Fundamental Cryobiology and Basic Physical, Thermodynamical and Chemical Aspects of Plant Tissue Cryopreservation

The greatest stability of in vitro plant materials with practical storage periods measured in decades can be achieved by cryogenic storage at ultra low temperatures. Liquid Nitrogen (LN) is the most common medium for cryostorage as it is relatively inexpensive and readily available (Withers, 1987; Panis and Lambardi, 2005). This process puts the cells in suspended animation where they can retain their viability indefinitely. Maintenance under these conditions effectively halts biological growth and development (Franks, 1985; Grout and Morris, 1987; Grout, 1990a; 1990b) because at below -140oC, the rates of chemical and biophysical reaction will be too slow to affect cell survival. Consequently, material that can be brought to the ultra-low temperature and recovered from it without acquiring lethal injury may be stored for extremely long periods. The challenge is to devise a protocol that allows in vitro plant material to be recovered from the cryogen at high viability, and without structural and functional changes (Kartha, 1997; Withers, 1987; Grout and Morris, 1987; Grout, 1990 a, 1990 b). Preservation of viability depends upon the ability to minimize the stresses of cryopreservation and protect against the damaging consequences. A variety of plant material can be used for cryopreservation including in vitro cultivated material, pollen, seeds, embryos, buds and meristematic tissues.