Techniques of Biotechnology for Medicinal Plants

Bio transformation Using Plant Cell Culture.

Introduction
Biotransformation is a process through which the functional groups of organic compounds are modified by living cells. This process can be done by using micro organism or plant cell suspension, hairy root culture and immobilized cell. Microbial systems provide a vast range of advantages for biotransformation process. The number and diversity of microbial species with their associated wide range of potential for enzymatic catalysis ,  the relative ease with which they can be  grown in large volumes ,  and high growth  and metabolism are factors which shows microbes are efficient  agents for biotransformation reactions . This potential of microorganism was exploited by human beings long ago. For  e.g.  Acidification of wine into vinegar in 6th  millennium BC.

In the past two decades significant achievements were accomplished in the field of plant biotechnology. There are hundreds of plantpecies in culture in different centers of the world especially Japan, Germany, USA and India. The cell cultures of Catharanthus roseus have been extensively studied in terms of their growth, primary and secondary metabolism the potential of plant tissue cultures for biotransformation process was realized soon after their establishment, and they are used as tools for biosynthetic studies.

Because of factors such as difficulty of maintaining culture sterility, slow growth rate etc. plant cell cultures cannot compete with microbial system for same biotransformation reaction. However, the plants are genetically very diverse and possess a rich repetory of enzymes. The industrial utility of biotransformation using plant cell culture system will be possible if the biotransformation reaction is unique to plant cells and the product has a high market value e.g. paclitaxel.

            A major disadvantage of plant tissue culture compared with the whole plant in connection with secondary metabolism is that the biosynthetic potential of the species in question is very often not expressed in culture. 

Conditions For Biotransformation

            The substrate of biotransformation reaction must be easily assimilated by the cell and reach the appropriate cellular compartment or organelle without significant degradation.

1. The substance must be non-toxic to the cell culture.
2. The rate of product formation must significantly exceed the rate of its further metabolism.
The advantage of biotransformation reactions by plant cells and microbial system over non-biochemical reaction system include.
1. Selectivity,  stereo-selectivity,  regio-selectivity
2. Mild reaction conditions
3. Environmentally friendly; avoiding extremes of PH  and metal  catalysts
4. Specificity; reaction on particular molecules
5. Wide range of catalytic activities available

              Biotransformation by plant cell cultures yield a wide range of reactions, such as Glycosylation,  Glucosylesterification,  Hydroxylation,  Oxido-reductions between alcohols and caronyl compounds,  Reduction of carbon double bonds,  Hydrolysis, Epoxidation, Isomerization, Methylation, Demethylation and Dehydrogenation etc.

        Glucose conjugations of exogenously added substances are considered tobe detoxificaton reactions. The terpenoids and cholesterol (hydrophobic) may disturb the membranes of cells and organelles, when the molecules are taken into the cells, or phenolics may cause generation of active oxygen in the cell. However if the substrate are non-toxic to cells,  the cells may not respond to them for e.g. Glycyrrhiza  cultured cells are sensitive to papaverine above 250mg and yielded several biotransformation products. Even normal metabolites of plant cells can be toxic for plants if these are supplied exogenously. For e.g. Cinnamic acid is usually metabolized to coumarin, flavone, and lignin and related compounds in plant cells, however, even cinnamic acid when added exogenously, was toxic at 100mg/l to cell cultures of several species. The reaction may depend on the concentration cinnamic acid added; it may be metabolized normally when supplied exogenously at a lower concentration.(2)