natural-products-in-plant-pest-management

Biotechnology and Natural Product Synthesis 273Hernandez-Vazquez et al. (2010) were able to increase the production ofcentellosides in cell cultures of Centella asiatica by feeding with α-amyrintogether with DMSO to assist the penetration of α-amyrin in to the cells.The secretion can be enhanced by manipulating the culture mediumeither by increasing the leakiness of tissues or by introducing a trappingsystem to trap the secreted metabolite. For example, Rudrappa et al. (2004)reported an increased recovery of betalaines (red natural pigment) productionby hairy roots of B. vulgaris up to 97.2% by using alumina:silica (1:1) inthe culture medium. The use of elicitors is a useful approach to enhance theproductivity as some secondary metabolites are naturally produced inresponse to a signal. This has been shown practically by incorporating bothlive and autoclaved bacteria in the conversion of hyoscyamine to scopolamineby hairy root cultures of Scopolia parviflora (Jung et al., 2003).Podophyllotoxin is a useful botanical extracted from Podophyllum hexandrumfor treating general warts. Chattopadhyay et al. (2002) used a 3-l bioreactorfor the cell suspension culture of P. hexandrum and successfullyrecovered podophyllotoxin. It has been noted that providing coniferin as aprecursor in the culture medium increases the productivity, but this is economicallyprohibitive. An innovative method to circumvent this problem isto co-cultivate P. hexandrum cell suspension with hairy roots of Linum flavum,which produces coniferin. This approach has increased the final productformation by 240% (Lin et al., 2003).A further step in bringing the substrate and enzymes from differentsources has been made possible through combinatorial biosynthesis. Here,rather than cocultivating the two individual plants in vitro, the genetic traitscontrolling the production of one compound, which will be the precursor ofthe final product, and the enzyme required for the transformation are broughttogether into one cell. A somatic hybrid of two Solanum species producingsolanidine and solanthrene (S. tuberosum) and tomatidine (S. brevidens) producedall three steroidal glycoalkaloid aglycones. In addition all hybrids alsoproduced a totally new compound, demissidine (Laurila et al., 1996). Theseauthors propose a hypothesis to describe this which explains the productionof demissidine by hydrogenating the double bond at position 5 of solanidineof S. tuberosum by a hydrogenase enzyme of S. brevidens.13.3 Expanding Natural Product DiversityIn the quest for natural products for the benefit of humankind, it can often bethought that the existing natural product diversity is not sufficient. The generationof mutants is a tool available for increasing natural product diversity.Random mutagenesis is stimulated by treating with chemical mutagens orradiation. Although these are useful and have been employed for makingvariants and subsequent screening, with the better understanding of DNAand development of new biotechnological tools, specific, site-directedmutagenesis is possible. This has reduced the effort in screening a largenumber of mutants for the expected outcome.