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TRANSGENIC PLANTS



INTRODUCTION:

Transgenic plant:

Transgenic plants possess a gene or genes that have been transferred from a different species. Although DNA of another species can be integrated in a plant genome by natural processes, the term “transgenic plants” refers to plants created in a laboratory using recombinant DNA technology. The aim is to design plants with specific characteristics by artificial insertion of genes from other species or sometimes entirely different kingdoms.

Varieties containing genes of two distinct plant species are frequently created by classical breeders who deliberately force hybridization between distinct plant species when carrying out interspecific or intergeneric wide crosses with the intention of developing disease resistant crop varieties. Classical plant breeders use a number of in vitro techniques such as protoplast fusion, embryo rescue or mutagenesis to generate diversity and produce plants that would not exist in nature

Such traditional techniques (used since about 1930 on) have never been controversial, or been given wide publicity except among professional biologists, and have allowed crop breeders to develop varieties of basic food crop, wheat in particular, which resist devastating plant diseases such as rusts. Hope is one such wheat variety bred by E. S. McFadden with a gene from a wild grass. Hope saved American wheat growers from devastating stem rust outbreaks in the 1930s.

Methods used in traditional breeding that generate plants with DNA from two species by non-recombinant methods are widely familiar to professional plant scientists, and serve important roles in securing a sustainable future for agriculture by protecting crops from pests and helping land and water to be used more efficiently.

So in other words we can say that transgenic plants are those plants whose DNA sequence has been disturbed/interrupted by humans or have DNA sequence that does not occur naturally.

REVIEW OF LITERATURE:

Transgenic plants are genetically engineered plants formed by the use of the RECOMBINANT DNA TECHNOLOGY. The need comes to our mind when human population increases exponentially. So we need more food and also our crops are being attacked be pests and path Organic microbes, so to protect them we have started work for this g.

Historically the Production of transgenic plants in wide-crosses by plant breeders has been a vital aspect of conventional plant breeding for about a century. Without it, security of our food supply against losses caused by crop pests such as rusts and mildews would be severely compromised [citation needed]. The first historically recorded interspecies transgenic cereal hybrid was actually between wheat and rye (Wilson, 1876).

For example the most important thing is invention of BT cotton. Which is pest resistant?

So in this we will discuss about the merits, demerits and how transgenic plants are formed.

BODY:

So by using a Variety of techniques it has become possible to transform plants with foreign genes. Expression of foreign genes in plants, it possible to produce a variety wide range of new plants variety.

Transgenic plants have been developed to resistant to a range of environmental stresses and including insects, viruses, herbicides pathogens and salt stress.

To have flowers with modified colors. To a modified nutritional contents including modification in amino acids, lipids, discoloration and sweetness.

Classification of transgenic plants:

1 .Virus-resistant plants:

Plant viruses often cause considerable damage and significantly reduce yield .breeding for disease resistant is best method to protect plants from viral and other infection .recently scientist have used techniques of genetic engineering to develop virus resistant transgenic plants .

For example: the ti binary vector system was used to transfer both protein produces sense and antisense RNA producing cDNA sequence to separate tobacco cells ,from which transgenic plants were regenerated .

2. Herbicide Resistant plants:

Certain herbicides can be used as pre emergence herbicides to kill weeds before the crops are implanted. If crop plant was resistant to these chemicals, they can be used with the crops.

Phosphhinothricin is an herbicide that acts by inhibiting another enzyme

Necessary for amino-acid. Inhibitting the activity of this enzyme leads to rapid

Accumulation of ammonia with in the plant cell. The higher conc. Of the

Ammonia are toxic to the cell. Scientist at plant genetic system Belgium obtain

A gene from these fungus that encodes an enzyme that convert Phosphinotricine

To a non herbicidal derivative by combining in with a cell metabolite this gene

Known as bar gene has been transferred in a tobacco and potato.

Where it is expressed showing herbicide tolerance in these plants.

3. Drought Resistance Plants:

A number of such genes have been identified isolated, cloned and expressed in plants, which are potential sources of resistance to abiotic stresses. These genes include Rab (responsible to absicisic acid) and SalT (including response to salt stress) genes of rice; genes for enzymes involved in proline bio synthesis in bacteria and plants. Spinach genes involved in betaine synthesis etc.

4. Insect Resistance Plants :

The efforts to produce the insect resistance transgenic plants have been quite successful;

Insect resistance transgenic varieties of several crops are already in commercial cultivation in U.S.A. insect resistance plants usually contain a gene from the bacterium bacillus thuringensis.B.thuringenisis has been used since the world war I, particularly in Europe to control some insects, pests. B.thuringenisis strain are usually classified on the basis of serological test, the cell type has very little relevance to the insecticidal activity of a strain.

