STRATEGIES FOR THE IMPROVEMENT OF SECONDARY METABOLITE PRODUCTION IN PLANT-CELL CULTURES

Plant cell and tissue cultures can be established routinely under ster ile conditions from explants, such as plant leaves or stems. Strain im provement, methods for the selection of high-producing cell lines, and medium optimizations can lead to an enhancement in secondary metaboli te production. However, most often trials with plant cell cultures fai l to produce the desired products. In such cases, strategies to improv e the production of secondary metabolites must be considered. One of t he main problems encountered is the lack of basic knowledge of the bio synthetic routes, and mechanisms responsible for the production of pla nt metabolites. Where the productivity of the desired metabolites is l imited by the lack of particular precursors, biotransformation using a n exogenous supply of biosynthetic precursors may improve the accumula tion of compounds. Feedback inhibition of metabolic enzymes as well as inhibition of membrane transport can be eliminated by the accumulatio n of synthesized products in a second phase introduced into the aqueou s medium. Organ cultures often have sites of synthesis and storage of secondary metabolites in separate compartments. Elicitors, compounds t riggering the formation of secondary metabolites, can be abiotic or bi otic. Natural elicitors include polysaccharides such as pectin and chi tosan, which are also used in the immobilization and permeabilization of plant cells. Immobilization provides several advantages, such as co ntinuous process operation, but for the development of an immobilized plant cell culture process natural or artifically induced secretion of the accumulated product into the surrounding medium is necessary.