Cardiac glycosides in partly submerged shoots of Digitalis lanata

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.