The present invention relates to methods for cryopreserving
plant cells and to methods for recovering viable
plant cells from long or short term
cryopreservation.
Plant cells to be cryopreserved can be grown in culture and pretreated with a solution containing an
cryoprotective agent and, optionally, a stabilizer. Stabilizers are preferably membrane stabilizers such as
ethylene inhibitors,
oxygen radical scavengers and
divalent cations. Cells can also be stabilized by subjecting the culture to a
heat shock. Pretreated cells are acclimated to a reduced temperature and loaded with a
cryoprotective agent such as DMSO,
propylene glycol or
polyethylene glycol. Loaded cells are incubated with a
vitrification solution which, for example, comprises a solution with a
high concentration of the
cryoprotective agent. Vitrified cells retain less than about 20%
water content and can be frozen at
cryopreservation temperatures for long periods of time without significantly altering the genotypic or phenotypic character of the cells.
Plant cells may also be cryopreserved by lyophilizing cells prior to
exposure to a
vitrification solution. The combination of lyophilization and
vitrification removes about 80% to about 95% of the
plant cell's water. Cells can be successfully cryopreserved for long periods of time and viably recovered. The invention also relates to methods for the
recovery of viable plant cells from
cryopreservation. Cells are thawed to about
room temperature and incubated in medium containing a cryoprotective agent and a stabilizer. The cryoprotective agent is removed and the cells successfully incubated and recovered in liquid or semi-
solid growth medium. The invention also relates to the cryopreserved cells and to viable plant cells which have been recovered from long or short term cryopreservation.