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Genetic engineering



TRANSEGNIC PLANTS .GM CROPS


Transgenic plants:

A transgenic crop plant contains a gene or genes which have been artificially inserted instead of the plant acquiring them through pollination. The inserted gene sequence (known as the transgene) may come form another unrelated plant, or form a completely different species: transgenic Bt corn, for example, which produces its own insecticide, contains a gene form a bacterium. Plants containing transgenes are often called genetically modified or GM crops. Although in reality all crops have been genetically modified form over long periods of time. On this web site we site we will use the term transgenic to describe a crop plant which has transgenic inserted.

Why make transgenic crop plats?

A plant breeder tries to assemble a combination of genes in a crop plant which will make it as useful and productive as possible. Depending on where and for what purpose the plant is grown, desirable genes may provide features such as higher yield or tolerance to heat, cold and drought, combining the best genes in one plant is a long and difficult process, especially as traditional plant breeding had been limited to artificially crossing plants within the same species or with closely related species to bring different genes together. For example, a gene for protein in soybean could not be transferred to a completely different crop such as corn using traditional techniques. Transgenic technology enables plant breeders to being together in one plant useful genes from a wide range of living sources, not just from within the crop species or form closely related plants. This technology provides the means for identifyi9ng and isolating genes controlling specific characteristics in one kind of organism, and for moving copies of those genes into another quite different organism, and for moving will then also have those characteristics. This powerful tool enables plant breeders to do what they have always done-generate more useful and productive crop varieties containing new combinations of genes-but it expands the possibilities beyond the limitations imposed by traditional cross-pollination and selection techniques.

Risks and Concerns:

The introduction of transgenic crops and foods into the existing food production system has generated a number of questions about possible negative consequences. People with concerns about this technology have reacted in many ways, form participating in letter-writing campaigns to demonstrating in the streets to vandalizing institutions where transgenic research is being conducted. What ate the main concerns? What scientific support is there for these concerns?

The issues surrounding objections to transgenic crops can be broadly grouped into concerns about

  • Damage to human health: allergen city, horizontal transfer and antibiotic resistance, eating foreign DNA, cauliflower mosaic virus promoter, changed nutrient levels.

  • Damage to the natural environment : Monarch butterfly, crop-to-weed gene flow, antibiotic resistance, leakage of GM proteins into soil,

  • Reductions in pesticide spraying : are they real?

  • Disruption of current practices of farming and food production in developed countries : Crop-to-crop gene flow

  • Disruption of traditional practices and economies in less developed countries.

FREQUENTLY ASKED QUESTIONS ON Bt- COTTON

  1. FREQUENTLY ASKED QUESTIONS ON Bt- COTTON

    Bt is the popular abbreviation for bacillus thruringiensis, a bacterium commonly found in soil with ubiquitous distribution. Hence it is popularly called a “soil bacterium’, but it is also quite common in other habitats like dead insects, water, dead plant grain dust etc. the insecticidal property of Bt was first discovered in 1901 in Japan by ishiwata and later in 1911 in Germany by Berliner who described this species and gave the present name. more than 80 varieties or sub-species of Bt have been described so far.

  2. How does Bt act?

    Bt- proteins require certain specific conditions for them to be active against the insect.

    In the first place, the concerned Bt protein has to be ingested by the susceptible insects as it has no contact effects. In the case of Bt-plants, this happens when the larvae feed on plant tissues.

    The protein requires an alkaline gut with a suitable pH (905 and above)for its activation.

    There should be specific receptors in the insect mid-gut epithelial cells for protein-binding before it can kill the insect.

    All these conditions are available only in the susceptible insects and therefore they succumb when they feed on Bt-plants.

  3. How exactly are the bollworms affected by Bt- cotton?

    In the commercialized transgenic Bt- cotton plants, the expression of Bt- protein is constitutive I,e., the protein is expressed in all parts of the plant. When the larvae feed on Bt plants, they ingest Bt protein along with the plat tissues. If it is a susceptible insect like boll worms, the Bt- protein gets activated in the mid-gut and the activated molecule bind themselves to certain receptors present on the gut membrane, very much like a specific key fitting into a lock such a specific interaction between the activated Bt protein and receptor results in ‘holes’ being formed in the insect intestine, causing destruction of the gut lining. The harm lymph (insect blood) carrying ions and vital nutrients leak into the intestine. This leads to paralysis of the insect gut as result the insect stops feeding. This sequence of events can take place within a few hours. The affected larvae may die after a day or two, but since it stops feeding, any further damage to plants is prevented. Bt proteins can affect only those insect species possessing the specific receptors and conditions for toxin lack such specific conditions in their gut. This includes warm blooded animals.

  4. Since when is Bt used for insect control?

    Bt proteins have served as the principal active ingredient of number of commercial bacterial insecticides and these have been used as spray formulations (a mixture of endospheres and insecticidal crystals) for control of various insect pests since themed-1950’s in several countries. The pests targeted included various caterpillars (Lepidoptera0 and beetles (Coleoptera) attacking several crops as also mosquito and black fly (dipteral) vectors of human and animal diseases. However, the concept of transgenic plant, including Bt- cotton, was as recent as the 1980’s.

