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 for14N and15N 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. © 1996 Academic Press, Inc.