REGULATION OF ENZYMES INVOLVED IN ANTHOCYANIN BIOSYNTHESIS IN CARROT CELL-CULTURES IN RESPONSE TO TREATMENT WITH ULTRAVIOLET-LIGHT AND FUNGAL ELICITORS
We. Glassgen et al., REGULATION OF ENZYMES INVOLVED IN ANTHOCYANIN BIOSYNTHESIS IN CARROT CELL-CULTURES IN RESPONSE TO TREATMENT WITH ULTRAVIOLET-LIGHT AND FUNGAL ELICITORS, Planta, 204(4), 1998, pp. 490-498
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.