Some of the achievements of transgenic crops are as follows:
1. Production of Protein Hirudin:
Hirudin is an anticoagulant and prevents blood clotting. The gene responsible for encoding hirudin is chemically synthesised. This gene is transferred to Brassica napus and hirudin synthesised gets accumulated in seeds. Hirudin is purified and used for medicinal purpose. In this, transgene product is the product of interest.
How hirudin is extracted artificially from Brassica napus is shown in Fig. 3.
2. Herbicide Tolerance:
Any unwanted herbaceous plant in field is weed. Weeds compete with the crop for light, water and nutrients. This affects the quality and quantity of crop yield. To overcome this, transgenic plants have been produced by introducing herbicide tolerant gene in chloroplast to degrade enzyme and detoxify herbicide.
Scientists isolated bar gene from Streptomyces hygroscopicus which can degrade phosphinothricin (non-selective herbicide). The bar gene was transferred into tobacco and potato. The transgenic tobacco and potato showed herbicide tolerance without change in yields.
3. Insect Resistance:
A large quantity of yield is lost by the attacks of insects and mites. One way to overcome this is the use of insecticides. Using too much of insecticide poses serious threat to environment, humans and animals. A novel and alternative method is to use transgenic technology. It is cost effective, eco-friendly, sustainable and effective in insect control.
The cry gene of Bacillus thuringiensis (commonly called as Bt cotton) was found to express proteinaceous toxin (beta endotoxin) inside the bacterial cell. When specific insects of Lepidoptera, Diptera, etc. ingest the toxin, they are killed. This happens due to the denaturation of the epithelial gut by creating holes at alkaline pH 7.5-8. This toxin does not harm silkworm or butterflies which are beneficial insects.
By using genetic engineering many transgenic crops having cry gene, i.e. Bt gene have been developed and commercialised. Example of Bt crop are cauliflower, brinjal, cabbage, corn, cotton, maize, potato, tomato, tobacco, rice, soyabean, etc. (Table 3).
In India Bt cotton was permitted to be sown on a large-scale in fields. It is resistant to ball worm Helicoperpa armigera.
4. Delayed Fruit Ripening:
Main problem faced by fruit marketing is the premature ripening and softening during transportation of fruits. The shelf life of fruit is short. For ripening the enzyme cellulose and polygalacturonase are synthesised. Ripening process can be delayed by interfering in the expression of these genes. This was successfully done in tomato. In USA, this transgenic tomato was named as Flavr savr in which the activity of polygalacturonase was lowered. Permission to commercialise Flavr savr was given in 1994 in U.S.
During fruit ripening and senescence, ethylene is produced in plant. This is synthesised from S-adenosylmethionone through an intermediate compound called 1-aminocyclopropane-l-carboxylic acid (ACC). There are bacteria which can degrade ACC. Bacterial gene (for ACC) deaminase associated with ACC degradation is isolated and introduced into tomato.
In transgenic tomato, fruit ripening is delayed because it synthesises lower amount of ethylene, which is due to the inhibition of ACC synthesis. Such tomatoes and fruits can be transported over long distance without spoilage.
5. Nutritional Quality:
Nutritional quality of plants can be improved by introducing genes. Transgenic plants have been produced that are capable of synthesising cyclodextrins, amino acids and vitamins. Consumption of such plants will help in improving the health of malnutritioned people in developing and underdeveloped countries. Throughout the world around 124 million children are suffering from vitamin A deficiency. Vitamin A is present in the retina of eye. Deficiency of vitamin A causes skin disorder and night blindness.
Rice is a staple diet for most of the countries and is low in vitamin A. Vitamin A is synthesised from carotenoids which are the precursors of vitamin A. Three genes are responsible for the synthesis of vitamin A. Professor Ingo Potrykus and Peter Beyer introduced these three genes in rice. This transgenic rice was rich in pro-vitamin A. Due to the presence of this gene, the seed colour of transgenic rice was yellow, so the name given was Golden Rice (Fig. 4).
In India work is in progress on introduction of amal gene (encoding balanced amino acid protein) from Amaranthus into potato. This will enhance nutritional value of low protein food. This transgenic potato having gene amal is undergoing field trial.
6. Edible Vaccines:
What will you like to take if suffering from diarrhoea – potato or a medicine shot? Certainly taking potatoes or even French fries is a better option. Recently 20 volunteers in USA were fed on potatoes which were genetically engineered to carry a vaccine against Norwalk virus, which causes diarrhoea, nausea and stomach cramp. A large population in the world suffers from the effects of Norwalk virus.
The potatoes used for this purpose contained a protein that formed a shell around the virus, preventing it from attacking the intestine. The presence of this virus caused the immune system to flood the body with antibodies. After feeding the volunteers for 3 weeks and testing them after 2 months, 19 volunteers had antibodies to the Norwalk virus in their blood and 6 had it in their faeces as well. This was a sign that antibodies were in plenty. Six volunteers who were given untreated potatoes showed no rise in antibody level.
Future work will focus on fruit and vegetables that are easily transported or common in tropical regions like banana and tomato.
7. Biodegradable Plastic:
Plastics are an important part of modern life and are used in different sectors of applications like building materials, packaging, consumer products and much more. Each year about 100 million tons of plastics are produced worldwide.
In the year 2001-02, demand for plastics in India reached about 4.3 million tons and is expected to increase to about 8 million tons in the year 2006-07. Currently, however, the per capita consumption of plastics in India is around five million tonnes which is expected to reach 12.5 million tonnes by 2010. The present market in India is of about Rs. 25,000 crore.
Most of today’s plastics and synthetic polymers are produced from petrochemicals. Improperly disposed plastic materials are a significant source of environmental pollution, which is potentially harming life.
The plastic sheets or bags do not allow water and air to go into earth which causes reduction in fertility status of soil, preventing degradation of other normal substances, depletion of underground water source and danger to animal life. In the seas too, plastic rubbish – from ropes and nets to the plastic bands from beer packs – choke and entangle the marine mammals.
Scientists are working on the possibility of producing bioplastic and biopolymers. Polyhydroxybutyrate (PHB) producing bacteria have been searched out to reach the goal. PHB is synthesised from acetyl coenzyme A in three steps, each catalysed by an enzyme. These genes are arranged linearly in a single operon.
Work has been done to produce plants containing genes for production of PHB, i.e. biodegradable plastic at low cost. By transferring PHB producing gene in the chloroplast of Arabiopsis, transgenic Arabiopsis is produced. This does not interfere with its normal growth and development.