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Updated: Jul 30, 2026

Biosynthesis of a Flavonol from a Flavanone by Establishing a One-pot Bienzymatic Cascade
Published on: August 14, 2019
Flavonols: pigments responsible for ultraviolet absorption in nectar guide of flower
Abstract:
The petals of the black-eyed susan (Compositae: Rudbeckia hirta) contain three flavonol glucosides (6,7-dimethoxy-3',4',5-trihydroxyflavone-3-O-glucoside, patulitrin, and quercetagetin). These compounds, which show intense spectral absorption at 340 to 380 nanometers, are restricted in distribution to the petal bases, which are ultraviolet absorbing as a result. Such ultraviolet-absorbing petal zones, known as "nectar guides," are invisible to us, but are visible and of orientation value to the pollinating insect that lands on the flower in search for food. This is the first time that ultraviolet absorption in a nectar guide has been interpreted in chemical terms. In view of the widespread occurrence of flavonols in flowers, it is suggested that these pigments serve specifically for demarcation of ultraviolet petal patterns visible and relevant to insects.
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