Internal doses in experimental mice and rats following exposure to neutron-activated 56MnO2 powder: results of an international, multicenter study.

The experiment was performed in support of a Japanese initiative to investigate the biological effects of irradiation from residual neutron-activated radioactivity that resulted from the A-bombing. Radionuclide 56Mn (T1/2 = 2.58 h) is one of the main neutron-activated emitters during the first hours after neutron activation of soil dust particles. In our previous studies (2016-2017) related to irradiation of male Wistar rats after dispersion of 56MnO2 powder, the internal doses in rats were found to be very inhomogeneous: distribution of doses among different organs ranged from 1.3 Gy in small intestine to less than 0.0015 Gy in some of the other organs. Internal doses in the lungs ranged from 0.03 to 0.1 Gy. The essential pathological changes were found in lung tissue of rats despite a low level of irradiation. In the present study, the dosimetry investigations were extended: internal doses in experimental mice and rats were estimated for various activity levels of dispersed neutron-activated 56MnO2 powder. The following findings were noted: (a) internal radiation doses in mice were several times higher in comparison with rats under similar conditions of exposure to 56MnO2 powder. (b) When 2.74 × 108 Bq of 56MnO2 powder was dispersed over mice, doses of internal irradiation ranged from 0.81 to 4.5 Gy in the gastrointestinal tract (small intestine, stomach, large intestine), from 0.096 to 0.14 Gy in lungs, and doses in skin and eyes ranged from 0.29 to 0.42 Gy and from 0.12 to 0.16 Gy, respectively. Internal radiation doses in other organs of mice were much lower. (c) Internal radiation doses were significantly lower in organs of rats with the same activity of exposure to 56MnO2 powder (2.74 × 108 Bq): 0.09, 0.17, 0.29, and 0.025 Gy in stomach, small intestine, large intestine, and lungs, respectively. (d) Doses of internal irradiation in organs of rats and mice were two to four times higher when they were exposed to 8.0 × 108 Bq of 56MnO2 (in comparison with exposure to 2.74 × 108 Bq of 56MnO2). (e) Internal radiation doses in organs of mice were 7-14 times lower with the lowest 56MnO2 amount (8.0 × 107 Bq) in comparison with the highest amount, 8.0 × 108 Bq, of dispersed 56MnO2 powder. The data obtained will be used for interpretation of biological effects in experimental mice and rats that result from dispersion of various levels of neutron-activated 56MnO2 powder, which is the subject of separate studies.

Determination of the thermal and epithermal neutron sensitivities of an LBO chamber.

An LBO (Li2B4O7) walled ionization chamber was designed to monitor the epithermal neutron fluence in boron neutron capture therapy clinical irradiation. The thermal and epithermal neutron sensitivities of the device were evaluated using accelerator neutrons from the 9Be(d, n) reaction at a deuteron energy of 4 MeV (4 MeV d-Be neutrons). The response of the chamber in terms of the electric charge induced in the LBO chamber was compared with the thermal and epithermal neutron fluences measured using the gold-foil activation method. The thermal and epithermal neutron sensitivities obtained were expressed in units of pC cm2, i.e., from the chamber response divided by neutron fluence (cm-2). The measured LBO chamber sensitivities were 2.23 × 10-7 ± 0.34 × 10-7 (pC cm2) for thermal neutrons and 2.00 × 10-5 ± 0.12 × 10-5 (pC cm2) for epithermal neutrons. This shows that the LBO chamber is sufficiently sensitive to epithermal neutrons to be useful for epithermal neutron monitoring in BNCT irradiation.

Internal exposure to neutron-activated 56Mn dioxide powder in Wistar rats: part 1: dosimetry.

