In this article we will about:- 1. Features of Transgenic Technology 2. Steps in Transgenic Technology 3. Achievements 4. Risks 5. Future.
Features of Transgenic Technology:
Important points related to gene technology are briefly presented as follows:
i. Direct Gene Transfer:
Gene technology permits direct gene transfer into the recipient parent bypassing sexual process. In other words, there is no need of union of male and female gametes in gene technology. The gene of interest can be directly inserted into the cell of recipient parent.
ii. Single Gene Transfer:
Gene technology permits transfer of one or two genes from donor species or organism to the recipient organisms. It hybridization method hundreds of genes are transferred to the recipient parent which are eliminated by repeated back, crossing from the recipient or recurrent parent.
iii. Rapid and Accurate Technique:
Gene technology is a rapid method of crop improvement. It takes 4-5 years for release of new cultivar against 10-12 years by conventional breeding method. Moreover, it is highly accurate and reliable technique.
iv. Free Gene Transfer:
Gene technology permits gene transfer between two totally unrelated organisms i.e. from bacteria to higher plant cell and even from animals to plants. Thus gene technology has overcome the natural barriers of gene transfer.
Steps in Transgenic Technology:
Development of transgenic (genetically engineered) plant is a lengthy process which consists of following important steps:
i. Identification of useful Genes:
The desirable genes may be located in wild species, unrelated plant species, unrelated organisms i.e., micro-organisms (bacteria, viruses or fungi) and animals. This work is carried out in the research laboratory.
ii. Designing Gene for Insertion:
The gene of interest is isolated from the donor source and cloned in the laboratory. The cloning is done generally using plasmids.
iii. Insertion of Gene into Target Plant:
The cloned gene i.e., multiple copies of the gene of interest are inserted into the host plant or the recipient plant. Two methods, viz. agrobacterium mediated and gene gun or particle bombardment methods are used for gene transfer. This is done in the research laboratory. Protoplast culture for plasmid method and meristematic tissues or embryogenic callus is used for gene gun method.
iv. Identification of Transgenic Cells:
Transformed cells are identified using selectable marker (Kanamycin) and are regenerated into whole plant in nutrient medium. The regenerated plant is compared with parent variety. It should look like parent variety except gene of interest. This work is done in the laboratory and glass house.
v. Small Scale Field Trials:
The transgenic plants are evaluated for their performance in small scale field trials. The seed of the transgenic plant such as cotton, soybean, rapeseed, etc. is tested in laboratory for biosafety i.e., allergen city and toxicity. These tests are conducted with animals such as rats, rabbits, poultry, goats etc.
vi. Larger Field Trials:
Transgenic plants which are passed by regulatory authority are evaluated in multiplication trials for their performance for the gene of interest. Superior performing genotypes are released after testing and stable performance for three years.
Achievements of Transgenic Technology:
Transgenic technology has played significant role in the genetic improvement of various crop plants. In field crops 1257 transgenic plants have been released till 1992 all over the world. The first transgenic plant was released in tobacco in 1983.
Later on transgenic plants were developed in different crops.
Practical achievements of transgenic technology can be divided into two groups, viz:
(i) Transgenic genotypes (cultivars) developed, and
(ii) Plant characters improved.
These are briefly discussed below:
i. Cultivars Developed:
As stated above, 1257 transgenic plants have been developed till 1992 in different field crops the world over. The maximum transgenic cultivars have been released in rapeseed, followed by potato, tobacco, tomato, maize, flax, soybean, cotton, sugar, beet, Lucerne etc. (Table 33.2).
ii. Characters Improved:
Various plant characters have been improved through transgenic technology in different crops.
Important characters which have been improved include:
(i) Insect resistance,
(ii) Disease resistance,
(iii) Herbicide resistance,
(iv) Quality traits,
(v) Development of male sterility system, and
(vi) Resistance to abiotic stresses such as freezing and cold resistance (Table 33.3).
All these plant characters have been modified (improved) by transferring desirable genes from different organisms/sources.
The character improvement can be classified into two groups, viz:
(i) Improvement in resistance traits, and
(ii) Improvement in the quality of the product.
These are briefly discussed below:
(i) Improvement in Resistance:
It includes insect resistance, disease resistance, freezing resistance, cold resistance and herbicide resistance. The insect resistance and herbicide resistance have been transferred in major field crops such as cotton, maize, soybean and rapeseed. The main target being on improving crop performance.
The main advantages of this approach are given below:
(i) Improvement in yield and production due to control of insects and diseases.
(ii) Reduction in cost of cultivation due less use of chemicals.
(iii) Reduction in environment pollution due less use of pesticides,
(iv) Multiplication of useful insects i.e. natural predators and parasites of insect pests. In other words, transgenes do not have adverse effect on beneficial insects.
(v) Thus resistance conferring genes are eco-friendly. As a result, there is no risk of health hazards to humans and animals.
