Which of the following factors leads to the conversion of the Bt toxin present in Bt cotton plant tissue into an active toxin? Choose the correct option:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Alkaline pH of the insect gut
The bacterium Bacillus thuringiensis makes protein crystals that contain the Bt toxin. Inside the bacterium, and in the tissue of a Bt cotton plant, the toxin is an inactive protoxin. It turns active only after an insect eats it: the alkaline pH of the insect gut dissolves the crystals and activates the toxin. The active toxin binds to the midgut cells, makes pores in them and kills the insect.
Option (1) Acidic pH of the insect gut — Incorrect. The gut of the insect is alkaline, not acidic, and it is this alkaline pH that activates the toxin.
Option (2) The action of gut microorganisms — Incorrect. Gut microorganisms play no part. The protoxin is activated by the pH of the gut, which dissolves the crystals.
Option (3) Alkaline pH of the insect gut — Correct. The alkaline pH solubilises the crystals and turns the inactive protoxin into the active toxin.
NCERT Extract:
Biotechnological Applications in Agriculture – “… 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.”