There were two sources of ionizing irradiation after the atomic bombings of Hiroshima and Nagasaki: (1) initial gamma-neutron irradiation at the moment of detonation and (2) residual radioactivity. Residual radioactivity consisted of two components: radioactive fallout containing fission products, including radioactive fissile materials from nuclear device, and neutron-activated radioisotopes from materials on the ground. The dosimetry systems DS86 and DS02 were mainly devoted to the assessment of initial radiation exposure to neutrons and gamma rays, while only brief considerations were given for the estimation of doses caused by residual radiation exposure. Currently, estimation of internal exposure of atomic bomb survivors due to dispersed radioactivity and neutron-activated radioisotopes from materials on the ground is a matter of some interest, in Japan. The main neutron-activated radionuclides in soil dust were 24Na, 28Al, 31Si, 32P, 38Cl, 42K, 45Ca, 46Sc, 56Mn, 59Fe, 60Co, and 134Cs. The radionuclide 56Mn (T 1/2 = 2.58 h) is known as one of the dominant beta- and gamma emitters during the first few hours after neutron irradiation of soil and other materials on ground, dispersed in the form of dust after a nuclear explosion in the atmosphere. To investigate the peculiarities of biological effects of internal exposure to 56Mn in comparison with external gamma irradiation, a dedicated experiment with Wistar rats exposed to neutron-activated 56Mn dioxide powder was performed recently by Shichijo and coworkers. The dosimetry required for this experiment is described here. Assessment of internal radiation doses was performed on the basis of measured 56Mn activity in the organs and tissues of the rats and of absorbed fractions of internal exposure to photons and electrons calculated with the MCNP-4C Monte Carlo using a mathematical rat phantom. The first results of this international multicenter study show that the internal irradiation due to incorporated 56Mn powder is highly inhomogeneous, and that the most irradiated organs of the experimental animals are: large intestine, small intestine, stomach, and lungs. Accumulated absorbed organ doses were 1.65, 1.33, 0.24, 0.10 Gy for large intestine, small intestine, stomach, and lungs, respectively. Other organs were irradiated at lower dose levels. These results will be useful for interpretation of the biological effects of internal exposure of experimental rats to powdered 56Mn as observed by Shichijo and coworkers.

Unraveling low-level gamma radiation--responsive changes in expression of early and late genes in leaves of rice seedlings at Iitate Village, Fukushima.

In the summer of 2012, 1 year after the nuclear accident in March 2011 at the Fukushima Daiichi nuclear power plant, we examined the effects of gamma radiation on rice at a highly contaminated field of Iitate village in Fukushima, Japan. We investigated the morphological and molecular changes on healthy rice seedlings exposed to continuous low-dose gamma radiation up to 4 µSv h(-1), about 80 times higher than natural background level. After exposure to gamma rays, expression profiles of selected genes involved in DNA replication/repair, oxidative stress, photosynthesis, and defense/stress functions were examined by RT-PCR, which revealed their differential expression in leaves in a time-dependent manner over 3 days (6, 12, 24, 48, and 72 h). For example, OsPCNA mRNA rapidly increased at 6, 12, and 24 h, suggesting that rice cells responded to radiation stress by activating a gene involved in DNA repair mechanisms. At 72 h, genes related to the phenylpropanoid pathway (OsPAL2) and cell death (OsPR1oa) were strongly induced, indicating activation of defense/stress responses. We next profiled the transcriptome using a customized rice whole-genome 4×44K DNA microarray at early (6h) and late (72 h) time periods. Low-level gamma radiation differentially regulated rice leaf gene expression (induced 4481 and suppressed 3740 at 6 h and induced 2291 and suppressed 1474 genes at 72 h) by at least 2-fold. Using the highly upregulated and downregulated gene list, MapMan bioinformatics tool generated diagrams of early and late pathways operating in cells responding to gamma ray exposure. An inventory of a large number of gamma radiation-responsive genes provides new information on novel regulatory processes in rice.

Comparison of external dose estimates using different retrospective dosimetry methods in the settlements located near Semipalatinsk Nuclear Test Site, Republic of Kazakhstan.

For correct assessment of health risks after low-dose irradiation, calculation of radiation exposure estimates is crucial. To verify the calculated absorbed doses, instrumental methods of retrospective dosimetry are used. We compared calculated and instrumental-based estimates of external absorbed doses in the residents of Dolon, Mostik and Cheremushki villages, Kazakhstan, affected by the first nuclear weapon test performed at the Semipalatinsk Nuclear Test Site (SNTS) on August 29, 1949. The 'instrumental' doses were retrospectively estimated using the Luminescence Retrospective Dosimetry (LRD) and Electron Spin Resonance (ESR) methods. Correlation between the calculated individual cumulative external absorbed whole-body doses based on typical input data and ESR-based individual doses in the same people was strong (r = 0.782). It was even stronger between the calculated doses based on individual questionnaires' input data and the ESR-based doses (r = 0.940). Application of the LRD method is useful for validation of the calculated settlement-average cumulated external absorbed dose to air. Reconstruction of external exposure can be supplemented with the data from later measurements of soil contamination with long-lived radionuclides, such as, 137Cs. Our results show the reliability of the calculational method used for the retrospective assessment of individual external doses.

