Effect of gamma-ray irradiation on Escherichia coli motility

The effects of ionizing radiation on bacteria are generally evaluated from the dose-dependent survival ratio, which is determined by colony-forming ability and mutation rate. The mutagenic damage to cellular DNA induced by radiation has been extensively investigated; however, the effects of irradiation on the cellular machinery in situ remain unclear. In the present work, we irradiated Escherichia coli cells in liquid media with gamma rays from ⁶⁰Co (in doses up to 8 kGy). The swimming speeds of the cells were measured using a microscope. We found that the swimming speed was unaltered in cells irradiated with a lethal dose of gamma rays. However, the fraction of motile cells decreased in a dose-dependent manner. Similar results were observed when protein synthesis was inhibited by treatment with kanamycin. Evaluation of bacterial swimming speed and the motile fraction after irradiation revealed that some E. coli cells without the potential of cell growth and division remained motile for several hours after irradiation.     

Possible "accelerated striatal aging" induced by 56Fe heavy-particle irradiation: implications for manned space flights.

The present experiments were carried out to determine the effects of energy deposition from energetic iron (56Fe particles, an important component of cosmic rays) on motor behavioral performance and to determine if the observed deficits were caused by alterations in the neostriatum (an important motor control area). Neostriatal function was assessed with two correlated parameters, i.e., motor behavioral performance (wire suspension task), and oxotremorine-enhanced K(+)-evoked release of dopamine from perifused striatal slices. Rats were exposed to one of several doses of 56Fe-particle irradiation (0.10-1.0 Gy) and tested on a wire suspension task at 3-180 days postirradiation. Results indicated that profound decrements occurred in both of these indices. The effects on K(+)-evoked release of dopamine were evident for as long as 180 days after irradiation, and a subsequent experiment indicated that these effects appeared as early as 12 h postirradiation. Since similar findings have been observed in aged rats, the results are discussed in terms of these particles producing a possible accelerated striatal aging effect.     

Can biophysics tell us something about the weak equivalence principle vis a vis the thought experiment of Einstein involving human subjects?

Over a period of several decades it has been noticed that most astronauts, either orbiting the earth or on trips to the moon, have observed phosphenes or light flashes (LF) including streaks, spots and clouds of light when their eyes are closed or they are in a darkened cabin. Scientists suspect that two separate components of cosmic rays cause these flashes due to direct interaction with the retina. This phenomenon is not noticed on the ground because of cosmic ray interaction with the atmosphere. The argument is advanced that this effect may provide us with a new method of exploring the weak equivalence principle from the standpoint of Einstein's original thought experiment involving human subjects. This can be done, utilizing the retina only, as an animate quantum mechanical measuring device or, in conjunction with the Anomalous Long Term Effects on Astronauts (ALTEA) facility.     

Double-strand Scissions in DNA of Gamma-irradiated Micrococcus radiodurans and their Repair during Postirradiation Incubation

Strand scissions in DNA of M, radiodurans after in vivo irradiation with ⁶⁰Co gamma rays were investigated by the sedimentation analysis using neutral sucrose gradients. Double-strand scission in DNA was estimated to occur at the rate of one double cut per 800 eV. This rate is in a good agreement of the value reported for mammalian cells. The rejoining of these double-strand scissions was observed during the repair process of the post-irradiation incubation and the mean rejoining time, i.e., the time reducing the remaining fraction of the double-strand scission to 0.37, was found to be 52 min. This rejoining repair was inhibited by adding chloramphenicol, tetracycline or actinomycin D to the postirradiation incubation medium. It is suggested that the high resistance character of M. radiodurans to gamma rays may be due to the efficient capacity of this rejoining repair.     

The oxidation of thiols by ionizing radiations

Thiol compounds, such as glutathione, 2,3-dimercaptopropanol (BAL), propane-1,3-dithiol, and N-phenylaminopropanedithiol, were readily oxidized by x-rays, beta rays, and gamma rays. The ionic yield for this oxidation was about the same, 3 at pH 7, on irradiation with x-rays and with beta rays; it was 23 per cent less on irradiation with gamma rays. The ionic yield varied with the hydrogen ion concentration, increasing as the pH value increased. There was no reduction of oxidized glutathione on irradiation with dosages of x-rays and gamma rays which produced oxidation of the reduced compound. In the absence of oxygen, the oxidation of thiols by ionizing radiations was only 33 per cent of that obtained in the presence of dissolved oxygen. When the thiol solutions were irradiated in the presence of dissolved oxygen, catalase protected them from oxidation by 17 to 27 per cent.     

