Many methods of delivering extra DNA into the nucleus of plant cells have been tried, and several have been successfully used to produce transgenic plants. The first to be discussed is the gene gun, also called particle acceleration or microprojectile bombardment. While this method was used to create several commercial events such as RoundupReady soybean, it has several limitations that make it less appealling than the use of Agrobacterium as a transformation method. We will describe the Agrobacterium method in the next section. The gene gun is a good example of a creative idea being developed into a practical technology.
The gene gun can be used on either tissue culture cells or seedlings (to make chimeric plants) of any species. As the name implies, this method works by shooting DNA into the plant cells. As seen in these figures from the animation, microscopic gold or tungsten particles are coated with hundreds of copies of the gene(s) to be introduced.
In earlier versions of the gene gun, DNA coated metal was loaded into a 22-caliber cartridge and then shot into plant tissue culture cells. Current versions place the tissue culture cells in a vacuum chamber and then propel the metal particles with a high pressure gas that is released in a sudden burst much like a popped balloon.