PNNL

Abstract

Utilization of high-resolution molecular tomography revealed that the soybean nodule is not metabolically uniform, with several distinctive patterns of metabolite distributions through the nodule’s anatomy. Specifically, using two- and three-dimensional matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry imaging (MALDI-FTICR MSI) metabolites showed i) cortex localization, ii) a gradual increase toward the central infection zone, iii) uniform localization through whole nodule, iv) uniform localization throughout the infection zone, or v) asymmetric distribution within the infection zone. Some molecules belonging to the same or correlated metabolic pathways were found localized with different patterns, indicating localized differences in their synthesis/turnover. Special attention was given to asymmetrical distributed metabolites (e.g., S-adenosylmethionine; SAMe), where some small-scale patterns were detected in individual sections, and 3D reconstruction enabled resolution of whole nodule molecular distributions. These results hint at a complex, spatially differentiated metabolism occurring in soybean root nodules.