Abiotic synthesis of amino acids and imidazole by proton irradiation of simulated primitive earth atmospheres

Proton irradiation of simulated primitive earth atmosphere was performed, and amino acids and imidazole were analyzed. A mixture of carbon monoxide and nitrogen over water was irradiated by high energy protons (3 MeV, 0.6 µA) generated by a Van de Graaff accelerator for 2–5 h. Various kinds of proteinous and non-proteinous amino acids were detected in the irradiation products. Imidazole present in the irradiation products was also detected by high-performance liquid chromatography and mass spectrometry. The present results suggest that compounds of biological importance such as amino acids could be synthesized from primitive earth atmosphere by radiation of cosmic rays and/or solar flare particles.     

Induction of Thioguanine- and Ouabain-Resistant Mutants and Single-Strand Breaks in the DNA of Chinese Hamster Ovary Cells by 3H-Thymidine

Cultured Chinese hamster cells were labeled with 6-³H-thymidine or 5-methyl-³H-thymidine and allowed to accumulate damage from ³H decays for various periods of time while frozen. The frequencies of cells resistant to 6-thioguanine or ouabain and the amount of DNA damage (i.e., number of single-strand breaks) were determined and compared with the mutation frequencies resulting from X and ultraviolet light irradiation. Whereas ³H decays and X rays made only 6-thioguanine-resistant mutants, ultraviolet light made both 6-thioguanine- and ouabain-resistant mutants. ³H decays originating at the 6 position were two to three times as effective as decays at the 5-methyl position in making drug-resistant mutants, but decays at both sites were equally effective in making single-strand breaks. Mutants and strand breaks produced by beta irradiation of the nucleus probably are the same irrespective of the site of the decay in thymine; these results indicate that the local transmutation effects of ³H decay produce more mutations when they occur at the 6 position than at the 5-methyl position.     

Rhizoid Differentiation in Spirogyra: III. Intracellular Localization of Phytochrome

Localization of phytochrome which mediates rhizoid differentiation in Spirogyra was investigated. The red-absorbing form of phytochrome (Pr) seems to be distributed all over the cell periphery which remained in the centripetal end part after the centrifugation, as rhizoids formed equally well with red spotlight irradiation of three different parts of an end cell, i.e. distal end, middle, and proximal end, and with irradiation of centrifugal and centripetal end parts of a centrifuged end cell. The Pr distribution was confirmed with an experiment using far red irradiation over the entire cell, centrifugation, and red spotlight irradiation. The Pr-phytochrome molecules appeared to be mobile because no dichroic orientation was shown with polarized red spotlight irradiation. On the contrary, it is suggested that far red-absorbing form of phytochrome molecules are evacuated from the centripetal end part by the centrifugation in an experiment involving red irradiation over the entire cell-centrifugation-far red spot irradiation. Rhizoid formation was repressed markedly by far red irradiation of the centrifugal end part but not of the centripetal end part.     

On heliotropism in tendrils of Pisum sativum: A response to infrared irradiation

Summary In 1876, Darwin observed that tendrils of Pisum sativum oriented the long axis of their circumnutational sweep to keep it approximately normal to the direction of the sun's rays. Using various types of irradiation sources, the present study confirms Darwin's findings. Although blue light slightly increases the rate of circumnutation, only infrared irradiation (i.e. heat), effects the reorientation. The response can therefore be termed Diathermotropic. Diathermotropism in circumnutating tendrils is probably a device to bend the leaves of the elongating weak-stemmed plant away from the shade and toward the sun.     

Assessment of radiosensitivity from the germination of jute seeds

Irradiation with X-rays and gamma rays reduced the speed of germination of seeds of jute cultivars,viz., JRO 632, JRO 620, Sudan Green ofCorchorus olitorius and JRC 212, Fanduk, D 154 ofC. capsularis. Though the first phase of germination(i.e. seed variability) remained apparently unaffected, the second phase (i.e. the sprouting ability) and the third phase(i.e. the attainment of autotrophic status) were found to be the best indicators of radiation injury and provided dependable data for the assessment of radiosensitivity. The jute cultivars have not shown accountable intervarietal differences in radiosensitivity in respect of LD 50 and LD 100 for the second and the third phases of germination.     

