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The Goal

Application of genetic engineering in manipulation with plants has opened great perspectives for using plants in the future. The main goal of molecular plant biotechnology is the construction of new varieties of cultivated plants (Transgenic plants), and the development of new plant varieties that give better yield or nutrient power.

Therefore, genetically modified plants which possess resistance to insects, pathogens (primarily on viruses), herbicides, certain stressful environmental conditions, whose fruits rot slowly or plants with altered quality of oil or protein are already designed. In the year 2000, the total area sown with transgenic plants was 44.2 million hectares, and increase comparing to 1999 was 11%.

The transgenic plants are grown in 13 countries worldwide: in the United States (30.3 million hectares), Argentina (10 million hectares), Canada (3 million hectares), China (0.5 million hectares), South Africa, Australia, Bulgaria, France, Germany, Mexico, Romania, Spain and Uruguay. In the year 2000 it is the most planted were transgenic soybeans (25.8 million ha), maize (10.3 million hectares) and cotton (5.3 million hectares).

Transgenic plants tolerant to herbicides were represented with 74%. Transgenic plants resistant to insects were constructed by inserting the Bt gene responsible for synthesis of the protein toxic for insects (Bt toxin), which originates from the bacterium Bacillus thuringiensis. This plant was presented with the 19% of sown land. Data from 2004. are saying that the transgenic plants are grown in 16 countries around the world and cover more than 200 million hectares, and that the majority of transgenic plants are resistant to herbicides.

Impact on The Environment

Since the transgenic plants and the product of human activitiy, and could not be found naturally, studies on following the possible effects of using transgenic plants on the environment where grown. In many countries growing transgenic plants is regulated by rules defined in legislation. That way, it is detected that Bt insecticidal toxin excreted from the roots of transgenic maize after 40 days of cultivation in laboratory conditions, but around the roots of mature corn in the field too, while Bt toxin is not found in the ground on which the transgenic plants of corn were not grown.

Bt Toxin Toxicity

The presence of Bt toxin in the soil can cause the development of harmful insects that are resistant to the Bt toxin. Such cases initiated development of a system for quantitative detection of genetic modifications in corn. But, results of research that followed the breakdown of Bt toxins in different seasons and lasted for 200 days, showed that Bt toxin does not decompose completely in the soil. Far more extensive, 4-year studies of Bt toxin decomposition in corn leftovers in the field, showed that Bt toxin is extremely unstable in those remaining and that a small percent may exist even in firm parts of plants. There are results that when applied in the fields, Bt toxin product in the form of spray, can exist and is active in the soil for 28 months.

Agrobacterium tumefaciens is a soil bacteria, which causes the formation of tumors in infected plant by transferring genes located on the plasmid (genes for virulence) in the plant genome, using the information contained in part of plasmids called the T-DNA. Transferred DNA incorporates anywhere in chromosome of the plants. This property A. tumefaciens is used for construction of vectors for plant transformation by genes for virulence being replaced with genes that determine resistance to antibiotics, and with a gene that carries useful properties (eg. herbicide tolerance).

For gene expression, a promoter of cauliflower mosaic virus (CaMV
35S) is most commonly used. But, A. tumefaciens can enter the body of insects or animals, that feed on infected plants. Therefore, the question arises whether the T-DNA of Agrobacterium can infect animal cells. Experiments in laboratory have shown that this bacterium binds to and can steadily transformed HeLa, neurons, and kidney cells n the culture. It is even noted that the installation of T-DNA in the human cell chromosomes is done by the same mechanism by which this occurs in plant cells. Integrated T-DNA may have a mutagenic effect when incorporated into a chromosome. It is also stated that the viral CaMV 35S promoter is active in human HeLa cells.

Therefore, nowadays, the question of security of using transgenic plants for preparation of food for humans is frequently asked.
Transgenic plants and their newly created traits

Using genetic engineering, scientists can tailor and modify various genomes to produce organisms with qualities that are beneficial for humans. Transgenic animals are useful in medical research. Diseased phenotype in the “dish” allows scientists to track the pathology, reveal unknown facts and test potential drugs…Transgenic plants are modified for other purposes: to provide better harvest, to increase amount of valuable nutrients, to strengthen the plants against herbicides, to delay ripening. Unlike transgenic animals, transgenic plants could be (and they usually are) part of our everyday meals.

