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Particle gun

“Ready, aim, fire!”

At the Max Planck Institute for Molecular Plant Physiology in Potsdam-Golm plant cells are ‘bombarded’ using a particle gun for the purpose of genetic modification. The main plants that come under fire at the institute are tobacco, tomato and maize plants.

Dr Stephanie Ruf explains the particle gun that the MPI uses for genetic modification of plants.

Particle gun: To transfer new genes to plants, plant tissue is ‘bombarded’ with gold particles coated in DNA.

Particle gun: A gas chamber filled with an inert gas opens under a certain pressure, propelling the gold particles coated with the DNA.

A tobacco leaf awaiting transformation

A tobacco leaf awaiting transformation.

To coat the gold or tungsten particles in DNA, both substances are shaken together in an aqueous solution on ice.

To coat the gold or tungsten particles in DNA, both substances are shaken together in an aqueous solution on ice.

DNA-coated gold particles on an orange carrier film

DNA-coated gold particles on an orange carrier film

The transformation of plant cells using a particle gun is also called ‘biolistic transformation’. The particle gun can be used to transform cells of any organisms. It has been used since 1988 for the genetic modification of plant cells or tissue, especially in cases where inserting foreign genes using Agrobacteria does not work well, if it all, as is the case with cereals.

The particle gun can be used to modify the genetic information in the plastids (e.g. chloroplasts) of plant cells as well as the DNA in the cell nucleus.

Particle guns or ‘gene guns’ fire DNA-coated gold particles at plant tissue at high speed. The plant tissue is placed in a vacuum chamber. The gold particles with the DNA are propelled into the plant cells under the pressure of an inert gas. “Before, people actually used gunpowder and the whole device had to be cleaned after every shot, until it occurred to a resourceful manufacturer to use helium,” recalls Stephanie Ruf, a scientist at the Max Planck Institute. The DNA enters the plant cells, where it is integrated into the genome. Any material can be transformed with the right pressure: the tender leaves of tobacco plants need only a slight pressure, while the stable callus material of some monocotyledonous plants requires a high pressure to reach deeper cell layers.

If plastids are to be transformed rather than the nuclear genome, the plants have to be bombarded with special gene constructs. These are given signals that enable the inserted genes to be expressed in the plastids, but not in the nuclear genome.

As with other transformation methods, a marker gene has to be inserted into the plant cells as well to aid selection. This is usually an antibiotic resistance gene. Once they have been ‘shot’, the leaf samples are placed on a culture medium containing an antibiotic. Only plant cells in which transformation has been successful are able to grow on this medium.