A small-scale MRI scanner and complementary imaging method to visualize and quantify xylem embolism formation.

Marco Meixner,Carel W Windt,Petra Foerst,Martina Tomasella

doi:10.1111/nph.16442

Marco Meixner, Carel W Windt + Show 2 more

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https://doi.org/10.1111/nph.16442

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Abstract

Magnetic resonance imaging (MRI) is a useful tool to image xylem embolism formation in plants. MRI scanners configured to accept intact plants are rare and expensive. Here, we investigate if affordable small-scale, custom-built low-field MRI scanners would suffice for the purpose. A small-scale, C-shaped permanent magnet was paired with open, plane parallel imaging gradients. The setup was small enough to fit between leaves or branches and offered open access for plant stems of arbitrary length. To counter the two main drawbacks of the system, low signal to noise and reduced magnetic field homogeneity, a multi-spin echo (MSE) pulse sequence was implemented, allowing efficient signal acquisition and quantitative imaging of water content and T2 signal relaxation. The system was tested visualizing embolism formation in Fagus sylvatica during bench dehydration. High-quality images of water content and T2 were readily obtained, which could be utilized to detect the cavitation of vessels smaller than could be spatially resolved. A multiplication of both map types yielded images in which filled xylem appeared with even greater contrast. T2 imaging with small-scale MRI devices allows straightforward visualization of the spatial and temporal dynamics of embolism formation and the derivation of vulnerability curves.

Highlights

As a result of shifts in temperature and precipitation patterns, forests worldwide are expected to experience an increase in duration and frequency of drought and widespread forest dieback events (Dai, 2013; Park Williams et al, 2013; Trenberth et al, 2014)
In this study we demonstrate how a small-scale Magnetic resonance imaging (MRI) scanner and complementary imaging method based on multi-spin echo (MSE) can be used to visualize and quantify embolism formation
Despite the low field strength and the relatively low resolution afforded by the small-scale magnetic resonance (MR) imager, our method was remarkably successful at visualizing the appearance and spread of embolism in the xylem

Summary

Introduction

As a result of shifts in temperature and precipitation patterns, forests worldwide are expected to experience an increase in duration and frequency of drought and widespread forest dieback events (Dai, 2013; Park Williams et al, 2013; Trenberth et al, 2014). High-resolution computed tomography (HRCT) is currently the most used noninvasive method and is known for the excellent resolution that it affords (Choat et al, 2016). It was found to damage living tissue (Savi et al, 2017) and cause growth inhibition (Dhondt et al, 2010) and disruption of cellular function (Petruzzellis et al, 2018) It is less suitable for long-term repeated observations or for investigations of recovery, even though current evidence suggests that xylem vulnerability per se, as it primarily depends on the integrity of the dead xylem structure rather than on its living cells and surroundings, is not affected by HRCT

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