In vivo monitoring of nicotine biosynthesis in tobacco leaves by low-temperature plasma mass spectrometry

Rapid and sensitive determination of legacy and emerging per- and poly-fluoroalkyl substances with solid-phase microextraction probe coupled with mass spectrometry

This study was designed to develop a rapid and sensitive method for quantifying legacy and emerging per- and polyfluoroalkyl substances (PFASs) in environmental samples with solid-phase microextraction (SPME) coupled with mass spectrometry (MS). An innovative SPME probe was fabricated via in situ polymerization, and the probe coating was optimized with response surface methodology to maximize the fluorine-fluorine interactions and electrostatic properties and ensure high selectivity for the target PFASs with enrichment factors of 48-491. The coupled SPME and MS provided a rapid and sensitive method for analyses of PFASs, with excellent linearity (r ≥ 0.9962) over the concentration range 0.001-1 μg/L and remarkably low detection limits of 0.1-13.0 ng/L. This method was used to analyze trace PFASs in tap water, river water, and wastewater samples and proved to be a simple and efficient analytical method for selective enrichment and detection of contaminants in the environment.

Identification of Plant Compounds with Mass Spectrometry Imaging (MSI)

The presence and localization of plant metabolites are indicative of physiological processes, e.g., under biotic and abiotic stress conditions. Further, the chemical composition of plant parts is related to their quality as food or for medicinal applications. Mass spectrometry imaging (MSI) has become a popular analytical technique for exploring and visualizing the spatial distribution of plant molecules within a tissue. This review provides a summary of mass spectrometry methods used for mapping and identifying metabolites in plant tissues. We present the benefits and the disadvantages of both vacuum and ambient ionization methods, considering direct and indirect approaches. Finally, we discuss the current limitations in annotating and identifying molecules and perspectives for future investigations.

An update on the formation in tobacco, toxicity and carcinogenicity of N'-nitrosonornicotine and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone

The tobacco-specific nitrosamines N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) are considered 'carcinogenic to humans' by the International Agency for Research on Cancer (IARC) and are believed to be important in the carcinogenic effects of both smokeless tobacco and combusted tobacco products. This short review focuses on the results of recent studies on the formation of NNN and NNK in tobacco, and their carcinogenicity and toxicity in laboratory animals. New mechanistic insights are presented regarding the role of dissimilatory nitrate reductases in certain microorganisms involved in the conversion of nitrate to nitrite that leads to the formation of NNN and NNK during curing and processing of tobacco. Carcinogenicity studies of the enantiomers of the major NNK metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and the enantiomers of NNN are reviewed. Recent toxicity studies of inhaled NNK and co-administration studies of NNK with formaldehyde, acetaldehyde, acrolein and CO2, all of which occur in high concentrations in cigarette smoke, are discussed.

From cultivation to cancer: formation of N-nitrosamines and other carcinogens in smokeless tobacco and their mutagenic implications

Tobacco use is a major cause of preventable morbidity and mortality globally. Tobacco products, including smokeless tobacco (ST), generally contain tobacco-specific N-nitrosamines (TSNAs), such as N'-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-butanone (NNK), which are potent carcinogens that cause mutations in critical genes in human DNA. This review covers the series of biochemical and chemical transformations, related to TSNAs, leading from tobacco cultivation to cancer initiation. A key aim of this review is to provide a greater understanding of TSNAs: their precursors, the microbial and chemical mechanisms that contribute to their formation in ST, their mutagenicity leading to cancer due to ST use, and potential means of lowering TSNA levels in tobacco products. TSNAs are not present in harvested tobacco but can form due to nitrosating agents reacting with tobacco alkaloids present in tobacco during certain types of curing. TSNAs can also form during or following ST production when certain microorganisms perform nitrate metabolism, with dissimilatory nitrate reductases converting nitrate to nitrite that is then released into tobacco and reacts chemically with tobacco alkaloids. When ST usage occurs, TSNAs are absorbed and metabolized to reactive compounds that form DNA adducts leading to mutations in critical target genes, including the RAS oncogenes and the p53 tumor suppressor gene. DNA repair mechanisms remove most adducts induced by carcinogens, thus preventing many but not all mutations. Lastly, because TSNAs and other agents cause cancer, previously documented strategies for lowering their levels in ST products are discussed, including using tobacco with lower nornicotine levels, pasteurization and other means of eliminating microorganisms, omitting fermentation and fire-curing, refrigerating ST products, and including nitrite scavenging chemicals as ST ingredients.

