Advantages of GM Food-Plants

GM food-plants offer several kinds of advantage.

1. Insect pest resistance. Reducing chemical-pesticide use lowers the cost of food production. A biological insecticide from the bacterium Bacillus thuringiensis (Bt) has been available for over 30 years, but its use as a spray is limited by the low field-stability of its protein -- which is why the cry gene from Bt, which produces a protein forming crystalline inclusions in the bacterium's spores, is instead inserted directly into the crop plant (Bt cotton being the best-known transgenic example). When a susceptible insect ingests this protein, the combination of the insect midgut's high pH and its own proteinase enzyme hydrolyses the crystal to release toxic fragments; within minutes this causes midgut paralysis, and ultimately disruption of the insect's midgut cells. Bt-toxin activity has been demonstrated against many insect species across the orders Lepidoptera, Diptera and Coleoptera. Alternatively, insect-resistant plants may carry the cowpea trypsin-inhibitor gene; similarly, an alpha-amylase inhibitor gene isolated from adzuki bean has been transferred into tobacco, where it works against pests such as Zabrotes subfasciatus and Callosobruchus chinensis.
2. Improved nutritional quality (biofortification). Transgenic plants have been developed to provide functional food and nutraceuticals -- Table 12.8 gives several examples, including provitamin A in rice, vitamin E in canola, flavonoids in tomato, fructans in sugar beet, and iron in rice. Rice is the main dietary staple for millions of people in developing countries but lacks many essential nutrients, so malnutrition -- including night-blindness from vitamin A deficiency -- is common where diets rely heavily on it. Swiss researchers created transgenic 'golden rice' and 'golden mustard', rich in beta-carotene (a precursor of vitamin A, and the source of their golden colour), hoping that growing and eating them in developing countries would reduce vitamin-A-deficiency disease. Similarly, because iron deficiency affects an estimated 30% of the world's population, ferritin genes (an iron-storage protein found in many animals, plants and bacteria) isolated from soybean and Phaseolus have been transferred into rice, to raise its iron content.
3. Modification of post-harvest characteristics. Disease, pests, bruising, heat/cold-storage stress, over-ripeness and loss of flavour all cause major losses during the storage and transport of fruits and vegetables, and most of these changes stem from ongoing enzyme activity inside the plant tissue. In tomato, for example, the enzyme polygalacturonase breaks down pectin in the cell wall, softening the fruit as it ripens and making it easy to bruise or damage during shipping. Genetic engineering has made it possible to slow this activity down, by inhibiting polygalacturonase with antisense genes -- giving rise to the genetically modified 'Flavr Savr' tomato, which can stay on the vine until fully mature, keep a long shelf life, and be transported in a firm, solid state.
4. Plants as factories. Beyond food traits, transgenic plants are also potential factories, or bioreactors, for producing novel biochemicals and vaccines (biopharmaceuticals) -- high-value biochemicals such as starch, sugar, lipids and proteins, and products like fine chemicals, perfumes, adhesive compounds, industrial lubricants, biodegradable plastic, and even renewable-energy crops to replace fossil fuels. Biopharmaceuticals are proteins, hormones, antibodies, vaccines or enzymes isolated from transgenic plants; examples produced by transgenic crop plants include human growth hormone (via a gene inserted into the chloroplast DNA of tobacco), humanised antibodies against infectious agents such as HIV, respiratory syncytial virus (RSV) and herpes simplex virus (HSV, the cause of 'cold sores'), and protein antigens used in vaccines, such as patient-specific anti-lymphoma vaccines (B-cell lymphomas being clones of malignant B cells expressing a unique antibody molecule on their surface). Improvements in the oil content and quality of oil crops such as soybean, oil palm, rapeseed and sunflower have also been achieved by transferring 'Arabidopsis genes' into them. …