Inter-population and inter-organ distribution of the main polyphenolic compounds of Epilobium angustifolium

Rosebay willowherb (Epilobium angustifolium) contains large amounts of polyphenolic compounds, including tellimagrandin I-based oligomeric ellagitannins (ETs). The aim of this study was to assess the interpopulational and inter-organ variability of the polyphenol fingerprint of E. angustifolium. Seven ETs, 11 flavonol glycosides and neochlorogenic acid were quantified by UHPLC-DAD-ESI-QqQ-MS in the leaves, flowers and stem parts of plants from 10 populations. Total polyphenol content of leaves and flowers ranged from 150 to 200 mg/g dry wt, of which 90% was constituted by dimeric to heptameric ETs. Flowers contained, on average, 10% more oenothein B (dimeric ET) and 2 times less oenothein A (trimeric ET) than leaves. Tetrameric and pentameric ETs exhibited rather similar levels in leaves and flowers whereas hexameric and heptameric were 3-4 times more abundant in flowers than in leaves. Quercetin-3-O-rhamnoside, myricetin-3-O-rhamnoside and kaempferol-3-O-rhamnoside were specific to flower tissue and were absent from leaves. The inflorescence stem showed the highest content in total polyphenols with an average of 250 mg/g dry wt and contained remarkably large amounts of oenothein B and A. Polyphenol content steadily decreased along the inflorescence stem and reached its lowest level in the vegetative part of the stem. The interpopulational variability of most polyphenols was within a two- to threefold range across the 10 sampled populations. Myricetin-3-O-glucoside and myricetin-3-O-glucuronide, however, showed a more population-specific distribution with concentrations varying from 0 to 2.3 mg/g dry wt. Finally, this study showed that the levels of oenothein B and A in the plant are not interdependent but that their relative abundance is constant within a population.