Cryopreservation of plant cell suspensions.

The cryopreservation of dedifferentiated cells, grown in suspension culture, is one of the portfolio of techniques employed for the long-term conservation of higher plant germplasm. Suspension cultures are also important in biotechnology, particularly in transformation studies and for the production of specific metabolites, and, here, there is also a pressing need for genetically stable, long-term storage of cell lines. Cryopreservation of suspension cell cultures can be exploited by either slow, or rapid, cooling techniques. During slow cooling the extracellular solutions are nucleated and the cells cryodehydrate during controlled cooling as a consequence of extracellular ice, to the point where their intracellular fluids will vitrify on subsequent transfer to liquid nitrogen. In the rapid cooling protocols, the cells are prepared by extreme osmotic dehydration, with cryoprotection, before plunging the samples directly into liquid nitrogen to achieve vitrification. Extensive success has been achieved with both techniques but rapid cooling is, currently, widely favored because of its simplicity.