An application of NMR microimaging to investigate nitrogen fixing root nodules

Various techniques to obtain high-resolution NMR images (voxel size down to 39 × 39 × 250 μm) of nitrogen-fixing root nodules from soybean [Glycine max (Merr.)] and peanut (Arachis hypogaea L.) are compared. We describe the artefacts arising from changes in the magnetic susceptibility throughout the sample and how these can be minimised. A series of T1 (TR = 220 to 3020 ms) and T2 (TE = 9.3 to 33.6 ms) weighted images are presented. From these it has been possible to locate the oxygen diffusion barrier. A possible interpretation in terms of nodule biochemistry and physiology are given. The data and parameters presented are shown to serve as a basis for more extensive investigations of root nodules (e.g., the oxygen diffusion barrier or the mechanisms driving the regulation of the oxygen concentration in the infected zone by leghemoglobin) by NMR microimaging.