Transfer of iridoid glucosides from host plant Galium verum to hemiparasitic Euphrasia stricta

Abstract

1. Subject and sourceEuphrasia stricta J. F. Lehm. is a small hemiparasitic annual plant growing in dry habitats. The genus Euphrasiahas traditionally been placed in the family Scrophulariaceae, but recently, it has been transferred to Orobanchaceae(Olmstead et al., 2001; APG II, 2003). The plants in the present work were collected on a dry shore meadow inlate September at the peninsula Odden of NW Sealand, Denmark. They were growing in a community with mainlyAchillea millefolium L., Artemisia campestris L. (Asteraceae), Armeria maritima (Miller) Willd. (Plumbaginaceae),Festuca ovina L. (Poaceae), Galium verum L. (Rubiaceae), Plantago lanceolata L. (Plantaginaceae) and SedumacreL. (Saxifragaceae). Avoucher number (IOK-31/2003) has been deposited at the Botanical Museum, The Univer-sity of Copenhagen.2. Previous workSome species of Euphrasia have been chemically investigated (Sticher and Salama, 1981; Salama and Sticher,1983; Kamalyan et al., 1996; Erso¨z et al., 2000, 2002) and the characteristic iridoid glucosides found are aucubin,iridoid aldehydes like plantarenaloside, ixoroside and euphroside, as well as caffeoyl phenylethanoid glycosides(CPGs) like verbascoside.Many species of Galium have been investigated for iridoids (Mitova et al., 2002, and cited references); the genus ischaracterized mainly by asperuloside and its congeners.The interaction and transfer of compounds between host and parasitic plants have been the subject of much dis-cussion (Rank et al., 2004, and cited references), however, not many specific compounds produced by the host planthave been isolated from the parasite with certainty. Published examples are transfer of petroselinic acid from Hederato Orobanche (Lotti and Paradossi, 1987); of pyrrolizidine (from Lolium and Senecio) and quinolizidine (from Faba-ceae genera) alkaloids to Castilleja, Orobanche, Orthocarpus, Pedicularis or Rhinanthus (Wink et al., 1981; Stermitz