Biolistic technology, or particle bombardment, is a physical method of introducing DNA into cells. In theory, all cells should be transformable by this method. The technique was originally developed to transform monocotyledonous plants, and has since been used to transform numerous species of both mono- and dicotyledenous plants (Klein, et al., 1990). Particle bombardment has also been used to transform a wide variety of tissue culture cells and animal organs (Johnston & Tang, 1993). Additionally, the technique has been used to transform bacteria and subcellular organelles (Boynton & Gillham, 1993, 1996; Butow & Fox, 1990; Smith, et al., 1992).
Transformation of all these different cell types requires optimization
of the physical parameters used in bombardment (Sanford, et al., 1993).
The parameters which have the greatest effect on transformation efficiency
include the vacuum in the bombardment chamber, the distance the particles
travel before striking the target cells, and the size and density of the
particles used in bombardment. Of less importance are the helium pressure,
the gap distance (the distance between the rupture disk and the macrocarrier),
and the macrocarrier travel distance. For most applications, a helium
pressure of about 1,100 psi, a gap distance of 510 mm, and a macrocarrier
travel distance of about 8 mm are near optimal. Each of these parameters
affects the particle velocity and each interacts with the others. The
greater the particle