Effect of Radiation Environment on the Thermal Resistance of Irradiated Spores of Bacillus subtilis

The degree of heat sensitization induced in spores of Bacillus subtilis by irradiation with gamma rays was not changed when irradiation was carried out at low oxygen tension (1 mm of Hg) as compared with irradiation in an air atmosphere. The degree of heat sensitization appeared to be slightly greater at pH 7.0 than at pH 4.5. The substrate was found to influence the degree of induced heat sensitivity with less of an effect produced in complex organic substrates.     

Amino Acid Formation in Gas Mixtures by High Energy Particle Irradiation

Amino acids were formed from carbon monoxide, nitrogen and water, which are possible constituents of the primitive earth's atmosphere, by irradiation with high energy particles (components of cosmic rays). Glycine yield was proportional to the total energy deposited to the gas mixture, and its G-value was as high as 0.02 when the carbon monoxide/nitrogen ratio was 1. Based on an estimate of the effective energies of various types of energy sources available in the primitive earth's atmosphere for amino acid synthesis, it is suggested that cosmic rays were one of the most important energy sources for the synthesis of amino acids on the primitive earth.     

Early cell repair of the lung and the intestine in mice, after irradiation by fast neutrons and gamma rays

Lung tolerance is assessed from LD50 at 180 days after thoracic irradiation, in mice, with d(50) + Be neutrons and 60Co gamma rays. Early intestinal tolerance is assessed from LD50 at 7 days after abdominal irradiation. Additional dose (Dr) to reach LD50 when a single dose Ds is split into 2 equal fractions Di separated by different time intervals "i", is determined (Dr = 2Di - Ds), Dr is larger after gamma than after neutron irradiation, for lung and intestine. After thoracic irradiation with gamma rays, Dr reaches 3.36, 4.38, 5.12 and 5.37 Gy for "i" = 2, 6, 12 and 24 hours respectively; after neutron irradiation, Dr reaches 0.66, 0.9, 1.29, 1.95 and 1.50 Gy for "i" = 1, 2, 4, 12 and 24 hours. Dr is smaller for intestine; after abdominal irradiation with gamma rays, it reaches 1.99, 2.59, 2.74, 3.11, 3.34, 4.44 and 4.56 Gy for "i" = 1, 2, 3.5, 8, 12, 18 and 24 hours; after neutron irradiation, it reaches 0.13, 0.45, 0.42 and 1.33 Gy for "i" = 1.5, 3.5, 5.5 and 24 hours. After gamma irradiation, early repair is complete after 3.5 hours for intestine and needs 12 hours for lung.     

HDF1 and RAD17 Genes are Involved in DNA Double-strand Break Repair in Stationary Phase Saccharomyces cerevisiae

DNA repair, checkpoint pathways and protection mechanisms against different types of perturbations are critical factors for the prevention of genomic instability. The aim of the present work was to analyze the roles of RAD17 and HDF1 gene products during the late stationary phase, in haploid and diploid yeast cells upon gamma irradiation. The checkpoint protein, Rad17, is a component of a PCNA-like complex—the Rad17/Mec3/Ddc1 clamp—acting as a damage sensor; this protein is also involved in double-strand break (DBS) repair in cycling cells. The HDF1 gene product is a key component of the non-homologous end-joining pathway (NHEJ). Diploid and haploid rad17Δ/rad17Δ, and hdf1Δ Saccharomyces cerevisiae mutant strains and corresponding isogenic wild types were used in the present study. Yeast cells were grown in standard liquid nutrient medium, and maintained at 30°C for 21 days in the stationary phase, without added nutrients. Cell samples were irradiated with ⁶⁰Co γ rays at 5 Gy/s, 50 Gy ≤ Dabs ≤ 200 Gy. Thereafter, cells were incubated in PBS (liquid holding: LH, 0 ≤ t ≤ 24 h). DNA chromosomal analysis (by pulsed-field electrophoresis), and surviving fractions were determined as a function of absorbed doses, either immediately after irradiation or after LH. Our results demonstrated that the proteins Rad17, as well as Hdf1, play essential roles in DBS repair and survival after gamma irradiation in the late stationary phase and upon nutrient stress (LH after irradiation). In haploid cells, the main pathway is NHEJ. In the diploid state, the induction of LH recovery requires the function of Rad17. Results are compatible with the action of a network of DBS repair pathways expressed upon different ploidies, and different magnitudes of DNA damage.     

