumed to catalyze the formation of the various intermediary metabolites serving as substrates for the light-induced reactions, remained unaffected by the irradiation program.