Shigeto Fujimura
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Featured researches published by Shigeto Fujimura.
Soil Science and Plant Nutrition | 2015
Naoto Kato; Nobuharu Kihou; Shigeto Fujimura; Masaharu Ikeba; Naruo Miyazaki; Yukio Saito; Tetsuya Eguchi; Sumio Itoh
Abstract Huge amounts of radionuclides, particularly radiocesium, were discharged from the Fukushima Daiichi Nuclear Power Plant (FDNPP), and widespread of contamination of the land, including paddy fields, was observed. Because rice is a staple food in Japan, contamination of paddy fields is a serious problem, and practical countermeasures to reduce radiocesium contamination of rice are urgently required. Potassium (K) fertilization was previously shown to be an effective countermeasure in fields contaminated by the Chernobyl accident, but researchers did not study the effects on rice (Oryza sativa L.). In the present study, we performed urgent field experiments to test the use of K fertilization, as well as other soil amendments, to reduce radiocesium contamination of rice. We found that K fertilization was an effective and practical countermeasure to reduce radiocesium uptake by rice from several soil types in Japanese paddy rice culture. Other treatments, including the application of expanded vermiculite or manure, were effective, and the effect appears to be explained by their K content. Based on these results, the recommended level of exchangeable soil potassium to lower the radiocesium content of rice to acceptable levels is about 200 mg K kg–1 soil before the usual fertilization. This K fertilizer application criterion was applied in a wide, low-contaminated area from the 2012 cropping season, and satisfactory results have been obtained generally.
Plant Production Science | 2013
Shigeto Fujimura; Kunio Yoshioka; Takashi Saito; Mutsuto Sato; Makoto Sato; Yuuki Sakuma; Yasuyuki Muramatsu
Abstract Radionuclides were released into the environment as a consequence of the Fukushima Daiichi Nuclear Power Plant accident that occurred on 11 March 2011. Radiocesium at an abnormal concentration was detected in brown rice produced in paddy fields located in northern part of Fukushima Prefecture. We examined several hypotheses that could potentially explain the excessive radiocesium level in brown rice in some of the paddy fields, including (i) low exchangeable potassium content of the soil, (ii) low sorption sites for cesium (Cs) in the soil, and (iii) radiocesium enrichment of water that is flowing into the paddy fields from surrounding forests. The results of experiments using pots with contaminated soil indicated that the concentration of radiocesium in rice plants was decreased by applying potassium or clay minerals such as zeolite and vermiculite. The obtained results indicated that high concentrations of radiocesium in rice are potentially a result of the low exchangeable potassium and sorption sites for Cs in the soils. Application of potassium fertilizer and clay minerals should provide an effective countermeasure for reducing radiocesium uptake by plants. Radiocesium-enriched water produced by leaching contaminated leaf litter was used to irrigate rice plants in the cultivation experiments. The results indicated that the radiocesium concentrations in rice plants increased when the radiocesium-enriched water was applied to the potted rice plants. This indicated the possibility that the radiocesium levels in brown rice will increase if the nuclide is transported with water into the rice paddy fields from surrounding forests.
Journal of Environmental Radioactivity | 2015
Shigeto Fujimura; Yasuyuki Muramatsu; Takeshi Ohno; Masaaki Saitou; Yasukazu Suzuki; Tomoyuki Kobayashi; Kunio Yoshioka; Yoshikatsu Ueda
The ability to predict radiocesium transfer from soil to agricultural products is necessary for assessing management options in a radiocesium contaminated area. In this study, we evaluated the differences in transfer factors among soil samples and the differences in transfer factors between the first and the second years of contamination in rice. We employed pot experiments using four types of soils that are representative of the agricultural soils present in the Fukushima Prefecture contaminated by (137)Cs released from the Fukushima Dai-ichi Nuclear Power Plant after the March 2011 accident. The experiments were conducted during the 2011 and 2012 growing seasons. The geometric mean of transfer factors for brown rice and inedible rice part was 0.011 and 0.031, respectively, in 2011 and 0.0061 and 0.020, respectively, in 2012. The average decreasing rate of the transfer factor was 40% and 30% in brown rice and inedible rice part, respectively, from 2011 to 2012, presumably owing to the irreversible sorption of (137)Cs to clay minerals.