Guided analysis of ambient ionization mass spectrometry data with the MQ_Assistant

RATIONALE

Ambient ionization mass spectrometry (AIMS) delivers realistic data from samples in their native state. In addition, AIMS methods reduce time and costs for sample preparation and have less environmental impact. However, AIMS data are often complex and require substantial processing before interpretation.

METHODS

We developed an interactive R script for guided mass spectrometry (MS) data processing. The "MQ_Assistant" is based on MALDIquant, a popular R package for MS data processing. In each step, the user can try and preview the effect of chosen parameters before deciding on the values with the best result and proceeding to the next stage. The outcome of the MQ_Assistant is a feature matrix that can be further analyzed in R and statistics tools such as MetaboAnalyst.

RESULTS

Using 360 AIMS example spectra, we demonstrate the step-by-step processing for creating a feature matrix. In addition, we show how to visualize the results of three biological replicates of a plant-microbe interaction between Arabidopsis and Trichoderma as a heatmap using R and upload them to MetaboAnalyst. The final parameter set can be saved for reuse in MALDIquant workflows of similar data.

CONCLUSIONS

The MQ_Assistant helps novices and experienced users to develop workflows for (AI)MS data processing. The interactive procedure supports the quick finding of appropriate settings. These parameters can be exported and reused in future projects. The stepwise operation with visual feedback also suggests the use of the MQ_Assistant in education.

Development of mass spectrometry imaging techniques and its latest applications

Mass spectrometry imaging (MSI) is a novel molecular imaging technology that collects molecular information from the surface of samples in situ. The spatial distribution and relative content of various compounds can be visualized simultaneously with high spatial resolution. The prominent advantages of MSI promote the active development of ionization technology and its broader applications in diverse fields. This article first gives a brief introduction to the vital parts of the processes during MSI. On this basis, provides a comprehensive overview of the most relevant MS-based imaging techniques from their mechanisms, pros and cons, and applications. In addition, a critical issue in MSI, matrix effects is also discussed. Then, the representative applications of MSI in biological, forensic, and environmental fields in the past 5 years have been summarized, with a focus on various types of analytes (e.g., proteins, lipids, polymers, etc.) Finally, the challenges and further perspectives of MSI are proposed and concluded.

Rapid Detection of Potential Natural Food Preservatives and Identification of Artemisia Species via High-Sensitivity Photoionization Mass Spectrometry

Natural food preservatives are being sought extensively as a safe alternative to chemical food preservatives. This study aimed to identify potential natural preservatives from herbs using single-photon ionization time-of-flight mass spectrometry (SPI-TOF-MS). Five Artemisia species and four other herbs were analyzed, and the random forest (RF) algorithm was used to simulate olfaction and distinguish the Artemisia species by identifying the characteristic peaks of volatile terpenoids (VTPs). Results showed that the terpenoid synthase (TPS) gene family was expanded in Artemisia species, potentially contributing to the increased production of VTPs, which have potential as natural preservatives and specifically identify these species. The limits of detections (LODs) for principle VTPs in Artemisia species were as low as 22-39 parts-per-trillion-by-volume (pptv) using SPI-TOF-MS. This study highlights the potential for headspace mass spectrometry to be used in the development of natural preservatives and the identification of plant species.

Plasma-based ambient mass spectrometry: Recent progress and applications

Ambient mass spectrometry (AMS) has grown as a group of advanced analytical techniques that allow for the direct sampling and ionization of the analytes in different statuses from their native environment without or with minimum sample pretreatments. As a significant category of AMS, plasma-based AMS has gained a lot of attention due to its features that allow rapid, real-time, high-throughput, in vivo, and in situ analysis in various fields, including bioanalysis, pharmaceuticals, forensics, food safety, and mass spectrometry imaging. Tens of new methods have been developed since the introduction of the first plasma-based AMS technique direct analysis in real-time. This review first provides a comprehensive overview of the established plasma-based AMS techniques from their ion source configurations, mechanisms, and developments. Then, the progress of the representative applications in various scientific fields in the past 4 years (January 2017 to January 2021) has been summarized. Finally, we discuss the current challenges and propose the future directions of plasma-based AMS from our perspective.

Monitoring of Indoor Farming of Lettuce Leaves for 16 Hours Using Electrical Impedance Spectroscopy (EIS) and Double-Shell Model (DSM)

An electrical impedance spectroscopy (EIS) experiment was performed using a double-shell electrical model to investigate the feasibility of detecting physiological changes in lettuce leaves over 16 h. Four lettuce plants were used, and the impedance spectra of the leaves were measured five times per plant every hour at frequencies of 500 Hz and 300 kHz. Estimated R-C parameters were computed, and the results show that the lettuce leaves closely fit the double-shell model (DSM). The average resistance ratios of R1 = 10.66R4 and R1 = 3.34R2 show high resistance in the extracellular fluid (ECF). A rapid increase in resistance (R1, R2, and R4) and a decrease in capacitance (C3 and C5) during water uptake were observed. In contrast, a gradual decrease in resistance and an increase in capacitance were observed while the LED light was on. Comparative studies of leaf physiology and electrical value changes support the idea that EIS is a great technique for the early monitoring of plant growth for crop production.

