Young plants (3- and 6-month-old) represent most appropri atestage of development for iridoid and phenylethanoid biosynthesis. Of the in vitro-propagated plants, the root tubers of 6-month-old plants were found to accumulate the highest total content of iridoids (4.15 mg g−1 DW) similar to that in root tubers of 6-month-old in
vivo-derived plants (4.18 mg g−1 DW). Another promising source of
iridoids are the leaves of 3-month-old in vitro regenerated plants,
which produced about 3.0 mg g−1 DW harpagoside and harpagide.
The harvesting of leaves does not require the plant to be cut down
and the material can be obtained within a short time of cultivation. Additionally,
the leaves were characterized by high production of
verbascoside and isoverbascoside. However, the pharmacological activity
of H. procumbens leaf extracts has not yet been studied.