protoplast

Protoplasts of cells from a petunia's leaf

This article discusses protoplasts in the biological sense. For the theological use, see Adam and Eve

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. This meaning is similar to the non-biological definition, the first from which all subsequent forms are derived.

Subsequently it has several biological definitions:

• A protoplast is a plant, bacterial or fungal cell that had its cell wall completely or partially removed using either mechanical or enzymatic means.
  • Protoplasts - Have their cell wall entirely removed
  • Spheroplasts - Have their cell wall only partially removed

• More generally protoplast refers to that unit of biology which is composed of a cell's nucleus and the surrounding protoplasmic materials.

Enzymes for the preparation of protoplasts

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:

During and subsequent 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.

Uses for protoplasts

Fused protoplast (left) with chloroplasts (from a leaf cell) and coloured vacuole (from a petal).

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. This technique may be used to generate somatic hybrids in tissue culture.

See also

• L-form bacteria

References