Photo courtesy Agricultural Biotechnology Council
What is biotechnology?
Biotechnology is the name that has been given to a very wide range of agricultural, industrial and medical technologies that make use of living organisms (e.g., microbes, plants or animals) or parts of living organisms (e.g., isolated cells or proteins) to provide new products and services.
Biotechnology's origins lie in the ancient crafts of brewing, baking and the production of fermented foods such as yoghurt and cheese. It was not until 1859 that microbes were identified as the cause of both desirable and undesirable changes in food. Louis Pasteur provided a scientific understanding of these natural processes, which helped to improve the reliability of traditional fermentations and ensure the safe preservation of food and drink.
Pasteur thought that microbes were always needed to bring about the changes which occur during fermentation. Towards the end of the last century, however, it was realised that non-living extracts from, for example, yeast cells could also cause changes that are normally associated with the activities of whole organisms. These extracts were named 'enzymes' (literally, 'in yeast'). We now know that all living things produce enzymes - proteins that are responsible for many of the processes of life.
During the 1940s, methods of growing microbes in large fermenter vessels were developed for the production of penicillin and other antibiotics used in medicine. Today this fermenter technology permits the commercial production of a wide range of products. These include enzymes for food and drink production processes, vitamins, amino acids and other useful chemicals.
Brewers have always maintained their own strains of yeast for beer production and similarly the producers of enzymes and other fermentation products nurture specially-selected strains of production organisms. These strains have inherited (i.e., genetic) characteristics that improve their performance. The traditional method of developing new strains involves laborious testing of populations of microbes to detect naturally-occurring genetic variants with useful properties.
In 1973, two scientists, Stanley Cohen and Herbert Boyer, managed for the first time to make very specific changes to the genetic make-up (i.e., the DNA) of microbes by means of 'genetic engineering' (also called genetic modification). The techniques developed using microbes have since been applied to plants and animals, and in a limited way they have also been applied to humans in an attempt to alleviate the symptoms of inherited illness.
Although the term biotechnology refers to a much older and broader technology than genetic engineering, the techniques of genetic engineering are of such importance that the two terms have become virtually synonymous, particularly in the USA.
You can read more about the history of biotechnology in Robert Bud's authoritative study 'The uses of life. A history of biotechnology' (1994) Cambridge University Press. ISBN: 0 521 47699 2 [Paperback].
What is plant biotechnology?
Traditional plant breeding is a relatively slow and labour-intensive process: if two parental plants are crossed, the seeds from them must be collected, planted and the resulting plants cultivated before the results of the cross can be seen. Furthermore, plant breeders must work with whole sets of inherited characteristics. Consequently a cross to introduce a desirable characteristic is likely to introduce one or more undesirable characteristics as well; and these must then be painstakingly 'bred out'. The techniques of biotechnology (including genetic modification) can be used to speed up the process and improve the precision of plant breeding compared with conventional methods such as random genetic changes introduced by radiation.
What are the main current applications of plant genetic MODIFICATION?
The majority of current plant biotechnology is directed towards the improvement of food plants; the remaining work is concerned with non-food crops such as cotton, tobacco, ornamental plants and pharmaceuticals. The initial emphasis has generally been on the improvement of qualities of value to the farmer. Most of this work has been initiated and funded by the seed industry. The second and third generations of genetically-modified food plants will bring benefits that more directly affect commercial food processors and consumers. Many thousands of field trials of genetically-modified plants have been carried out world-wide.
Athough several different modified crops are grown in the USA and elsewhere, none have so far been approved for commercial production in the UK. This means that, in Britain, all food derived from GM crops is imported. Only a handful of GM-derived products have been approved for food use in the EU: processed soya derivatives such as lecithin; oil from oil seed rape; processed tomato purée and maize. No fresh GM products (such as tomatoes, potatoes or unprocessed soya beans) have been approved for human consumption in the EU. The only GM crop currently grown to any extent (and then only in limited amounts) in the EU is maize, which is produced for animal feed.
What are the main techniques of plant biotechnology?
Plant tissue culture is the cultivation of plant cells or tissues on specially-formulated nutrient media. In appropriate conditions, an entire plant can be regenerated from each single cell, permitting the rapid production of many identical plants. Tissue culture is an essential tool in modern plant breeding. Since it was first developed the early 1960s, plant tissue culture has become the basis of a major industry, providing high-value plants for nurseries. Where a crop (e.g., banana) does not produce seeds, plants derived from tissue culture are sometimes planted directly in farmers' fields. However this is rarely done for seed-bearing species - more often tissue-cultured plants are used to produce the seeds from which crops are subsequently grown. Over the years, several attempts have been made to cultivate plant cells in fermenter vessels with the aim of producing valuable products such as medicines and natural food flavourings. To date, success in this area has been limited. Cell culture is also used for the conservation of those plant varieties that cannot be maintained in a normal seed bank.
Genetic engineering is the controlled modification of genetic material (DNA) by artificial means. It relies upon scientists' ability to isolate specific stretches of DNA using specialised enzymes which cut the DNA at precise locations. Selected DNA fragments can then be transferred into plant cells. This can be done in several ways.
The best-established gene-transfer method for plants uses a soil bacterium as a go-between. This organism, Agrobacterium, has a natural ability to alter the genetic material of plant cells so that outgrowths (or galls) are formed on the plant. Biologists have adapted the mechanism used by Agrobacterium so that desirable genetic information rather than that which promotes the formation of galls is transferred into plants. The Agrobacterium method has been used successfully with a wide variety of plants and has proved particularly useful for the modification of tree species which, because they are large and slow-growing are difficult to alter by conventional breeding. However, the most important cereal crops are not affected by Agrobacterium, so other mechanisms have to be used for them.
Ballistic impregnation is an unlikely-sounding method that has achieved some success with cereals and other crops. It involves sticking the DNA to be introduced into the plant onto minute gold or tungsten particles, then firing these (like bullets) into the plant tissue. A proportion of the plant cells treated in this way take up the DNA from the metal pellets. Whole plants are then re-grown from the cells by tissue culture.
Electroporation works best with plant tissues that have no cell walls (such as the tubes which develop from pollen grains). Micro- to millisecond pulses of a strong electric field cause minute pores to appear momentarily in the plant cells, allowing DNA to enter from a surrounding solution.
A more recent yet similar method uses microscopic crystals to puncture holes in the plant cells, again allowing DNA to enter them. Another novel method involves the direct injection of DNA into chloroplasts, which have their own DNA. Chloroplast DNA is usually found only in the female parts of plants, and not in pollen. This means that plants modified using this technique cannot transfer their introduced genes through pollen.
With all current transfer techniques, only a small proportion of the treated cells successfully incorporate the novel DNA. Therefore, so-called marker genes are usually linked to the DNA fragments before their transfer. These marker genes can then be detected easily, enabling scientists to see whether transfer of the desired DNA has taken place. To date, the main markers used have been genes which allow the plant to grow in the presence of a specific antibiotic or herbicide. Other marker systems are being developed.
Antisense technology is used to 'neutralise' the action of specific undesirable genes (such as those involved in the excessive softening of fruit). The same technique can be utilised to combat the activity of plant viruses, providing a means of controlling viral infection. Antisense technology lies behind many of the current applications of plant biotechnology.
Although genetic engineering receives much attention, of as much significance is the application of genetic mapping to plant breeding. By determining the location and likely action of many plant genes, conventional plant breeding is being conducted with greater precision, as it becomes possible to detect quickly and exactly those plants which carry desirable characteristics.