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For many years, the main source of technogenic radioactive substances entering the Enisei River were two straightthrough reactors at the mining-chemical complex (MCC). Radioactive substances were dumped into the river through a discharge at the bottom. In 1992 (30 June and 29 September, respectively) these reactors were decommissioned. At present, cooling waters for the system controlling the shielding of a closed-type power reactor, which will continue to operate up to the year 2000, as well as the drain waters from the reactor and radiochemical production are being discharged into the river. The discharge level is 15 times greater than in 1991, and at present the discharge is made after the holding basin (to decrease the radioactivity of the short-lived nuclides) through a water drain located at a new location several kilometers downstream. Once again, the discharge is deep and dispersed [1]. In the present paper, which is a continuation of [2], a comparative analysis is given of the present radiation environment on the Enisei River before and after the decommissioning of the straight-through reactors.Contamination of Water. After the straight-through reactors were shutdown, the concentration of the short-lived radionuclides in the waste waters dropped sharply and according to measurements performed in 1993 and 1994 it amounted to the following (in Bq/liter) in the zone where mixing with the river waters occurred: 24Na 3-4, 51Cr 0.3-1, 76As 0.4-0.8, 239Np 0.4, which is 100-I000 times lower than the concentration of the same radionuclides before 1992. The content of the long-lived radionuclides below the discharge at the MCC in 1994 did not exceed hundredths of a Bq/liter [2].In the fall of 1994, in the region of mixing of the waste and river waters the exposure dose rate of v-radiation at a depth of 1 m from the surface, as measured with a submersible radiometer, was equal to 100/~R/h, i.e., 30 times lower than in 1991.It should be noted that up to 80% of the activity of the dose-forming long-lived nuclides, such as 6~ and 137Cs, starting from the mixing zone, is carried along the Enisei River in a sorbed state on suspensions.The content of these nuclides in the water is influenced by, besides the waste waters, the secondary contamination of the water due to the transfer of nuclides into the water from contamined bottom deposits and the flood-plain sections of the river. For this reason, after the discharges decrease, the concentration of these nuclides in the water will decrease over a long period of time. At present the ('~ and t37Cs concentrations below the town of Atamanovo has practically not decreased at all.A forecast made with the aid of the model in [3] shows that the maximum concentration of 137Cs and other long-lived nuclides in the water from secondary contamination does not exceed 0.005 Bq/liter. Contamination of Bottom Deposits. Discharges, over a period of many years, of long-lived radionuclides have strongly contaminated the bottom deposits and flood-plain sections of the river. Stopping of the...

Ethylene is known to influence the cell cycle (CC) via poorly characterized roles whilst nitric oxide (NO) has well-established roles in the animal CC but analogous role(s) have not been reported for plants. As NO and ethylene signaling events often interact we examined their role in CC in cultured cells derived from Arabidopsis thaliana wild-type (Col-0) plants and from ethylene-insensitive mutant ein2-1 plants. Both NO and ethylene were produced mainly during the first 5 days of the sub-cultivation period corresponding to the period of active cell division. However, in ein2-1 cells, ethylene generation was significantly reduced while NO levels were increased. With application of a range of concentrations of the NO donor, sodium nitroprusside (SNP) (between 20 and 500 μM) ethylene production was significantly diminished in Col-0 but unchanged in ein2-1 cells. Flow cytometry assays showed that in Col-0 cells treatments with 5 and 10 μM SNP concentrations led to an increase in S-phase cell number indicating the stimulation of G1/S transition. However, at ≥20 μM SNP CC progression was restrained at G1/S transition. In the mutant ein2-1 strain, the index of S-phase cells was not altered at 5–10 μM SNP but decreased dramatically at higher SNP concentrations. Concomitantly, 5 μM SNP induced transcription of genes encoding CDKA;1 and CYCD3;1 in Col-0 cells whereas transcription of CDKs and CYCs were not significantly altered in ein2-1 cells at any SNP concentrations examined. Hence, it is appears that EIN2 is required for full responses at each SNP concentration. In ein2-1 cells, greater amounts of NO, reactive oxygen species, and the tyrosine-nitrating peroxynitrite radical were detected, possibly indicating NO-dependent post-translational protein modifications which could stop CC. Thus, we suggest that in Arabidopsis cultured cells NO affects CC progression as a concentration-dependent modulator with a dependency on EIN2 for both ethylene production and a NO/ethylene regulatory function.