Chromosomal aberrations induced by (12)C6+ ions and 60Co gamma-rays in mouse immature oocytes

The ovaries of Kun-Ming strain mice (3 weeks) were irradiated with different doses of (12)C6+ ion or (60)Co gamma-ray. Chromosomal aberrations were analyzed in metaphase II oocytes at 7 weeks after irradiation. The relative biological effectiveness (RBE) of (12)C6+ ion was calculated with respect to 60Co gamma-ray for the induction of chromosomal aberrations. The (12)C6+ ion and 60Co gamma-ray dose-response relationships for chromosomal aberrations were plotted by linear quadratic models. The data showed that there was a dose-related increase in frequency of chromosomal aberrations in all the treated groups compared to controls. The RBE values for (12)C6+ ions relative to 60Co gamma-rays were 2.49, 2.29, 1.57, 1.42 or 1.32 for the doses of 0.5, 1.0, 2.0, 4.0 or 6.0 Gy, respectively. Moreover, a different distribution of the various types of aberrations has been found for (12)C6+ ion and 60Co gamma-ray irradiations. The dose-response relationships for (12)C6+ ion and 60Co gamma-ray exhibited positive correlations. The results from the present study may be helpful for assessing genetic damage following exposure of immature oocytes to ionizing radiation.     

Induction of cytogenetic adaptive response in spermatogonia and spermatocytes by pre-exposure of mouse testis to low-dose (12)C(6+) ions

To investigate the effects of pre-exposure of mouse testis to low-dose (12)C(6+) ions on cytogenetics of spermatogonia and spermatocytes induced by subsequent high-dose irradiation, the testes of outbred Kun-Ming strain mice were irradiated with 0.05Gy of (12)C(6+) ions as the pre-exposure dose, and then irradiated with 2Gy as challenging dose at 4h after per-exposure. Poly(ADP-ribose) polymerase (PARPs) activity and PARP-1 protein expression were respectively measured by using the enzymatic and Western blot assays at 4h after irradiation; chromosomal aberrations in spermatogonia and spermatocytes were analyzed by the air-drying method at 8h after irradiation. The results showed that there was a significant increase in the frequency of chromosomal aberrations and significant reductions of PARP activity and PARP-1 expression level in the mouse testes irradiated with 2Gy of (12)C(6+) ions. However, pre-exposure of mouse testes to a low dose of (12)C(6+) ions significantly increased PARPs activity and PARP-1 expression and alleviated the harmful effects induced by a subsequent high-dose irradiation. PARP activity inhibitor 3-aminobenzamide (3-AB) treatment blocked the effects of PARP-1 on cytogenetic adaptive response induced by low-dose (12)C(6+) ion irradiation. The data suggest that pre-exposure of testes to a low dose of heavy ions can induce cytogenetic adaptive response to subsequent high-dose irradiation. The increase of PARP-1 protein induced by the low-dose ionizing irradiation may be involved in the mechanism of these observations.     

Adaptive response of human lymphocytes for the repair of radon-induced chromosomal damage

In human lymphocytes low doses of X-rays can decrease the number of chromatid deletions induced by subsequent high doses of sparsely ionizing X-rays. Because of the concern with the carcinogenic effects of low doses of -particles from radon in homes, experiments were carried out to see if low doses of X-rays could also decrease the yield of chromosomal aberrations induced by subsequent exposure to radon. Human peripheral blood lymphocytes were irradiated with low doses of X-rays (2 cGy) at 48 h of culture, exposed to radon at 72 h of culture, and analyzed for the presence of chromatid aberrations at subsequent intervals. The frequency of chromatid aberrations induced by radon alone increased with time after exposure, indicating exaggerated differences in the stage sensitivity of cell cycle stages to high-LET radiation. Furthermore, the numbers of aberrations per cell did not follow a Poisson distribution but were over dispersed, as might be expected since high-LET radiations have a high relative biological effectiveness compared with low-LET radiations. Nevertheless, lymphocytes exposed to 2 cGy of X-rays before radon exposure contained approximately one-half the number of chromatid deletions compared with lymphocytes treated with radon alone and analzed at the same time. Thus, the putative chromosomal repair mechanism induced by low doses of sparsely ionizing radiation is also effective in reducing chromosomal aberrations induced by radon, which hitherto had been thought to be relatively independent of repair processes.     

