Abstract
In the present study, the major flavonoids of white clover (Trifolium repens L.) cv. Sonja were extracted, isolated and identified. The major flavonoids in leaves and stems were the four flavonol glycosides: kaempferol-3-O-{Xyl(1→2)-Gal} (kaempferol-Xyl-Gal), kaempferol-3-O-{Rha(1→6)-[Xyl(1→2)]-Gal} (kaempferol-Rha-Xyl-Gal), quercetin-3-O-{Xyl(1→2)-Gal} (quercetin-Xyl-Gal), and quercetin-3-O-{Rha(1→6)-[Xyl(1→2)]-Gal} (quercetin-Rha-Xyl-Gal). Quercetin-Rha-Xyl-Gal has never been reported before and kaempferol-Rha-Xyl-Gal has not previously been identified in clover aerial parts. Concentrations of those compounds, together with aglyconic flavonoids previously described in white clover, as well as their glycosides, were quantified in leaves/stems and flowers of four white clover cvs Rabani, Klondike, Ramona and Aran using tandem mass spectrometry. There were significant differences in flavonoid concentrations in the two plant parts, with the highest concentrations of most aglycones in flowers and the highest concentrations of most glycosides in leaves/stems. This distribution of compounds may indicate different ways of storage and/or different mechanisms of action of the compounds. The cultivars were selected for genetic diversity, which resulted in distinctly different amounts of flavonoids in the plants. Concentrations of 17 of 24 compounds varied significantly – for some compounds up to a factor of 10 – among cultivars. Total flavonoid concentrations in flowers did not vary greatly among cultivars, at 28.9–35.8 mmol/g dry material (DM). In contrast, in leaves/stems, the cvs Rabani and Klondike had lower concentrations of most flavonoids (total concentrations 10.0 and 12.7 mmol/gDM, respectively) compared to cvs Aran and Ramona (32.3 and 22.1 mmol/gDM, respectively). There is a potential for breeding/selection of cultivars with targeted concentrations of particular flavonoids.