Measuring Nitrate in Plant Cells by in Vivo NMR Using Gd3+ as a Shift Reagent

NMR investigations of nitrate in plant cells and tissues have hitherto been limited by the indistinguishability of the signals from intracellular and extracellular nitrate. Gd3+ is shown to be an effective shift reagent for 14N and 15N nitrate NMR signals, resolving the internal and external nitrate signals in plant tissues, including cell suspensions and root material. However, time-course experiments show that, while the use of Gd3+ allows nitrate levels to be monitored over extended periods, it also has adverse effects on growth and nitrate uptake. Accordingly, a number of chelated forms of gadolinium were investigated, and it is concluded that the NMR contrast agent Gd(DTPA-BMA) is likely to be a suitable shift reagent for physiologically relevant studies of nitrate transport in roots.