Antioxidant status and genotypic tolerance of Ribes in vitro cultures to cryopreservation

Cold tolerance studies are required to improve understanding of how plant tissues survive and regenerate from cryogenic temperatures. Ribes genotypes with different survival responses following cryopreservation were examined to determine the role of oxidative stress and ethylene in cryo-injury. In vitro shoot cultures of Ribes ciliatum (cryo-sensitive) and Ribes nigrum (cryo-tolerant) were analysed for antioxidant status, hydroxyl radicals and ethylene production at different stages of an encapsulation-dehydration cryopreservation protocol. Differential genotypic responses occurred during sucrose-simulated cold acclimation, where tolerance was associated with greater increases in hydroxyl radical activity, antioxidant status, phenolic accumulation, anthocyanin pigmentation, and protein SH group status. Elevated antioxidant levels persisted through recovery in the more tolerant genotype, while no changes in oxidative stress markers were found in shoots recovered from the sensitive genotype. Genotypic differences in the production of the stress hormone ethylene also occurred during recovery, where the cryo-sensitive genotype produced more ethylene than the tolerant species. This study indicates elevated antioxidant status and phenolic accumulation may be determinants of cryogenic stress tolerance and that their manipulation could improve recovery after cryopreservation.