In reference to Bt cotton, select the correct statement(s) :

(A) The alkaline pH of an insect gut solublises the crystals of Bt toxin
(B) The acidic pH of an insect gut solublises the crystals of Bt toxin
(C) The Bt toxin does not kill the tobacco budworm
(D) Specific Bt toxin genes were isolated from Bacillus thuringiensis

Choose the correct answer from the options given below :

(A) and (D) only

The correct answer is Option (1) → (A) and (D) only

Bt toxin is produced by a bacterium called Bacillus thuringiensis (Bt for short). Bt toxin gene has been cloned from the bacteria and been expressed in plants to provide resistance to insects without the need for insecticides; in effect created a bio-pesticide. Examples are Bt cotton, Bt corn, rice, tomato, potato and soyabean etc.

Bt Cotton: Some strains of Bacillus thuringiensis produce proteins that kill certain insects such as lepidopterans (tobacco budworm, armyworm), coleopterans (beetles) and dipterans (flies, mosquitoes). B. thuringiensis forms protein crystals during a particular phase of their growth. These crystals contain a toxic insecticidal protein.Actually, the Bt toxin protein exist as inactive protoxins but once an insect ingest the inactive toxin, it is converted into an active form of toxin due to the alkaline pH of the gut which solubilise the crystals. The activated toxin binds to the surface of midgut epithelial cells and create pores that cause cell swelling and lysis and eventually cause death of the insect.