Examination of the translocation of sulfonylurea herbicides in sunflower plants by matrix-assisted laser desorption/ionisation mass spectrometry imaging

Uptake, translocation, and metabolism of organophosphate esters (OPEs) in plants and health perspective for human: A review

Plant uptake, accumulation, and transformation of organophosphate esters (OPEs) play vital roles in their geochemical cycles and exposure risks. Here we reviewed the recent research advances in OPEs in plants. The mean OPE concentrations based on dry/wet/lipid weight varied in 4.80-3,620/0.287-26.8/12,000-315,000 ng g-1 in field plants, and generally showed positive correlations with those in plant habitats. OPEs with short-chain substituents and high hydrophilicity, particularly the commonly used chlorinated OPEs, showed dominance in most plant samples, whereas some tree barks, fruits, seeds, and roots demonstrated dominance of hydrophobic OPEs. Both hydrophilic and hydrophobic OPEs can enter plants via root and foliar uptake, and the former pathway is mainly passively mediated by various membrane proteins. After entry, different OPEs undergo diverse subcellular distributions and acropetal/basipetal/intergenerational translocations, depending on their physicochemical properties. Hydrophilic OPEs mainly exist in cell sap and show strong transferability, hydrophobic OPEs demonstrate dominant distributions in cell wall and limited migrations owing to the interception of Casparian strips and cell wall. Additionally, plant species, transpiration capacity, growth stages, commensal microorganisms, and habitats also affect OPE uptake and transfer in plants. OPE metabolites derived from various Phase I transformations and Phase II conjugations are increasingly identified in plants, and hydrolysis and hydroxylation are the most common metabolic processes. The metabolisms and products of OPEs are closely associated with their structures and degradation resistance and plant species. In contrast, plant-derived food consumption contributes considerably to the total dietary intakes of OPEs by human, particularly the cereals, and merits specifical attention. Based on the current research limitations, we proposed the research perspectives regarding OPEs in plants, with the emphases on their behavior and fate in field plants, interactions with plant-related microorganisms, multiple uptake pathways and mechanisms, and comprehensive screening analysis and risk evaluation.

Using Mass Spectrometry Imaging to Visualize Pesticide Accumulation and Time-Dependent Distribution in Fungicide-Coated Seeds

Pesticide seed treatment provides efficient crop protection in the early season and enables a reduction in the quantity of fungicides used later. Hence, it has been a practical application for crop protection in major crop sectors such as corn, soybean, wheat, and cotton. The chemicals on pesticide-treated seeds may show different distributions depending on the structure of the seeds and the physical properties of the chemicals, but they have not been well studied because of a lack of versatile analytical tools. Here, we used mass spectrometry imaging to visualize the distribution of a fungicide (ethaboxam) in corn and soybean seeds coated with it. Contrasting distribution patterns were noted, which are likely dependent on the seed structure. We also obtained information on fungicide distribution after the seedings, which will contribute to a better understanding of the fungicide delivery pathway within plants. Using this new analytical method, we were able to obtain hitherto unavailable time-dependent, dynamic information on the ethaboxam. We expect that this method will be a useful tool with widespread applications in pesticide development and use. Copyright © 2023 Shuichi Shimma, Hiromi Saito, Takuya Inoue, and Fukumatsu Iwahashi. This is an open-access article distributed under the terms of Creative Commons Attribution Non-Commercial 4.0 International License, which permits use, distribution, and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Spatial Distribution and Migration Characteristic of Forchlorfenuron in Oriental Melon Fruit by Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry Imaging

Forchlorfenuron is a widely used plant growth regulator to support the pollination and fruit set of oriental melons. It is critical to investigate the spatial distribution and migration characteristics of forchlorfenuron among fruit tissues to understand its metabolism and toxic effects on plants. However, the application of imaging mass spectrometry in pesticides remains challenging due to the usually extremely low residual concentration and the strong interference from plant tissues. In this study, a matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) method was developed for the first time to obtain the dynamic images of forchlorfenuron in oriental melon. A quantitative assessment has also been performed for MALDI-MSI to characterize the time-dependent permeation and degradation sites of forchlorfenuron in oriental melon. The majority of forchlorfenuron was detected in the exocarp and mesocarp regions of oriental melon and decreased within two days after application. The degradation rate obtained by MALDI-MSI in this study was comparable to that obtained by HPLC-MS/MS, indicating that the methodology and quantification approach based on the MALDI-MSI was reliable and practicable for pesticide degradation study. These results provide an important scientific basis for the assessment of the potential risks and effects of forchlorfenuron on oriental melons.

