Give a brief account of Bt cotton.

Explanation

Bt Cotton : Bt cotton is created by using some strains of a bacterium, Bacillus thuringiensis (Bt is short form)
(i) This bacterium produces protein that kill certain insects such as lepidopterans (tobacco, bud worm, army worm), coleopterans (beetles) and dipterans (flies, mosquitoes).
(ii) B.thuringiensis forms protein crystals during a particular phase of their growth. These crystals contain a toxin insecticidal protein.
(iii) Bt toxin protein exists as inactive protoxins but once an insect ingests the inactive toxin, it is converted into an active form of toxin due to alkaline pH of the gut which solubilise the crystals.
(iv) The activated toxin binds to the surface of midgut epithelial cells and create pores that cause cell swelling and lysis leading to death of an insect.
(v) Specific Bt toxin genes were isolated from Bacillus thuringiensis and incorporated into several crop plants.
(vi) Most Bt toxins are insect group specific. Hence, the toxin is coded by a gene named .cry.. For example, the protein encoded by the genes Cry I AC and Cry II Ab control the cotton bollworms and Cry I Ab controls corn borer.