[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).

[Genetic changes in yeast cells Saccharomyces irradiated by fast neutrons with different dose rate].

No neutron dose rate effects in the wide range of 10(-3) Gy/s to 10(6) Gy/s were observed in yeast diploid cells for induction of mitotic segregation and crossing-over. The RBE values for these effects were determined as doses ratio (Dgamma/D(n)) at maximum effects. The RBE were 2.2-1.9 for neutrons of the reactor BR-10 (E = = 0.85 MeV) and the pulse reactor BARS-6 (E = 1.44 MeV). The RBE values for genetic effects were 1.0 at the equal survival level for neutrons and gamma-rays 60Co.

[Study of dose-rate effects of neutron radiation in a wild-type and a repair-deficient yeasts saccharomyces].

We report here a comparative analysis of RBE for lethality of a single pulse (duration 65 micros) of fast neutron with ultra high dose rates (up to 6 x 10(6) Gy/s) and continuous neutron radiation (3.6 x 10(3) s) of the pulse reactor BARS-6. Three diploid strains, one haploid strain and three diploid repair-deficient strains (rad52-1/rad52-1; rad54/rad54; rad2/rad2) were used. The RBE values (D(0gamma)/1D(0n)) of a single pulse and continuous neutron irradiation were equal (1.7-1.8) with maximum RBE (4.1-3.1) in region of low doses (shoulder region). Haploid cells were found to be more (3 times) sensitive to both gamma-rays and neutrons than the wild type. There was no obvious decrease in the RBE of 1.9 in highly sensitive haploid cells as compared with highly resistant diploid cells. The repair-deficient strains (rad52-1/rad52-1; rad54/rad54) were more (up to 10 fold) sensitive to both neutrons and gamma-rays as compared with their parent line. The RBE values of 1.5-1.7 of neutrons for these mutants (independent by of the mode of irradiation) were found. The repair-deficient mutant rad2/rad2 had similar sensitivity as a wild type and a RBE value was 2.0. We have concluded that biological effectiveness of the neutrons of pulse reactor BARS-6 was independent of the dose-rate, differing up to 10(8) fold. The RBE didn't vary significantly with the capacity of cells to repair DNA damages.

[Biological effectiveness of pulsed and continuous neutron radiation for Saccharomyces yeast cells]. / Biologicheskaia éffektivnost' impul'snogo i nepreryvnogo neitronnogo izlucheniia dlia kletok drozhzhei Saccharomyces.

The article presents the data on biological effectiveness of neutrons generated by the pulsed reactor BARS-6 (dose-rate up to 6 x 10(6) Gy/s) in comparison with fast neutrons of the reactor BR-10 (dose-rate 6.3 x 10(-2) Gy/s). It was shown for yeast cells of a wild type that the RBE values of pulsed neutrons varied insignificantly with a dose (2.0-1.7) white for continuous neutron irradiation clear RBE dependence on the dose was observed. It was also found that the yeast cells had identical capability of postirradiation recovery in non-nutrient medium (LHR) following both gamma-irradiation and neutron exposure irrespective of neutron dose-rate.

[Current problems of neutron radiobiology]. / Aktual'nye problemy radiobiologii neitronov.

A brief review of up-date problems of neutron radiobiology, related to neutron therapy development and setting up of radiation safety standards for neutrons, is present. The main attention is paid to the effects of combined gamma-neutron irradiation, peculiarities of reactor neutrons biological action and new approaches in neutron capture therapy. On the basis of own and literature data the results of cellular and whole-body studies as well as the applicability of biophysical modelling for description and interpretation of experimental data are discussed.

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.

[Photoreactivation in Saccharomyces cerevisiae cells after irradiation with electrons (25 MeV). The role of photoreactivated damage in the manifestation of oxygen effects in radio- and UV-sensitive mutants of Saccharomyces cerevisiae]. / Fotoreaktivatsiia u kletok drozhzhei Saccharomyces cerevisiae posle oblucheniia élektronami (25 MéV). Vliianie fotoreaktiviruemykh povrezhdenii na proiavlenie kislorodnogo éffekta u radio- i UV-chuvstvitel'nykh mutantov drozhzhei Saccharomyces cerevisiae.

Significant photoreactivation was noted in radio- and UV-sensitive rad-mutants of Saccharomyces cerevisiae cells exposed to 25 MeV electrons. In order to make the photoreactivable damage be manifest anoxic conditions of irradiation should be chosen as optimal ones. It was shown that the low oxygen effect was partially associated with the photoreactivable damage involved in the lethal effect of ionizing radiation.