Über den Abbau von Flavonolen in pflanzlichen Zellsuspensionskulturen / Degradation of Flavonols in Plant Suspension Cultures

Abstract

The flavonols kaempferol, quercetin and isorhamnetin were labelled with 14C by keeping seven day old Cicer arietinum L. plants in an atmosphere of 14CO2 for five days. The purified (U-14C) flavonols were applied to cell suspension cultures of Cicer arietinum L., Phaseolus aureus Roxb., Glycine max and Petroselinum hortense. Based on the rates of 14CO2 formation and distribution of radioactivity after fractionation of the cells, the flavonols were shown to be catabolized to a very high extent. All four cell suspension cultures possess the enzymatic activity transforming flavonols to the recently discovered 2,3-dihydroxyflavanones. Upon incubation of the flavonols datiscetin and kaempferol with enzyme preparations from Cicer arietinum L. cell suspension cultures, it was demonstrated that the enzymatically formed 2,3-dihydroxyflavanones are further transformed in an enzyme catalyzed reaction. Salicylic acid was found as a degradation fragment of ring B of the 2,3,5,7,2′-pentahydroxyflavanone derived from datiscetin. Neither phloroglucinol nor phloroglucinol carboxylic acid were observed as metabolites of ring A. These in vitro findings were further substantiated by in vivo data because the flavonols kaempferol, quercetin and datiscetin when applied to cell suspension cultures of Cicer arietinum L. and Glycine max gave rise to para-hydroxybenzoic acid, protocatechuic acid and salicylic acid, respectively. It was thus concluded that flavonols are catabolized via 2,3-dihydroxyflavanones with the B-ring liberated as the respective benzoic acid. The data are discussed in connection with earlier findings on the catabolism of chalcones, cinnamic and benzoic acids.