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Agroinfiltration is a method in plant biology to induce transient expression of genes in a plant or to produce a desired protein. In the method a suspension of Agrobacterium tumefaciens is injected into a plant leaf, where it transfers the desired gene to plant cells. The benefit of agroinfiltration when compared to traditional plant transformation is speed and convenience.
First step of the protocol is to introduce a gene of interest to a strain of Agrobacterium. Subsequently the strain is grown in a liquid culture and the resulting bacteria are washed and suspended into a suitable buffer solution. This solution is then placed in a syringe (without a needle). The tip of the syringe is pressed against the underside of a leaf while simultaneously applying gentle counterpressure to the other side of the leaf. The Agrobacterium solution is then injected into the airspaces inside the leaf through stomata, or sometimes through a tiny incision made to the underside of the leaf.
Vacuum infiltration is another way to penetrate Agrobacterium deep into plant tissue. In this procedure, leaf disks, leaves, or whole plants are submerged in a beaker containing the solution, and the beaker is placed in a vacuum chamber. The vacuum is then applied, forcing air out of the stomata. When the vacuum is released, the pressure difference forces solution through the stomata and into the mesophyll.
Once inside the leaf the Agrobacterium remains in the intercellular space and transfers the gene of interest in high copy numbers into the plant cells. The gene is then transiently expressed (no selection for stable integration is performed). The plant can be monitored for a possible effect in the phenotype, subjected to experimental conditions or harvested and used for purification of the protein of interest. Many plant species can be processed using this method, but the most common ones are Nicotiana benthamiana and Nicotiana tabacum'.'