Ashwani Kumar

Predicted growth in world population is posing a serious challenge to crop production and food security, particularly in developing countries. The augmentation of conventional breeding with the use of marker-assisted selection and transgenic plants promises to facilitate substantial increases in food production. However, knowledge of the physiology and biochemistry of plants is extremely important for interpreting the information from molecular markers and deriving new and more effective paradigms in plant breeding Bourgaud et al (2001). Secondary metabolites are currently being obtained commercially by extraction from whole plants. Large scale plant tissue culture is an attractive alternative to the traditional methods of plantation, as it offers two advantages: (1) controlled supply of biochemicals independent of plant availability (politics, climate, pests,), and (2) well defined production systems which result in higher yields and more consistent quality of the product. Several organizations such as Rockefeller Foundation, United Nations Educational, Scientific and Cultural Organization (UNESCO), Intrnational Cooperation Program of the European Union, International Service for the Acquisition of Agrobiotech Applications (ISAAA), and International Service for National Agricultural Research (ISNAR) are attempting to play a major role in technology transfer from public and private sector institutions in the developed to the developing countries. During the last 30 years, plant cell and tissue cultures have been comprehensively studied for the production of secondary metabolites. However, despite promising results, this technology has led to only a few realisations for the production of commercial compounds, at the industrial scale. This lack of industrial success can be attributed to severe bottlenecks that have been identified during the last decades. Among them are insufficient knowledge on the biosynthetic pathways leading to erratic production, or bioreactor facilities nonadapted to plant cell characteristics (shear stress sensitiveness) giving poor biomass productivity. Rational engineering of secondary metabolic pathways in plants requires a thorough knowledge of the whole biosynthetic pathway and a detailed understanding of the regulatory mechanisms controlling the onset and the flux of the pathways. Such information is not yet available for the vast majority of secondary metabolites, explaining why only limited success has been obtained by metabolic engineering. Today, only a few pathways (e.g. flavonoids, terpenoid indole and isoquinoline alkaloids) in plants are well understood as a result of many years’ classical biochemical research Secondary plant metabolism: Plants synthesize an extensive array of secondary metabolites, often with highly complex structures.Currently, most pharmaceutically important secondary metabolites are isolated from wild or cultivated plants because their chemical synthesis is not economically feasible. Biotechnological production in plant cell cultures is an attractive alternative, but to date this has had only limited commercial success because of a lack of understanding of how these metabolites are synthesized. Based on their biosynthetic origins, plant secondary metabolites can be structurally divided into five major groups: polyketides, isoprenoids (e.g. terpenoids), alkaloids, phenylpropanoids and flavonoids. The polyketides are produced via the acetatemevalonate pathway; the isoprenoids (terpenoids and steroids) are derived from the five-carbon precursor isopentenyl diphosphate (IPP), produced via the classical mevalonate pathway or the novel MEP (non-mevalonate or Rohmer) pathway; the alkaloids are synthesized from various amino acids; phenylpropanoids having a C6–C3 unit are derived from aromatic amino acids phenylalanine or tyrosine; and the flavonoids are synthesized by the combination of phenylpropanoids and polyketides (Verpoorte, 2000). The biosynthetic pathways of secondary metabolites are often long, complex multi-step events catalyzed by various enzymes, and still largely unknown. The best-studied class of secondary metabolites is the alkaloids; more than 12 000 structures are known (Facchini, et al.2004) The production of specific alkaloids is often restricted to certain plant families. By contrast, flavonoids are abundant in many plant species. Kirsi-Marja Oksman-Caldentey1 and Dirk Inze (2004) reviewed the work on production of designer metabolites in the post genomic area. It is estimated that there are 400 000 higher plant species in the world [7], of which only w10% have been characterized chemically to some extent. Nevertheless, several important pharmaceuticals have been discovered from plants and their properties have been investigated for w200 years. Many of these pharmaceuticals are still in use today and often no useful synthetic substitutes have been found that possess the same efficacy and pharmacological specificity to, for example, a particular disease. Currently one-fourth of all prescribed pharmaceuticals in industrialized countries contain compoundsthat are directly or indirectly, via semi-synthesis, derived from plants. Furthermore, 11% of the 252 drugs considered as basic and essential by WHO are exclusively derived from flowering plants [8]. Plant-derived drugs in western countries also represent a huge market value. Prescription drugs containing phytochemicals were valued at more than US$30 billion in 2002 in the USA In contrast to primary metabolism where only limited investigations have been carried out,the literature is full on the investigations on secondary metabolism.The difference in the variablitiy of information is due to the fact that the intermediate products and end products of the primary metabolism can be obtained from agriculture in huge amounts in cheap costs as compared to secondary plant products of high value and fetch high price for small amounts to be used in cosmetic or pharmaceutical industry. There has been continuous increase in the present of patent filed for the tissue culture produced products of pharmaceutical industries.They included aditives to food and pigments.The substances have been obtain from the raw materials imported from tropical and subtrpical regions.Besides thisfor conrinuous production storage of significant amount of raw material was involved which required concidrable cost and risks .In addition to this there is deviation in quality depending on the year of production and between the regions of import.Besides this the pure economic considrations like lowering of world price plays important role.All these factors support the production of secondary products under control conditions in plant tissue culture. In the beginning of 70s the plant cell culture has attained a developmental status the possibility of emplyoing the methods of microorganisms fermentation techniques e.g. antibiotic production was expected to be used for large scale cultures from plants in order to avoid above mentioned problems of imports of raw materials. Shikonin was the first product from tissue culture obtained from Lithospermum erythrorhizon which was produced under economically viable conditions (Fujita and Tabata 1987). Despite of that the products of pharmaceutical importance whose raw materials are imported come in economic considerations and in some cases have been synthesised . Still tissue culture plays an important role in synthetic chemical area. In our times around 30 percent of the prescriptions are based on plants or contain plant components. These problems are dealt in detail. Traditional medicinal systems utilise plant based medicines and now there is revivial of traditional medicinal systems all over the world putting great pressure on biodiversity and its being destroyed in developing countries to fulfill the demands of global markets. Tissue culture could provide alternatives. The products of market interest in the first place belong to glycosides and alkaloids. Besides steroids, enzymes and pigments are of considerable interest. The following table provides some of the important plants and their products which have potential in tissue culture. Products of industrial interest produced in plant tissue culture. 1. Antimicrobial effects Agrostemma/ Phytolacca ( Virus) Catharanthus (Protozoan) Lithospermum (Bacteria) Ruta (Fungi) 2. Antitumor effects Camptotheca, Antharanthus, Maytenus, Podophyllum, Tripterygium 3. Antipain working Chamomilla, Valeriana 4. Enzyme for proteolysis Papaya, Scopolia, Ananas. 5. Enzyme for biotransformation Cannabis, Digitalis, Lupinus, Mentha, Papaver. 6. Apetitizers or taste enhancers Asparagus, Apium graveolens, Allium, Capsicum, Sinapis, 7. Hydrocarbon yielding Asclepias, Euphorbia. 8. Sweeteners Glycyrrhiza, Hydrangea, Stevia, 9 Tonics Bluperum, Cinchona, Coptis, Phellodendron, Panax 10 Insecticides