The Application of Contrast Media for In Vivo Feature Enhancement in X-Ray Computed Tomography of Soil-Grown Plant Roots

Abstract

The use of in vivo X-ray microcomputed tomography (μCT) to study plant root systems has become routine, but is often hampered by poor contrast between roots, soil, soil water, and soil organic matter. In clinical radiology, imaging of poorly contrasting regions is frequently aided by the use of radio-opaque contrast media. In this study, we present evidence for the utility of iodinated contrast media (ICM) in the study of plant root systems using μCT. Different dilutions of an ionic and nonionic ICM (Gastrografin 370 and Niopam 300) were perfused into the aerial vasculature of juvenile pea plants via a leaf flap (Pisum sativum). The root systems were imaged via μCT, and a variety of image-processing approaches used to quantify and compare the magnitude of the contrast enhancement between different regions. Though the treatment did not appear to significantly aid extraction of full root system architectures from the surrounding soil, it did allow the xylem and phloem units of seminal roots and the vascular morphology within rhizobial nodules to be clearly visualized. The nonionic, low-osmolality contrast agent Niopam appeared to be well tolerated by the plant, whereas Gastrografin showed evidence of toxicity. In summary, the use of iodine-based contrast media allows usually poorly contrasting root structures to be visualized nondestructively using X-ray μCT. In particular, the vascular structures of roots and rhizobial nodules can be clearly visualized in situ.

Tracking the Biological Incorporation of Exogenous Molecules into Cellulose Fibers with Non‐Radioactive Iodinated Glucose

“…In plant sciences, these compounds have been used to identify water and ion movement in plants, saplings and segments of Vitis vinifera L., Olea europaea L. and Laurus nobilis L. [18] and Castanea dentata (Marshall) Borkh. [19] Also, these compounds have been utilized for the spatial, in-vivo, dynamic visualization of water movement in roots [20] or conductive conduits (xylem) during tissue desiccation/rehydration, embolism resistance [21] and repair. [22] Interestingly, the combination of CT and non-radioactive, metabolizing iodinated glucose 2-deoxy-2-iodo-D-glucose (DIG) for exploring sugar transport and accumulation in smaller plants still remains largely unexplored.…”

Stabilizing gold nanoparticles for use in X-ray computed tomography imaging of soil systems

“…For example, when tobacco ( Nicotiana xanthi L.) seedlings were exposed to AuNP suspensions, the nanoparticles only appeared to induce visually observable leaf damage after 14 days of exposure [18]. By comparison, Keyes et al [19] exposed winter pea ( Pisum sativum L. cv. frisson) to iodinated contrast media (Gastrografin) and observed severe tissue damage after 1 day.…”

Developing a system for in vivo imaging of maize roots containing iodinated contrast media in soil using synchrotron XCT and XRF

“…The aim of our study was to develop an experimental system which enables the contrast media to be applied directly to an exposed section of root for uptake and translocation, and which is also compatible with timeresolved SRXCT to facilitate in vivo imaging of plant root material in soil. We hypothesised that by supplying the contrast media directly to the roots we would circumnavigate the issues of translocation highlighted above in the work of Karunakaran et al (2015) and Keyes et al, (2017b). In this study we demonstrate the efficacy of this experimental setup and outline example data which can be gathered using such a system.…”

“…However, when imaging ex vivo or harvested plant material it is not possible to capture plant processes over time and much structural information can be lostparticularly when studying root systems which are removed from soil. Karunakaran et al (2015) and Keyes et al, (2017b) are two of only very few examples of the use of contrast media for in vivo XCT phytological imaging. Karunakaran et al (2015) used the non-ionic iodinated contrast agent Ioversol to undertake synchrotron phase contrast imaging of wheat seed spikes and canola stems by introducing the contrast media directly into the vasculature via injection.…”

“…However, the plant samples featured in this study were imaged against a background of air which is considerably less attenuating than soil and thus the complications of limited contrast introduced when imaging plant material in soil were not present. Keyes et al, (2017b) submerged cut leaf material of a live winter pea plant in non-ionic iodinated contrast media (both Gastrografin and Niopam contrast agents) and after 24 h undertook XCT imaging of the in vivo soil borne roots to capture contrast media which had translocated from the leaves to the roots via the plant's vasculature. This further confirmed the promising potential for using iodinated contrast media to image in vivo root systems.…”