Abstract
Digitalis lanata plants were grown on water culture in a controlled environment and in the young,
growing leaves free sterols (0.335 µmol/g FW), triacylglycerols (0.97 µmol/g FW) and
cardenolides (1.82 µmol/g FW) were the major apolar and polar lipids. The cardenolide-containing
fraction from these tissues was separated into 26 cardenolides by HPLC. The 5 major
components (accounting for 60 % of the occurring glycosides) lanatosides A and C,
acetyldigoxin, acetyldigitoxin, and glucoevatromonoside were identified by FABMS.
Incorporation experiments with [2-14
C]-acetate, [2-14
C]-malonate, [2-14
C]-mevalonate, and [U-14
C]-sucrose (absorbed by excised, young, growing leaves) showed the labelling of all
the occurring cardenolides after a 3 day incorporation period (as judged by HPLC).
Comparing the simultaneous synthesis of labelled sterols and triacylglycerols, malonate
could be considered as the most effective precursor in cardenolide synthesis, reaching
an incorporation value of 4.1 % in a 4 day incorporation period. A time-course experiment
revealed a temporary accumulation of 14C in glucoevatromonoside, which may play a role as an intermediate in cardenolide
production of Digitalis lanata.
Key words
Biosynthesis - cardenolide -
Digitalis lanata
- malonate
