The interplay of rhizosphere components such as root exudates, microbes, and minerals
results in small-scale gradients of organic molecules in the soil around roots. The current
methods for the direct chemical imaging of plant metabolites in the rhizosphere often
lack molecular information or require labeling with fluorescent tags or isotopes. Here,
we present a novel workflow using laser desorption ionization (LDI) combined with
mass spectrometric imaging (MSI) to directly analyze plant metabolites in a complex soil
matrix. Undisturbed samples of the roots and the surrounding soil of Zea mays L. plants
from either field- or laboratory-scale experiments were embedded and cryosectioned to
100 mm thin sections. The target metabolites were detected with a spatial resolution of
25 mm in the root and the surrounding soil based on accurate masses using ultra-high
mass resolution laser desorption ionization Fourier-transform ion cyclotron resonance
mass spectrometry (LDI-FT-ICR-MS). Using this workflow, we could determine the
rhizosphere gradients of a dihexose (e.g., sucrose) and other plant metabolites (e.g.,
coumaric acid, vanillic acid). The molecular gradients for the dihexose showed a
high abundance of this metabolite in the root and a strong depletion of the signal
intensity within 150 mm from the root surface. Analyzing several sections from the same
undisturbed soil sample allowed us to follow molecular gradients along the root axis.
Benefiting from the ultra-high mass resolution, isotopologues of the dihexose could be
readily resolved to enable the detection of stable isotope labels on the compound level.
Overall, the direct molecular imaging via LDI-FT-ICR-MS allows for the first time a nontargeted
or targeted analysis of plant metabolites in undisturbed soil samples, paving
the way to study the turnover of root-derived organic carbon in the rhizosphere with
high chemical and spatial resolution.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:84428 |
| Date | 30 March 2023 |
| Creators | Lohse, Martin, Haag, Rebecca, Lippold, Eva, Vetterlein, Doris, Reemtsma, Thorsten, Lechtenfeld, Oliver J. |
| Publisher | Frontiers Research Foundation |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:article, info:eu-repo/semantics/article, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | 1664-462X, 753812 |
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