Cytological characterization of Chinese hamster ovary X-ray-sensitive mutant cells xrs 5 and xrs 6. I. Induction of chromosomal aberrations by X-irradiation and its modulation with 3-aminobenzamide and caffeine

We have studied two X-ray-sensitive mutants xrs 5 and xrs 6 (derived from the CHO-K1 cell line), known to be defective in repair of double-strand breaks, for cell killing and frequency of the chromosomal aberrations induced by X-irradiation. The survival experiments showed that mutants are very sensitive to X-rays, the D0, for the wild-type CHO-K1 was 6-fold higher than D0 value for the mutants. The modal number of chromosomes (2 n = 23) and the frequency of spontaneously occurring chromosomal aberrations were similar in all 3 cell lines. X-Irradiation of synchronized mutant cells in G1-phase significantly induced both chromosome- and chromatid-type of aberrations. The frequency of aberrations in xrs mutants was 12-fold more than in the wild-type CHO-K1 cells. X-Irradiation of G2-phase cells also yielded higher frequency of aberrations in the mutants, namely 7-8-fold in xrs 5 and about 3.5-fold in xrs 6 compared to the wild-type CHO-K1 cells. There was a good correlation between relative inability to repair of DNA double-strand breaks and induction of aberrations. The effect of 3-aminobenzamide (3AB), an inhibitor of poly(ADP-ribose) synthetase on the frequency of X-ray-induced chromosomal aberrations in these 3 cell lines was also studied. 3AB potentiated the frequency of aberrations in G1 and G2 in all the cell types. In the mutants, 3AB had a potentiating effect on the frequency of X-ray-induced chromosomal aberrations only at low doses. X-Ray-induced G2 arrest and its release by caffeine was studied by cytofluorometric methods. The relative speed with which irradiated S-G2 cells progressed into mitosis in the presence of caffeine was CHO-K1 greater than xrs 5 greater than xrs 6. Caffeine could counteract G2 delay induced by X-rays in CHO-K1 and xrs 5 but not in xrs 6. Large differences in potentiation by caffeine were observed among these cells subjected to X-rays and caffeine post-treatment for different durations. These responses and possible reasons for the increased radiosensitivity of xrs mutants are discussed and compared to ataxia telangiectasia (A-T) cells and a radiosensitive mutant mouse lymphoma cell line.     

Cytogenetical characterization of Chinese hamster ovary X-ray-sensitive mutant cells xrs 5 and xrs 6. III. Induction of cell killing, chromosomal aberrations and sister-chromatid exchanges by bleomycin, mono- and bi-functional alkylating agents

