Cryopreservation of Quercus robur L. Embryogenic Calli

Embryogenic calli of pedunculate oak (Quercus robur L.) were cryopreserved using direct immersion in liquid nitrogen. The pretreatment consisted of culture on a solid medium with increasing sucrose concentrations (0.25 M for 1 day, 0.5 M for 1 day, 0.75 M for 2 days, and 1.0 M for 3 days), followed by air desiccation of embryogenic calli to 17.3% (fresh weight basis). This method of cryoprotection was compared to a liquid cryoprotection treatment using high concentrations of sucrose solutions, followed by glycerol solutions. Regrowth of frozen tissue pretreated on a solid medium was significantly higher than those pretreated in the liquid solutions (Fig. 2).