Accumulation of phenolic acid conjugates and betacyanins, and changes in the activities of enzymes involved in feruloylglucose metabolism in cell-suspension cultures of Chenopodium rubrum L

Cell-suspension cultures of Chenopodium rubrum accumulate various soluble secondary phenolic metabolites such as the hydroxybenzoic acid glycosides 4-hydroxybenzoic acid-beta-glucoside, vanillic acid-beta-glucoside, the hydroxycinnamic acid acylglycosides 1-O-(4-coumaroyl)-beta-glucose, 1-O-feruloyl-beta-glucose, 1-O-sinapoyl-beta-glucose and 1-O-feruloyl-(beta-1,2-glucuronosyl)-beta -glucose, the hydroxycinnamic acid amide N-feruloylaspartate, and the betacyanins betanin, amaranthin and celosianin II. In addition, accumulation of the insoluble cell wall-bound hydroxycinnamic acids with ferulic acid as the major component occurs parallel to culture growth. The changes of three pivotal enzymatic activities, all O-transferases which are involved in the formation of the dominant ferulic acid conjugates, were determined. These are (i) uridine 5'-diphosphate(UDP)- glucose-hydroxycinnamic acid O-glucosyltransferase (EC 2.4.1), (ii) UDP-glucuronic acid:1-O- hydroxycinnamoyl-beta-glucose O-glucuronosyltransferase (EC 2.4.1) and (iii) 1-O-hydroxycinnamoyl-beta- glucose:amaranthin O-hydroxycinnamoyltransferase (EC 2.3.1). The patterns of metabolite accumulation associated with these enzyme activities show that the hydroxycinnamic acid-glucose esters play a central role as metabolically active intermediates in the secondary metabolism of Ch. rubrum. Two cell lines of this culture (CH, CHN), differing in their betacyanin content, were compared with respect to this metabolism. A markedly higher total betacyanin content in the CHN line might possibly be the consequence of an increased supply of the key precursor for betalain biosynthesis, i.e. 3,4-dihydroxyphenylalanine (DOPA). In addition, the enhanced accumulation of celosianin II in the CHN line correlates well with a higher activity of the enzyme catalyzing the transfer of ferulic acid from 1-O-feruloyl-beta-glucose to amaranthin.