Internal organ dose rate conversion coefficients of Japanese macaques to 134Cs,137Cs and 131I†.

The purpose of this study was to estimate the internal dose of radiation in Japanese macaques (aka Nihonzaru or snow monkey) due to the Fukushima nuclear power plant accident. Images of a male Japanese macaque weighing ~10 kg were acquired using a multi-slice computed tomography (CT) scan with a 64-row segment detector. The CT images were used to create voxel phantoms of the bones, bone marrow, brain, eyes, heart, lungs, stomach, liver, spleen, pancreas, kidneys, intestines, bladder, testes, thyroid and miscellaneous tissue. The Particle and Heavy Ion Transport System (PHITS) Monte Carlo code was used to calculate the internal exposure rate conversion factors for 134Cs, 137Cs and 131I isotopes for the created voxel phantoms with a statistical precision higher than 1%. The PHITS-calculated energy deposits were compared with those for rhesus monkeys. The results showed that the fractions of energy deposits for ß-radiation in different organs were almost identical between the two species. For γ-radiation, there was excellent agreement in the self-absorption rate with the approximate curve of the Japanese macaque, with an average deviation of 2%. The maximum deviation of 12% was for the kidney, which has two organs, so the error with the approximate curve is slightly larger due to the energy loss created between organs.

Tooth enamel ESR dosimetry for Hiroshima 'black rain' zone residents.

Electron spin resonance (ESR) dosimetry was applied to human tooth enamel in order to obtain individual absorbed doses for victims of the Hiroshima bomb who lived in the 'black rain' area. The so-called 'black rain' fell in the form of precipitation on the western part of Hiroshima city and the northwestern suburbs within a few hours after the explosion of the atomic bomb on 6 August 1945, and exposed the population in this area. Only three tooth samples were collected from this area. Since the teeth were located at positions 1, 2 and 4, only the lingual portion was used for the analysis. The results showed that the excess dose after subtracting natural radiation for one (position 4; hh1) was background, for the second (position 2; hh2) it was 133 mGy, and for the other (position 1; hh3) it was 243 mGy. Based on these results, we further investigated the radiation dose attributed to dental X-rays and head CT scan. Such dose of the hh3 radiographic examination was estimated to be 57-160 mGy, which implies an additional exposure around 135 mGy after subtraction. On the other hand, the dose data of hh1 after subtracting dental X-rays was negative. This may mean that such additional doses are an overestimation. In addition, the effect of sunlight should be considered, which is the same direction of overestimation. As a result, the residual dose of 140 mGy suggests the inclusion of radiation from the 'black rain.'

Microdistribution of internal radiation dose in biological tissues exposed to 56Mn dioxide microparticles.

Manganese-56 (56Mn) was one of the dominant neutron-activated radionuclides during the first hours following the atomic-bombing of Hiroshima and Nagasaki. The radiation spectrum of 56Mn and the radiation emission from excited levels of 56Fe following 56Mn beta-decay include gamma-quanta, beta-particles, Auger electrons and X-rays. The dispersion of neutron activated 56Mn in the air can lead to entering of radioactive microparticles into the lungs. The investigation of spatial microdistribution of an internal dose in biological tissue exposed to 56Mn is an important matter with regards to the possible elevated irradiation of the lung alveoli and alveolar ducts. The Monte Carlo code (MCNP-4C) was used for the calculation of absorbed doses in biological tissue around 56Mn dioxide microparticles. The estimated absorbed dose has a very essential gradient in the epithelium cells of lung alveoli and alveolar duct: from 61 mGy/decay on the surface of simple squamous cells of epithelium to 0.15 mGy/decay at distance of 0.3 µm, which is maximal cell thickness. It has been concluded that epithelial cells of these pulmonary microstructures are selectively irradiated by low-energy electrons: short-range component of beta-particles spectrum and Auger electrons. The data obtained are important for the interpretation of biological experiments implementing dispersed neutron-activated 56Mn dioxide powder.

Estimation of 'dose-depth' profile in the surface layers of a quartz-containing tile from the former Hiroshima University building indicates the possible presence of beta-irradiation from residual radioactivity after A-bombing.

