Cryopreservation of Plant Cells

Abstract

Cryopreservation, storage of living tissues in or above liquid nitrogen, is increasingly used to preserve germplasm in the long term. When cooling plant tissue to low temperatures, water may destroy cells by osmotic drying or disruption of organelles by forming ice crystals. The organisms accumulate cryoprotective substances to adapt to freezing. Cryoprotectants trigger glass transition (vitrification), when temperature is cooled down rapidly. In the course of cryopreservation, tissues are imposed by various influences causing oxidative stress: wounding, dehydration, and direct liquid nitrogen effect. Occurring reactive oxygen species may be measured and antioxidant substances may be added. Cell structure alterations, water status, regeneration from cryopreservation injury, and genetic and epigenetic changes, which may occur, were investigated. Various plant tissues were cryopreserved: dedifferentiated cells and tissues; shoot tips; axillary buds and other meristematic plant parts; dormant buds of woods species, seeds, embryos, and embryo axes; and pollen. Several main methods were used: slow freezing, vitrification, and encapsulation. Liquid nitrogen can also be used to eliminate viruses from the organs (cryotherapy). The existence of endogenous or contaminating microorganisms needs special attention. Furthermore, technological considerations and the use of cryopreservation to maintain transgenic or patented material need to be mentioned.