The localization of the alkaloids in Coptis chinensis rhizome by time-of-flight secondary ion mass spectrometry

BACKGROUND

Understanding the spatial distribution of active compounds can effectively evaluate the quality of decoction pieces of traditional Chinese medicine (TCM). Traditional methods are economical and practical but lack chemical information on the original distribution. Time-of-flight secondary ion mass spectrometry (TOF-SIMS), with the advantage of non-destructive detection of samples, can directly analyze the distribution of chemical compounds on the surface of various samples.

METHODS

In this study, TOF-SIMS image analysis technology was used to detect TCM for the first time. Taking Coptis rhizome (CR) as an example, a commonly used TCM, the distribution of the compounds in the cross-section of CR was studied. Meanwhile, ultra-high-performance liquid chromatography coupled with triple quadrupole mass spectrometry (UPLCQQQ-MS/MS) was used to verify the results of TOF-SIMS.

RESULTS

The distribution of nine active compounds: berberine, epiberberine, coptisine, palmatine, columbamine, jatrorrhizine, tetrahydricheilanthifolinium, and oxyberberine, was well imaged in the cross-section of CR by TOF-SIMS. The content of berberine and epiberberine was the highest; Palmatine distribution in the pith was more than that in other parts; Oxyberberine was mainly concentrated in the cork and xylem rays. Normalization analysis showed contents of these compounds increased along with the growth years. The result was consistent with UPLC-QQQ-MS/MS.

CONCLUSION

The TOF-SIMS method can display the spatial distribution status of the active compounds of herbs, providing a basis for selecting the medicine site with non-destructive and fast detection.

Visualizing the Distribution of Phthalate Esters and Plant Metabolites in Carrot by Matrix-Assisted Laser Desorption/Ionization Imaging Mass Spectrometry

The accumulation of organic pollutants in vegetables is a major global food safety issue. The concentrations of pollutants in vegetables usually differ across different tissues because of different transport and accumulation pathways. However, owing to the limitations of conventional methods, in situ localization of typical organic pollutants such as phthalate esters (PAEs) in plant tissues has not yet been studied. Here, we developed a quick and efficient method for in situ detection and imaging of the spatial distribution of PAEs in a typical root vegetable, carrot, using matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS). The use of a 2,5-dihydroxybenzoic acid matrix with a spray-sublimation coating method led to the successful identification of PAEs ion signals. The IMS results showed that a typical PAE-di-(2-ethylhexyl)phthalate (DEHP) was broadly distributed in the cortex, phloem, and metaxylem, but was barely detectable in the cambium and protoxylem. Interestingly, MALDI-IMS data also revealed for the first time the spatial distribution of sugars and β-carotene in carrots. In summary, the developed method offers a new and practical methodology for the in situ analysis of PAEs and plant metabolites in plant tissues. As a result, it could provide a more intuitive understanding of the movement and transformation of organic pollutants in soil-plant systems.

A Review on Recent Innovations of Pretreatment and Analysis Methods for Sulfonylurea Herbicides

Sulfonylurea herbicides (SUHs) are widely used in agriculture because of their low dosage, low cost, and high selectivity. However, due to improper use and lack of effective management, their residues pose a threat to the human health through environment and food pollution. Therefore, there is a need for simple, quick, economical, and effective methods to analyze SUHs in plant-derived foods, crops, and environmental samples. The present article presents a comprehensive review of the pretreatment and analytical technologies used for SUHs in various sample matrices, focusing on the developments since 2010. The main pretreatment methods include liquid-liquid extraction, solid-phase extraction, QuEChERS, and different microextraction methods, whereas analytical methods mainly include liquid chromatography coupled with different detectors, capillary electrophoresis, among others. In addition, the present study also compared the advantages and disadvantages of the methods and the future development is prospected.

