No abstract

An HPLC method for the quantitative analysis of cardenolides was developed and applied. The procedure was optimised for analysing small samples (40 mg dw) of plant and tissue culture material. ISOPLEXIS CANARIENSIS plants obtained from seeds accumulated cardenolides to about 20 - 40 micromol g (-1) dw as calculated from the levels of cardenolide genins released after acidic hydrolysis of methanolic extracts. The relative contents of xysmalogenin, digitoxigenin, uzarigenin and canarigenin were 5 - 15 %, 0 - 5 %, 10 - 15 % and 70 - 90 %, respectively. Shoot cultures were initiated from seeds, established as permanent cultures and cultivated on agar-solidified or in liquid medium. Shoot cultures maintained on solid medium contained an average of about 6 micromol cardenolides g (-1) dw. A relatively high proportion of digitoxigenin was found in two-thirds of the shoot cultures examined. The cardenolide content of amphibian shoot cultures averaged to about 1 micromol g (-1) dw. Plants regenerated from shoot cultures and maintained under hydroponic conditions accumulated the same amount of cardenolides as plants collected in the field. No cardenolides could be detected in callus cultures.

Isoplexis is a plant genus closely related to Digitalis. Members of this genus contain cardenolides considered more "primitive" than those present in Digitalis. Isoplexis plants, tissue cultures, and isolated cardenolides may thus be used to elucidate the biosynthesis of cardenolides in the Scrophulariaceae. Therefore, a method was developed to cultivate and propagate Isoplexis canariensis (L.) Lindl. ex. G. Don in vitro. Seeds were germinated in liquid modified MS medium and shoot cultures were established and propagated in liquid modified MS medium containing 0.1 mg/l IAA and 1 mg/l BAP. Shoot cultures were also established from excised axillary buds and propagated on solid culture medium containing 0.1 mg/l IAA and 1 mg/l BAP. Shoots of either origin were rooted in medium containing 1 to 5 mg/l IAA and 0.5 to 4 mg/l IBA. Rooted plantlets were cultivated for 2 to 3 weeks in hormone-free modified MS medium and then transferred to the greenhouse, where they developed into healthy plants.