  5. What is a Bt plant?

    Depending upon the type of pests to be controlled- whether it is Lepidoptera, coleopteran etc.- the relevant genes form the soil bacterium, Bacillus thuringiensis (Bt), are isolated, studied, suitably modified and introduced into the desired plant species by genetic engineering the new Bt- gene gets stably integrated in the host genome and becomes an inheritable trait. Such transgenic plants containing the Bt-gens(S) are popularly called “Bt-plants’. For example, Bt- cotton is incorporated with the lepidopteron specific gene(s) as it is designed to control bollworms which belong to this insect order. Similarly we have Bt-cotton Bt-potato, Bt-brinjal (egg plant), Bt- rice etc. with their encoded proteins providing insect control.

  6. How exactly can an ordinary cotton plant be converted into a Bt cotton plant?

    It can be accomplished by introducing the required Bt gene into the desired cotton cultivars by genetic engineering. For example, the cry1Ac gene encoding the insecticidal protein Cry1Ac id first isolated form the soil bacterium, bacillus thuringiensis. The gene is then modified to be more similar to a plant gene and combined with the 35-S promoter (derived form cauliflower mosaic virus) to achieve the expression of Cry1Ac protein in all parts of the plant (i.e., constitutive expression), in order to identify plant cells that contain this new gene, a selectable marker is needed. In this case, the npt ll gene which encodes the enzyme neomycin phosphotransferace II (NPTII) is used. plant cells containing these new genes are isolated on a medium containing the antibiotic kanamycin. The aad gene is a bacterial selectable marker 3”(9)-0-aminoglycoside adenyltransferace (AAD) which allows selection of bacteria containing the Cry1AC plasmid on a medium containing pectinomycin or streptomycin. Cotton reformation is achieved through tissue culture (starting with the American cotton variety Coker 312) technique that allows the soil bacterium, agro bacterium tumefactions, to transfer the DNA contained on the plasmid with the above sequences. The transformed cotton lines were screened to identify those with these genes inserted into the cotton genome in the most favorable position to achieve the desired insect control and agronomic performance.

  7. What are the differences between using Bt as spray and Bt in transgenic plants for insect control?

    The major differences are:

    • In order to spray. Bt spray, Bt formulation has to be purchased separately whereas in transgenic BT-plants. Bt is incorporated in the seed itself.

    • During spray, Bt is applied externally on the plants whereas in transgenic plants. Bt protein is produced within the plant.

    • When sprayed, it is difficult to get uniform coverage of the entire plant/crop and also there is wastage of spray fluid whereas in transgenic plants. Bt protein is present in all the plants. In all the parts and all the time.

    • When sprayed, Bt may get rapidly degraded if exposed directly to solar radiation or washed of by rain whereas in transonic plats, as Bt is present within the plant , it is not greatly affected by external conditions.

    • One needs to monitor the pests closely so as to appropriately time effective sprays, whereas in transgenic plants, since the control measure is in-built, the insecticidal activity is always present, providing protection day and night.

    • Spray formulations can be applied, as and when required, on any crop which may be considered as an advantage whereas in the case of transgenic. The advantage is restricted only to those crops that have been transformed into Bt-plants.

  8. What are the advantages of Bt-cotton?

    Bt-cotton has several advantages. Some of these are:

    • Bt-technology for control of bollworms is made available in the seed itself. Farmers have to just sow the Bt-cotton seeds as they do with conventional seeds. The resulting plants have the in-built ability to produce Bt-protein within their body and defend themselves form bollworms No extra efforts or equipment are needed to utilize this technology.

    • Bt protein is expressed in all parts of the plant(i.e., constitutive expression), providing bollworm control day and night, almost throughout the plant life no need to monitor he bollworms to initiate control measures.

    • The newly hatched larvae feeding on any part of the plant will ingest Bt-protein and die within one or two days. Thereby preventing any potential serious damage to the crop.

    • Bt-proteins, being lepidopteron specific, affect only the bollworms and are safe to biological control agents and other non-target beneficial organisms, higher animals and plants.

    • Bt-cotton is compatible with other control measures such as biological control, pheromones, botanical insecticides and also chemicals that are recommended for integrate pest management. In fact, Bt-cotton can serve as a major component of IPM in cotton crops.

    • Bt-cotton helps to avoid or minimize chemical sprays, thus contributing to cleaner environment and conservation of biological control agents and biodiversity .

    • Bt-cotton offers protection form bollworms right form the early days of the crop, leading to a health y crop, better boll retention, greater harvest and more profit.

    • The Bt-famers experience a far lower tension and are certainly better off than the earlier scenario of “spray &pray”

  9. Are there any limitations of this technology?

    It is important to know that Bt-cotton offers protection only against bollworms, not sucking pests and other non-lepidopteron pests. Therefore separate control measures have to be taken against such pests as and when required. Another factor is that the expression of Bt-protein I cotton plants may decline after 90-100 days, calling for supplementary control measures on the Bt-trait cannot be de-linked from the seeds even if there is no serious bollworm infestation. Bt should be always treated as an insurance against bollworms. Further, enforcing “refuge crop on famers poses several practical challenges. It always necessary to understand clearly the scope of a technology for its proper utilizat

  10. Will Bt-cotton controls all pests?

    The Bt-genes that are currently incorporated in the commercialized cotton plants are Lepidoptera specific. They are primarily targeted against bollworms which have been the most destructive and difficult pests to control. Besides bollworms, Bt-cotton is effective against secondary lepidopteron pests like the semilooper (anomis flava) and leaf roller (slyepta derogate) however, it is not designed to offer protection against sucking pests (whiteflies, aphids, thrips, jassids), and other non lepidopteron pest, or against diseases and adverse environmental conditions like drought, cold, salinity etc. appropriate remedial measures will have to be taken against these as and when warranted.



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