Journal of Environmental Radioactivity | 2014
Shigeto Fujimura; Junko Ishikawa; Yuuki Sakuma; Takashi Saito; Mutsuto Sato; Kunio Yoshioka
After the accident at the Fukushima Dai-ichi Nuclear Power Plant owned by Tokyo Electric Power Company on 11 March 2011, potassium was applied to fields in the Tohoku and Kanto areas of Japan to reduce radiocesium uptake by crops. Despite the intense studies relating to the effect of potassium application on availability of radiocesium in the soil, physiological changes of radiocesium uptake by crops in response to K(+) concentration around roots remains elusive. In the present study, we developed physiological models describing the effect of K(+) on the uptake of radiocesium by rice. Two Cs(+):K(+) competition models were evaluated using a wide range of data obtained from pot and field experiments: the model assuming a uniformity in the gene expression of K(+) transporter (Model I) and the model assuming the increase in the gene expression of K(+) transporter in response to K(+) concentration below threshold (Model II). The root-mean-square deviation between the measured and estimated values was larger in Model I than in Model II. Residuals were positively correlated with K(+) in Model I but showed no deflection in Model II. These results indicate that Model II explains the effect of K(+) on the uptake of radiocesium better than Model I. Model II may provide the appropriate countermeasures in inhibiting the transfer of radiocesium from soil to crop. The effect of changes in the variables in Model II on the relationship between available K(+) in soil and (137)Cs uptake by plant was simulated. An increase in available (137)Cs(+) in soil enhanced the response of (137)Cs uptake to K(+). The effects of Michaelis-Menten constant for Cs(+) were the inverse of the (137)Cs(+) effect. The effect of Michaelis-Menten constant for K(+) showed the same tendency as that of (137)Cs(+), but the effect was much less than that of (137)Cs(+). An increase in the threshold of K(+) below which the gene expression of K(+) transporter increases enhanced the response of (137)Cs uptake to K(+) in the high-K(+) range.
Soil Science and Plant Nutrition | 2015
Yasukazu Suzuki; Tetsuo Yasutaka; Shigeto Fujimura; Takao Yabuki; Mutsuto Sato; Kunio Yoshioka; Kazuyuki Inubushi
Abstract In 2011, the radiocesium concentration of brown rice grown (Oryza sativa L.) in mountainous areas with irrigation water that flowed from a nearby mountain forest, in Fukushima Prefecture, Japan, exceeded 500 Bq kg–1. Migration of radiocesium from contaminated irrigation water was suspected. Here, we investigated the migration of dissolved radiocesium (137Cs) from irrigation water into brown rice by determining the concentration of 137Cs in brown rice grown in pots irrigated with water containing dissolved 137Cs (0.1, 1.0 or 10 Bq L–1 137Cs). The treatment water was prepared by extracting 137Cs from conifer branches collected from the contaminated area and diluting the stock solution with tap water. We used two Gray Lowland soils (soils A and B) collected from two paddy fields in Fukushima Prefecture. Rice plants (Oryza sativa L. cv. Hitomebore) were grown in pots and treatment water was kept at a depth of 3–5 cm throughout the growing season. We calculated the amount of 137Cs absorbed by the plants by subtracting 137Cs concentrations in brown rice grown with tap water from that in brown rice grown with treatment water. The concentration of 137Cs in brown rice increased in proportion to that in the treatment water. The concentration of 137Cs in brown rice grown with water containing 10 Bq L–1 137Cs in soil A was 4.9 times that in brown rice grown in soil B, but the concentration of 137Cs in brown rice grown in either soil was not significantly different when grown with water containing 0.1 Bq L–1 137Cs. Before plants were grown, the exchangeable potassium in soil B was 3.8 times that in soil A. At least, even with irrigation water containing about 0.1 Bq L–1 of radiocesium, the migration of radiocesium into brown rice is negligible for the provisional regulation value for radiocesium in brown rice under the condition of our experiment.
Scientific Reports | 2017
Satoru Ishikawa; Shimpei Hayashi; Tadashi Abe; Masato Igura; Masato Kuramata; Hachidai Tanikawa; Manaka Iino; Takashi Saito; Yuji Ono; Tetsuya Ishikawa; Shigeto Fujimura; Akitoshi Goto; Hiroki Takagi
In Japan, radiocesium contamination in foods has become of great concern and it is a primary issue to reduce grain radiocesium concentration in rice (Oryza sativa L.). Here, we report a low-cesium rice mutant 1 (lcs1) with the radiocesium concentration in grain about half that in the wild-type cultivar. Genetic analyses revealed that a mutation in OsSOS2, which encodes a serine/threonine-protein kinase required for the salt overly sensitive (SOS) pathway in plants, is responsible for the decreased cesium (Cs) concentrations in lcs1. Physiological analyses showed that Cs+ uptake by lcs1 roots was significantly decreased under low-potassium (K+) conditions in the presence of sodium (Na+) (low K+/Na+). The transcript levels of several K+ and Na+ transporter genes, such as OsHAK1, OsHAK5, OsAKT1, and OsHKT2;1 were significantly down-regulated in lcs1 grown at low K+/Na+. The decreased Cs+ uptake in lcs1 might be closely related to the lower expression of these genes due to the K+/Na+ imbalance in the lcs1 roots caused by the OsSOS2 mutation. Since the lcs1 plant had no significant negative effects on agronomic traits when grown in radiocesium-contaminated paddy fields, this mutant could be used directly in agriculture for reducing radiocesium in rice grains.
