Genetically Modified Organisms (GMO)
Farmers constantly seek alternative methods to obtain maximum yield while minimising the use of artificial fertilisers and chemicals. Reducing chemical usage is essential to lower the harmful effects on the environment. The development of genetically modified crops provides a highly effective solution to this problem.
Plants, bacteria, fungi, and animals whose genes have been altered by direct genetic manipulation are called Genetically Modified Organisms (GMO).
Advantages of Genetically Modified Crops:
Genetic modification has made agricultural crops highly useful in several ways:
- Abiotic Stress Tolerance: It has made crops more tolerant to environmental stresses such as cold, drought, salt, and extreme heat.
- Pest Resistance: It has reduced the reliance on harmful chemical pesticides by creating pest-resistant crops.
- Reduced Spoilage: It has helped to significantly reduce post-harvest losses.
- Efficient Mineral Usage: It has increased the efficiency of mineral usage by plants, which prevents the early exhaustion of soil fertility.
- Nutritional Enhancement: It has enhanced the nutritional value of food. A prominent example is Golden Rice, which is genetically modified to be enriched with Vitamin ‘A’.
In addition to food production, genetic modification is used to create tailor-made plants that supply alternative resources to modern industries in the form of starches, fuels, and pharmaceuticals.
Pest-Resistant Plants and Bt Toxin
A major application of biotechnology in agriculture is the production of pest-resistant plants. This innovation drastically decreases the amount of chemical pesticide sprayed on fields.
A naturally occurring soil bacterium called Bacillus thuringiensis (commonly referred to as Bt) produces a specific pest-killing substance known as Bt toxin. Scientists have successfully cloned the Bt toxin gene from the bacteria and expressed it directly inside crop plants. This provides the plants with an inbuilt resistance to insects, effectively acting as a natural bio-pesticide. Examples of such genetically modified crops include Bt cotton, Bt corn, rice, tomato, potato, and soybean.
Bt Cotton and Mechanism of Toxin Action: Some strains of Bacillus thuringiensis produce proteins that are highly toxic to certain groups of insects, such as lepidopterans (tobacco budworm, armyworm), coleopterans (beetles), and dipterans (flies, mosquitoes). During a particular phase of their growth, the bacteria form protein crystals that contain a toxic insecticidal protein.
The Bt toxin does not kill the Bacillus bacteria itself. This is because the toxin initially exists in an inactive form known as a protoxin. The process of eliminating the pest follows a specific sequence:
- An insect feeds on the genetically modified plant and ingests the inactive protoxin.
- The alkaline pH of the insect’s gut solubilises the protein crystals, instantly converting the protoxin into an active form of the toxin.
- The activated toxin binds to the surface of the midgut epithelial cells within the insect.
- This binding creates pores in the cell membrane, causing the cells to swell and undergo lysis (bursting). This process eventually causes the death of the insect.
The Role of cry Genes: Specific Bt toxin genes were isolated from the bacteria and carefully incorporated into crop plants like cotton. The choice of genes depends strictly upon the crop and the targeted pest, as most Bt toxins are insect-group specific.
The toxin is coded by a gene named cry. There are several different variations of this gene. For example, the specific proteins encoded by the genes cryIAc and cryIIAb are used to control cotton bollworms, whereas the protein encoded by the gene cryIAb is used to control the corn borer.
