Journal of Radioanalytical and Nuclear Chemistry, Vol. 255, No. 1 (2003) 149–153 0236–5731/2003/USD 20.00 Akadémiai Kiadó, Budapest © 2003 Akadémiai Kiadó, Budapest Kluwer Academic Publishers, Dordrecht Water movement in a plant sample by neutron beam analysis as well as positron emission tracer imaging system T. M. Nakanishi, 1 * Y. Okuni, 1 J. Furukawa, 1 K. Tanoi, 1 H. Yokota, 1 N. Ikeue, 2 M. Matsubayashi, 2 H. Uchida, 3 A. Tsiji 3 1 Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, 113-8657, Japan 2 Japan Atomic Energy Research Institute, Tokai Establishment, 319-1195, Japan 3 Hamamatsu Photonics, Co., Hamamatsu, 434-8601, Japan (Received April 18, 2002) We present water imaging of a plant sample both by neutron beam and positron emission tracer imaging system (PETIS). The former method provided static water profile in a plant sample as well as that in the vicinity of a root imbedded in soil. Not only X-ray film but also CT method using a cooled CCD camera is presented. Through non-destructive water image in an X-ray film, root development as well as 2-dimensional water movement toward the root was analyzed. Spatial water image was constructed from 180 CT projection images, taken at an interval of one degree while rotating the sample, through a CCD camera. In the case of a soybean root, there was a water gradient toward a root in soil and gave minimum value at about 1 mm far from the surface of a root. The water absorbing part in a root was gradually shifted downward with the root development. We also present real time water movement by PETIS, where water was labeled with a positron emitting nuclide, 15 O. The transportation of 15 O- water within a plant was relatively slow and water uptake was observed only at the lowest internode, between a root and the first leaf, during 20-minute measurement. Introduction Though water plays an important role in plant physiology, the behavior of water has not been known well because of tools lacking for the research. Although, the imaging by X-ray beam is an effective technique to visualize comparatively heavy elements in living samples. Neutron beam has an advantage to detect light elements, such as hydrogen, lithium and boron. When the plants are irradiated with neutrons beam, hydrogen image is produced, for the attenuation efficiency of hydrogen is about 100–1000 times higher compared to those of the other common elements. Since more than 80% of living organism is consisted of water, an image by neutron beam can be regarded as water image of a living plant. Recently, NAKANISHI et al., 1-8 has developed neutron beam analysis to get water image of a living plant. This method provides nondestructive water specific image in a plant with high resolution. We also performed a neutron beam imaging through a cooled CCD camera to construct CT images (computer tomography; cross-sectional image), and spatial water distribution was analyzed according to the method developed. Though the neutron method showed the static water distribution in a living plant, it was difficult to trace the real-time water movement in a plant tissue. Therefore, we tried a method, namely the positron emitting tracer imaging system (PETIS), where the radioactive nuclide emits two gamma-rays, with identical energy, to 180 degree. Setting the sample between a pair of gamma-ray detector, the position and amount of the labeled water absorbed can be measured. * E-mail: atomoko@mail.ecc.u-tokyo.ac.jp First of all, we tried to use 18 F-labeled water (T 1/2 = 110 min), produced by a cyclotron, to measure a short term water uptake and transport in a plant, 9-11 which method was developed by KUME et al. 12 However, there was always a problem whether tracing an activity from 18 F really indicates the water movement itself. Though only a small amount of 18 F was produced from water target, without any carrier of F - ions, the movement of 18 F - ions could be different from that of water itself. To solve this problem, the application of 15 O-labeled water was necessary. But because of the extremely short half-life of 15 O (2 min), it was difficult to produce enough amount of tracer and to perform the tracer work. Using the special system developed by one of the authors, we could produce sufficient amount of 15 O-water to measure the real time movement of water itself in a soybean plant. In this paper we present the water image obtained by neutron beam as well as PETIS using 15 O-water. Experimental Neutron imaging Soybean seedlings (Glycine max c.v. Tsurunoko) were grown in an aluminum container (7 cm 15 cm 2 mm) containing Toyoura’s standard sand (silt type, 197–203 m, in pore size) with 15% (w/w) of water. The sample was grown in a phytotron at 27 °C and was periodically taken out to get neutron image. Neutron irradiation was performed at a research reactor, JRR-3M at the Japan Atomic Energy Research