Liquid Culture Systems for in vitro Plant Propagation

Comparison of secondary plant metabolite production 533
the composition varied considerably. Some of the compounds were more
concentrated in the in vitro material compared to the field grown plant.
For the other three species tested the content of bioactive compounds was
always lower in the in vitro cultures compared to field grown plants.
However, comparing the different in vitro culture systems, the content was
higher in shoot cultures compared to cell cultures. Moreover, the biomass of
Lavandula and Hypericum from TIS vessels was fractionated according to
the colour of the material: depending on the position of the material within
the vessel, the biomass was green (top and side layers), yellow (inner part of
the vessel) or brown (bottom layer). The result of the analysis of the
different fractions is shown in table 3. For Lavandula the highest
concentration of rosmarinic acid (7.5 mg g -1 dry weight) was found in the
green top layer and nothing in the brown biomass from the vessel centre. In
contrast, the highest content of hypericin in the biomass of Hypericum was
found in brown material (0.23 mg g -1 dry weight) and lower concentrations
in the yellow (0.11 mg g -1 dry weight) and green (0.12 mg g -1 dry weight)
biomass.
4. Discussion
The in vitro production of plant secondary metabolites as bioactive
compounds for the pharmaceutical and cosmetic industry presents several
advantages compared to the extraction of these compounds from field grown
plants: in vitro cultures are independent of season, climate and weather and
there is no risk of crop failure due to natural hazards. Moreover, the danger
of extinction of species due to over collection from natural populations is
avoided (Bhojwani and Razdan, 1996). Starting in the nineteen seventies,
much work has been carried out on the use of plant cell cultures for the
production of secondary metabolites (for reviews see e.g Charlwood and
Rhodes, 1990; Fowler, 1992; Bhojwani and Razdan, 1996), however, only
few products from cell cultures have been commercialised so far, e.g.
shikonin from Lithospermum erythrorhizon (Fujita, 1988, 1990). In most
cases, cell culture has not become a cost-effective technology, since scale-up
in bioreactors is expensive and the yield of metabolites from cell cultures is
often low and unstable (Bhojwani and Razdan, 1996). Therefore, we
cultivated plant shoots in temporary immersion systems to compare with
sophisticated bioreactor technology, TIS are low-cost culture systems,
moreover shoots are genetically and physiologically more stable compared
to cell cultures.
Working with the model species Lavandula, Hypericum, Cymbopogon
and Fabiana, there were considerable differences between the content of