Two X-ray-sensitive mutants of CHO-K1 cells, xrs 5 and xrs 6, were characterised with regard to their responses to genotoxic chemicals, namely bleomycin, MMS, EMS, MMC and DEB for induction of cell killing, chromosomal aberrations and SCEs at different stages of the cell cycle. In addition, induction of mutations at the HPRT and Na+/K+ ATPase (Oua) loci was evaluated after treatment with X-rays and MMS. Xrs 5 and xrs 6 cells were more sensitive than wild-type CHO-K1 to the cell killing effect of bleomycin (3 and 13 times respectively) and for induction of chromosomal aberrations (3 and 4.5 times). In these mutants a higher sensitivity for induction of chromosomal aberrations to MMS, EMS, MMC and DEB was observed (1.5-3.5 times). The mutants also showed increased sensitivity for cell killing effects of mono- and bi-functional alkylating agents (1.7-2.5 times). The high cell killing effect of X-rays in these mutants was accompanied by a slight increase in the frequency of HPRT mutation. The xrs mutants were also more sensitive to MMS for the increased frequency of TGr and Ouar mutants when compared to wild-type CHO-K1 cells. Though bleomycin is known to be a poor inducer of SCEs, an increase in the frequency of SCEs in xrs 6 cells (doubling at 1.2 micrograms/ml) was found in comparison to no significant increase in xrs 5 or CHO-K1 cells. The induced frequency of SCEs in all cell types increased in a similar way after the treatment with mono- or bi-functional alkylating agents. MMS treatment of G2-phase cells yielded a higher frequency of chromatid breaks in the mutants in a dose-dependent manner compared to no effect in wild-type CHO-K1 cells. Treatment of synchronised mutant cells at G1 stage with bleomycin resulted in both chromosome- and chromatid-type aberrations (similar to the response to X-ray treatment) in contrast to the induction of only chromosome-type aberrations in wild-type CHO-K1 cells. The frequency of chromosomal aberrations chromosome and chromatid types) also increased with MMC treatment in G1 cells of xrs mutants. DEB treatment of G1 cells induced mainly chromatid-type aberrations in all cell types. The possible reasons for the increased sensitivity of xrs mutants to the chemical mutagens studied are discussed and the results are compared to cells derived from radiosensitive ataxia telangiectasia patients.     

Mentha piperita (Linn.) leaf extract provides protection against radiation induced chromosomal damage in bone marrow of mice

Oral administration of M. piperita (1 g/kg body weight/day) before exposure to gamma radiation was found to be effective in protecting against the chromosomal damage in bone marrow of Swiss albino mice. Animals exposed to 8 Gy gamma radiation showed chromosomal aberrations in the form of chromatid breaks, chromosome breaks, centric rings, dicentrics, exchanges and acentric fragments. There was a significant increase in the frequency of aberrant cells at 6 hr after irradiation. Maximum aberrant cells were observed at 12 hr post-irradiation autopsy time. Further, the frequency of aberrant cells showed decline at late post-irradiation autopsy time. However, in the animals pretreated with Mentha extract, there was a significant decrease in the frequency of aberrant cells as compared to the irradiated control. Also significant increase in percentage of chromatid breaks, chromosome breaks, centric rings, dicentrics, exchanges, acentric fragments, total aberrations and aberrations/damaged cell was observed at 12 hr post-irradiation autopsy time in control animals, whereas Mentha pretreated irradiated animals showed a significant decrease in percentage of such aberrations. A significant decrease in GSH content and increase in LPO level was observed in control animals, whereas Mentha pretreated irradiated animals exhibited a significant increase in GSH content and decrease in LPO level but the values remained below the normal. The radioprotective effect of Mentha was also demonstrated by determining the LD(50/30) values (DRF = 1.78). The results from the present study suggest that Mentha pretreatment provides protection against radiation induced chromosomal damage in bone marrow of Swiss albino mice.     

mFISH analysis of chromosomal damage in bone marrow cells collected from CBA/CaJ mice following whole body exposure to heavy ions (<Superscript>56</Superscript>Fe ions)