Journal of Asian Ceramic Societies | 2015
Yomei Tokuda; Yuya Takahashi; Hirokazu Masai; Shunichi Kaneko; Yoshikatsu Ueda; Shigeto Fujimura; Toshinobu Yoko
Abstract We report the structural analysis of Na+ and Cs+ in sodium cesium borate crystals and glasses using 23Na and 133Cs magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The composition dependence of NMR spectra of the borate was similar to that of the silicate: (1) the peak position of cesium borate crystals shifted to upfield for structures with larger Cs+ coordination numbers, (2) the MAS NMR spectra of xNa2O-yCs2O-3B2O3 (x = 0, 0.25, 0.5, 0.75, 1.0, x + y = 1) glass showed that the average coordination number (CN) of both the alkali cations decreases with increasing Cs+/(Na+ + Cs+) ratio. However, the degree of decrement in borates is much smaller than that in silicates. We have considered that the small difference in CN is due to 4-coordinated B, because it is electrically compensated by the alkali metal ions resulting in the restriction of having various coordinations of O to alkali metal.
Plant and Cell Physiology | 2017
Hiroki Rai; Saki Yokoyama; Namiko Satoh-Nagasawa; Jun Furukawa; Takiko Nomi; Yasuka Ito; Shigeto Fujimura; Hidekazu Takahashi; Ryuichiro Suzuki; ELMannai Yousra; Akitoshi Goto; Shin-ichi Fuji; Shin-ichi Nakamura; Takuro Shinano; Nobuhiro Nagasawa; Hiroetsu Wabiko; Hiroyuki Hattori
Incidents at the Fukushima and Chernobyl nuclear power stations have resulted in widespread environmental contamination by radioactive nuclides. Among them, 137cesium has a 30 year half-life, and its persistence in soil raises serious food security issues. It is therefore important to prevent plants, especially crop plants, from absorbing radiocesium. In Arabidopsis thaliana, cesium ions are transported into root cells by several different potassium transporters such as high-affinity K+ transporter 5 (AtHAK5). Therefore, the cesium uptake pathway is thought to be highly redundant, making it difficult to develop plants with low cesium uptake. Here, we isolated rice mutants with low cesium uptake and reveal that the Oryza sativa potassium transporter OsHAK1, which is expressed on the surfaces of roots, is the main route of cesium influx into rice plants, especially in low potassium conditions. During hydroponic cultivation with low to normal potassium concentrations (0-206 µM: the normal potassium level in soil), cesium influx in OsHAK1-knockout lines was no greater than one-eighth that in the wild type. In field experiments, knockout lines of O. sativa HAK1 (OsHAK1) showed dramatically reduced cesium concentrations in grains and shoots, but their potassium uptake was not greatly affected and their grain yields were similar to that of the wild type. Our results demonstrate that, in rice roots, potassium transport systems other than OsHAK1 make little or no contribution to cesium uptake. These results show that low cesium uptake rice lines can be developed for cultivation in radiocesium-contaminated areas.
Archive | 2014
Takashi Saito; Yasukazu Suzuki; Shigeto Fujimura; Hirofumi Tsukada
After the Fukushima Daiichi Nuclear Power Plant (Tokyo Electric Power Company) accident occurred in March 2011, the concentration of radiocesium in brown rice produced in several areas of Fukushima Prefecture has exceeded a provisional regulation value. Therefore, we attempted research on decreasing the radiocesium concentration in agricultural plants.
Journal of Asian Ceramic Societies | 2014
T. Minami; Yomei Tokuda; Hirokazu Masai; Yoshikatsu Ueda; Yuji Ono; Shigeto Fujimura; Toshinobu Yoko
Abstract We report the structural analysis of Na+ and Cs+ in sodium cesium silicate glasses by using 23Na and 133Cs magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. In the NMR spectra of cesium silicate crystals, the peak position shifted to higher magnetic field for structures with larger Cs+ coordination numbers and to lower magnetic field for smaller Cs+ coordination numbers. The MAS NMR spectra of xNa2O-yCs2O-2SiO2 (x = 0, 0.2, 0.33, 0.5, 0.66, 0.8, 1.0; x + y = 1) glass reveal that the average coordination number of both the alkali cations decreases with increasing Cs+/(Na+ + Cs+) ratio. In addition, the coordination number of Na+ in xNa2O-yCs2O-2SiO2 glass is smaller than that of Cs+. This difference between the average coordination numbers of the alkali cations is considered to be one structural reason of the mixed alkali effect.