A Two-Step or Equilibrium Freezing Procedure for the Cryopreservation of Plant Cell Suspensions

Plant cell and tissue culture is widely used in fundamental research (cell physiology, molecular biology and genetics, developmental biology, and so on) as well as in commercial activities (breeding and vegetative multiplication of food and feed crops and ornamentals). Several factors inherent to these types of work render the long-term storage of the materials urgent. Some of these are: 1. Costs of maintenance: Compared to the culture of many microorganisms, maintenance of plant cells and tissues is costly in terms of labor and equipment. 2. Stability: Plant cells have a remarkable flexibility, with respect to both composition of the genome (endoreduplication to higher ploidy levels is not uncommon in the plant kingdom; somatic mutations, aneuploidy, and amplification frequently occur in tissue cultures) and epigenetics (gene expression patterns are less stable than for most animal cell types). These mechanisms may render material with desired traits valueless. A well-recognized phenomenon is the loss during subculture of cells or tissues of the potential to regenerate into complete plants. 3. Patenting: As a rule, patented material has to be deposited in a publicly accessible culture collection.