What are transgenic plants ? Explain with any two examples.

Explanation

1. Transgenic plants are produced with the help of techniques using Biotechnology.
2. Biotechnology has revolutionised research activities in the area of agriculture.
3. Transgenic plants carrying desirable traits like disease resistance, insect resistance, and herbicide resistance are produced.
4. Plants with better photosynthetic efficiency, nitrogen fixing ability and higher nutrients e.g., proteins, vitamin content can be produced.
Most of the current commercial applications of modern biotechnology in agriculture aim at reducing the dependence of farmers on agrochemicals, pesticides so insect resistant crops or Bt crops are produced.
Bacillus thuringiensis (Bt) is a soil bacterium that produces a protein with insecticidal qualities.
Mechanism of action :
1. Bt toxin proteins occur as inactive protoxins.
2. When an insect ingests it, due to the alkaline pH of the gut, it gets converted into the active form .
3. The activated toxin causes swelling in the gut and death of the insect.
4. There are several Bt toxins and each one is specific to certain target insect.
5. Crop plants have now been engineered using r-DNA technology, to contain and express the gene for Bt toxin.
6. The gene is called 'cry' gene.
7. It produces inactive protoxins. When an insect ingests the transgenic crop, it dies.
8. Bt cotton is now commercially available in India to control the disease affecting the cotton bolls.
9. Bt toxin gene has been cloned and introduced in many plants to provide resistance to insects without the need of insecticides.
10. Other examples are Bt corn, rice, tomato, potato and soyabean.
Agrobacterium tumefaciens is a soil bacterium which causes crown gall tumours in dicotyledonous plants. A gall producing gene (T DNA) occurs in a large plasmid called tumour inducing plasmid or Ti plasmid.
Cry gene from B. Thuringiensis or `N_(2)` fixing gene from Rhizobium is cloned inside A. tumefaciens and then transferred into other plant. Many Bt crops, transgenic plants or genetically modified plants (GM plants) are produced using A. tumefaciens.
Example :
1. Flaver saver tomato is developed by introducing an additional copy of polygalacturonase encoding gene in the 'antisense' orientation.
This results in less production of pectin degrading enzyme polygalacturonase.
These tomatoes have longer shelf life.
Flavour is saved, which is an additional advantage.
2. Golden rice is genetically engineered rice with greater pro-vitamin A (`beta` carotene) content.