To date, there is scant information on in vivo induction of chromosomal damage by heavy ions found in space (i.e. ⁵⁶Fe ions). For radiation-induced response to be useful for risk assessment, it must be established in in vivo systems especially in cells that are known to be at risk for health problems associated with radiation exposure (such as hematopoietic cells, the known target tissue for radiation-induced leukemia). In this study, the whole genome multicolor fluorescence in situ hybridization (mFISH) technique was used to examine the in vivo induction of chromosomal damage in hematopoietic tissues, i.e. bone marrow cells. These cells were collected from CBA/CaJ mice at day 7 following whole-body exposure to different doses of 1 GeV/amu ⁵⁶Fe ions (0, 0.1, 0.5 and 1.0 Gy) or ¹³⁷Cs γ rays as the reference radiation (0, 0.5, 1.0 and 3.0 Gy, at the dose rate of 0.72 Gy/min using a GammaCell40). These radiation doses were the average total-body doses. For each radiation type, there were four mice per dose. Several types of aberrations in bone marrow cells collected from mice exposed to either type of radiation were found. These were exchanges and breaks (both chromatid- and chromosome-types). Chromosomal exchanges included translocations (Robertsonian or centric fusion, reciprocal and incomplete types), and dicentrics. No evidence of a non-random involvement of specific chromosomes in any type of aberrations observed in mice exposed to ⁵⁶Fe ions or ¹³⁷Cs γ rays was found. At the radiation dose range used in our in vivo study, the majority of exchanges were simple. Complex exchanges were detected in bone marrow cells collected from mice exposed to 1 Gy of ⁵⁶Fe ions or 3 Gy of ¹³⁷Cs γ rays only, but their frequencies were low. Overall, our in vivo data indicate that the frequency of complex chromosome exchanges was not significantly different between bone marrow cells collected from mice exposed to ⁵⁶Fe ions or ¹³⁷Cs γ rays. Each type of radiation induced significant dose-dependent increases (ANOVA, P < 0.01) in the frequencies of chromosomal damage, including the numbers of abnormal cells. Based upon the linear-terms of dose-response curves, ⁵⁶Fe ions were 1.6 (all types of exchanges), 4.3 (abnormal cells) and 4.2 (breaks, both chromatid- and chromosome-types) times more effective than ¹³⁷Cs γ rays in inducing chromosomal damage.     

Inhibition of ADP-ribosylation increases X-ray-induced chromosomal damage in mouse testis and bone-marrow cells in vivo

The effect of 3-aminobenzamide (3AB) treatment on chromosomal radiosensitivity of mouse spermatogonial stem cells and bone-marrow cells was studied using various doses of X-rays. The results show that 3AB increases the induction of reciprocal translocations in slowly cycling spermatogonia as well as the frequency of chromosomal aberrations in actively dividing bone-marrow cells. The experiments indicate that both types of tissue are suitable to study the ability of inhibitors of ADP-ribosylation to modulate chromosome-breaking damage induced by ionizing radiation in vivo.     

Cytogenetic adaptive response induced by pre-exposure in human lymphocytes and marrow cells of mice

The frequencies of chromosomal aberrations bith in human lymphocytes and in mouse marrow cells exposed to low-level radiation were higher than in their unexposed controls. However, the frequencies of chromosomal aberrations in two kinds of cells pre-exposed to low-level radiation induced by a subsequent high dose of X-rays or γ-rays were lower than those of the groups only exposed to high-level radiation. This implies that adaptive responses for cytogenetic indicators might be induced by pre-exposure to low-level radiation. The results also show the existence of possible variations between individual lymphocytes.     

Mutations and chromosomal aberrations in hMTH1-transfected and non-transfected TK6 cells after exposure to low dose rates of gamma radiation

The aim of the present study was to analyse the dose rate effect of gamma radiation at the level of mutations, chromosomal aberrations, and cell growth in TK6 cells with normal as well as reduced levels of hMTH1 protein. TK6 cells were exposed to gamma radiation at dose rates ranging from 1.4 to 30.0 mGy/h (chronic exposure) as well as 24 Gy/h (acute exposure). Cell growth, frequency of thymidine kinase mutants, and of chromosomal aberrations in painted chromosomes 2, 8, and 14 were analysed. A decline in cell growth and an increase in unstable-type chromosomal aberrations with increasing dose rate were observed in both cell lines. A dose rate effect was not seen on mutations or stable-type chromosomal aberrations in any of the two cell lines. Reduction in the hMTH1 protein does not influence the sensitivity of TK6 cells to gamma radiation. This result fits well with data of others generated with the same cell line.     

