Real time visualization of N-13-translocation in rice under different environmental conditions using positron emitting tracer imaging system

The ammonium ion is an indispensable nitrogen source for crops, especially paddy rice (Oryza sativa L. cv Nipponbare). Until now, it has been impossib le to measure ammonium uptake and nitrogen movement in plants in real time. Using the new technologies of PETIS (positron emitting tracer imaging syst em) and PMPS (positron multi-probe system), we were able to Visualize the r eal time translocation of nitrogen and water in rice plants. We used positr on-emitting N-13-labeled ammonium ((NH4+)-N-13) and O-15-water to monitor t he movement. In plants cultured under normal conditions,(NH4+)-N-13 supplie d to roots was taken up, and a N-13 Signal was detected at the discriminati on center, the basal part of the shoots, within 2 minutes. This rapid trans location of N-13 was almost completely inhibited by a glutamine synthetase inhibitor, methionine sulfoximine. In general, nitrogen deficiency enhanced N-13 translocation to the discrimination center. In the dark, N-13 translo cation to the discrimination center was suppressed to 40% of control levels , whereas O-15-water flow from the root to the discrimination center stoppe d completely in the dark. In abscisic acid-treated rice,N-13 translocation to the discrimination center was doubled, whereas translocation to leaves d ecreased to 40% of control levels. Pretreatment with NO3- for 36 hours incr eased N-13 translocation from the roots to the discrimination center to 5 t imes of control levels. These results suggest that ammonium assimilation (f rom the roots to the discrimination center) depends passively on water flow , but actively on NH4+-transporter(s) or glutamine synthetase(s).