Question

Agrobacterium tumefaciens: Gene transfer in plants :: Bacillus thuringiensis: _________

• A. Herbicide
  
• B. Pesticide
  
• C. Biopesticide
  
• D. Bio Fertilizer
  

Answer 1

The correct option is C Biopesticide


Agrobacterium tumefaciens is a bacterial plant pathogen which carries the Ti Plasmid or Tumour inducing plasmid. The T-DNA segment of the Ti plasmid integrates itself into the plant cell’s genome to induce tumour formation. This property of the plasmid makes it an effective vector for transferring foreign genes into plant cells.

Pests are organisms that destroy plants. Substances of biological origin, i.e, obtained from plants, animals or microbes, that are used to kill pests are known as biopesticides. Bacillus thuringiensis is a soil bacterium which is widely used as a biopesticide in the field of agriculture. Often, spores of B. thuringiensis are spread over crops to kill lepidopteran insect pests.

The cry genes, present in B. thuringiensis, code for a crystalline protoxin (inactive toxin) protein or cry protein, commonly known as Bt toxin. The protoxin remains inactive,upon ingestion of the spores by the insects, the protoxin is released and the alkaline medium of the insect gut activates the protoxin.

The active toxin binds to the epithelial cells of the midgut of the insects and creates pores in the gut wall. The insect stops eating at this point and eventually dies due to starvation. The pores also allow normal gut bacteria of the insect to invade and cause infection, leading to the death of the insect.

Alternatively, the cry genes of B.thuringiensis can also be genetically engineered into the genome of some plants, e.g, cotton, brinjal etc. This practice helps to create genetically modified pest-resistant crops.

Herbicides are synthetic chemical substances that are used to kill herbs or weeds that grow along with the main crop in the agricultural fields, for example, glyphosate, glufosinate. The herbs compete with the main crop for resources and are hence eliminated with the use of herbicides.

Pesticides are synthetic chemical substances that are used to kill pests like insects, rats, etc, that can damage the crops, for example, DDT, metaldehyde, etc.

Biofertilizers are living organisms that can increase the fertility of the soil by natural processes. For example, Rhizobium bacteria which lives as a symbiont in the root nodules of leguminous plants. This bacteria fixes atmospheric nitrogen into nitrates and thus increases soil fertility.