5-Deoxynevadensin, a Novel Flavone in Sunflower and Aspects of Biosynthesis during Trichome Development

Abstract

Fluorescent microscopy of sunflower glandular trichomes from anther appendages showed a strong autofluorescence, caused by flavonoids. Chemical analysis with NMR and HRMS lead to the identification of 7-hydroxy-6,8,4′-trimethoxyflavone, a novel 5-deoxyflavone, exclusively found in capitate glandular trichomes. 5-Deoxy flavones are rarely found in Asteraceae and this is the first report for the genus Helianthus. Semiquantitative RT-PCR showed the presence of transcripts for phenylalanine ammonia lyase (PAL) and chalcone synthase (CHS) in all biosynthetically active trichome stages. PAL and CHS are key steps in flavonoid biosynthesis indicating that flavonoid production occurs directly within the trichomes. This offers the possibility for examination of 5-deoxyflavone biosynthesis within Asteraceae.