Secondary metabolite production, yield enhancement

Since most organic solvents are harmful to plant cell growth, the selection of an adequate lipophilic phase is essential for successful in situ extraction. Elicitation in conjunction with in situ extraction could alter the pattern of secondary metabolite production and enhance the product yield. 

Plant cell cultures represent a potentially rich source of secondary metabolites of commercial importance and have been shown to produce them in higher concentrations than the related intact plants. However, plant cell cultures often produce metabolites in lower concentrations than desired and commonly store them intracellularly. These limitations can be overcome by product yield enhancement procedures, including immobilization of cultured cells, and permeabilization, or ideally using a combined immobilization/ permeabilization process with retained plant cell viability. Complex coacervate capsules consisting of chitosan and alginate or carrageenan proved to be effective biomaterials for entrapment, controlled permeabilization of cells and to allow control of capsule membrane diffusivity. 

Plant cell and organ cultures can produce higher metabolite concentrations than found in the corresponding intact plant organs (6, 9). However, plant cells grown in culture may also produce lower quantities of the desired secondary metabolites which are commonly stored intracellularly. The challenges to increase product yield and to enhance the release of secondary metabolites can be met in various ways (7). These include immobilization (9), permeabilization (12, ), the use of precursors (12,13), and the induction of secondary metabolite production via elicitors (14). 

To date, progress achieved clearly demonstrates the potential of cultured plant cells for secondary metabolite production. Use of concurrent immobilization/permeabilization procedures, as well as precursor and elicitor treatments, may open new avenues of increasing product yields and will consequently affect the economic aspects of plant cell culture in a positive manner. However, our understanding of the many biosynthetic pathways of desired secondary metabolites is incomplete and successful industrial scale plant cell culture processes are still limited. Results of research in the area of plant cell culture will increase our understanding of the biosynthesis of plant metabolites, enhance our knowledge of plant-microorganism or plant-plant interactions and can lead to entirely new products or product lines of desirable compounds currently not available to use. Such work can also lead to development of industrial scale production processes for products now produced and recovered by conventional methods. Also, the genetic variety of the 250,000 to 750,000 plant species available remains to be explored. Presently only 5 to 15% of these species have been subject to even... 

The aqueous two-phase system can be applied to plant cell suspension cultures as an in situ extraction method to enhance the production of hydrophobic secondary metabolites or extracellular proteins such as enzymes. Selective removal of the product during bioconversion using plant cells may also be possible in ATPS. Prior to obtaining phy to chemicals with high yields using ATPS, however, reliable cultivation of plant cells in ATPS should be proven. 

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