Laser ablation tomography for visualization of root colonization by edaphic organisms

Abstract

Soil biota have important effects on crop productivity, but can be difficult to study in situ. Laser ablation tomography (LAT) is a novel method that allows for rapid, three-dimensional quantitative and qualitative analysis of root anatomy, providing new opportunities to investigate interactions between roots and edaphic organisms. LAT was used for analysis of maize roots colonized by arbuscular mycorrhizal fungi, maize roots herbivorized by western corn rootworm, barley roots parasitized by cereal cyst nematode, and common bean roots damaged by Fusarium. UV excitation of root tissues affected by edaphic organisms resulted in differential autofluorescence emission, facilitating the classification of tissues and anatomical features. Samples were spatially resolved in three dimensions, enabling quantification of the volume and distribution of fungal colonization, western corn rootworm damage, nematode feeding sites, tissue compromised by Fusarium, and as well as root anatomical phenotypes. Owing to its capability for high-throughput sample imaging, LAT serves as an excellent tool to conduct large, quantitative screens to characterize genetic control of root anatomy and interactions with edaphic organisms. Additionally, this technology improves interpretation of root–organism interactions in relatively large, opaque root segments, providing opportunities for novel research investigating the effects of root anatomical phenes on associations with edaphic organisms.

Three‐dimensional digital image construction of metaxylem vessels in root tips of Zea mays subsp. mexicana from thin transverse sections

“…The former produces reasonably good results at a fairly high resolution (3 μm) following the infiltration of an appropriate “contrast agent” such as phosphotungstate and critical‐point drying (Staedler et al., ). The latter, LAT, has the advantage of high throughput, but is limited in resolution to >0.1 mm (Strock et al., ), so it is even less useful for studying fine anatomical details than MRI and has the disadvantage of destroying and discarding the sample as it proceeds. Wu et al.…”

“…Neither MRI nor CLSM is suitable for observing fine cell structure, which currently requires a fixation technique that maintains cell ultrastructural features, appropriate staining, and the thin to ultrathin sectioning of tissue required for a good resolution of detail and contrast (Niki et al., ). Other methods relying on advanced technology have been successfully used for the 3D reconstruction of plant structures, such as X‐ray tomography (micro‐CT) (Staedler et al., ) and laser ablation technology (LAT) (Strock et al., ), but the latter obliterates the specimen and neither method provides as high a level of resolution as CLSM or the new method we present here.…”

The genetic architecture of host response reveals the importance of arbuscular mycorrhizae to maize cultivation

“…It has been proposed that the differing demands placed on root system architecture and anatomy by direct foraging and AM symbiosis prevent co-optimization for both (Lambers et al, 2008;Wen et al, 2019). For example, although increasing the proportion of root cortical aerenchyma (root air space) reduces the "carbon cost" of the root system, promoting foraging efficiency (Postma & Lynch, 2011), the reduction in cortical tissue may limit AMF colonization and, potentially, host response (Strock et al, 2019). It was somewhat surprising to see a QTL for a morphological trait such as tassel branch number to be conditional on AM susceptibility; such observations may indicate the action of pleiotropic systemic signals on host plant development.…”

Infection by cyst nematodes induces rapid remodelling of developing xylem vessels in wheat roots

“…Laser ablation tomography has been applied to segments of barley roots infected by the cereal cyst nematode (CCN; Heterodera avenae W.) 28 . This approach revealed the shapes and relative positions of nematodes, feeding sites and surrounding tissue, but with less detail than can be seen with microscopy.…”