Cryopreservation of gametophytic thalli of Porphyra yezoensis (Rhodophyceae) by one-step fast cooling

This study investigated the toxicity and effectiveness of various cryoprotectant solutions to develop a cryopreservation technique by one-step fast cooling for gametophytic thalli of Porphyra yezoensis. Dimethyl sulfoxide (DMSO) was not harmful at concentrations up to 30 % after 30 s of immersion. However, an increase in concentration beyond 40 % was seriously detrimental, and the detrimental effect occurred at lower concentrations in the case of 60 s of immersion. Diglycerol was the least harmful among cryoprotectants tested, and its harmful effect was not found at concentrations up to 50 %, even after 60 s of immersion. The thalli loaded into a straw were directly plunged into liquid nitrogen after 30 s of immersion in various cryoprotectant solutions. When 5 % DMSO was added to diglycerol, high survival rates (more than 80 %) were achieved at diglycerol concentrations of 15-25 %, and the maximum survival was 94.6 % at diglycerol concentrations of 20 %. The thawed thalli restarted growth without any difference in comparison with unfrozen thalli.