Assessment of genome damage in occupational exposure to ionising radiation and ultrasound

The mutagenic effects of low doses of radiation on occupationally exposed subjects were studied on lymphocyte culture using two methods: analysis of structural chromosome aberrations and micronucleus assay. The results obtained in subjects exposed to ionising radiation alone were compared to those exposed to both ionising radiation and ultrasound. A correlation between the total number of chromosome aberrations and distribution of micronuclei in the genome of somatic cells show higher deviation in the group exposed to X-ray and ultrasound than in the group exposed to X-rays alone. The degree of genome damage in occupational exposure to X-rays and ultrasound were discussed.     

Chromosomes lacking telomeres are present in the progeny of human lymphocytes exposed to heavy ions

High-charge and energy (HZE) nuclei represent one of the main health risks for human space exploration, yet little is known about the mechanisms responsible for the high biological effectiveness of these particles. We have used in situ hybridization probes for cross-species multicolor banding (RxFISH) in combination with telomere detection to compare yields of different types of chromosomal aberrations in the progeny of human peripheral blood lymphocytes exposed to either high-energy iron ions or gamma rays. Terminal deletions showed the greatest relative variation, with many more of these types of aberrations induced after exposure to accelerated iron ions (energy 1 GeV/nucleon) compared with the same dose of gamma rays. We found that truncated chromosomes without telomeres could be transmitted for at least three cell cycles after exposure and represented about 10% of all aberrations observed in the progeny of cells exposed to iron ions. On the other hand, the fraction of cells carrying stable, transmissible chromosomal aberrations was similar in the progeny of cells exposed to the same dose of densely or sparsely ionizing radiation. The results demonstrate that unrejoined chromosome breaks are an important component of aberration spectra produced by the exposure to HZE nuclei. This finding may well be related to the ability of such energetic particles to produce untoward late effects in irradiated organisms.     

Analysis of chromosomal aberration frequencies in the peripheral blood lymphocytes of smokers exposed to uranyl compounds

One hundred fifteen smokers working in a nuclear fuel manufacturing facility were analysed for various types of chromosomal aberrations. They experienced exposure for a period of 1-25 years. Their age ranges from 23 to 52 years. A total of 94 smokers and 118 non-smokers who were not exposed to uranyl compounds or to any other known mutagens and belong to the same age group formed the control subjects. The results showed that there is a significant increase in the frequency of chromosomal aberrations in the exposed smokers when compared to the control smokers. In the control group, the smokers showed a high frequency of chromosomal aberrations when compared to non-smokers suggesting clastogenic effect of smoking. Chromosomal aberrations observed in the exposed smokers could be due to the cumulative effect of both smoking and exposure to uranyl compounds.     

The bystander effect-induced formation of micronucleated cells is inhibited by antioxidants, but the parallel induction of apoptosis and loss of viability are not affected

X-rays induce various DNA damages including strand breaks that lead to formation of micronuclei and chromosomal aberrations as well as increased number of apoptotic cells. Similar effects appear when non-irradiated cells are treated with medium collected from cultures of irradiated cells (irradiation conditioned medium - ICM). This phenomenon was termed "bystander effect". A number of studies suggest that bystander effect appears to be associated with up-regulation of oxidative metabolism. We thus compared the effects of antioxidant Vitamins C and E on the frequency of micronuclei and apoptotic cells in both directly irradiated cell cultures and in cultures exposed to ICM. Addition of Vitamins C or E (1-40 microg/ml) to culture medium after exposure to radiation or ICM reduced the frequency of micronuclei in a concentration-dependent manner. These vitamins had no effect on cell viability, clonogenic survival or the frequency of apoptotic cells under both conditions tested. These results show that the bystander effect causes micronucleation in addition to other known effects and suggest that the factors causing micronucleation by X-irradiation, oxidative DNA damage and incomplete repair, are regulated by apoptosis-independent pathways.     