The effects of boron neutron capture irradiation on oral mucosa: evaluation using a rat tongue model.

The ventral surface of the tongue of male Fisher 344 rats was used to evaluate the response of oral mucosa to boron neutron capture irradiation. Three hours after i.p. injection of 700 mg/kg of the boron delivery agent p-boronophenylalanine (BPA), the boron concentrations in blood and tongue mucosal epithelium were approximately 21 and 23 microgram (10)B/g, respectively. The doses required to produce a 50% incidence of ulceration with X rays, the Brookhaven Medical Research Reactor thermal neutron beam alone, or the thermal neutron beam in the presence of BPA were 13.4 +/- 0.2, 4. 2 +/- 0.1, and 3.0 +/- 0.1 Gy, respectively. Ulceration of the tongue was evident by 6 to 7 days after irradiation, irrespective of the irradiation modality; healing was related to dose and was relatively rapid (相似文献   

The active form of phytochrome: a new hypothesis based on phytochrome pelletability studies

Difficulties arising from the current dogma that the far-red absorbing form of phytochrome (P_fr) is the only active form are discussed.A new hypothesis is proposed in which phytochrome is held to be the photoreceptor for both low energy (pulse) and high energy (HIR) responses. There is a common basic mechanism of action involving interaction between phytochrome and a binding site within the cell. The phytochrome involvement in low energy responses exhibits an action spectrum for binding that matches the P_r absorption spectrum and reversibility by far-red irradiation. Upon prolonged irradiation the phytochrome-binding site interaction acquires different characteristics that are reminiscent of those displayed in HIR, e.g. dependence on sustained irradiation for continual binding, dependence of the degree of binding on irradiance and the similarity of the action spectrum with that of HIR action spectra, e.g. that for inhibition of lettuce hypocotyl lengthening.As expected on the basis of the new hypothesis the particulate fraction of phytochrome contains both P_r and P_fr. Arguments are advanced that the presence of P_r in pellets of particulate phytochrome cannot be accounted for by (i) the “induced fit” hypothesis, (ii) the “pigment cycling” hypothesis, and (iii) the “open phytochrome-receptor model”. We conclude that phytochrome molecules, after being sufficiently energized can interact with their intracellular binding sites irrespective of their chromophoric configuration.     

Cell death (apoptosis) in mouse intestine after continuous irradiation with gamma rays and with beta rays from tritiated water

Apoptosis is a pattern of cell death involving nuclear pycnosis, cytoplasmic condensation, and karyorrhexis. Apoptosis induced by continuous irradiation with gamma rays (externally given by a 137Cs source) or with beta rays (from tritiated water injected ip) was quantified in the crypts of two portions of mouse bowel, the small intestine and descending colon. The time-course change in the incidence of apoptosis after each type of radiation could be explained on the basis of the innate circadian rhythm of the cells susceptible to apoptotic death and of the excretion of tritiated water (HTO) from the body. For 6-h continuous gamma irradiation at various dose rates (0.6-480 mGy/h) and for 6 h after injection of HTO of various radioactivities (0.15-150 GBq per kg body wt), the relationships between dose and incidence of apoptosis were obtained. Survival curves were then constructed from the curves for dose vs incidence of apoptosis. For the calculation of the absorbed dose from HTO, the water content both of the mouse body and of the cells was assumed to be 70%. One megabecquerel of HTO per mouse (i.e., 40 MBq/kg body wt) gave a dose rate of 0.131 mGy/h. The mean lethal doses (D0) were calculated for gamma rays and HTO, and relative biological effectiveness values of HTO relative to gamma rays were obtained. The D0 values for continuous irradiation with gamma rays were 210 mGy for small intestine and 380 mGy for descending colon, and the respective values for HTO were 130 and 280 mGy, indicating the high radiosensitivity of target cells for apoptotic death. The relative biological effectiveness of HTO relative to 137Cs gamma rays for cell killing in both the small intestine and the descending colon in the mouse was 1.4-2.1.     

