Proline and the Cryopreservation of Plant Tissues: Functions and Practical Applications

Cryopreservation has been proven to be an effective technology for the cost-effective, longterm preservation of genetic material. A wide range of plant material including cultured cells, tissues, embryos, meristems, pollen and seeds can be effectively preserved for extended periods of time and, when thawed, can be used to rapidly produce stock plants, with good preservation of genetic and physiological characteristics. Numerous protocols including controlled rate cooling, PVS2 vitrification, encapsulation-vitrification, and encapsulation-dehydration have been developed that allow the cryopreservation of a wide range of plant germplasm (Burritt, 2008), but irrespective of the protocol used each step in a cryopreservation protocol has the potential to impose a stress on plant cells. Low temperatures that lead to freezing can impose stress on cells and tissues in two ways, by the direct effects of low temperatures on cell function and integrity or by the cellular dehydration that occurs when the cells water freezes. Several of the mechanisms by which these two forms of stress can damage plant cells are shown in Figure 1.