natural-products-in-plant-pest-management

Biotechnology and Natural Product Synthesis 271generation of somaclonal variations is intentionally done for the furtherimprovement of the selected plant variety. The screening can be done inmuch the same way as for microorganisms – in Petri dishes rather than in agreenhouse or a field. Therefore overproducers and producers of new metabolitescan be easily and rapidly selected. The generation of variants can alsobe achieved by somatic fusion of two protoplasts of cells from two differentparents. The parents may be closely or distantly related. This can bringgenetic information required, for example, for synthesis of one metaboliteand an enzyme that can further transform it into a more useful product orproducts. This section of science is called combinatorial biosynthesis. Thevariants made by either method can usually be regenerated into whole plantsor, if desired, can be maintained in cell or organ cultures.Certain metabolites are tissue specific. Even for metabolites that are nottissue specific, the higher yield is given in compacted tissues rather than inloose-cell suspensions. For this, organogenesis is necessary. A very goodsolution is available as plant tissues transformed by Agrobacterium rhizogenescan grow indefinitely as roots in appropriate culture media. Once transformed,the cells can grow as hairy roots without the bacterium. When productsare formed and secreted or made to secrete into the medium, productrecovery is easy as it is not contaminated by cells. Further, continuousremoval is also possible. While all these facts are fascinating and encouraging,the published literature shows only two plant metabolites that areproduced on a commercial scale. Shikonin is the first botanical produced ona commercial scale using plant cell cultures of Lithospermum erythrorhizon.The specific productivity of shikonin has been increased 25-fold by simultaneousin situ extraction using n-hexadecane added before 15 days and immobilizationof cells in algenate beads, in comparison with production in cellsuspension culture (Kim and Chang, 2004).Immobilized cells have shown to be better producers in general. Whencomparing yields of scopadulcic acid B, a diterpene that has antiviral andanti-tumour activity, production by Scoparia dulcis in suspension culture andcells immobilized in Luffa sponge, Mathew and Jayachandran (2009) noted350.57 mg/g of cells by the 19th day by immobilized cells in contrast to 50.85mg/g of cells after 30 days of incubation in suspension culture. This is asevenfold increase with a shorter time of incubation. Continuous removalof products and inhibitory substances is an added advantage of usingimmobilized cells.The only other compound produced using plant cell culture that hassuccessfully entered the market is ginseng saponin originating from Panaxginseng. Further improvements to the yield have been shown in hairy rootcultures fed with specific nitrogen and phosphorous sources (Jeong andPark, 2006).Catharanthus roseus is one of the plants that showed success in the productionof alkaloids in cell suspension culture. These are indole alkaloids, ofwhich the bisindole alkaloids vinblastine and vincristine are antineoplasticmedicines and the monoindole alkaloids (ajmalicine and serpentine) are antihypertensiondrugs. Since the first results published 30 years ago (Kurz et al.,