Microprojectile Gun Method - To overcome the limitations of protoplast regeneration, high velocity microprojectiles are being used to deliver nucleic acids directly into intact plant cells or tissues.

In this method DNA is coated on the surface of tungsten particles which are projected by means of a particle gun into intact cells or tissues.

The particles can penetrate through several layers of cells and can transform cells within tissue/explants.

Soybean, tobacco, and maize have been transformed by this method.

The particle gun is manufactured by DuPont. The DNA to be transformed is first coated on microbeads composed of tungsten or gold.

The target cells are placed in a partially evacuated chamber to expel the air generated by the velocity of the microprojectiles.

For transformation of monocots such as corn and wheat a particle gun could be useful, but for dicots the electroporation of PEG-mediated transformation of protoplasts appears attractive.

Another approach is to shoot plant tissue with extremely fine metallic pellets coated with DNA by means of a 0.22 calibre gun.

These pellets do not harm or damage the tissues but some deliver the DNA directly into the cells.

In one experiment bacterial and viral genes were fired into onion plants and the plants began to produce the foreign proteins.