Research with radiation and radioisotopes to better understand plant physiology and agricultural consequences of radioactive contamination from the Fukushima Daiichi nuclear accident

J Radioanal Nucl Chem (2017) 311:947–971 DOI 10.1007/s10967-016-5148-z Research with radiation and radioisotopes to better understand plant physiology and agricultural consequences of radioactive contamination from the Fukushima Daiichi nuclear accident Tomoko M. Nakanishi1 Received: 10 November 2016 / Published online: 4 January 2017 Ó The Author(s) 2017. This article is published with open access at Springerlink.com Abstract Research carried out by me and my group over the last almost four decades are summarized here. The main emphasis of my work was and continues to be on plant physiology using radiation and radioisotopes. Plants live on water and inorganic elements. In the case of water, we developed neutron imaging methods and produced 15O-labeled water (half-life 2 min) and applied them to understand water circulation pattern in the plant. In the case of elements, we developed neutron activation analysis methods to analyze a large number of plant tissues to follow element specific distribution. Then, we developed realtime imaging system using conventional radioisotopes for the macroscopic and microscopic observation of element movement. After the accident in Fukushima Daiichi nuclear power plant, we, the academic staff of Graduate School, have been studying agricultural effects of radioactive fallout; the main results are summarized in two books published by Springer. Keywords Neutron imaging
Water imaging and measurement
Radioisotope
Real-time radioisotope imaging system
Plant physiology
Fukushima nuclear accident
Agricultural impact of contamination & Tomoko M. Nakanishi 1 Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1, Yayoi, Bunkyo-Ku, Tokyo 113-8657, Japan Introduction First of all, I would like to express my sincere thanks to the members of Hevesy Medal Award Selection Panel 2016 as well as to all the people who supported me for the Hevesy Medal Award. I would like to summarize in this paper the kind of research I have been doing in my life. After determining the half-lives of long-lived nuclides, namely 91Nb and 92Nb for my PhD thesis, I have been targeting plant physiology for many years and applying radiochemical approaches. Though plants live on only inorganic elements and water, little is known about the distribution or movement of these and water in a living plant. For example, photosynthesis is known to produce sucrose out of CO2 and water but water itself has not been gathering the attention. Water was simply granted to exist there but is playing an important role for the chemical process of the energy conversion, form light to chemical energy. However, we do not know how water is absorbed and transferred in the plant. Therefore, my first interest was water, in particular how water is distributed and move within a living plant as well as its absorption from roots. To study water distribution in plants, neutron beam was applied which produced waterspecific image of the plant. The neutron beam allowed imaging not only water itself but also the morphological development of the plant tissue which was not visualized earlier, such as seed formation in pods or roots imbedded in soil. Then, 15O labeled water was used to trace the water movement in detail and we found that tremendous amount of water was always flowing out from xylem and re-entered the xylem again, indicating that there is a circulation of water flow in the stem of a soybean plant. Element was another target of my research. There are 17 essential elements for plant growth, but little is known 123 948 about the overall accumulation or movement manner of the elements. Activation analysis was performed for a large number of plant tissues and the element-specific accumulation pattern in the plant was found; and this pattern was maintained in the same way throughout the developmental stage. When flowering was induced, Mg-specific distribution pattern disappeared which led later to develop the production of the radioactive magnesium tracer, 28Mg (half-life: 21 h). Since each element showed its specific distribution pattern in a plant, next step was the development of realtime imaging of the elements. Though imaging using positron emitters has been developed especially in medical field known as PET (Positron Emission Tomography), its resolution cannot be less than mm because of the relatively high positron energy. In the case of fluorescence imaging, imaging under light condition is not possible and the amount of the element in the image could not be measured. Therefore, the real-time RI imaging system was developed by us using not only gamma-ray but also beta emitters which are commercially available so that other people can also use them. We have been successful in developing the systems both for macroscopic and microscopic imaging. The real-time movement of the elements can now be visualized and analyzed using 14C, 22Na, 28Mg, 32P, 33P, 35 S, 42K, 45Ca, 54Mn, 55Fe, 59Fe,65Zn, 86Rb, 109Cd, 137Cs, etc. The image of 14CO2 gas fixation provided that the photosynthate was moved quickly to produce the meristem of the root tip. After Fukushima nuclear accident, our group studied the agricultural consequences of radioactive contamination from the Fukushima Daiichi reactors. I was able to edit two English books summarizing our data, published by Springer. The on-line version of the first book was accessed more than 50,000 times a year and the third book is now going to be published next year. A brief survey of many research projects carried out over the years by me and my group is given below. J Radioanal Nucl Chem (2017) 311:947–971 Fig. 1 Application of radiation or radioisotopes to plant study highest resolution yet attainable for water in tissue. With high specificity for water, neutron beam could image water movement in seeds or in roots imbedded in soil as well as in wood disks and meristems during the development. Through neutron image analysis, we were able to analyze the activity of intact cells or tissue. Since more than 80% of the living plant is consisted of water, water image indicates the tissue image itself. Figure 2 is one of the examples of the water-specific image of lily and from this image we can estimate how the pistil and stamen inside the bud are developing. Similar to the flower bud, the seed formation inside the pod became visible. In the case of agricultural industry, to create the sterile plant which does not develop the seed, is one of the important feature to be able to provide the seeds every year. (not clear what the author wants to say in the last sentence). Another requirement from flower industry is to keep the flowering time of the cult flowers longer. One of the Research topics: methodology, results and discussion Since plants live on water and inorganic elements, the applied radiation or radioisotope method used in presented in Fig. 1. Neutron beam imaging: water distribution [1–27] Flower, wood disk and se (...truncated)