Radioprotective effect of rhizome extract of Zingiber montanum in Rattus norvegicus

The present study aims at determining the ability of 60% ethanol extract of the rhizome of Zingiber montanum (J. K?nig) A. Dietr. to protect bone marrow cells in vivo from radiation-induced chromosomal aberrations. Albino rats (Rattus norvegicus, 2n = 42) were used to carry out investigations on the radioprotective properties of Z. montanum. Acute toxicity of the extract was determined, and a suitable injectable dose was selected for intra-peritoneal administration. The LD(50) of the extract calculated for 72 h was 2.9 g/kg, and the calculated LD(10) dose was 1.7 g/kg. The calculated maximum tolerated dose of the rhizome extract was 1.3 g/kg. Rats were divided into 12 groups (with or without the administration of extract) and exposed to different radiation doses from 1 to 5 Gy. Whole-body irradiation of rats showed a significant dose-dependent increase in different types of chromosomal aberrations. The most common chromosomal aberrations were breaks, fragments, gaps, rings, endoreduplications and dicentric chromosomes. Ethanol extract of rhizome at a dose of 0.5 g/kg did not show any significant increase in chromosomal aberrations in unirradiated animals as compared to that of the control group. Intra-peritoneal administration of the extract at a dose of 0.5 g/kg considerably reduced the frequency of the aberrations stated above in irradiated animals with DMF value of 1.36 at 1 to 5 Gy dose range of gamma radiation. The incidence of micronucleated polychromatic erythrocytes and micronucleated normochromatic erythrocytes due to the radiation exposure was considerably reduced in extract-treated groups of animals with DMFs 1.34 and 1.17, respectively, as compared to that of the extract-untreated groups. Our results suggest that rhizome extract of Z. montanum may have a potential in protecting normal hematopoietic cells from radiation-induced damage.     

mBAND analysis of chromosomal aberrations in human epithelial cells exposed to low- and high-LET radiation

Energetic heavy ions pose a potential health risk to astronauts who have participated in extended space missions. High-LET radiation is much more effective than low-LET radiation in the induction of biological effects, including cell inactivation, genetic mutations, cataracts and cancer. Most of these biological end points are closely correlated with chromosomal damage, which can be used as a biomarker for radiation damage. Multicolor banding in situ hybridization (mBAND) has proven to be highly useful for the study of intrachromosomal aberrations, which have been suggested as a biomarker of exposure to high-LET radiation. To investigate biological signatures of radiation quality and the complexity of intrachromosomal aberrations, we exposed human epithelial cells in vitro to (137)Cs gamma rays or iron ions (600 MeV/nucleon) and collected chromosomes using a premature chromosome condensation technique. Aberrations in chromosome 3 were analyzed using mBAND probes. The results of our study confirmed the observation of a higher incidence of inversions for high-LET radiation. However, detailed analysis of the inversion type revealed that both iron ions and gamma rays induced a low incidence of simple inversions. Half of the inversions observed in the low-LET-irradiated samples were accompanied by other types of intrachromosome aberrations, but few inversions were accompanied by interchromosome aberrations. In contrast, iron ions induced a significant fraction of inversions that involved complex rearrangements of both inter- and intrachromosome exchanges.     

The correlation between the frequency of micronuclei and specific chromosome aberrations in human lymphocytes exposed to microwave radiation in vitro.

Human whole-blood samples were exposed to continuous microwave radiation, frequency 7.7 GHz, power density 0.5, 10 and 30 mW/cm2 for 10, 30 and 60 min. A correlation between specific chromosomal aberrations and the incidence of micronuclei after in vitro exposure was observed. In all experimental conditions, the frequency of all types of chromosomal aberrations was significantly higher than in the control samples. In the irradiated samples the presence of dicentric and ring chromosomes was established. The incidence of micronuclei was also higher in the exposed samples. The results of the structural chromosome aberration test and of the micronucleus test were comparatively analyzed. The values obtained showed a positive correlation between micronuclei and specific chromosomal aberrations (acentric fragments and dicentric chromosomes). The results of the study indicate that microwave radiation causes changes in the genome of somatic human cells and that the applied tests are equally sensitive for the detection of the genotoxicity of microwaves.     

