Protoplast, from the ancient Greek πρῶτον (first) + verb πλάθω or πλάττω (to mould: deriv. plastic), initially referred to the first organized body of a species.
Protoplast has several biological definitions:
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Cell walls are made of a variety of polysaccharides. Protoplasts can be made by degrading cell walls with a mixture of the appropriate polysaccharide-degrading enzymes:
| Type of cell | Enzyme |
|---|---|
| Plant cells | Cellulase, pectinase, xylanase |
| Gram-positive bacteria | Lysozyme (+EDTA) |
| Fungal cells | Chitinase |
During and subsequent to digestion of the cell wall, the protoplast becomes very sensitive to osmotic stress. This means cell wall digestion and protoplast storage must be done in an isotonic solution to prevent rupture of the plasma membrane.
Protoplasts can be used to study membrane biology, including the uptake of macromolecules and viruses.
Protoplasts are widely used for DNA transformation (for making genetically modified organisms), since the cell wall would otherwise block the passage of DNA into the cell.[1] In the case of plant cells, protoplasts may be regenerated into whole plants first by growing into a group of plant cells that develops into a callus and then by regeneration of shoots (caulogenesis) from the callus using plant tissue culture methods.[2] Growth of protoplasts into callus and regeneration of shoots requires the proper balance of plant growth regulators in the tissue culture medium that must be customized for each species of plant. Unlike protoplasts from vascular plants, protoplasts from mosses, such as Physcomitrella patens, do not need phytohormones for regeneration, nor do they form a callus during regeneration. Instead, they regenerate directly into the filamentous protonema mimicking a germinating moss spore.[3]
Protoplasts may also be used for plant breeding, using a technique called protoplast fusion. Protoplasts from different species are induced to fuse by using an electric field or a solution of polyethylene glycol. Originally, non Ti-plasmid dependent DNA uptake has been demonstrated 1985 by R. Hain and A.P. Czernilofsky et al., entitled "uptake, integration, expression and genetic transmission of a selectable chimaeric gene by plant protoplasts" using the Ca-phosphate coprecipitation technique (Mol Gen Genet, 199:161-168, 1985). This technique may be used to generate somatic hybrids in tissue culture.