When the genetic material of an individual cell is changed by the insertion of a foreign DNA into the cell's genome then the process is called as genetic transformation. This technique is of great significance in the field of molecular biology. This method is similar to the bacterial conjugation in which genetic alteration occurs only in one cell and then it passes to the next generation. Using bacteria for this technique is also useful because it is unicellular. Alteration in the genetic makeup of bacteria makes them to adopt the new environment.
Genetic transformation in higher plants is very difficult to take place because they are multicellular and the transformation will have to take place in each type of the cells to make it completely genetically altered. So this process is time consuming and complicated. If the genetic transformation of multicellular plants is concerned then the changes should be made in an individual plant cell and then regenerate it so that it develops into a new organism.
Genetic transformation is the natural process which is carried out in plants through bacteria. There are some viruses also which are involved in the genetic transformation. They transfer part of their DNA or RNA into the plant's genome and cause significant changes.
Techniques of genetic Transformation in Plants:-
Agrobacterium mediated gene transfer:-
The process which is most commonly used for the gene transformation is the method of Agrobacterium mediated gene transfer. In this method, the bacterium Agrobacterium tumefaciens is used for the transformation of Bt corn. This bacterial plasmid is used as a vector to insert the Bt gene into the corn plants. Commonly this bacterium has Ti plasmid in its genome and is the cause of inducing tumor in the dicotyledonous plants that is why it can serve as a vector for transferring the foreign gene. Due to this reason, this bacterium is used by the scientists because they can remove the tumor inducing gene from the bacterium and can insert the foreign gene. It is the source of causing efficient transformation in the plants.
The Agrobacterium is usually responsible for causing the crown gall disease in the plants. It takes a small part of its genome that is DNA and inserts it where the wound of the plant is located causing the tumor.
Injection of the foreign DNA into the target cell under the microscope is called microinjection. Microinjection is applied on the target cell of embryo, ovule and meristematic cells. In this method, the cell in which foreign DNA has to be injected is held by gentle suction and controlled with the use of a capillary. Using a pipette, the DNA is inserted into the cell's cytoplasm or directly in the nucleus. This method is not commonly used because it is not very efficient.
In this process, the desired cells are mixed with the solution which contains the DNA molecules. A short electric current makes the DNA penetrate into the cells through the cytoplasm. There will be some cells in which DNA will neo enter, while the cells having foreign DNA will incorporate the new DNA and will express the desired genes. If the DNA is introduced directly into the monocots, then this technique proves successful.
It happens especially in plant cells that they do not accept foreign genes sometimes. For this purpose, scientists have developed the method of biolistics in which gene gun is used. In this technique, the particles mostly gold or tungsten are coated with DNA. Using the gene gun, the particles are bombarded into the cells and this is the foreign gene is expressed in the plant cells or tissues.
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