The problem of differentiating between primary irradiation and exposure due to residual radioactivity following A-bombing (including beta-exposure), is the subject of special attention and discussions in order to understand the health effects following the Hiroshima and Nagasaki A-bombings, especially among newcomers to cities soon after the detonations. In this work, the method of single quartz grain luminescence retrospective dosimetry was applied for a retrospective estimation of the 'dose-depth' profile in a quartz-containing tile extracted from the building of former Hiroshima University (HU), which was a 'witness' of the Hiroshima atomic bombing on the 6 August 1945. It has been shown that results of retrospective estimates of the 'dose-depth' profile using the method of optically stimulated luminescence (OSL) from inclusions of quartz grains in very thin layers of the sample, in combination with the calculations of the 'dose-depth' profile using the Monte Carlo method, indicates the possible presence of beta irradiation of thin layers of the sample located near the surface of the tile facing the air, where there is no electronic equilibrium from gamma radiation.

External dose estimates of laboratory rats and mice during exposure to dispersed neutron-activated 56Mn powder.

Estimates of external absorbed dose in experimental animals exposed to sprayed neutron-activated 56Mn powder are necessary for comparison with internal absorbed doses estimated under the same exposure conditions, which is required for a correct interpretation of the observed biological effects. It has been established that the measured dose of external absorbed dose as a result of gamma irradiation range 1-15 mGy, which is order of magnitude less than the maximal dose of internal gamma and beta irradiation of the whole body of the same experimental animals irradiated under the same conditions: according to the available literature data, the maximal values ​​of absorbed dose of internal gamma-beta irradiation of the whole body are in the range of 330 mGy-1200 mGy for mice and 100 mGy-150 mGy for rats. It is concluded that under the conditions of experiments with dispersed neutron-activated powder 56MnO2, internal gamma-beta irradiation of experimental animals is the main factor of radiation exposure compared to external gamma irradiation.

pSLA2-M of Streptomyces rochei is a composite linear plasmid characterized by self-defense genes and homology with pSLA2-L.

The 113,463-bp nucleotide sequence of the linear plasmid pSLA2-M of Streptomyces rochei 7434AN4 was determined. pSLA2-M had a 69.7% overall GC content, 352-bp terminal inverted repeats with 91% (321/352) identity at both ends, and 121 open reading frames. The rightmost 14.6-kb sequence was almost (14,550/14,555) identical to that of the coexisting 211-kb linear plasmid pSLA2-L. Adjacent to this homologous region an 11.8-kb CRISPR cluster was identified, which is known to function against phage infection in prokaryotes. This cluster region as well as another one containing two large membrane protein genes (orf78 and orf79) were flanked by direct repeats of 194 and 566 bp respectively. Hence the insertion of circular DNAs containing each cluster by homologous recombination was suggested. In addition, the orf71 encoded a Ku70/Ku80-like protein, known to function in the repair of double-strand DNA breaks in eukaryotes, but disruption of it did not affect the radiation sensitivity of the mutant. A pair of replication initiation genes (orf1-orf2) were identified at the extreme left end. Thus, pSLA2-M proved to be a composite linear plasmid characterized by self-defense genes and homology with pSLA2-L that might have been generated by multiple recombination events.

Development of a real-time neutron beam detector for boron neutron capture therapy using a thin silicon sensor.

We have developed a new real-time neutron detector, which is able to measure a direct neutron beam of boron neutron capture therapy. The detector consists of both a 40-µm-thick pn diode and around 0.09-µm-thick LiF neutron converter. Experimental results indicate that this neutron detector can measure neutron flux up to 1 × 109 (cm-2 s-1), separately from gamma rays around 500 mGy/h. The measured depth distribution of neutron flux in an acrylic block is in agreement with the activation results of gold.

Dosimetric verification of the anisotropic analytical algorithm in lung equivalent heterogeneities with and without bone equivalent heterogeneities.

PURPOSE: In this study, the authors evaluated the accuracy of dose calculations performed by the convolution/superposition based anisotropic analytical algorithm (AAA) in lung equivalent heterogeneities with and without bone equivalent heterogeneities. METHODS: Calculations of PDDs using the AAA and Monte Carlo simulations (MCNP4C) were compared to ionization chamber measurements with a heterogeneous phantom consisting of lung equivalent and bone equivalent materials. Both 6 and 10 MV photon beams of 4 x 4 and 10 x 10 cm(2) field sizes were used for the simulations. Furthermore, changes of energy spectrum with depth for the heterogeneous phantom using MCNP were calculated. RESULTS: The ionization chamber measurements and MCNP calculations in a lung equivalent phantom were in good agreement, having an average deviation of only 0.64 +/- 0.45%. For both 6 and 10 MV beams, the average deviation was less than 2% for the 4 x 4 and 10 x 10 cm(2) fields in the water-lung equivalent phantom and the 4 x 4 cm(2) field in the water-lung-bone equivalent phantom. Maximum deviations for the 10 x 10 cm(2) field in the lung equivalent phantom before and after the bone slab were 5.0% and 4.1%, respectively. The Monte Carlo simulation demonstrated an increase of the low-energy photon component in these regions, more for the 10 X 10 cm(2) field compared to the 4 x 4 cm(2) field. CONCLUSIONS: The low-energy photon by Monte Carlo simulation component increases sharply in larger fields when there is a significant presence of bone equivalent heterogeneities. This leads to great changes in the build-up and build-down at the interfaces of different density materials. The AAA calculation modeling of the effect is not deemed to be sufficiently accurate.