Spatially Resolved Investigation of Herbicide-Safener Interaction in Maize (Zea mays L.) by MALDI-Imaging Mass Spectrometry

Monitoring agrochemical distribution within plant tissues delivers significant insights into the adsorption, distribution, metabolism, and elimination of agrochemicals. Detection and imaging of the safener cyprosulfamide (CSA) and the herbicide thiencarbazone-methyl (TCM) after micro-droplet application on the surface of maize leaves (Zea mays L.) have been achieved using matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI). The agrochemicals were deposited onto the adaxial surface of maize leaves on growing plants, and their uptake, distribution, and metabolism were investigated at four timepoints (3 h, 24 h, 4 days, and 7 days) to assess the influence of CSA treatment on TCM metabolism. MALDI MSI visualized significant changes for the metabolism of TCM after 24 h. Although TCM metabolism was detected neither in the control without the safener nor in the approach with CSA on the second leaf, the co-application on the same leaf showed significant metabolism of the herbicide by detecting the metabolite N-demethylated TCM. These findings suggest that safener protection against herbicide injury is a rapid process in which CSA and TCM need to be present in the same tissues. This study showcases the use of MALDI MSI to visualize and analyze indirect interactions of two substances in planta.

The Role of the Xylem in Oxytetracycline Translocation within Citrus Trees

Antibiotics have been successfully used to control plant diseases for more than fifty years. Recently, oxytetracycline and streptomycin have been approved for the treatment of Huanglongbing, which is threatening the citrus industry in many regions. Because the efficiency of antibiotics in planta is highly affected by their movement and distribution, understanding the mechanism of antibiotics' uptake and distribution could lead to a better control of plant pathogens. Herein, we investigated the movement of oxytetracycline within citrus plants. Oxytetracycline was applied by root drenching to both girdled and non-girdled citrus seedlings. In addition, oxytetracycline was applied by trunk injection to girdled and non-girdled citrus trees. After the exposure time (24 h), citrus seedlings were dissected and the levels of oxytetracycline in the different tissues were measured using an oxytetracycline ELISA kit. Upon root application (laboratory experiment), oxytetracycline was detected in the inner part of the stem (xylem-associated tissue), cortex (phloem-associated tissue), and leaves above and below the girdled area. Likewise, oxytetracycline was also detected in leaves of trunk-injected field trees (girdled and non-girdled) three days post treatment. Interestingly, cortex girdling did not affect the distribution and translocation of oxytetracycline, indicating that the xylem is the main path for oxytetracycline translocation. Taken together, our results indicate that oxytetracycline translocation mainly occurs via xylem vessels, and that movement into the phloem occurs subsequent to xylem translocation. Our findings also clearly demonstrated that upon trunk injection, only trace levels of oxytetracycline reached the roots, minimizing its therapeutic value there. Thus, our recommendation is to time tree injections to coincide with the flushing periods when the bacteria are moving into new shoots to maximize the efficiency of oxytetracycline.

A Low-Cost Beam-Scanning Second Harmonic Generation Microscope with Application for Agrochemical Development and Testing

A low-cost second harmonic generation (SHG) microscope was constructed, and, for the first time, SHG microscopy was used for imaging agrochemical materials directly on the surface of common commercial crop leaves. The microscope uses a chromatically fixed (1560 nm) femtosecond fiber laser, a commercial 2D galvanometer mirror system, and a PCIe digital oscilloscope card, which together kept total instrument costs under $40 000 (USD), a significant decrease in cost and complexity from common systems (commercial and home-built) using tunable lasers and faster beam-scanning architectures. The figures of merit of the low-cost system still enabled a variety of measurements of agrochemical materials. Following confirmation of largely background-free SHG imaging of common crop leaves (soybean, maize, wheatgrass), SHG microscopy was used to image active ingredient crystallization after solution-phase deposition directly on the leaf surface, including at industrially relevant active ingredient concentrations (<0.05% w/w). Crystallization was also followed in real-time, with differences in crystallization time observed for different application procedures (spraying vs single droplet deposition). A strong dependency of active ingredient crystallization on the substrate was found, with an increased crystallization tendency observed on leaves vs on glass slides. Different crystal habits for the same active ingredient were also observed on different plant species. Finally, a model extended-release formulation was prepared, with a decrease in active ingredient crystallinity observed vs solution-phase deposition. These collective results demonstrate the need for making diagnostic measurements directly on the leaf surface and could help inform the next generation of pesticide products that ensure optimized agricultural output for a growing world population.

Xenobiotics metabolization in Salix alba leaves uncovered by mass spectrometry imaging

INTRODUCTION

Micropollutants are increasingly monitored as their presence in the environment is rising due to human activities, and they are potential threats to living organisms.

OBJECTIVES

This study aimed at understanding the role of plants in xenobiotics removal from polluted environments by following xenobiotics metabolism in leaf tissues.

