Particle Gun Method,Tungsten,Electrostatic Energy,Ballistic Method,Microprojectiles

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	Particle Gun Method - In this method, 1-2μm tungsten or gold particles, coated with the DNA to be used for transformation, are accelerated to velocities, which enable their entry into plant cells/nuclei. Particle aceleration is achieved by using a device, which varies considerably in design and function. The most successful devices accelerate particles in one of the two ways: (1) by using pressurised helium gas or (2) by the electrostatic energy released by a droplet of water exposed to a high voltage.
The earlier devices used blank cartridges in a modified firing mechanism to provide the energy for particle acceleration; this is the reason for the name particle gun to this approach. The method is also called biolistic or ballistic method of DNA delivery. This technique has general applicability to plant species and can be used to deliver DNA into virtually all tissues. More importantly, it can be used to transform shoot apical meristems, leaf blades, immature and mature embryos, mature pollen, and root and shoot sections etc. Meristematic cells show higher transformation frequency than nondividing cells. The main components of a helium pressure device are, gas acceleration tube, rupture disc., stopping screen, macrocarrier carrying particles coated with DNA, and target cells. These components are enclosed in a chamber to enable the creation of partial vacuum, which facilitates particle acceleration and reduces damage to plant cells. After creation of partial vacuum sufficiently pressurised helium gas is released in the acceleration tube to break the rapture disc.
This generates helium shock waves, which accelerate the macroprojectile to which DNA coated microprojectiles are attached. The macroprojectile is stopped by a stopping screen, and the microprojectiles pass through this screen and become embedded in the cells kept about 10 mm below the stopping screen. Helium is preferable to air since it is lighter and offers certain advantages. Generally a 1000 psi (pounds per square inch) of helium pressure is used for acceleration. The macrocarrier or macroprojectile is a 2.5 cm diameter 0.06 mm thick plastic membrane, which is used only once. The microprojectiles, micropartic1es or microcarriers vary in diameter from 0.5 to 2.0 µm; the average size of 1.0 11m is commonly used. Tungsten particles are cheaper, but are of irregular shape and size, may be toxic to certain cell types and show surface oxidation which may lead to precipitation of DNA.
In addition, they tend to form aggregates after addition of DNA, which reduces particle dispersion. In comparison gold particles are more uniform in size (1-3 µm) and shape and show much lower toxicity, but they are much costlier and show variable coating with DNA.

Transgenic Plants - Part III
Properties of Crowngall Cells
Ti Plasmid
Organisation of T-DNA
Organisation of vir Region
Transfer of TDNA
Transformation Techniques
Agrobacterium Mediated Gene Transfer
Direct Gene Transfers
Electroporation
Particle Gun Method
Lipofection
Microinjection
Fibre Mediated DNA Delivery
DNA Delivery via Growing Pollen Tubes
Macroinjection
Direct DNA Uptake by Mature Zygotic Embryos
Comparison of Some of the Important DNA Delivery Techniques for Plant Cells