Transgenic Plants
For thousand of years human has manipulated different genetic characteristics of plants by selective breeding.
However, as the development of recombinant DNA technology, it is more likely for scientists to construct transgenic plants with desired characteristics.
This modern biotechnology provides entirely new mechanisms for the development of new crops, enhancing the quality and nutritive values of existing crops.
Possible Targets for Crop Plant Improvement
Disease Improve productivity of crops and reduce their loss due to biological agents Insect Herbicde Virus Cold Permit growth of crops in areas that are physically unsuitable at present Drought Salt Reduction of
photorespirationIncrease efficiency of energy conversion Nitrogen fixation Conferability to fix atmospheric nitrogen to a wider range of species Nutritional value Improve nutritional value of storage proteins by protein engineering Storage properties Improve nutritional value of storage proteins by protein engineering Consumer appeal Make fruits and vegetables more appealing with respect to colour, shape, size etc. Reference︰ Desmond S.T. Nicholl. (1994) An introduction to genetic engineering. Cambridge. Pp 132 - 138.
How to Generate Transgenic Plants
The most commonly used method is by the infection of Agrobacterium tumefaciens which contains the genes of the desired characteristics.
1. Construct a recombinant DNA by inserting the target gene into the Ti plasmid and pack back into the A. tumefaciens cell.
2. Introduce this Agrobacterium tumefaciens into a plant cell protoplasts by infection.
3. Incorporate the recombinant DNA, consisting of both Ti DNA and the inserted target gene, into the host plant genome.
4. A new whole plant is then regenerated. This is a transgenic plant with the desired characteristic.
5. Once a plant incorporates the Ti DNA with the inserted target gene, it will pass it to future generations of the plant .
Limitation of A. tumefaciens Infection
In nature, Agrobacterium tumefaciens infects only dicotyledons.
Dicotyledons include such plants as roses, apples, soybeans, potatoes, pears, and tobacco.
Unfortunately, many important crop plants, including corn, rice, and wheat, are monocotyledons. And thus they could not be easily transfected using this bacterium.
Overcoming the Limited Range of A. tumefaciens Infection
Scientists discovered that the following processes can be used to introduce new genes into the plant cell types.
1. Microinjection
- direct injection of materials into a host cell using a finely drawn micropipette needle.
2. Electroporation
- application of high voltage electricity (brief pulses) to induce the formation of transient pores in the membrane of the host cell.
- such pores appear to act as passageways through which the new genes can enter the host cell.
3. Particle bombardment
- shooting DNA-coated microscopic pellets through a plant cell wall.
4. Gene gun
- insertion of genes into plant tissues directly.
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