How to image carbon dynamics of photosynthesis and photosynthetic products

Radionuclide imaging technologies have opened up experimental opportunities for biological research. However, the conventional measurement tools used in plant science are invasive and require calibration by statistical analysis over a large number of test plants. RI imaging is one of the most powerful tools for conducting research on the distribution and translocation nutrition of water, nitrogen, mineral nutrients, etc., and environmental pollutants in plants, noninvasively. For analysis of carbon kinetics in a plant body, it is possible with the positron-emitting radioisotope C-11, which has a short half-life, and positron imaging systems. The carbon kinetics makes it a strong potential candidate for application to the analysis of physiologies involved in photosynthesis and photoassimilate translocation. The C-11 imaging approach has been used for real-time and quantitative video imaging of tracer dynamics during carbon fixation, photosynthesis, and photoassimilate translocation. In this paper, we describe the latest method to image the dynamics of C-11 compounds in the plant body using RI imaging method and discuss its applicability to investigations of the kinetics of carbon nutrients during photosynthesis and photoassimilate translocation and unloading. Elucidation of the carbon kinetics in a plant body clearly leads to agricultural study on the growth and development of grains and fruits.World Congress on Light and Life (17th Congress of the International Union of Photobiology and 18th Congress of the European Society for Photobiology

Noninvasive imaging of hollow structures and gas movement revealed the gas partial-pressure-gradient-driven long-distance gas movement in the aerenchyma along the leaf blade to submerged organs in rice

Rice (Oryza sativa) plants have porous or hollow organs consisting of aerenchyma, which is presumed to function as a low-resistance diffusion pathway for air to travel from the foliage above the water to submerged organs. However, gas movement in rice plants has yet to be visualized in real time. In the present study involving partially submerged rice plants, the leaves emerging from the water were fed [13N]N2 tracer gas. The subsequent monitoring of the [13N]N2 tracer gas indicated it moved rapidly downward along the leaf blade, leaf sheath, and internode over time, arriving at the bottom of the plant within 10 min, which was 20 min earlier than 11C-photoassimilates. The [13N]N2 gas movement was presumably mediated by diffusion along the aerenchyma network from the leaf blade to the root via nodes functioning as junctions, which were detected by X-ray computed tomography. These findings imply the diffusion of gas along the aerenchyma, which does not consume energy, has enabled plants to adapt to aquatic environments. Additionally, there were no major differences in [13N]N2 gas movement between paddy rice and deepwater rice plants, indicative of a common aeration mechanism in the two varieties, despite the difference in their response to flooding

Non-invasive imaging of radiocesium dynamics in a living animal using a positron-emitting 127Cs tracer

Visualizing the dynamics of cesium (Cs) is desirable to understand the impact of radiocesium when accidentally ingested or inhaled by humans. However, visualization of radiocesium in vivo is currently limited to plants. Herein, we describe a method for the production and purification of 127Cs and its use in visualizing Cs dynamics in a living animal. The positron-emitting nuclide 127Cs was produced using the 127I (α, 4n) 127Cs reaction, which was induced by irradiation of sodium iodide with a 4He2+ beam from a cyclotron. We excluded sodium ions by using a material that specifically adsorbs Cs as a purification column and successfully eluted 127Cs by flowing a solution of ammonium sulfate into the column. We injected the purified 127Cs tracer solution into living rats and the dynamics of Cs were visualized using positron emission tomography; the distributional images showed the same tendency as the results of previous studies using disruptive methods. Thus, this method is useful for the non-invasive investigation of radiocesium in a living animal

Plant root PET: visualization of photosynthate translocation to roots in rice plant

Roots are essential to plants for uptake of water and nutrients. For the improvement of crop production, it is necessary to understand the elucidation of the root development and its function under the ground. Espeially, photosynthate translocation from plant leaves to roots is an important physiological function that affects the root elongation, adaptation to the soil environment and nutrients uptake. To evaluate the translocation dynamics to roots, positron emission tomography (PET) and 11C tracer have been used. However, the spatial resolution is degraded at roots that develop around the peripheral area of field of view (FOV) due to parallax errors. In this study, to overcome this problem, we developed a small OpenPET prototype applying four-layer depth-of-interaction detectors. We demonstrated the imaging capability of 11C-photosynthate translocation to rice roots that develop throughout the entire PET field. We also tried to obtain structural information of roots by high-throughput X-ray computed tomography (CT) system using the same test plant. As a result, we succeeded in visualizing the root structure that developed around the peripheral region of FOV and imaging the accumulation of 11C-photosynthate to the roots in those areas without degrading the spatial resolution. From obtained images, we also succeeded in evaluating the translocation dynamics varied by roots. The combined use of the high-throughput CT system and the OpenPET prototype was demonstrated to be appropriate for structural and functional analysis of roots

Fruit PET: 3-D imaging of carbon distribution in fruit using OpenPET

Research on the distribution and dynamics of photoassimilates in plants, especially those in fruits, is important for increasing food production. Positron emission tomography (PET) and carbon-11 (C-11) can be used for obtaining 3-D images of photoassimilates. For plant experiments, however, it is important to adjust the system to the plant’s growth environment. A small OpenPET prototype can visualize an open space between two detector rings, and thus facilitate adjustment of the environment around a target plant during fruit PET imaging. In this work, we improve the OpenPET for plant studies and discuss its applications in the analysis of the dynamics and distributions of photoassimilates in plants with fruits. C-11-labeled photoassimilate translocation into the fruit of a strawberry plant is imaged using C-11-labeled carbon dioxide and the OpenPET. The OpenPET has been found to be promising for researching the physiological functions of the photoassimilates in plants with fruits