[Quantitative estimation of the recovery parameters of yeast cells irradiated in the presence of cysteamine].

Study of the postirradiation recovery parameters of diploid yeast cells showed that the irreversible component of radiation damage was identical after the cell exposure in the presence and absence of cysteamine. On this basis, it is concluded that the radioprotector equally reduced the number of both irreversible and repairable primary radiation damages. Application of the mathematical model of recovery processes to the results obtained allowed us to draw a conclusion that the probability of cell recovery from the radiation damage per time unit was also identical after cell exposure in the presence and absence of cysteamine.

[Radiobiological effects irradiated by fast (0.85 meV) neutrons in yeast cells Saccharomyces cerevisae].

Radiobiological effects of homozygous Saccharomyces cerevisae strains of different ploidy from haploid to hexaploid were studied. Radiation (gamma-radiation of 60Co and fast 0.85 MeV neutrons) inactivation showed the minimum of resistance of haploid strain, the maximum of resistance of diploid strain and a decrease of resistance with further increase genome ploidy. All studied strains (except haploid) have the same capability to recovery in non-nutrient media during incubation at postradiation period by gamma-radiation and fast neutrons damage. Also it was found that values relative biological effectiveness (RBE) of fast neutrons for lethality are 2.6-2.7 and is independents from ploidy (2 and higher).

[Some effects of radiation hormesis for bacterial and yeast cells]. / Nekotorye éffekty radiatsionnogo gormezisa bakterial'nykh i drozhzhevykh kletok.

A comparative study of chronic and acute action of ionizing radiation on the processes of aging and dying off of bacterial and yeast cells was carried out. It was ascertained that chronic action of ionizing radiation, 2-10,000 times exceeded the natural background, resulted in slowing down of aging and dying off of both pro- and eukaryotic cells. A single acute irradiation of yeast also resulted in the retardation of dying off of the yeast cells surviving after irradiation. The data is presented demonstrating a great increase in the survival of yeast cells under their repeated irradiation after recovery from potentially lethal radiation.

[Comparative study of RBE of densely ionizing radiation for various types of cell death in yeast]. / Sravnitel'noe izuchenie OBE plotnoioniziruiushchego izlucheniia dlia razlichnykh form gibeli drozhzhevykh kletok.

A comparative study of the relative biological effectiveness (RBE) of alpha-particles 249Pu for reproductive and interphase forms of killing of haploid and diploid yeast cells of wild-type and their radiosensitive mutants has been carried out. The correlation between the RBE of alpha-particles and cell repair capacity was confirmed for reproductive death: it was the highest for diploid cells, smaller for haploid cells and the smallest for their radiosensitive mutants. To achieve the interphase cell killing much higher irradiation doses were used after which cells were incapable of liquid-holding recovery during the storing of exposed cells in non-nutrient media at 30 degrees C. The RBE values for this form of killing were significantly lower in comparison with reproductive death. These data are an additional argument supporting the point of view that the RBE of densely ionizing radiation is determined not merely by physical processes of energy absorption as it is traditionally believed but also by ability of cells to recover from DNA damages inflicted by ionizing radiation.

[Rapid recovery in diploid yeast cells irradiated sequentially with fast electrons and alpha particles]. / Issledovanie bystrogo vosstanovleniia u diploidnykh drozhzhevykh kletok, obluchennykh posledovatel'no bystrymi élektronami i al'fa-chastitsami.

In the present work, fast repair after combined irradiation by fast electrons and alpha particles was studied in diploid yeast cells Saccharomyces cerevisiae of wild-type XS 800 and its radiosensitive mutant XS 1898. It was shown, that the fast repair significantly contribute to detected survival of the wild-type cells, while this repair is absent in XS 1898 mutant cells. An efficiency of the fast repair under combined irradiation (electrons + alpha particles), assessed on DMF of alpha particles, is lower, than that under irradiation by electrons and alpha particles separately.

[The effects of the simultaneous combined irradiation of diploid yeast cells of different genotypes using radiation with different LETs]. / Issledovanie éffektov odnovremennogo kombinirovannogo oblucheniia diploidnykh drozhzhevykh kletok razlichnogo genotipa izlucheniiami s razlichnoi LPE.

Effects of simultaneous irradiation of diploid yeast cells with various genotypes with alpha-particles, gamma-rays or fast electrons were studied. When contribution of sparsely ionizing radiation to the overall dose is small (up to 25%) antagonism was observed, while at the 95% contribution there seems to be a tendency towards synergistic effect; at 50% contribution the results of the simultaneous combined irradiation do not contradict hypothesis on independent effect of radiation with different LET, which also implies a change in the RBE of simultaneous irradiation.

[Fast repair in diploid yeast cells after combined exposure to ionizing radiation with different LET]. / Issledovanie bystrogo vosstanovleniia u diploidnykh drozhzhevykh kletok posle kombinirovannogo vozdeistviia ioniziruiushchikh izluchenii s razlichnymi LPE.

Fast repair in diploid yeast cells Saccharomyces cerevisiae XS800 exposed to the combined irradiation (alpha-particles + high-velocity electrons) was studied. It has been shown that fast repair was significantly more effective after combined irradiation with high doses than after exposure to high-velocity electrons or alpha-particles alone. The regions of radioresistance in the cell survival curves after combined irradiation can be explained by fast post-irradiation repair.

Contribution of a photoreactivable component to the oxygen effect observed in certain rad mutants of Saccharomyces cerevisiae after exposure to high energy electrons.

It is shown that a fraction of damage induced by high energy electrons (25 MeV) in certain rad mutants of the yeast Saccharomyces cerevisiae can be photoreactivated. The photoreactivable damage contributes to the lethal effect of this type of irradiation and modifies the oxygen effect. Using photoreactivating light or nigrosin, the amount of photoreactivable damage is reduced and the oxygen enhancement ratio (OER) for yeast mutants increases approximately to the OER found in wild-type cells.

Rbe of densely ionizing radiation for wild-type and radiosensitive mutants of yeast.

Survival curves were obtained for haploid and diploid yeasts, Saccharomyces cerevisiae, of wild-type strains and radiosensitive mutants exposed to gamma-rays and alpha-particles. A correlation between the values of the relative biological effectiveness (RBE) of high-LET radiation and cell-repair capacity was found. The difference in radiosensitivities of the wild-type diploid strain and homozygous rad mutants incapable of recovery was significantly higher after low-LET radiation than after high-LET radiation. Possible reasons for the observed radiation responses to low- and high-LET exposure of yeast cells with various genotype are discussed.

[Post-radiation recovery and the ploidy factor]. / Postradiatsionnoe vosstanovlenie i faktor ploidnosti

Radiobiologicae effects on extensively homozygous Sacharomyces cerevisiae strains of different ploidy from haploid to hexaploid (developed by W. Laskovski) were studied. Radiation (gamma-rays of 60Co) inactivation studies showed a minimum of resistance of haploid strains, a maximum of resistance of diploid or triploid strains and a decrease of resistance with further increasing genome number. The explanation of such dependence of radiosensitivity on ploidy is usually due to the increase of dominant lethal damages and the corresponding decrease of recessive lethal damages with the increase of ploidy. All studied strains (except haploids) were capable of recovery of radiation damages after their storage in non-nutrient media during postradiation period. Since haploids are inactivated almost exclusively by recessive lethal damages, one may suppose that reversible part of radiation damages is due to dominant lethal damages. Then an irreversible part of radiation injury must decrease with the increase of ploidy. Indeed, in studied strains an irreversible component of radiation injury was significantly reduced with the increasing genome number. Any correlation of the probability of recovery from the primary damages with ploidy was not discovered.