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Tissue culture: a getaway to genetic engineering
Dr. Azra Quraishi

Plant tissue culture is the regeneration of plants from bacteria-free plant parts. 
These are grown on artificial nutritive media under controlled environmental conditions. Tissue culture is essentially vegetative or asexual reproduction. It is a simple and a straightforward component of biotechnology which has a proven
potential to deliver virus-free plants,enhance propagation rates and enrich genetic diversity in reduced time spans. 

In essence, tissue culture is considered a cost-effective technology but with a palpable impact which is clearly visible in the form of improved yields, supply of virus-free clones of true-to-type cultivars with provision of improved germplasm. All these factors could have an enormous economic impact on the agricultural front and play a decisive role in boosting the per hectare yields of value added commodities.

A step ahead in tissue culture is genetic engineering which has even a broader spectrum as genes from any living organism e.g. viruses, bacteria and fungi could be isolated and inserted into the candidate crops for desired results. Worth mentioning are the efforts made by researchers who have introduced three alien genes into rice, two from daffodils and one from a micro-organism. 

The transgenic rice exhibits an increased production of beta-carotene as a precurser to vitamin A and the seed is yellow in colour. Such yellow or golden rice may be a useful tool to help treat the problem of vitamin A deficiency in young children living in the Tropics. Other developments resulting in commercially produced varieties in countries such as USA and Canada have centered on increasing shelf life of fruits and vegetables, conferring resistance to insect pests or viruses and producing tolerance to specific herbicides. In fact, in less than six years, the acreage of biotech crops in the US ! have increased from zero to 100 million hectares making biotechnology the most rapidly adopted technology ever.

Golden rice and golden mustard are examples of the potential improvements in food that are possible, enriching diets by improving the nutritional value of the products people eat every day. Research by biotech companies suggest an array of additional benefits including de-toxification of polluted soils, drought tolerant corn and fruits with proteins that could prevent tooth decay. Among other things, scientists are exploring whether it is possible to increase cancer-fighting ingredients in food to deliver vaccines in fruit and to rescue threatened species such as the American chestnut tree.

So far so good! but the fact of the matter is that at the doorstep of 21st century, the major obstacles to the genetic manipulation of many plant species is still the lack of an effective tissue culture system for the regeneration of whole plants from tissue parts. Most of the methods of biotechnology presently used or envisaged require the culture of cells and subsequent regeneration of plants. Therefore, tissue culture must be considered a gateway through which all forms of genetic engineering must pass.

The most important area in the field of plant tissue culture with proven practical applications is the shoot tip culture technique. This has been used for a considerable time in rapid clonal propagation and in the production of virus-free plants when used in combination with heat treatment. 

Since the constituent cells of shoots of apical buds are less differentiated than cells of other organs invitro culture of these plants parts would also result in the recovery of genetically identical progeny and this unique attribute makes shoot tip an ideal candidate for the long term storage of germplasm and their international exchange. Success in genetic engineering therefore relies heavily on the availability of efficient tissue culture protocols.

The Chinese experience

China could be quoted as a role model as it first embarked massively on the practical applications of tissue culture techniques in the early seventies. During this period the research focus of biotechnology was primarily tissue culture. Results of research in cell and tissue culture covered crops including rice, wheat, maize, cotton, vegetables and others. Several advanced rice varieties were generated through anther culture in 1970s and 1980s which covered field areas of several thousand hectares.

Transgenic techniques were popularized in 1983, and the pace of biotechnology research increased significantly after China started a bold national policy supporting biotechnology programs in 1986. Science then agricultural biotechnology laboratories have been established in almost every agricultural academy and major universities. 
By the late 1990s, there were over 100 laboratories in China involved in trasngenic research. 

Six transgenic cotton varieties with resistance to ballworm diseases have been produced by Chinese agricultural research institutes by 2000 and were approved 
for commercialization in 1997. In addition, other transgenic plants with resistance 
to insects diseases e.g. cotton resistance to fungal disease, rice resistant to insect pests, maize resistant to insects or with improved quality, soybeans resistant to herbicides, trasngenic potato resistant to bacterial blight have also been produced. State of the art in Pakistan

In Pakistan, Institute of Agri. Biotech and Genetic Resources (IABGR) of the PARC, is the only research set-up which took off with a strong base in tissue culture. Production of quality seed potato through tissue culture resulted in substantial 
decline in seed potato imports during 1980s and 1990s. This research has now disseminated to several institutes and private firms both at the Federal and 
Provincial levels. 

Other success stories in tissue culture are virus-free banana plantlets, mass multiplication of elite varieties of sugarcane, besides the perfection of tissue culture techniques in a number of horticultural and ornamental protocols. With efficient tissue culture system in a number of crops, the IABGR (PARC) embarked on plant transformation research in rice and later on in tomato. Presently, the scientists are working on the development of basmati rice with resistance to bacterial blight and virus resistance in tomato.

If genetic engineering is to be promoted in Pakistan there is a need to review that the researchers have perfected the tissue culture technologies, otherwise all efforts would go down the drain. Perhaps, it is one of the many reasons why a major breakthrough in genetic engineering has yet to be witnessed in Pakistan despite the fact that the government is investing heavily in projects related to biotechnology.

 (The author is CSO/DDG Agricultural Biotechnology Programme, National Agriculture Research Centre (NARC), Islamabad.);


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