One of the best known applications of biotechnology is the production of pest resistant plants. How is this achieved in Bt Cotton?

Bt cotton(Bacillus thuringiensis) some strains of Bt produce proteins that kill certain insects such as lepidopterans, coleopterans and dipterans.

B.thuringiensis forms protein crystals during a particular phase of their growth, these crystals contain a toxic insecticidal protein.

Bt toxin protein exist in inactive protoxins but once an insect injest the inactive toxin gets converted into toxin due to the alkaline pH of the gut which solubilise the crystals.

The activated toxin binds to the surface of the midgut epithelial cells and create pores that cause cell swelling and lysis and finally death of the insect.

Specific Bt toxin genes were isolated from Bt and incorporated into the several crop plants.The choice of the genes depends upon the crop and the targeted pest.

The toxin is coded by the gene named Cry.There are many of them, for e.g:the proteins encoded by the genes crylAc control the cotton bollworms, while crylAb control corn borer.