Applications of Transgenic Plants :

1. They have proved to be extremely valuable tools in studies n plant molecular biology, regulation of gene action, identification of regulatory/promotary sequences, etc.

2. Specific genes have been transferred into plants to improve there agronomic or other features.

3. Genes for resistance to various biotic stresses have been engineered to generate transgenic plants resistance to insect, viruses etc.

4. Several genes transfer have been aimed at improving the produce quality.

5. Transgenic plants are being used to produce novel biochemicals like Hirudine etc which are not produced by normal plants.

6. Transgenic plants can be used vaccines for immunization against pathogens; this is fast emerging and important objective.

Examples:

Golden rice

White rice and golden rice

Golden rice is a variety of rice (Oryza sativa) produced through genetic engineering to biosynthesize beta-carotene, a precursor of pro-vitamin A in the edible parts of rice. The scientific details of the rice were first published in in 2000. Golden rice was developed as a fortified food to be used in areas where there is a shortage of dietary vitamin A. In 2005 a new variety called Golden Rice 2 was announced which produces up to 23 times more beta-carotene than the original variety of golden rice. Neither variety is currently available for human consumption. Although golden rice was developed as a humanitarian tool, it has met with significant opposition from environmental and anti-globalization activists.

Creation of golden rice

A simplified overview of the carotenoid biosynthesis pathway in golden rice. The enzymes expressed in the endosperm of golden rice, shown in red, catalyze the biosyntheis of beta-carotene from geranylgeranyl diphosphate. Beta-carotene is assumed to be converted to retinal and subsequently retinol (vitamin A) in the animal gut

Golden rice was created by Ingo Potrykus

of the Institute of Plant Sciences at the Swiss Federal Institute of Technology, working with Peter Beyer of the University of Freiburg. The project started in 1992 and at the time of publication in 2000, golden rice was considered a significant breakthrough in biotechnology as the researchers had engineered an entire biosynthetic pathway.

Golden rice was designed to produce beta-carotene, a precursor of Vitamin A, in the part of rice that people eat, the endosperm. The rice plant can naturally produce beta-carotene, which is a carotenoid pigment that occurs in the leaves and is involved in photosynthesis. However, the plant does not normally produce the pigment in the endosperm since photosynthesis does not occur in the endosperm.

Golden rice was created by transforming rice with two beta-carotene biosynthesis genes:

  • psy (phytoene synthase) from daffodil (Narcissus pseudonarcissus)
  • crt1 from the soil bacterium Erwinia uredovora
  • (The insertion of a lyc (lycopene cyclase) gene was thought to be needed but further research showed that it is already being produced in wild-type rice endosperm.)

    The psy and crt1 genes were transformed into the rice nuclear genome and placed under the control of an endosperm specific promoter, so that they are only expressed in the endosperm. The exogenous lyc gene has a transit peptide sequence attached so that it is targeted to the plastid, where geranylgeranyl diphosphate formation occurs. The bacterial crt1 gene was an important inclusion to complete the pathway, since it can catalyze multiple steps in the synthesis of carotenoids, while these steps require more than one enzyme in plants. The end product of the engineered pathway is lycopene, but if the plant accumulated lycopene the rice would be red. Recent analysis has shown that the plant’s endogenous enzymes process the lycopene to beta-carotene in the endosperm, giving the rice the distinctive yellow colour for which it is named. The original Golden rice was called SGR1, and under greenhouse conditions it produced 1.6 µg/g of carotenoids.

    Subsequent development

    Golden rice has been bred with local rice cultivars in the Philippines, Taiwan and with the American rice variety Cocodrie. The first field trials of these golden rice cultivars were conducted by Louisiana State University Agricultural Center in 2004. Field testing will allow a more accurate measurement of the nutritional value of golden rice and will enable feeding tests to be performed. Preliminary results from the field tests have shown that field-grown Golden rice produces 4 to 5 times more beta-carotene than Golden rice grown under greenhouse conditions

    In 2005, a team of researchers at biotechnology company Syngenta produced a variety of golden rice called “Golden Rice 2”. They combined the phytoene synthase gene from maize with crt1 from the original golden rice. Golden rice 2 produces 23 times more carotenoids than golden rice (up to 37 µg/g), and preferentially accumulates beta-carotene (up to 31 µg/g of the 37 µg/g of carotenoids). To receive the Recommended Dietary Allowance (RDA), it is estimated that 144 g of this rice would have to be eaten. Bioavailiability of the carotene from either variety has not been tested in any model.

    In June 2005, researcher Peter Beyer received funding from the Bill and Melinda Gates Foundation to further improve Golden rice by increasing the levels of or the bioavailability of pro-vitamin A, vitamin E, iron, and zinc, and to improve protein quality through genetic modification.

