Development of matrix-assisted laser desorption ionization-mass spectrometry imaging (MALDI-MSI) for plant metabolite analysis

This thesis presents efforts to improve the methodology of matrix-assisted laser desorption ionization-mass spectrometry imaging (MALDI-MSI) as a method for analysis of metabolites from plant tissue samples. The first chapter consists of a general introduction to the technique of MALDI-MSI, and the sixth and final chapter provides a brief summary and an outlook on future work. The second chapter (following a general introduction) illustrates how MALDI-MSI of metabolites can be combined with genomics knowledge to infer functional genomic information. Wild-type Arabidopsis flower petals were investigated for their content of three flavonoids (kaempferol, quercetin, and isorhamnetin) and their glucosides, and compared to a well-understood flavonoid mutant (tt7). Spatially non-uniform accumulation/depletion of flavonoids is observed between the wild-type and mutant, and metabolite abundances are compared to infer information about localized gene expression. The third chapter demonstrates a novel small molecule application for a matrix previously used for MALDI-MSI of lipids (1,5-diaminonaphthalene, DAN). DAN was compared to other common MALDI matrices for its efficiency in ionization of several plant metabolite standards, and was found to be comparable or superior for all tested metabolites. DAN was then applied to image a range of classes of metabolites from a cross-section of corn leaf. The fourth chapter presents a novel acquisition method, in which high-mass resolution and tandem MS scans are acquired in alternating polarities during a single MALDI-MSI experiment. This methodology yields highly information-rich datasets, allowing for the generation of images from either high-resolution, accurate mass measurements or specific MS/MS or MSn transitions in both polarities, greatly expanding the number of detectable metabolites. The fifth chapter describes modifications made to the instrument laser optics to significantly enhance the achievable spatial resolution for MALDI-MSI on the system. A combination beam expander/spatial filter and aspheric focusing optics are used to reduce the laser spot size at the sample surface. This high-resolution configuration is then used to image metabolites from a corn leaf cross-section at 5 µm resolution, revealing single-cell metabolite localizations within the tissue

When stuff gets old: material surface characteristics and the visual perception of material change over time

YesMaterials’ surfaces change over time due to chemical and physical processes. These processes can significantly alter a material’s visual appearance, yet we can recognise the material as the same. The present study examined the extent of changes the human visual system can detect in specific materials over time. Participants (N = 5) were shown images of different materials (Banana, Copper, Leaf) from an existing calibrated set of photographs. Participants indicated which image pair (of the 2 pairs shown) displayed the largest difference. Estimated perceptual scales showed that observers were able to rank the images of aged materials systematically. Next, we examined the role that global and local changes in material surface colour play in the perception of material change. We altered the information about colour and geometrical distribution in the images used in the first experiment, and participants repeated the task with the altered images. Our results showed significant differences between individual observers. Most importantly, participants’ ability to rank the images varied with material type. The leaf images were particularly affected by our alteration of the geometrical distribution. Together, our findings show the factors contributing to the perception of material change over time.This work was supported by the European Union’s Horizon 2020 research and innovation programme [Grant Agreement No 765121]

A Novel Bayesian Spatio-Temporal Surveillance Metric to Predict Emerging Infectious Disease Areas of High Disease Risk

ABSTRACT Identification of areas of high disease risk has been one of the top goals for infectious disease public health surveillance. Accurate prediction of these regions leads to effective resource allocation and faster intervention. This paper proposes a novel prediction surveillance metric based on a Bayesian spatio-temporal model for infectious disease outbreaks. Exceedance probability, which has been commonly used for cluster detection in statistical epidemiology, was extended to predict areas of high risk. The proposed metric consists of three components: the area's risk profile, temporal risk trend, and spatial neighborhood influence. We also introduce a weighting scheme to balance these three components, which accommodates the characteristics of the infectious disease outbreak, spatial properties, and disease trends. Thorough simulation studies were conducted to identify the optimal weighting scheme and evaluate the performance of the proposed prediction surveillance metric. Results indicate that the area's own risk and the neighborhood influence play an important role in making a highly sensitive metric, and the risk trend term is important for the specificity and accuracy of prediction. The proposed prediction metric was applied to the COVID-19 case data of South Carolina from March 12, 2020, and the subsequent 30 weeks of data