METHODS

Different classes of micropollutants were investigated using liquid chromatography (LC) coupled to quadrupole-time of flight (Q-TOF) high resolution mass spectrometry (HRMS). The tissue localization of xenobiotics in the leaves of a spontaneous (not planted by humans) Salix alba growing near the water flux was further investigated using matrix-assisted laser desorption ionization (MALDI) mass spectrometry imaging (MSI).

RESULTS

The LC-Q-TOF analysis revealed the distribution of micropollutants in three different compartments of a tertiary treatment wetland. When further investing the metabolic profile of S. alba leaves using MSI, different distribution patterns were observed in specific leaf tissues. Xenobiotic metabolites were predicted and could also be tentatively identified in S. alba leaves, shedding new light on the metabolic processes at play in leaves to manage xenobiotics uptake from a polluted environment.

CONCLUSION

Using complementary metabolomics approaches, this study performed a large-scale exploration of micropollutants spreading in the environment at the exit of a tertiary treatment wetland. The use of MSI coupled with the prediction of xenobiotic metabolites yielded novel insights into plant metabolism during chronical exposure to low doses of a mixture of micropollutants.

In situ localization of micropollutants and associated stress response in Populus nigra leaves

Micropollutants and emerging organic contaminants (EOCs) have been widely studied in terms of persistance, removal, human risk assessment, toxicology, etc. Mass spectrometry imaging (MSI) offers the possibility of following the fate of a single pesticide in a plant leaf or a drug in the whole body of an animal, organ by organ. However, the admissibility of chronic low doses of complex mixtures for the ecosystem has not been assessed. How do micropollutants diffuse in the environment? How do living organisms cope with chronic exposure to a low dose of diverse micropollutants? Is there a cocktail effect or a chance for hormesis? Combining mass spectrometry imaging (MSI) and targeted and nontargeted liquid chromatography coupled to mass spectrometry (LC-MS), we attempt to answer these questions. We investigate the diversity of micropollutants at the exit of a water treatment facility, their diffusion in sludge and black poplar (Populus nigra), and their impact on a living organism. We reveal a specific tissue localization of micropollutants in peripheral leaf tissues, and an associated stress response from the plant, with stress hormones and tissue degradation markers induced in the plant growing near the water efflux.

Metabolism and spatial distribution of metalaxyl in tomato plants grown under hydroponic conditions

Knowledge about translocation of plant protection products (PPP's) in plants is important to understand the uptake via the root system. Here we report the combination of analysis of tissue extracts by LC-HRMSⁿ, autoradiography of ¹⁴C-labeled compounds and MALDI-MSI, which combine qualitative and quantitative information of chemical composition and the spatial distribution of PPP's and their metabolites in situ. Therefore, the uptake of the phenylamide fungicide metalaxyl was studied in tomato plants (Solanum lycopersicum) using a hydroponic system. The plants have been cultivated in perlite until the two-leaf stage and were transferred into the hydroponic test system afterwards. The radioactive labeled fungicide was readily taken up by the roots during the normal water consumption and radioactivity was translocated uniformly to the aboveground part of the tomato plants, while only small proportion of the applied radioactivity were observed in the roots. The distribution of metalaxyl after the plant uptake experiment in the primary roots where analyzed by a transversal tissue section in the zone of maturation. Metalaxyl is mainly localized in root xylem and in cortex located at the epidermis. With LC-HRMSⁿ and radiochemical analyses of stem and leaf, no parent compound was detectable. Four polar metabolites were the main identified components of the residue and could be visualized by MALDI-imaging mass spectrometry. With these results we could show, that the fungicide metalaxyl is taken up by the plant via the roots during the regular water consumption and transported to xylem.

Detecting and Mapping Harmful Chemicals in Fruit and Vegetables Using Nanoparticle-Enhanced Laser-Induced Breakdown Spectroscopy

Residues of harmful chemicals in fruit and vegetables pose risks to human health. Ordinary laser-induced breakdown spectroscopy (LIBS) techniques are unsatisfactory for detecting harmful chemicals in fruit and vegetables. In this study, we applied metal nanoparticles to fruit and vegetables samples to improve the ability of LIBS to detect trace pesticide and heavy metal residues in the samples. The nanoparticle-enhanced LIBS technique gave pesticide residue detection limits for fruit and vegetables two orders of magnitude lower than achieved using standard LIBS and heavy metal detection limits markedly better than achieved using standard LIBS. We used the nanoparticle-enhanced LIBS technique to study the distributions of harmful chemicals in vegetable leaves. We found that heavy metals are distributed unevenly in edible plant leaves, the heavy metal concentrations being higher in the veins than in the mesophyll.

