Figure 2
High-resolution MR imaging and optical microscopy of root nodules. (a) FLASH image of fixed root nodule at 7 × 7 × 7 µm3 resolution with an acquisition time of 34 h24 m. Individual cells containing bacteroids (ba) can be discerned by the dark rings inside the cells, where S. meliloti cells accumulate. The nodule exhibits a double meristem (m) on opposed directions with cells becoming smaller towards the meristem until individual cells can no longer be resolved. Air pockets appear as hypo-intense regions marked with an arrowhead. (b) Optical transmission microscopy of nodule section (thickness 5 µm) stained with Toluidine blue. (c) FLASH image of in situ root nodule at 7 × 7 × 7 µm3 resolution with an acquisition time of 34 h24 m. Though lower in signal-to-noise, both uninfected cells (black arrow) and infected cells (ba) can be discerned. Abbreviations: rc, root cortex; xy, xylem; ph, phloem; nc, nodule cortex; vb, vascular bundle; fx, fixation zone; if, infection zone; ba, bacteroid containing cells; m, meristem. Scale bars 200 µm.
