Protoplast fusion is the joining of two plant cells together to form one cell with multiple nuclei. Spontaneous fusion occurs in the degradation of the cell wall by enzymes, as adjacent cells expand and press on one another. This phenomenon results in cells with two or more nuclei.
Protoplast fusion can be caused by mechanical means, although this can result in damage to the protoplasts. This method of fusing protoplasts involves simply pressing two plant cells together without chemical fusing agents. Certain protoplasts may be easily fused together with gentle tapping in a depression slide when in an enzyme solution.
Various chemical methods exist for chemically inducing protoplasts to fuse. These treatments aim to create protoplasts with opposite-charged surfaces, as isolated protoplasts are often negatively charged and repel one another. Chemical methods include using a sodium nitrate solution to suspend the protoplasts, or using a calcium ion solution. A high-pH solution is also used to chemically induce fusion. Many of these methods involve an initial centrifugation of the protoplasts, suspension in the solution, a second centrifugation, and then a water bath for 30 minutes. Electric stimulation of protoplasts is also a method of inducing fusion, and may result in a "pearl chain" of cells. A low strength electric field causes the protoplasts to arrange according to their dielectrophoretic poles and then fuse.