In-Field, In Situ, and In Vivo 3-Dimensional Elemental Mapping for Plant Tissue and Soil Analysis Using Laser-Induced Breakdown Spectroscopy

Sensing and mapping element distributions in plant tissues and its growth environment has great significance for understanding the uptake, transport, and accumulation of nutrients and harmful elements in plants, as well as for understanding interactions between plants and the environment. In this study, we developed a 3-dimensional elemental mapping system based on laser-induced breakdown spectroscopy that can be deployed in- field to directly measure the distribution of multiple elements in living plants as well as in the soil. Mapping is performed by a fast scanning laser, which ablates a micro volume of a sample to form a plasma. The presence and concentration of specific elements are calculated using the atomic, ionic, and molecular spectral characteristics of the plasma emission spectra. Furthermore, we mapped the pesticide residues in maize leaves after spraying to demonstrate the capacity of this method for trace elemental mapping. We also used the system to quantitatively detect the element concentrations in soil, which can be used to further understand the element transport between plants and soil. We demonstrate that this method has great potential for elemental mapping in plant tissues and soil with the advantages of 3-dimensional and multi-elemental mapping, in situ and in vivo measurement, flexible use, and low cost.

Potential of MALDI imaging for the toxicological evaluation of environmental pollutants

Risk assessment related to the exposure of humans to chemicals released into the environment is a major concern of our modern societies. In this context, toxicology plays a crucial role to characterize the effects of this exposure on health and identify the targets of these molecules. MALDI imaging mass spectrometry (IMS) is an enabling technology for biodistribution studies of chemicals. Although the majority of published studies are presented in a pharmacological context, the concepts discussed in this review can be applied to the toxicological evaluation of chemicals released into the environment. The major asset of IMS is the simultaneous localization and identification of a parent molecule and its metabolites without labeling and without any prior knowledge. Quantification methods developed in IMS are presented with application to an environmental pollutant. IMS is effective in the localization of chemicals and endogenous species. This opens unique perspectives for the discovery of molecular alterations in metabolites and protein biomarkers that could help for a better understanding of toxicity mechanisms. Distribution studies of agrochemicals in plants by IMS can contribute to a better understanding of their mode of action and to a more effective use of these chemicals, avoiding the current concern of environmental damage.

Stimulated Raman scattering microscopy: an emerging tool for drug discovery

Optical microscopy techniques have emerged as a cornerstone of biomedical research, capable of probing the cellular functions of a vast range of substrates, whilst being minimally invasive to the cells or tissues of interest. Incorporating biological imaging into the early stages of the drug discovery process can provide invaluable information about drug activity within complex disease models. Spontaneous Raman spectroscopy has been widely used as a platform for the study of cells and their components based on chemical composition; but slow acquisition rates, poor resolution and a lack of sensitivity have hampered further development. A new generation of stimulated Raman techniques is emerging which allows the imaging of cells, tissues and organisms at faster acquisition speeds, and with greater resolution and sensitivity than previously possible. This review focuses on the development of stimulated Raman scattering (SRS), and covers the use of bioorthogonal tags to enhance sample detection, and recent applications of both spontaneous Raman and SRS as novel imaging platforms to facilitate the drug discovery process.

MALDI-MS Imaging Analysis of Fungicide Residue Distributions on Wheat Leaf Surfaces

Improved retention and distribution of agrochemicals on plant surfaces is an important attribute in the biological activity of pesticide. Although retention of agrochemicals on plants after spray application can be quantified using traditional analytical techniques including LC or GC, the spatial distribution of agrochemicals on the plants surfaces has received little attention. Matrix assisted laser desorption/ionization (MALDI) imaging technology has been widely used to determine the distribution of proteins, peptides and metabolites in different tissue sections, but its application to environmental research has been limited. Herein, we probed the potential utility of MALDI imaging in characterizing the distribution of three commercial fungicides on wheat leaf surfaces. Using this MALDI imaging method, we were able to detect 500 ng of epoxiconazole, azoxystrobin, and pyraclostrobin applied in 1 μL drop on the leaf surfaces using MALDI-MS. Subsequent dilutions of pyraclostrobin revealed that the compound can be chemically imaged on the leaf surfaces at levels as low as 60 ng of total applied in the area of 1 μL droplet. After application of epoxiconazole, azoxystrobin, and pyraclostrobin at a field rate of 100 gai/ha in 200 L water using a track sprayer system, residues of these fungicides on the leaf surfaces were sufficiently visualized. These results suggest that MALDI imaging can be used to monitor spatial distribution of agrochemicals on leaf samples after pesticide application.