Measurement of microdosimetric spectra produced from a 290 MeV/n Spread Out Bragg Peak carbon beam.

This study describes measurements on secondary particles produced by a 290 MeV/n Spread Out Bragg Peak (SOBP) carbon beam. Microdosimetric distributions of secondary fragments from the SOBP carbon beam have been measured by using a new tissue equivalent proportional counter (TEPC) system at the Heavy Ion Medical Accelerator in Chiba of the National Institute of Radiological Sciences. The new TEPC system consists of a TEPC, two solid-state detectors (SSD) and a scintillation counter (FSC: forward scintillation counter). The SSDs and FSC can separately identify charged fragments and secondary neutrons produced by the incident carbon ions. Microdosimetric distributions were measured for secondary particles including neutrons produced by a body-simulated phantom consisting of various PMMA plates (thickness: 0, 34.81, 55.2, 60.95, 64.83, 95.03, 114.79, 124.69, 135.2 and 144.98 mm, respectively) to cover the SOBP (at 60-125 mm depth). The new system can separately determine produced fragments from the incident SOBP carbon beam in a body-simulated phantom.

A simulation study on beam property of 124Sb-Be isotope-based neutron for BNCT.

The 9Be(γ,n) neutrons with the energies at 21-24 keV generated by 1.691 MeV photons from 124Sb was investigated as a source of epithermal neutrons for BNCT, using PHITS code. A beam shaping assembly composed of 13 mm thick Be target, a gamma ray shield made of 30 cm thick Bi, and a reflector of 30 cm thick Pb satisfied the beam requirements of IAEA-TECDOC-1223. The needed 124Sb activity was estimated in the order of 1016-1017 Bq. Feasibility of BNCT using 124Sb-Be neutrons would be influenced by the capability of periodic supply of short-lived 124Sb (half-life: 60 days) with such high activity.

Internal exposure rate conversion coefficients and absorbed fractions of mouse for 137Cs, 134Cs and 90Sr contamination in body.

The aim of this study was to determine parameters for estimating the internal exposure of all organs in mouse experiments from the radioactivity concentration in organs. The estimation of internal exposure rate conversion coefficients and absorbed fractions for 137Cs, 134Cs and 90Sr by the Particle and Heavy Ion Transport code System (PHITS) with a voxel-based mouse phantom is presented. The geometry of the voxel phantom is constructed from computer tomography images of a mouse 9 cm in length weighing 23.9 g. The voxel-based mouse phantom has the following organs: brain, skull, heart, lungs, liver, stomach, spleen, kidneys, bladder, testis and tissue (tissue and other organs). Gamma- and beta-rays from 137Cs, 134Cs and 90Sr sources in each source organ are generated and scored for every target organ. The internal exposure rate conversion coefficients and absorbed fractions are calculated from deposition energies in each target organ from each source organ and are used to generate an internal exposure rate conversion coefficient matrix and an absorbed fraction matrix. The absorbed fractions of beta-rays in the source organs are roughly 0.5-0.8 for 137Cs and 134Cs, and the absorbed fractions of gamma-rays are <0.04 for 137Cs and <0.03 for 134Cs. The internal exposure rate conversion coefficient matrix is defined using the absorbed fractions. The calculated internal exposure rate coefficient matrix is tested under a uniform radioactivity concentration of 1 Bq/kg for 137Cs, 134Cs and 90Sr. The estimated internal exposure rates in the mouse whole body for 137Cs, 134Cs and 90Sr are 3.28 × 10-3, 2.55 × 10-3 and 1.20 × 10-2 µGy/d, respectively. These values are very similar to those for an ellipsoid frog (31.4 g) and an ellipsoid crab egg mass (12.6 g) reported in ICRP Publication 108.

