Fig. 1

a Anatomy of the soybean nodule as viewed through an optical image of a section (left) and the MALDI spectral spatial segmentation, which distinguishes areas based on their spectral composition (right). b Distribution of SAM, ADP, and heme B in the central cross-section of seven randomly selected WT nodules. Nodules were analyzed in different experiments to minimize analytical bias. In nodule No 5, SAM and heme B show symmetrical distribution pattern, which suggest that asymmetry in nodule metabolism can be consequence of nodule development over time. c For SAM, ADP, and heme B imaged in WT and nifH⁻ nodules, both nodules were imaged in the same experiment, so that the relative intensity of ion signals can be compared. Scale bars are 1 mm