Plants produce natural products which can be primary or secondary metabolites. Primary metabolites are needed for the day to day processes such as development and growth in the plant. Secondary metabolites are not as essential but are produced when needed by plants for protection against stress and diseases. Interest on these metabolites has grown worldwide since they are natural and do not have hazardous side effects compared to artificially synthesised products. To date, nearly two thirds of approved drugs since 1981 (Wu and Chappel, 2008), are derived from secondary metabolites. The World Healthy Organisation has estimated that about 80% of the developing world depends on traditional herbal remedies for their healthcare needs.
As these important metabolites are produced in small quantities, an alternative approach is therefore needed to increasing their production at the same time conserving the plants. Through tissue culture, where plants are produced in vitro under strictly regulated conditions, and genetic engineering where the target metabolite's production can be increased by manipulating the genes linked to their synthesis, the products of interest can be produced in quite significant quantities. A good example of these is artemisinin, a secondary metabolite produced by Artemisia annua. Artemisinin have been shown to have anti-malarial biological activities as shown by studies where malaria symptoms disappeared when patients were treated with A.annua tea. Malaria kills close to a million people worldwide, mainly children, in the developing world, who cannot afford available drugs in the market, thus artemisinin tea is an alternative cheap treatment.
Chinese wormwood-Artemisia annua
Artemisia annua is a single stemmed annual herb indigenous to Asia and grows to a height of about 2m. It has tiny yellow nodding flowers and the leaves are aromatic. It was used by the Chinese for the treatment of fever as indicated in their Chinese Handbook of Prescriptions for Emergency Treatments of 340AD. More studies on metabolic profiling and bioactivity of A.annua extracts are on going. Some researches have shown that artemisinin might have anti-cancer and anti-inflammation properties. Biotechnology techniques have been recently applied on A.annua to increase the production of artemisinin as naturally extracts from wildtype plants produce about only 0.01% to 0.4%.
Conventional agricultural vegetative propagation methods to improve the plant artemisinin yield and cross breeding plants from different localities have been practised and utilised, but these are not enough to meet the world demand at a commercial level. Growing of the plant in vitro in tissue culture coupled with hairy root cultures, have been harnessed in order to increase production of artemisinin. Hairy root cultures where plants were transformed via Agrobacterium-mediated transformation, using Agrobacterium rhizogenes strains, have been shown to produce higher concentrations of artemisinin and even higher concentration when continuously cultured in liquid suspension cultures. This was successfully shown by Liu et al. (1998), where hairy root cultures were established in a modified inner loop airlift bioreactor. They recorded maximum production of 577.5 mg/L in 20 days at pH 5.5-6, ≥3.0dm3/min air flow rate, and ≥ 16h/d photo radiation at 28°C.
More studies aiming at improving artemisinin production at hairy roots tissue culture level (Waraporn et al. 2007) and by genetic manipulation, targeting genes involved in artemisinin production such as a study by Zhang et al. (2008), still continue to increase production of this highly significant compound. From this, it is significant that Biotechnology indeed is a very important tool in increasing production of important secondary metabolites in plants which are needed for our well being and that it can be coupled with other techniques from other fields to produced important products.
About Author / Additional Info:
I am working on medicinal plants currently, aiming at increasing their important secondary metabolites.