Occurrence of flavonoids in Ophrys (Orchidaceae) flower parts

The flower parts (i.e. sepals. labellum, gynostemium and isolated pollinia) of four Ophrys species (Ophrys argolica., Ophrys apifera, Ophrys cornuta, and Ophrys delfinensis [O. argolica x O. cornuta]) native in Greece, were examined for the presence of polyphenolic compounds. The chernical composition was studied by chromatographic and spectroscopic techniques (UV-vis and 1D and 2D NMR), whereas the localization of the phenolic compounds was depicted by epifluorescence microscopy. The chemical composition was highly variable among the different flower parts. Pollinia and sepals contained the highest concentrations of flavonoids, while the labellum contained the lowest. Among species, O. apifera showed the highest (up to 6-fold) concentration of flavonoid compounds compared with the other three species. Microscopic observations showed that flavonoids are localized in the protoplast, especially in proximity of the nucleus. They are concentrated on cuticle and cell walls of epidermal cells and in parenchyma cells of the sepals. The pollinia contained high concentrations of flavonols which were deposited in the pollen grains. Three kaempferol (Kin) glycosides, Km 3-O-beta-D-glucoside, Km 3-O-beta-D-rutinoside and Km 3-O-beta-D-rhamnoside, were the dominant compounds in the pollinia. The above results Suggest a UV-protective role for flavonoids in the flower parts of these plants. Additionally, the pollen-specific flavonols could also be related to the flavonol-depended male fertility known from other plant species. (c) 2008 Elsevier GmbH. All rights reserved.