In Vivo Low-Temperature Plasma Ionization Mass Spectrometry (LTP-MS) Reveals Regulation of 6-Pentyl-2H-Pyran-2-One (6-PP) as a Physiological Variable during Plant-Fungal Interaction

Volatile organic compounds (VOCs) comprises a broad class of small molecules (up to ~300 g/mol) produced by biological and non-biological sources. VOCs play a vital role in an organism's metabolism during its growth, defense, and reproduction. The well-known 6-pentyl-α-pyrone (6-PP) molecule is an example of a major volatile biosynthesized by Trichoderma atroviride that modulates the expression of PIN auxin-transport proteins in primary roots of Arabidopsis thaliana during their relationship. Their beneficial relation includes lateral root formation, defense induction, and increased plant biomass production. The role of 6-PP has been widely studied due to its relevance in this cross-kingdom relationship. Conventional VOCs measurements are often destructive; samples require further preparation, and the time resolution is low (around hours). Some techniques enable at-line or real-time analyses but are highly selective to defined compounds. Due to these technical constraints, it is difficult to acquire relevant information about the dynamics of VOCs in biological systems. Low-temperature plasma (LTP) ionization allows the analysis of a wide range of VOCs by mass spectrometry (MS). In addition, LTP-MS requires no sample preparation, is solvent-free, and enables the detection of 6-PP faster than conventional analytical methods. Applying static statistical methods such as Principal Component Analysis (PCA) and Discriminant Factorial Analysis (DFA) leads to a loss of information since the biological systems are dynamic. Thus, we applied a time series analysis to find patterns in the signal changes. Our results indicate that the 6-PP signal is constitutively emitted by T. atroviride only; the signal shows high skewness and kurtosis. In A. thaliana grown alone, no signal corresponding to 6-PP is detected above the white noise level. However, during T. atroviride-A. thaliana interaction, the signal performance showed reduced skewness and kurtosis with high autocorrelation. These results suggest that 6-PP is a physiological variable that promotes homeostasis during the plant-fungal relationship. Although the molecular mechanism of this cross-kingdom control is still unknown, our study indicates that 6-PP has to be regulated by A. thaliana during their interaction.

A simple and rapid approach for on-site analysis of nicotine in tobacco based on a screen-printed electrode as an electrochemical sensor

In this study, we report a portable kit consisting of a portable workstation, gold screen-printed electrode (SPE), 0.45 μm filter membrane, phosphate buffer solution (PBS), and acetic acid (1%) for point-of-use (POU) analysis of nicotine in tobacco. The activated-screen-printed electrode (A-SPE) displayed superior electron transmission efficiency, and the A-SPE without modification was employed for high-performance analysis of nicotine in actual tobacco after simple sample pretreatment. Remarkably, the fabricated nicotine sensor exhibited a broad working range of 10-100 μg g-1, a low limit of detection (LOD) of 6.4 μg mL-1, good stability, selectivity, and practicality under the optimal conditions. The method was applied to the determination of nicotine in (spiked) samples. Satisfactory recovery results demonstrated that the as-prepared portable kit method with outstanding electrocatalysis ability was feasible for analysis of nicotine in tobacco. Moreover, the values obtained using the A-SPE were in good agreement with those determined by gas chromatography-flame ionization detection (GC-FID), which confirms the feasibility and validity of the present method. The results of the as-proposed portable kit provided a new strategy for analyzing nicotine in actual tobacco samples.

Build, Share and Remix: 3D Printing for Speeding Up the Innovation Cycles in Ambient Ionisation Mass Spectrometry (AIMS)

Ambient ionisation mass spectrometry (AIMS) enables studying biological systems in their native state and direct high-throughput analyses. The ionisation occurs in the physical conditions of the surrounding environment. Simple spray or plasma-based AIMS devices allow the desorption and ionisation of molecules from solid, liquid and gaseous samples. 3D printing helps to implement new ideas and concepts in AIMS quickly. Here, we present examples of 3D printed AIMS sources and devices for ion transfer and manipulation. Further, we show the use of 3D printer parts for building custom AIMS sampling robots and imaging systems. Using 3D printing technology allows upgrading existing mass spectrometers with relatively low cost and effort.

