Visualization of Uptake of Mineral Elements and the Dynamics of Photosynthates in Arabidopsis by a Newly Developed Real-Time Radioisotope Imaging System (RRIS)

Minerals and photosynthates are essential for many plant processes, but their imaging in live plants is difficult. We have developed a method for their live imaging in Arabidopsis using a real-time radioisotope imaging system. When each radioisotope, Na-22, Mg-28, P-32-phosphate, S-35-sulfate, K-42, Ca-45, Mn-54 and Cs-137, was employed as an ion tracer, ion movement from root to shoot over 24 h was clearly observed. The movements of Na-22, K-42, P-32, S-35 and Cs-137 were fast so that they spread to the tip of stems. In contrast, high accumulation of Mg-28, Ca-45 and Mn-54 was found in the basal part of the main stem. Based on this time-course analysis, the velocity of ion movement in the main stem was calculated, and found to be fastest for S and K among the ions we tested in this study. Furthermore, application of a heat-girdling treatment allowed determination of individual ion movement via xylem flow alone, excluding phloem flow, within the main stem of 43-day-old Arabidopsis inflorescences. We also successfully developed a new system for visualizing photosynthates using labeled carbon dioxide, (CO2)-C-14. Using this system, the switching of source/sink organs and phloem flow direction could be monitored in parts of whole shoots and over time. In roots, C-14 photosynthates accumulated intensively in the growing root tip area, 200-800 A mu m behind the meristem. These results show that this real-time radioisotope imaging system allows visualization of many nuclides over a long time-course and thus constitutes a powerful tool for the analysis of various physiological phenomena.