REGULATION OF ENZYMES INVOLVED IN ANTHOCYANIN BIOSYNTHESIS IN CARROT CELL-CULTURES IN RESPONSE TO TREATMENT WITH ULTRAVIOLET-LIGHT AND FUNGAL ELICITORS

The accumulation of anthocyanins in cell cultures of Daucus carota L. and the enzymes involved in their biosynthesis were investigated under growth in the dark, continuous irradiation with UV light, incubation with elicitors from Pythium aphanidermatum, and elicitor treatment of UV-irradiated cells. Upon UV irradiation, anthocyanin accumulation was strongly enhanced, and the enzymes of the phenylpropanoid and flavono id pathways, including the ''late'' enzymes cyanidin galactosyltransfe rase, cyanidin galactoside xylosyltransferase, cyanidin triglycoside s inapoyltransferase and sinapic acid glucosyltransferase, all showed tr ansient increases in their activities. The time courses of the enzyme activities exhibited successive maxima with an ordered sequence corres ponding to their position in the biosynthetic pathway, suggesting a co ordinated induction of the entire set of enzymes, The key enzymes phen ylalanine ammonia-lyase and chalcone synthase are regulated on a trans criptional level. Incubation of dark-grown carrot cells with fungal el icitors led to a rapid and transient induction of phenylalanine ammoni a-IS ase corresponding to the formation of 4-hydroxybenzoic acid, but the amount of anthocyanin did not increase and there was no enhancemen t of ally of the enzyme activities which are part of the anthocyanin p athway including the enzymes catalyzing glycosylation and acylation re actions. Treatment with UV light and elicitors resulted in a rapid ind uction of the phenylpropanoid pathway, whereas the inducing effect of UV light on the anthocyanin content, on chalcone synthase and on the e nzymes catalyzing the final steps of anthocyanin biosynthesis was supp ressed. These results indicate a coordinated regulation of the enzymes involved in anthocyanin biosynthesis, an independent inducibility of the phenylpropanoid pathway, and a hierarchy of the different effector s, as shown by the dominating role of the elicitor-signal over the UV stimulus.