Effect of high-frequency electromagnetic fields with a wide range of SARs on chromosomal aberrations in murine m5S cells

To investigate the induction of chromosomal aberrations in mouse m5S cells after exposure to high-frequency electromagnetic fields (HFEMFs) at 2.45 GHz, cells were exposed for 2 h at average specific absorption rates (SARs) of 5, 10, 20, 50 and 100 W/kg with continuous wave-form (CW), or at a mean SAR of 100 W/kg (with a maximum of 900 W/kg) with pulse wave-form (PW). The effects of HFEMF exposure were compared with those in sham-exposed controls and with mitomycin C (MMC) or X-ray treatment as positive controls. We examined all structural, chromatid-type and chromosome-type changes after HFEMF exposures and treatments with MMC and X-rays. No significant differences were observed following exposure to HFEMFs at SARs from 5 to 100 W/kg CW and at a mean SAR of 100 W/kg PW (a maximum SAR of 900 W/kg) compared with sham-exposed controls, whereas treatments with MMC and X-rays increased the frequency of chromatid-type and chromosome-type aberrations. In summary, HFEMF exposures at 2.45 GHz for 2 h with up to 100 W/kg SAR CW and an average 100 W/kg PW (a maximum SAR of 900 W/kg) do not induce chromosomal aberrations in m5S cells. Furthermore, there was no difference between exposures to CW and PW HFEMFs.     

Cytogenetic analysis in lymphocytes from radiation workers exposed to low level of ionizing radiation in radiotherapy,CT-scan and angiocardiography units

Ionizing radiation is known as a classical mutagen capable of inducing various kinds of stable and unstable chromosomal aberrations. The percentage of cells with chromosomal aberrations was analyzed in peripheral blood lymphocytes of occupationally exposed workers in radiotherapy, CT-scan, angiography and healthy controls. The incidence of all types of aberrations (gap, acentric fragment, dicentric and ring) in exposed subjects were higher than those observed in healthy controls (P = 0.0001). However, the frequency of aberrant cells with dicentric and ring chromosome in exposed subjects were not significantly different from those in controls. To see whether there is a significant difference in the incidence of chromosomal aberrations among three groups, they were compared for all types of observed aberrations. No significant difference was found between radiotherapy and CT-scan groups (P = 0.838). The percentage of aberrant cells observed, for angiography groups were significantly higher than radiotherapy (P = 0.0001) and CT-scan (P = 0.0001) group. Taken together these data suggest that the cumulative effects of low level chronic exposure to ionizing radiation is higher for those who occupationally exposed in angiography.     

Evaluation of cytological effects of Zn2+ in relation to germination and root growth of Nigella sativa L. and Triticum aestivum L

The effects of different treatments with zinc sulfate (Zn(2+)) on the cytology and growth of Nigella sativa and Triticum aestivum were investigated. Five concentrations of zinc sulfate ranging from 5 to 25mg/l were applied for 6, 12, 18, and 24h. The treatments reduced the germination percentages of N. sativa seeds and T. aestivum grains and inhibited the root growth of both plants. Concentrations higher than 25mg/l of Zn(2+) applied for 24h were toxic for both plants. The non-lethal concentrations of Zn(2+) showed an inhibitory effect on cell division in root tips of both plants and caused a decrease in their mitotic index values. The reduction in MI in root tips of T. aestivum was more evident than that of N. sativa. All treatments changed the frequency of mitotic phases as compared with the control values. The total percentage of abnormalities in N. saliva was more than that in T. aestivum. Zn(2+) treatments produced a number of mitotic abnormalities in dividing cells in root tips of both plants resulting from its action on the spindle apparatus such as C-metaphases, lagging chromosomes and multipolar anaphases and telophases. Also, Zn(2+) induced vacuolated nuclei and irregular prophases. The induction of chromosomal stickiness and chromosomal aberrations such as bridges and breaks indicates its action on the chromosome. These abnormalities (chromosome breaks and chromosomal bridges at ana-telophases) indicate true clastogenic potential of the ions tested.