CRYOPRESERVATION AND SOME CHARACTERISTICS OF DIOSCOREA-DELTOIDEA CELL-CULTURES IN THE VITAMIN-FREE MEDIUM

The extermal cryopreservation procedure for Dioscorea deltoidea Wall. suspension cell cultures is briefly described, and the main causes of cell injury are discussed. The effect of long-term culturing in the vitamin-free medium on cell freezing tolerance, ploidy, aggregation level, and growth rate were studied in two D. deltoidea strains: DM-0.5 and DM-8. The ploidy distributions within the cell populations were affected by vitamin deficiency. As a result, the high-ploidy cells prevailed in the DM-0.5 strain and haploid cells were predominant in the DM-8 strain. The level of cell aggregation declined in the DM-8 strain. The cultures retained both high viability and the capacity to actively grow. However, after programmed freeze-thaw cycles, the survival rates of both strain cells dropped two- to threefold. After returning to a vitamin-containing medium, the initial ploidy distribution and cell cryotolerance were restored High-ploidy and haploid D. deltoidea cells turned out to be poorly resistant to cryodamage, whereas di- and triploid cells were the most resistant. Gene dosage and balance presumably provide for the cell metabolism to alleviate the cryoinjury and for the optimum composition of the plasmalemma, a primary target for cryoinjury.