Pharmaceutical industry is highly dependent on wild plant populations for supply of raw materials for extraction of medicinally important compounds.

Based on current research and financial investments, medicinal plants will continue to play an important role in health care. The use of traditional medicines and medicinal plants in developing countries for the maintenance of good health has been widely observed. The World Health Organisation has estimated that more than 80 per cent of the world's population in developing countries depends primarily on herbal medicine for basic healthcare needs.

The practice of traditional medicine is widespread in China, India, Japan, Pakistan, Sri Lanka and Thailand. Africa is a rich source of medicinal plants.

In Pakistan, pharmaceutical companies import raw spices and medicinal herbs. In 2001, the Central Board of Revenue (CBR) allowed duty-free temporary import of medicinal herbs for subsequent exportation. No authentic data is available regarding cultivation of medicinal plants. But, according to a report, almost 2,000 medicinal plant species exist in the country. However, very few of them are put to use and 90 per cent of requirement is imported.

Over 50 per cent of the country's population is being cured by traditional medicines by over 40,000 traditional herbal practitioners. The agricultural research and development programmes are focused mainly on major crops and to some extent on minor crops. The medicinal herbs and spices have been ignored altogether and consequently this sector is facing problems.

The use of controlled environments can overcome cultivation difficulties and could be a means to manipulate phenotypic variation in bioactive compounds and toxins. Obstacles to bringing medicinal plants into successful commercial cultivation include the difficulty of predicting which extracts will remain marketable and the likely market preference for what is seen as naturally sourced extract.

Due to the lack of proper cultivation practices, destruction of plant habitats, and illegal and indiscriminate collection of plants from these habitats, many medicinal plants are severely threatened. Advanced biotechnological methods of culturing plant cells and tissues will provide new means of conserving and rapidly propagating valuable, rare, and endangered medicinal plants.

There is a great potential in using plant cell cultures to produce important products not produced by intact plants from which the cultures were derived. Studies now indicate that plant cell cultures can synthesise not only such products, but in some cases, valuable compounds never detected before on any plant species.The large scale commercial propagation of plant material based on plant tissue culture has been pioneered in the United States.

Over the last 30 years, tissue culture-based plant propagation has emerged as one of the leading global agro-technologies. Advantages of in vitro propagated plants over in vivo include

Virus elimination and production of pathogen-free plants; rapid multiplication of superior plants; production of haploids and homozygous diploid plants by anther or pollen culture; production of inter-specific hybrids by test tube fertilisation and embryo rescue; production of secondary metabolites via callus or cell suspension culture; production of new genetic resources by somaclonal variation; preservation and international movement of germplasm; protoplast technology and gene transfer.

Medicinal industry mainly involves the use of secondary metabolites. Secondary metabolites are compounds usually of an ecological nature as they are used as defences against predators, parasites and diseases, for interspecies competition, and to facilitate the reproductive processes. Several forms of suspension culture used for extraction of secondary metabolites include batch suspension culture, semi-continuous culture, and continuous culture.

These cultures can be initiated from parenchymatous tissues of shoots, roots and other plant structures. Maintenance of culture depends on an adequate supply of nutrients, including growth factors and a controlled sterile environment. Much interest has been aroused by these aspects of cell culture for growing particulate plant cell on a commercial scale for production of valuable metabolites.

Low production of desired metabolites is associated with in vivo cultivated plants that can be enhanced by using various in vitro cell culture techniques. Factors which need to be addressed with cell culture as a source of pharmaceuticals are instability of cell lines, compartmentalisation and isolation of the products and the nature of the metabolites produced.

Moreover, by using cell culture techniques, biochemistry of the subsequent products can be determined. Improved metabolic production may some time be achieved by the addition of precursors to the culture medium. Light intensity and selective wavelengths of light have been shown to have a stimulating effect on the production of some secondary metabolites in various tissue culture techniques.

It has been reported that isolation of active metabolites is desirous from the cells so in vitro culture is also advantageous at this step as metabolites can be excreted into the medium rather than be retained with in the cells. Two- phase culture systems are specially devised for this purpose.

The removal of entrapped metabolites from immobilised cells without killing the cells is another recent innovation. Stress related compounds (e.g. phytoalexins) produced in the normal plants as a result of damaging stimuli from physical, chemical or microbiological factors.

When cell cultures are subjected to such elicitors, some genes are de-repressed, resulting, among other things, in the formation of the secondary metabolites which are found in the entire plant. Some compounds not detected in the original plant appear in the cultures. Other plants yield culture which produced a different spectrum of secondary metabolites from those found in the intact plant. These aspects of cell culture, although generally unhelpful for the promotion of these techniques for industrial purposes, have important implications for other areas of phytochemistry.

Many biochemical transformations by cell culture have been demonstrated and include epoxidations, ester formation and sponification, glycosylation, hydroxylation, isomerisation, methylation and demethylation and oxidation. For this technique to be commercially viable, the product must be sufficiently important the substrate must be available in reliable amounts.

As all cells of the callus are derived from a single meristem, all regenerated plants should be genetically identical. This fact has obvious commercial applications for the production in a short period of time of uniform crops derived from a small number of desirable plants.

We can not use medicinal plants on a large scale without modifying the characteristics of the plant populations available to us, be they wild or domesticated. If medicinal plants are brought into cultivation, then we can at least attempt to do this in a controlled fashion and at the same time attempt to conserve wild populations.

Otherwise, increasing understanding of what the active components in herbs are and how they work will simply lead to their isolation as plant- derived drugs, and biotechnological interest in the plants and whole extracts from them will not be justifiable.