Most common modifications on plants

Plants release protective chemicals when exposed to the stressful environmental conditions such as very high or low temperature, drought, and increased salinity of the soil... These chemicals include sugars like trehalose and fructans, sugar alcohols like mannitol, amino acids like proline, glycine, betaine and proteins such as antifreeze proteins. Scientists created plants that overexpress genes responsible for stress-releasing chemicals, resulting in better adapted and stronger plants that could survive in the harsh environmental conditions. Glycine betaine is a cellular osmolyte produced via combined activity of choline dehydrogenase, choline monooxygenase and few other enzymes. When choline oxidase gene (derived from Arthrobacter sp.) was introduced into rice genome, transgenic rice developed resistance to drought due to increased level of glycine betaine.

Tolerance against herbicide

Herbicides are inevitable part in plant cultivation because weed grows wherever crop is growing (and competes for water and nutrient with crop). Since herbicides are very aggressive chemicals, crops need to be modified to remain safe. Herbicides target enzymes that are essential for the survival of the plant. Without selected enzyme, biological pathway can’t be completed and lack of vital nutrient eventually lead to plant death. Several approaches are applied while designing transgenic plants resistant to the herbicide. Plant will remain safe if it becomes genetically modified to produce excessive amount of target protein or if target protein underwent genetic modification. Detoxifying system of the plant could be enhanced by boosting natural systems for detoxification or by incorporating foreign genes that could help in toxin elimination. All these methods proved to be effective. Glyphosate is widely used herbicide because it kills 76 out of 78 problematic weed species. He is competitive inhibitor (competes with pyruvate) of 5-enoyl-pyruvylshikimate 3-phosphate synthase (EPSPS) enzyme. It was noted that petunia has several copies of EPSPS gene. Insertion of petunia's EPSPS genes into crop’s DNA increased resistance against herbicides 2-4 times. EPSPS gene can be altered by simple switch of cytosine with thymine, which results in modified final protein that can’t combine with glycophosphate. Introduction of foreign gene that encodes glycophosphate oxidase (derived from Ochrobactrum anthropi) increases transformation of glyphosate into glyoxylate and aminomethylphosponic acid and accelerates detoxification.

Tolerance against insecticides

Insects, mites and nematode can damage the harvest greatly. That means that either synthetic insecticides or genetic engineering methods must be applied to ensure safe and rich harvest. Transgenic plants are more eco-friendly compared to synthetic insecticides and so far, 40 gene candidates of various microorganisms that live on higher plants and animals were detected as useful in increasing plant’s tolerance against insecticides. The most popular and often used are Bt-genes isolated from the bacterium Bacillus thuringiensis. List of transgenic plants containing Bt-toxin increased since 1996 (when first Bt-plant became commercially available) and they include: corn, soybeans, cotton, rice, maize, potato, and tomato….Authorities claim that Bt-toxin is not harmful to the humans because it undergoes metabolic degradation after ingestion. Latest studies proved them wrong. According to the results from the Sherbrooke University Hospital in Quebec, Bt-toxin was found in 93% of pregnant women, in 80% of tested umbilical cord blood and in 67% of non-pregnant women. Bt-toxin is associated with cancer development, autism, food allergies and auto-immune diseases and number of diagnosed cases is increasing constantly for the past couple of years. People exposed to the Bt-toxin spray (another way to repel insects is to cover plant's surface with Bt-toxin via spray) showed symptoms like flu and allergy. Same symptoms were recorded in people in India who were in direct contact with genetically altered Bt-cotton. Although creators of the Bt-toxin claim that Bt-food is safe, it turned out that toxin can be found in the body several years after last transgenic meal is consumed.

Last example of genetically modified food is not the only experiment that shows how dangerous transgenic plants can be. While waiting for the final conclusion on transgenic plants safety, you can always choose not to eat them.