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Shoot cultures were established from axillary buds (11 strains) or seeds (1 strain) of individual Digitalis lanata Ehrh. plants and propagated partially submerged in liquid medium. Five of these shoot culture strains were characterized with regard to their growth and cardenolide content. The cultures were observed for more than one year and found to be relatively stable with regard to their growth and cardenolide spectrum and yield. The strains examined differed in terms of their total cardenolide yield, which ranged from about 30 nmol g DW-1 to almost 1000 nmol g DW-1. Cardenolide content was correlated with leaf size and development. Depending on the strain investigated up to ten different cardenolides could be detected by HPLC. The main cardenolides were identified by comparing HPLC and TLC results with those of authentic samples and chemical degradation as being the mono- and diglycosides glucodigifucoside, glucoverodoxin, odorobioside G, and odoroside H; minor amounts of digitalinum verum and glucoevatromonoside were also found. In addition, the tetrasaccharides lanatoside A and C were present. The shoots were cardenolide-free when cultivated in the dark for more than 30 weeks, but regained their characteristic cardenolide profile when transferred back to light. For the dark cultivation of chlorophyll-free cultures a medium containing 3.5% glucose was found to be optimal.

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.

Posters protein solubilization. Among the compounds tested, the zwitterionic detergent CHAPS {3-[(3-cholamidopropyl)dimethylammonio]propane-1-sulphonic acid} was found to be the best suited for solubilizing the enzyme. In addition, the influence of some protective reagents as glycerol, KC1, and sodium citrate was tested.