Magnetic Resonance Microscopy at Cellular Resolution and Localised Spectroscopy of Medicago truncatula at 22.3 Tesla

Area of Science:

• Plant Biology
• Microbiology
• Biophysics

Background:

• Plant-microbe interactions are vital for soil health and agriculture.
• Investigating these interactions in situ is complex due to intertwined morphology and metabolism.
• Medicago truncatula root nodules are a key model for symbiotic nitrogen fixation.

Purpose of the Study:

• To develop and apply advanced Magnetic Resonance (MR) Microscopy for in situ analysis of plant root nodules.
• To elucidate the morphology and metabolic profiles of individual cells within Medicago truncatula root nodules.
• To visualize spatial distribution of metabolites across different nodule zones.

Main Methods:

• Utilized high-field (22.3 T) MR Microscopy with a custom solenoid RF coil for imaging individual root nodules.
• Employed a 3D imaging sequence with isotropic (7 μm)³ resolution to distinguish infected and uninfected cells.
• Applied localized MR spectroscopy and chemical shift imaging to map metabolite concentrations and spatial distribution.

Main Results:

• Achieved cellular resolution, enabling differentiation between rhizobia-infected and uninfected cells.
• Identified distinct concentrations of metabolites such as betaine, asparagine/aspartate, and choline across nodule zones.
• Successfully visualized the spatial distribution of these key metabolites within the nodule structure.

Conclusions:

• High-field MR Microscopy is a powerful tool for dissecting plant-microbe interactions at the cellular level.
• This technique provides insights into nodule metabolism and cellular differentiation.
• Future applications include in vivo MR microscopy of intact root systems for a comprehensive understanding of symbiosis.