Abstract
Cell suspensions of carrot (Daucus carota L.) can be cryopreserved by slow freezing (about 2 C per minute) in medium containing dimethylsulfoxide as a cryoprotectant. After storage in liquid nitrogen and thawing they demonstrate a high viability and are able to resume growth. Such a method entirely fails to preserve clonal plantlets; somatic embryos cease organized development at the time of freezing and recover growth only by secondary embryogenesis. Modification of the procedure, involving the removal of superficial moisture from cryoprotectant-treated embryos and plantlets and enclosing them in a foil envelope before freezing, greatly improves their survival potential. The use of dimethylsulfoxide at levels between 2.5 and 20% (v/v) and freezing at rates between 1 and 5 C per minute yielded viable preparations under appropriate thawing conditions. In general, treatments which increased tissue dehydration before or during freezing were most successful when followed by relatively slow thawing. Conversely where dehydration to a lesser degree was achieved, more rapid thawing was advantageous. Postthawing washing or inoculation into liquid media was inhibitory to recovery. On semisolid regrowth medium, somatic embryos resumed normal development, whereas in plantlets the root and shoot meristem regions gave rise to new growth. In both cases, inclusion of activated charcoal in the medium promoted organized growth.