Regularity of Sets with Quasiminimal Boundary Surfaces in Metric Spaces

This paper studies regularity of perimiter quasiminimizing sets in metric measure spaces with a doubling measure and a Poincare inequality. The main result shows that the measure theoretic boundary of a quasiminimizing set coincides with the topological boundary. We also show that such a set has finite Minkowski content and apply the regularity theory to study rectifiability issues related to quasiminimal sets in strong A_{\infty}-weighted Euclidean case.Peer reviewe

Subcellular-level resolution MALDI-MS imaging of maize leaf metabolites by MALDI-linear ion trap-Orbitrap mass spectrometer

A significant limiting factor in achieving high spatial resolution for matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS) imaging is the size of the laser spot at the sample surface. Here, we present modifications to the beam-delivery optics of a commercial MALDI-linear ion trap-Orbitrap instrument, incorporating an external Nd:YAG laser, beam-shaping optics, and an aspheric focusing lens, to reduce the minimum laser spot size from ~50 μm for the commercial configuration down to ~9 μm for the modified configuration. This improved system was applied for MALDI-MS imaging of cross sections of juvenile maize leaves at 5-μm spatial resolution using an oversampling method. A variety of different metabolites including amino acids, glycerolipids, and defense-related compounds were imaged at a spatial resolution well below the size of a single cell. Such images provide unprecedented insights into the metabolism associated with the different tissue types of the maize leaf, which is known to asymmetrically distribute the reactions of C4 photosynthesis among the mesophyll and bundle sheath cell types. The metabolite ion images correlate with the optical images that reveal the structures of the different tissues, and previously known and newly revealed asymmetric metabolic features are observed

Large Scale Nanoparticle Screening for Small Molecule Analysis in Laser Desorption Ionization Mass Spectrometry

Nanoparticles (NPs) have been suggested as efficient matrixes for small molecule profiling and imaging by laser-desorption ionization mass spectrometry (LDI-MS), but so far there has been no systematic study comparing different NPs in the analysis of various classes of small molecules. Here, we present a large scale screening of 13 NPs for the analysis of two dozen small metabolite molecules. Many NPs showed much higher LDI efficiency than organic matrixes in positive mode and some NPs showed comparable efficiencies for selected analytes in negative mode. Our results suggest that a thermally driven desorption process is a key factor for metal oxide NPs, but chemical interactions are also very important, especially for other NPs. The screening results provide a useful guideline for the selection of NPs in the LDI-MS analysis of small molecules

Spatial Mapping and Profiling of Metabolite Distributions During Germination

Germination is a highly complex process by which seeds begin to develop and establish themselves as viable organisms. In this paper, we utilize a combination of GC-MS, LC-fluorescence, and mass spectrometry imaging (MSI) approaches to profile and visualize the metabolic distributions of germinating seeds from two different inbreds of maize seeds, B73 and Mo17. GC and LC analyses demonstrate that the two inbreds are highly differentiated in their metabolite profiles throughout the course of germination, especially with regard to amino acids, sugar alcohols, and small organic acids. Crude dissection of the seed followed by GC-MS analysis of polar metabolites also revealed that many compounds were highly sequestered among the various seed tissue types. To further localize compounds, matrix-assisted laser desorption/ionization MSI is utilized to visualize compounds in fine detail in their native environments over the course of germination. Most notably, the fatty acyl chain-dependent differential localization of phospholipids and TAGs were observed within the embryo and radicle, showing correlation with the heterogeneous distribution of fatty acids. Other interesting observations include unusual localization of ceramides on the endosperm/scutellum boundary, and subcellular localization of ferulate in the aleurone

Thank You to Our 2018 Peer Reviewers

On behalf of the journal, AGU, and the scientific community, the Editors would like to sincerely thank those who reviewed manuscripts for Geophysical Research Letters in 2018. The hours reading and commenting on manuscripts not only improves the manuscripts but also increases the scientific rigor of future research in the field. We particularly appreciate the timely reviews, in light of the demands imposed by the rapid review process at Geophysical Research Letters. With the revival of the “major revisions” decisions, we appreciate the reviewers’ efforts on multiple versions of some manuscripts. Many of those listed below went beyond and reviewed three or more manuscripts for our journal, and those are indicated in italics. In total, 4,484 referees contributed to 7,557 individual reviews in journal. Thank you again. We look forward to the coming year of exciting advances in the field and communicating those advances to our community and to the broader public.Key PointIn total, 4,484 referees contributed to 7,557 individual reviews in journalPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/152982/1/grl59194.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/152982/2/grl59194_am.pd