CBSE · Class 12 · Biology · Biotechnology and its ApplicationsExplain the process of creating Genetically Modified (GM) crops with special reference to pest-resistant plants like Bt cotton. Discuss how Bacillus thuringiensis toxins work and their significance in sustainable agriculture.

Introduction to Genetically Modified (GM) Crops and Bt Cotton\nGenetically modified crops are plants whose DNA has been altered using genetic engineering techniques. These modifications are generally aimed at enhancing productivity, improving nutritional quality, and providing resistance against various biotic and abiotic stresses. One of the most successful applications of plant biotechnology in agriculture is the development of insect-resistant crops, prominently exemplified by Bt cotton.

Role of Bacillus thuringiensis

• Bacillus thuringiensis (often abbreviated as Bt) is a soil-dwelling bacterium that naturally produces specific proteins during a particular phase of its growth cycle.
• These proteins possess insecticidal properties that can kill certain specific orders of insects, including lepidopterans (tobacco budworm, armyworm), coleopterans (beetles), and dipterans (flies, mosquitoes).

Mechanism of Action of Bt Toxin

• Protoxin Formation: The bacterium produces protein crystals containing insecticidal crystal proteins known as Cry proteins. These proteins exist in an inactive form called protoxin within the bacterium.
• Ingestion by Insect: When an insect pest ingests the plant tissues containing these Bt crystals, the inactive protoxin enters the insect's alimentary canal.
• Alkaline pH Activation: The gut of these insects has a highly alkaline pH, which solubilizes the protein crystals. This alkaline environment triggers the conversion of the inactive protoxin into its active form.
• Lysis and Death: The activated toxin binds to the specific epithelial cells lining the midgut, creating microscopic pores. These pores cause cell swelling and lysis, leading to the disruption of the digestive tract, subsequent starvation, and ultimately the death of the insect.

Specificity and Genetic Integration

• The toxin genes (such as cryIAb, cryIIAb, or cryAc) are specific to particular insect groups. For instance, the gene cryIAb controls corn borer infestations, whereas cryAC and cryIIAb control cotton bollworms.
• Scientists successfully isolated these specific genes from Bacillus thuringiensis and incorporated them into the nuclear genome of cotton plants using recombinant DNA technology. As a result, the transgenic cotton plant expresses the insecticidal protein within its own tissues.

Significance in Sustainable Agriculture

• Reduction in Pesticide Usage: Since the plants are intrinsically protected against targeted insect pests, farmers do not need to spray chemical insecticides heavily.
• Environmental Safety: Lower chemical pesticide runoff protects non-target beneficial insects, soil microflora, and aquatic ecosystems from toxic contamination.
• Increased Yields: Crop damage is significantly minimized, ensuring higher productivity and better economic returns for farmers worldwide.