The biliprotein C-phycocyanin modulates the early radiation response: A pilot study

This study analyzed the effects of biliprotein C-phycocyanin (C-PC) on the enzymatic antioxidant defence system in lymphocytes of nuclear power-plant workers and non-exposed controls. Changes in the protein levels of manganese super oxide dismutase (MnSOD), catalase and glutathione-S-transferase (GST) were used as markers for early biological effects of a single in vitro exposure of cells to: (i) 2 Gy gamma rays; (ii) 5 μM C-PC; and (iii) a combination of C-PC plus irradiation with 2 Gy. The results showed that C-PC selectively stimulated the lymphocyte antioxidant defence system of occupationally exposed subjects. The activation of the antioxidant protective mechanisms as part of the early radiation response was probably related to the chronic low-dose occupational exposure. The modulating capacity of C-PC at the molecular level may be of interest for the protection of occupationally exposed persons.     

Proteomic Analysis of Trypanosoma cruzi Response to Ionizing Radiation Stress

Trypanosoma cruzi, the causative agent of Chagas disease, is extremely resistant to ionizing radiation, enduring up to 1.5 kGy of gamma rays. Ionizing radiation can damage the DNA molecule both directly, resulting in double-strand breaks, and indirectly, as a consequence of reactive oxygen species production. After a dose of 500 Gy of gamma rays, the parasite genome is fragmented, but the chromosomal bands are restored within 48 hours. Under such conditions, cell growth arrests for up to 120 hours and the parasites resume normal growth after this period. To better understand the parasite response to ionizing radiation, we analyzed the proteome of irradiated (4, 24, and 96 hours after irradiation) and non-irradiated T. cruzi using two-dimensional differential gel electrophoresis followed by mass spectrometry for protein identification. A total of 543 spots were found to be differentially expressed, from which 215 were identified. These identified protein spots represent different isoforms of only 53 proteins. We observed a tendency for overexpression of proteins with molecular weights below predicted, indicating that these may be processed, yielding shorter polypeptides. The presence of shorter protein isoforms after irradiation suggests the occurrence of post-translational modifications and/or processing in response to gamma radiation stress. Our results also indicate that active translation is essential for the recovery of parasites from ionizing radiation damage. This study therefore reveals the peculiar response of T. cruzi to ionizing radiation, raising questions about how this organism can change its protein expression to survive such a harmful stress.     

The effect of graded doses of fission neutrons or X rays on the lymphoid compartment of the thymus in mice

Young adult CBA/H mice were exposed to graded doses of whole-body irradiation with either fast fission neutrons or 300 kVp X rays at center-line dose rates of 0.1 and 0.3 Gy/min, respectively. Dose-response curves were determined at Days 2 and 5 after irradiation for the total thymic cell survival and for the survival of thymocytes defined by monoclonal anti-Thy-1, -Lyt-1, -Lyt-2, and -T-200 antibodies as measured by flow cytofluorometric analysis. Cell dose-response curves of thymocytes show, 2 days after irradiation, a two-component curve with a radiosensitive part and a part refractory to irradiation. The radiosensitive part of the dose survival curve of the Lyt-2+ cells, i.e., mainly cortical cells, has a D0 value of about 0.26 and 0.60 Gy for neutrons and X rays, respectively, whereas that of the other cell types has corresponding D0 values of about 0.30 and 0.70 Gy. The radiorefractory part of the dose-response curves cannot be detected beyond 5 days after irradiation. At that time, the Lyt-2+ cells are again most radiosensitive with a D0 value of 0.37 and 0.99 Gy for neutrons and X rays, respectively. The other measured cell types have corresponding D0 values of about 0.47 Gy. The fission neutron RBE values for the reduction in the thymocyte populations defined by either monoclonal anti-Thy-1, -Lyt-1, -Lyt-2, or -T-200 antibodies to 1.0% vary from 2.6 to 2.8. Furthermore, the estimated D0 values of the Thy-1-, T-200- intrathymic precursor cells which repopulate the thymus during the bone marrow independent phase of the biphasic thymus regeneration after whole-body irradiation are 0.64-0.79 Gy for fission neutrons and 1.32-1.55 Gy for X rays.