Flavonoid metabolism in Forsythia flowers

The flavonoid pathway metabolism was studied in petals and sepals of Forsyt hia X intermedia cv. 'Spring Glory'. The activities of the flavonoid enzyme s chalcone synthase (CHS), flavanone 3-hydroxylase (FHT) and flavonol synth ase (FLS) were measured. The dihydroflavonol 4-reductase (DFR) role was als o studied by comparing flavonoid accumulation in transgenic plants for a he terologous DFR gene and wild-type F. X intermedia cv. 'Spring Glory', alrea dy investigated for DFR gene expression and activity. HPLC analyses complem ented enzymatic investigations, showing that: (i) rutin (quercetin 3-rutino side) is the major flavonol accumulated in petals and sepals (ca. 90% of th e flavonol pool) and; (ii) quercetin and cyanidin derivatives are the exclu sive flavonols and anthocyanins in sepals, respectively. The overall data d emonstrated that the flavonoid pathway in F. X intermedia flower organs lea ds to the major accumulation of 3',4'-dihydroxylated compounds? and that 3' -hydroxylation of the B-ring occurs mainly at flavonoid intermediate stage( s). Comparative HPLC analyses of F. X intermedia cv. 'Spring Glory' and thr ee other genotypes (F. giraldiana, F. X intermedia 'Korfor' Goldzauber(R) a nd F. ovata 'Robusta') confirmed the major production of flavonols by Forsy thia flavonoid metabolism and suggested a method for screening Forsythia ge notypes based on anthocyanin accumulation pattern in sepals. (C) 1998 Elsev ier Science Ireland Ltd. All rights reserved.