Flavonoid metabolism in Forsythia flowers

Abstract

The flavonoid pathway metabolism was studied in petals and sepals of Forsythia X intermedia cv. ‘Spring Glory’. The activities of the flavonoid enzymes chalcone synthase (CHS), flavanone 3-hydroxylase (FHT) and flavonol synthase (FLS) were measured. The dihydroflavonol 4-reductase (DFR) role was also studied by comparing flavonoid accumulation in transgenic plants for a heterologous DFR gene and wild-type F. X intermedia cv. ‘Spring Glory’, already investigated for DFR gene expression and activity. HPLC analyses complemented enzymatic investigations, showing that: (i) rutin (quercetin 3-rutinoside) is the major flavonol accumulated in petals and sepals (ca. 90% of the flavonol pool) and; (ii) quercetin and cyanidin derivatives are the exclusive flavonols and anthocyanins in sepals, respectively. The overall data demonstrated that the flavonoid pathway in F. X intermedia flower organs leads 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 three other genotypes (F. giraldiana, F. X intermedia ‘Korfor’ Goldzauber® and F. ovata ‘Robusta’) confirmed the major production of flavonols by Forsythia flavonoid metabolism and suggested a method for screening Forsythia genotypes based on anthocyanin accumulation pattern in sepals.