Microdosimetry on a mini-reactor UTR-KINKI for educational uses and biological researches.

Microdosimetry study has been carried out at the education and research mini-reactor of Kinki University (UTR-KINKI) using a tissue equivalent gas proportional counter (TEPC). The microdosimetric single event spectra for 0.5, 1, 2, 3 and 5 microm site sizes were obtained in the lineal energy range from 1 to 1000 keV/microm. Neutron and gamma-ray fractional doses were estimated from the single event spectra. The neutron dose fraction was varied from 35 to 55% for 0.5 to 5 microm site size. The averaged lineal energy, y(D), for each site size was likewise estimated and found to be dependent on the site size. The averaged lineal energy for neutron was slightly larger than that of the fission neutrons from (252)Cf, and the averaged lineal energy for gamma-ray had similar site-size-dependence of 25 keV gamma-rays and 250 kV X-rays. Relative biological effectiveness was found to be 4.1 +/- 0.13 for UTR-KINKI using Tilikidis's 2 Gy-response function. The estimated RBE for UTR-KINKI neutrons is quite close to the previous biological experimental value of 4.3 +/- 0.6 for micronucleated cells in gill cell of Medaka and 4.6 +/- 0.5 for induction of lymphocyte apoptosis in the thymus of ICR mice.

ESR dosimetry study on population of settlements nearby Ust-Kamenogorsk city, Kazakhstan.

The method of electron spin resonance (ESR) dosimetry has been applied to human tooth enamel, to obtain individual absorbed doses of residents of settlements in vicinity of Ust-Kamenogorsk city, Kazakhstan (located about 400 km to the east from the epicenter of explosion at the Semipalatinsk Nuclear Test Site, SNTS). This region developed as a major mining and metallurgical center during the Soviet period (uranium production). Most of the investigated settlements (Ust-Kamenogorsk city, Glubokoe, Tavriya, Gagarino) are located near the central axis of the radioactive fallout trace that originated from the surface nuclear test on 24 August 1956, while the Kokpekty settlement (located 400 km to the Southeast from SNTS) was chosen as a control because it was not subjected to any radioactive contamination. In total, 44 samples were measured. It was found that the excess doses obtained after subtraction of natural background radiation ranged up to about 114 mGy for residents of Ust-Kamenogorsk city, whose tooth enamel was formed before 1956. For residents of Gagarino, excess doses did not exceed 47 mGy for all ages. For residents of Tavriya, the maximum excess dose was 54 mGy, while for residents of Glubokoe it was about 58 mGy. For the population of the Shemonaikha settlements located at a distance of about 70 km from the central axis of the radioactive fallout trace, highest excess doses were 110 mGy. These high doses may be due to the influence of uranium enterprises located in that region, but probably not due to dental X-ray irradiation. For a final conclusion on the radiological situation in this region, the number of samples was too small and, therefore, more work is required to obtain representative results.

Ultra low-dose radiation: stress responses and impacts using rice as a grass model.

We report molecular changes in leaves of rice plants (Oryza sativa L. - reference crop plant and grass model) exposed to ultra low-dose ionizing radiation, first using contaminated soil from the exclusion zone around Chernobyl reactor site. Results revealed induction of stress-related marker genes (Northern blot) and secondary metabolites (LC-MS/MS) in irradiated leaf segments over appropriate control. Second, employing the same in vitro model system, we replicated results of the first experiment using in-house fabricated sources of ultra low-dose gamma (gamma) rays and selected marker genes by RT-PCR. Results suggest the usefulness of the rice model in studying ultra low-dose radiation response/s.

Growth retardation and death of rice plants irradiated with carbon ion beams is preceded by very early dose- and time-dependent gene expression changes.

The carbon-ion beam (CIB) generated by the heavy-ion medical accelerator in Chiba (HIMAC) was targeted to 7-day-old rice. Physiological parameters such as growth, and gene expression profiles were examined immediately after CIB irradiation. Dose-dependent growth suppression was seen three days post-irradiation (PI), and all the irradiated plants died by 15 days PI. Microarray (Agilent rice 22K) analysis of the plants immediately after irradiation (iai) revealed effects on gene expression at 270 Gy; 353 genes were up-regulated and 87 down-regulated. Exactly the same set of genes was affected at 90 Gy. Among the highly induced genes were genes involved in information storage and processing, cellular processes and signaling, and metabolism. RT-PCR analysis confirmed the microarray data.