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Parasitic plants of the genus Cuscuta (Cuscutaceae) including C. platyloba Progel and C. reflexci Roxb., which are usually alkaloid-free, are able to grow on a plethora of alkaloid-producing host plants such as Duboisia myoporoides R. Br. (Solanaceae), Lupinus albus (Fabaceae), and Nicotiana xanthi (Solanaceae). During parasitism alkaloids of the host plants are accumulated by the parasites as shown for the examples of L. albus and C. platyloba (1). The quinolizidine alkaloids of L. albus are passed on to the parasite through the "haustoria" which tap the xylem and phloem vessels of the host, as has been revealed by microscopical analysis of cross-sections of C. reflexa infesting L. albus. The highest concentrations of host plant alkaloids in the parasite are usually found in the haustorial region (up to l7mg/g dry weight, calculated as sparteine), the alkaloid pattern closely resembling that of the host. The concentrations of alkaloids decrease towards the shooting tip of the parasite (2mg/dry dw). Alkaloid esters such as 13-O-cinnamoyllupanine present in the host plant as well as in the haustorial region of the parasite likewise tend to decrease towards the shooting tip of Cuscuta which is characterized by 13-hydroxylupanine as sole detectable alkaloid. Similar results are obtained with D. myoporoides as host plant with regard to tropane alkaloids. Large concentrations of, e.g. scopolamine or hyoscyamine, are detected in parasitizing C. platyloba. However only traces of tobacco alkaloids including nornicotine and anabasine are detected in the parasite even though these compounds are the main alkaloids of D. myoporoides. C. reflexa and C. platyloba growing on N. xanthi likewise yielded only traces of nicotine and related compounds (20-4Opg/g dw) although these alkaloids are present in the host plant in appreciable quantities (up to 5 mg/g dw).At present, we assume that nicotine and related compounds, which are known to be transported through the xylem vessels of tobacco plants (2), are metabolized by Cuscuta species following uptake via the haustoria. Further studies aiming at determination of the fate of nicotine in Cuscuta species are now in progress.Financial support by the Deutsche Forschungsgemeinschaft is gratefully acknowledged.

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