The main drawback of this achievement is that such crops have direct benefit for producers and only limited benefits for the consumer.
(ii) Improvement in Quality:
Significant achievements have been made in quality of various field crops. Important achievements include improvement in starch content in potato, protein content in potato, arfalfa and tobacco, increased methionine in soybean and rapeseed, carotene content in rice, ripening and storage quality in tomato.
The improvement in protein content will help in solving problems of protein malnutrition in the poor people. These achievements are beneficial for both producers and consumers.
Risks of Transgenic Technology:
Everything has some merits and some demerits. Gene technology is no exception. There are mixed feelings about gene technology. Some people reject it by saying that it is intervention in the God’s domain while others consider it as means to fight hunger.
The most important concerns on plant gene technology are briefly presented below:
i. The consumption of modified (transgenic) food and vegetables may have adverse effect on human and animal health (toxicity, pathogenicity and allergenicity). Six crops (with transgenes) such as soybean, maize, cotton, canola, potato and sugarbeet have been approved for human consumption in Australia. However, no adverse effect of these crops on human and animal health has been reported so far.
ii. There is a fear that natural crossing of herbicide resistant cultivars with wild relatives may lead to development of herbicide resistant weed (super weed).
iii. The toxin produced by Bt gene in resistant cultivars of maize may kill larvae of Lady bird beetle and monarch butterfly when they feed on the pollen of maize or cotton crop. However, no such confirmed case has been reported so for.
iv. It may lead to development of antibiotic resistance by insect pests and other pathogens.
v. It may disturb ecosystem by eliminating the target insects. However, it will not happen because each insect has alternate host for its survival.
vi. Transgenic plants developed using virus particles may lead to evolution of new viruses, some of which may pose danger to existing crops.
vii. The transfer of genes from animal (such as from fish) to plants will have ethical problems.
viii. The use of terminator gene (a gene that leads to embryo abortion) which allows germination of seed in F1 plants only will force farmers to purchase fresh seed every year. However, use of terminator technology has not been approved.
ix. The seed of transgenic crops is very expensive which cannot be afforded by small and marginal farmers.
Future of Transgenic Technology:
Transgenic technology is expected to make the better achievements in further.
The main focus will be on three important aspects viz:
(i) Development of resistant cultivars,
(ii) Improvement in quality, and
(iii) Development of new useful products.
These are briefly discussed below:
i. Improvement in Resistance:
Improvements in insect, disease and herbicide resistance have already been made in several field crops. The main focus will be on development of drought and salinity tolerant crop cultivars so that the cultivation of such crops can be extended to rainfed and salt effected soils.
A tomato plant which is able to tolerate high levels of salt has been developed at the university of California and the University of Toronto. This tomato plant holds the salts in its leaves and the fruits don’t taste salty. In grapes, a transgenic plant resistant to Pierce’s disease (a fatal bacterial disease) has been developed at the university of Florida by transferring a gene from silkworms.
ii. Improvement in Quality:
Several remarkable improvements are likely to be made in the product quality.
Few examples are cited below:
(i) Golden Rice:
Golden rice with high carotene and iron contents has been developed by Swiss researchers. This has been developed by transferring two genes from daffodil and one gene from bacterial species. Golden rice will benefit millions of people the world over who suffer from health problem caused by vitamin A deficiency.
High and natural iron content such as ferritin and plant haemoglobins will help in correcting iron deficiency in millions of people. These high carotene and high iron content genes are being transferred from golden rice to high yielding cultivars of rice.
(ii) Protein Rich Potato:
Protein packed potatoes have been developed by Indian scientists by transferring a gene from Amaranth. This transgenic potato contains about 33% higher protein than non-transgenic potato. It is referred to as protein rich potato. It is in the final stage of Biosafety testing and is expected to be released for commercial cultivation.
(iii) Nicotine free tobacco:
Nicotine free tobacco has been developed. Genetically engineered nicotine free tobacco does not synthesize nicotine in the leaf. It will lead to introduction of nicotine free cigarettes.
(iv) Canola (rape seed) is a major oil seed crop. Transgenic research has focused on improving the nutritional quality of Canola oil by enhancing vitamin E content or by modifying the composition of fatty acids.
(v) Transgenic bananas containing inactivated viruses that cause cholera, hepatitis B and diarrhoea have been produced and are under testing.
(vi) Gene technology will improve keeping quality of many fruit and vegetable crops. It can be achieved by delaying ripening and senescence. Many such examples can be cited.
iii. New useful Products:
In future, gene technology will lead to development of several useful products.
Some examples are cited below:
(i) Production of oral vaccines and other pharmaceuticals in plants.
(ii) Production of biodegradable polymers for the plastic industry.
(iii) Plants that can be used in bioremediation of polluted soils.
(iv) Forest trees with enhanced growth and improved timber properties.
(v) Production of enhanced quantity of chemicals for chemical industries.