Main radiation pathways in the landscape of Armenia.

PURPOSE: To investigate sources, accumulation, and vertical migration of radionuclides in Armenia, and their impact on biota. CONCLUSIONS: This review describes the radiation status in the landscape of Armenia and features of the impact of natural and human-generated radiation on human and non-human biotas, according to studies of Armenian scientists carried out since the middle of the last century. The mountain landscape demonstrates the diversity, speciation, and radioresistance of the biota, which arise under radiation exposure in a variable environment. Although the effects of radiation have been described for a long time, some of them require further study. It is important to present the data collected in order to produce a base line for future studies of radiation effects and interactions with other stressors caused by climate change.

[Bimodal changes in germinability of pea seeds under the influence of low doses of gamma-radiation].

Pea seeds (cv. 'Nemchinovskii-85', harvest of 2002, 80%-germination percentage) were exposed to gamma-radiation with doses ranging from 19 cGy to 100 Gy. One week after the irradiation with doses of 19 cGy and 3 Gy. the germination percentage decreased to 58 and 45%, respectively; at doses of 7 and 10 Gy it was 73 and 70% respectively. At greater doses (25, 50, and 100 Gy), germination percentage decreased in proportion. Anomalous changes in seed germination percentage (as a function of irradiation dose) were caused by the redistribution of irradiated seeds between fractions I and II. The measurements of room temperature phosphorescence in air-dry seeds and the phosphorescence of endogenous porphyrines of imbibing seeds showen that the germination decrease after the irradiation with low doses (19 cGy and 3 Gy) was caused by the increase in the number of weak seeds of fraction II, which had high rates of water uptake and suffered from hypoxia under seed coat. Some of these seeds suffocated from hypoxia, and other seeds produced seedlings with morphological defects (such seeds were considered incapable of germination). During storage of seeds irradiated at doses 19 cGy-10 Gy, the recovery of germination percentage (after its initial decrease) was caused by the decrease in seed number in fraction II. The subsequent germination decrease was caused by seed death. The higher was the irradiation dose, the faster were changes in germination percentage during storage of irradiated seeds. Bimodal changes in pea seed germination with the increase of y-irradiation dose has apparently the same origin as the changes in seed germination during accelerated ageing.

[Evaluation of the consequences of stress factors on plant seeds growing in a 30-km zone of Balakovo AES]. / Otsenka posledstvii vliianiia stressovykh faktorov na semena rastenii, proizrastaiushchikh v 30-kilometrovoi zone Balakovskoi AES.

The effect of stress factors (small doses of radiation and maximum temperatures in the econiche of the tested plants (tmax)) as well as aging on pea seeds, both acting independently and in combination, is estimated. Here we evaluate the influence of oxidizing stress on pea seeds in the laboratory (gamma-irradiated with 7 cGy at 0.3-19.1 cGy/h, tmax approximately 30-32 degrees C) and on natural plantain seeds collected in a 30-km zone of NPP (radiation exposure approximately 15 R/h, tmax approximately 38-40 degrees C). We have mathematically modeled CAs frequencies in root seedlings meristeme by invoking an enhancing factor transmitted from cell to cell. It is shown under the stress conditions: 1) CA frequency decreases whereas the fraction of inviable seeds (IS) increases, the dependence of IS on CA frequency being inversed; 2) a stimulation of proliferation of cell was observed; 3) a bystander effect appears; 4) antioxidative status (AOS) of seeds influences on adaptation on the all levels of the organization; 5) IS increases up to 73-80% under the combined effect of radiation and heat stresses.

[The antioxidant status of the seeds in populations of the great plantain (Plantago major L.) growing in an area exposed to the Balakovo Atomic Electric Power Station and to chemical enterprises]. / Antioksidantnyi status semian populiatsii rastenii podorozhnika bol'shogo (Plantago major L.), proizrastaiushchikh v raione deistviia Balakovskoi AES i khimicheskikh predpriiatii.

The results of the determination of radionuclide and chemical (multielement analysis) soil pollution are presented. The data on antioxidant status of plantain (Plantago major L.) in conjunction with the data on radionuclide and chemical pollution are analyzed. The most significant decrease in antioxidant activity of plant seeds was observed in areas situated along the most frequent wind direction in the region in summer 1998. It is suggested that lower antioxidant status is caused by the chronic radionuclide release on the chemically polluted territories.

[Features of action of low doses of gamma-radiation on yeast cells]. / Osobennosti deistviia malykh doz gamma-izlucheniia na drozhzhevye kletki.

Lethal effect of low doses and adaptive response to low doses of prolonged irradiation were investigated in experiments on yeast cells. The phenomenon of hypersensitivity at low dozes was not found in yeast cells at gamma-irradiation. The adaptive response was observed after exposure to low doses of prolonged irradiation, the degree of the reaction depends on a dose rate. The adaptive reaction was kept for some time after the termination of adaptive irradiation then the sensitivity of cells increased even in comparison with unirradiated ones.

[Characteristics of spontaneous mutagenesis in haploid yeast]. / Kharakteristiki spontannogo mutageneza u gaploidnykh drozhzhei.

The dynamics of appearance of spontaneous revertants was studied in haploid strains of Saccharomyces cerevisiae, auxotrophic for adenine or leucine. Mathematic models of this process were used. It was confirmed that in the case of adenine auxotrophs, an increase in the number of revertants, depending on decreasing adenine content, was caused by a change in mutation rate of the ade2 gene. For leucine auxotrophs, a similar phenomenon was determined by an increase in the rate of appearance of Leu+ revertants due to a decrease in size of initial auxotrophic cell colonies. Alteration in leucine content in the medium from 3 to 300 mg/l did not lead to a change in the reversion rate for the leu2 gene. The heterogeneity of revertants detected at different times was described.

Characteristics of spontaneous revertants in haploid yeast.

The appearance dynamics of spontaneous revertants in adenine- or leucine-auxotrophic haploid Saccharomyces cerevisiae strains has been studied using mathematical simulation methods. In the case of adenine auxotrophs an increase in the number of revertants with decreasing metabolite content is found to result mainly from increasing the rate of intragenic suppressor mutations. In the case of leucine auxotrophs revertants result from increasing the appearance of mutants formed at similar rates under different cultivation conditions. In the latter case the appearance of mutant colonies increases with decreasing size of colonies of the initial auxotrophic cells. The last can simulate so-called adaptive mutagenesis. The heterogeneity of revertants appearing in different time periods is described.

On the dependence of spontaneous mutation rates on the functional state of genes.

Spontaneous mutation of some genes was studied in haploid adenine and leucine auxotrophic yeast Saccharomyces. It was shown that a decrease in the amount of adenine (from 500 to 0 mg l-1) or leucine (from 300 to 0.3 mg l-1) in the medium, simultaneously with the transition from repression to derepression of the biosynthesis of these metabolites, resulted in a 15- to 150-fold increase in the reversion rate of genes ade 2 and leu2, respectively, for different strains. At the same time the mutation rate of suppressor genes varied relatively little (up to five-fold), and that of gene lys did not change at all. It was also demonstrated (on gene leu2) that the mutation rate is determined by the composition of the nutrient medium at the time of the S-phase of the cell cycle and it does not depend on the cultivation conditions during the presynthetic period. We discuss the hypothesis that derepressed genes mutate with a significantly higher rate than genes in the repressed state.