    Opposition To Golden rice

    Critics of genetically engineered crops have raised various concerns. One of these is that golden rice originally did not have sufficient vitamin A, but new strains were developed that solve this problem.

    Greenpeace opposes all genetically modified organisms, and is concerned that golden rice is a Trojan horse that will open the door to more widespread use of GMOs

    Vandana Shiva, an Indian anti-GMO activist, argued that the problem was not particular deficiencies in the crops themselves, but problems with poverty and loss of biodiversity in food crops. These problems are aggravated by the corporate control of agriculture based on genetically modified foods. By focusing on a narrow problem (vitamin A deficiency), Shiva argued, the golden rice proponents were obscuring the larger issue of a lack of broad availability of diverse and nutritionally adequate sources of food. Other groups have argued that a varied diet containing vitamin A rich foods like sweet potato, leafy green vegetables and fruit would provide children with sufficient vitamin A. While this is true, others contend that a varied diet is beyond the means of many of the poor, which they say is why they subsist on a diet mainly of rice. The poorest people may not have an option to eat a varied diet, necessarily relying on one or few foods to provide complete nutrition.

    The aleurone layer that surrounds the rice endosperm is removed by a process called milling or polishing in most countries to improve the shelf life of the rice. Brown rice with the aleurone intact contains more B vitamins, iron, manganese, selenium, zinc and phosphorus than milled rice. The Institute of Science in Society claims that if rice was not milled that supplementation would not be necessary. However USDA data shows that brown rice does not contain any more beta carotene than milled rice. Scientists at the International Rice Research Institute are screening rice germplasm, and trying conventional breeding approaches for breeding varieties with increased beta carotene in the aleurone

    CONCLUSION& SUMMARY:

    There is an explosion of interest in transgenic research leading to an ever expanding list of plant species in which transgenics have been produced.

    For e.g. in 1989 transgenic s were produced in 15 plant species, but while 1994, this list has crossed 30. several transgenic crop variety have been cleared for human use and are either already in the market or are likely to rich the market soon. It may be projected that transgenic plant will play an important role in the world agriculture and most likely industry during the coming years. The expectation is more then validated by the rapid increase in the total area on which transgenic varies were grown during 1997 to 2002; each year the area increased by 10% more similarly, there has been a remarkable increase in the no. of countries growing these varieties. India permitted cultivation of insect resistance transgenic cotton variety in the year 2000. in addition the no. of crops in which transgenic verities were available has also increased steadily.

    The intentional creation of transgenic plants by laboratory based recombinant DNA methods is more recent (from the mid-70s on) and has been a controversial development in the field of biotechnology opposed vigorously by many NGOs, and several governments, particularly within the European Community. These transgenic recombinant plants (biotech crops, modern transgenics) are transforming agriculture in those regions that have allowed farmers to adopt them, and the area sown to these crops has continued to grow globally in every years since their first introduction in 1996.[]

    Transgenic recombinant plants are generated in a laboratory by adding one or more genes to a plant’s genome ,and the techniques frequently called transformation. Transformation is usually achieved using gold particle bombardment or through the process of Horizontal gene transfer using a soil bacterium, Agrobacterium tumefaciens, carrying an engineered plasmid vector, or carrier of selected extra genes.

    Transgenic recombinant plants are identified as a class of genetically modified organism(GMO); usually only transgenic plants created by direct DNA manipulation are given much attention in public discussions.

    Transgenic plants have been deliberately developed for a variety of reasons: longer shelf life, disease resistance, herbicide resistance, pest resistance, non-biological stress resistances, such as to drought or nitrogen starvation, and nutritional improvement (see Golden rice). The first modern recombinant crop approved for sale in the US, in 1994, was the FlavrSavr tomato, which was intended to have a longer shelf life. The first conventional transgenic cereal created by scientific breeders was actually a hybrid between wheat and rye in 1876 (Wilson, 1876). The first transgenic cereal may have been wheat, which itself is a natural transgenic plant derived from at least three different parenteral species.

    Genetically modified organisms were prior to the coming of the commercially viable crops as the FlavrSavr tomato, only strictly grown indoors (in laboratories). However, after the introduction of the Flavr Savr tomato, certain GMO-crops as GMO-soy and GMO-corn where in the USA being grown outdoors on large scales.

    Commercial factors, especially high regulatory and research costs, have so far restricted modern transgenic crop varieties to major traded commodity crops, but recently R&D projects to enhance crops that are locally important in developing counties are being pursued, such as insect protected cow-pea for Africa., and insect protected Brinjal eggplant for India

    Transgenic plants have been used for bioremediation of contaminated soils. Mercury, selenium and organic pollutants such as polychlorinated biphenyls (PCBs) have been removed from soils by transgenic plants containing genes for bacterial enzymes.

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