Emerging Technologies for Monitoring Plant Health in Vivo

In the coming decades, increasing agricultural productivity is all-important. As the global population is growing rapidly and putting increased demand on food supply, poor soil quality, drought, flooding, increasing temperatures, and novel plant diseases are negatively impacting yields worldwide. One method to increase yields is plant health monitoring and rapid detection of disease, nutrient deficiencies, or drought. Monitoring plant health will allow for precise application of agrichemicals, fertilizers, and water in order to maximize yields. In vivo plant sensors are an emerging technology with the potential to increase agricultural productivity. In this mini-review, we discuss three major approaches of in vivo sensors for plant health monitoring, including genetic engineering, imaging and spectroscopy, and electrical.

A facile approach for rapid on-site screening of nicotine in natural tobacco

Nicotine (Nic) exposed to the environment which comes from tobacco products is the main addictive agent and specific classes of hazardous compound that merit concern. In this study, we have established a fast and reliable method to achieve specific detection of Nic in natural nicotiana tabacum within 30 s through a miniaturized platform based on screen printed gold electrode (SPE). A simple electrochemical pretreatment mean was employed on gold surface that led to the exposure of Au (111) facet and a convenient sample pretreatment method was adopted to realize the extraction of Nic in tobacco. The present electrochemical sensor exhibits an ample range of sensing from 10 μg/g to 200 μg/g, which is able to compliance with tobacco industry testing standards of actual samples. Over 60 sampling points from different origins in China or other countries were performed with direct analysis using this method and satisfactory results have been obtained. The proposed approach was demonstrated to be a very promising platform for significantly improving analytical efficiency in laboratories as well as for monitoring the source reduction control of Nic in the environment.

Smells from the desert: Microbial volatiles that affect plant growth and development of native and non-native plant species

The plant microbiota can affect host fitness via the emission of microbial volatile organic compounds (mVOCs) that influence growth and development. However, evidence of these molecules and their effects in plants from arid ecosystems is limited. We screened the mVOCs produced by 40 core and representative members of the microbiome of agaves and cacti in their interaction with Arabidopsis thaliana and Nicotiana benthamiana. We used SPME-GC-MS to characterize the chemical diversity of mVOCs and tested the effects of selected compounds on growth and development of model and host plants. Our study revealed that approximately 90% of the bacterial strains promoted plant growth both in A. thaliana and N. benthamiana. Bacterial VOCs were mainly composed of esters, alcohols, and S-containing compounds with 25% of them not previously characterized. Remarkably, ethyl isovalerate, isoamyl acetate, 3-methyl-1-butanol, benzyl alcohol, 2-phenylethyl alcohol, and 3-(methylthio)-1-propanol, and some of their mixtures, displayed beneficial effects in A. thaliana and also improved growth and development of Agave tequilana and Agave salmiana in just 60 days. Volatiles produced by bacteria isolated from agaves and cacti are promising molecules for the sustainable production of crops in arid and semi-arid regions.

Elucidating the Distribution of Plant Metabolites from Native Tissues with Laser Desorption Low-Temperature Plasma Mass Spectrometry Imaging

Secondary metabolites of plants have important biological functions, which often depend on their localization in tissues. Ideally, a fresh untreated material should be directly analyzed to obtain a realistic view of the true sample chemistry. Therefore, there is a large interest for ambient mass-spectrometry-based imaging (MSI) methods. Our aim was to simplify this technology and to find an optimal combination of desorption/ionization principles for a fast ambient MSI of macroscopic plant samples. We coupled a 405 nm continuous wave (CW) ultraviolet (UV) diode laser to a three-dimensionally (3D) printed low-temperature plasma (LTP) probe. By moving the sample with a RepRap-based sampling stage, we could perform imaging of samples up to 16 × 16 cm2. We demonstrate the system performance by mapping mescaline in a San Pedro cactus ( Echinopsis pachanoi) cross section, tropane alkaloids in jimsonweed ( Datura stramonium) fruits and seeds, and nicotine in tobacco ( Nicotiana tabacum) seedlings. In all cases, the anatomical regions of enriched compound concentrations were correctly depicted. The modular design of the laser desorption (LD)-LTP MSI platform, which is mainly assembled from commercial and 3D-printed components, facilitates its adoption by other research groups. The use of the CW-UV laser for desorption enables fast imaging measurements. A complete tobacco seedling with an image size of 9.2 × 15.0 mm2 was analyzed at a pixel size of 100 × 100 μm2 (14 043 mass scans), in less than 2 h. Natural products can be measured directly from native tissues, which inspires a broad use of LD-LTP MSI in plant chemistry studies.