A method to prevent protein delocalization in imaging mass spectrometry of non-adherent tissues: application to small vertebrate lens imaging

MALDI imaging requires careful sample preparation to obtain reliable, high-quality images of small molecules, peptides, lipids, and proteins across tissue sections. Poor crystal formation, delocalization of analytes, and inadequate tissue adherence can affect the quality, reliability, and spatial resolution of MALDI images. We report a comparison of tissue mounting and washing methods that resulted in an optimized method using conductive carbon substrates that avoids thaw mounting or washing steps, minimizes protein delocalization, and prevents tissue detachment from the target surface. Application of this method to image ocular lens proteins of small vertebrate eyes demonstrates the improved methodology for imaging abundant crystallin protein products. This method was demonstrated for tissue sections from rat, mouse, and zebrafish lenses resulting in good-quality MALDI images with little to no delocalization. The images indicate, for the first time in mouse and zebrafish, discrete localization of crystallin protein degradation products resulting in concentric rings of distinct protein contents that may be responsible for the refractive index gradient of vertebrate lenses.

Efficiency of the dry-wet method for the MALDI-MSI analysis of latent fingermarks

Matrix-assisted laser desorption/ionisation mass spectrometry imaging (MALDI-MSI) has proven to be a powerful analytical tool to investigate problems in several fields of life science. A novel application is in the field of forensics, particularly in the analysis of latent fingermarks. This technology enables images of the fingermark ridge detail and additional intelligence to be simultaneously obtained. Although several methods are available to deposit the MALDI matrix, to make the technology forensically operational, another deposition approach was devised and reported, namely the 'dry-wet' method. In the present study, the efficiency of the dry-wet method was evaluated and compared with the conventional spray coat methodology. Results indicate that the dry-wet method is superior for all the donors' typologies in terms of ion signal intensity and clarity of the ridge details. To underpin the reasons of this efficiency, scanning electron microscopy analyses were carried out in parallel to MALDI-MSI experiments using matrices of different particle size. Results have confirmed that the particle size plays an important role in the efficiency of the method as higher quality images and higher intensity spectra are produced as the matrix particle size decreases.

HR-MALDI-MS imaging assisted screening of β-carboline alkaloids discovered from Mycena metata

Fruiting bodies of Mycena metata were screened for the presence of new secondary metabolites by means of HPLC-UV, LC-HR-ESIMS, and high-resolution matrix-assisted laser desorption/ionization mass spectrometry imaging (HR-MALDI-MS imaging). Thus, a new β-carboline alkaloid, 6-hydroxymetatacarboline D (1d), was isolated from fruiting bodies of M. metata. 6-Hydroxymetatacarboline D consists of a highly substituted β-carboline skeleton, which is likely to be derived biosynthetically from l-tryptophan, 2-oxoglutaric acid, l-threonine, and l-proline. The structure of the alkaloid was established by 2D NMR spectroscopic methods and HR-ESIMS. Moreover, by extensive application of LC-HR-ESIMS, LC-HR-ESIMS/MS, and LC-HR-ESIMS(3) techniques we were able to elucidate the structures of a number of accompanying β-carboline alkaloids, 1a-1c, 1e-1i, and 2a-2g, structurally closely related to 6-hydroxymetatacarboline D, which are present in M. metata in minor amounts. The absolute configuration of the stereogenic centers of the β-carboline alkaloids was determined by GC-MS comparison with authentic synthetic samples after hydrolytic cleavage and derivatization of the resulting amino acids.

Mass spectrometry based imaging techniques for spatially resolved analysis of molecules

Higher plants are composed of a multitude of tissues with specific functions, reflected by distinct profiles for transcripts, proteins, and metabolites. Comprehensive analysis of metabolites and proteins has advanced tremendously within recent years, and this progress has been driven by the rapid development of sophisticated mass spectrometric techniques. In most of the current "omics"-studies, analysis is performed on whole organ or whole plant extracts, rendering to the loss of spatial information. Mass spectrometry imaging (MSI) techniques have opened a new avenue to obtain information on the spatial distribution of metabolites and of proteins. Pioneered in the field of medicine, the approaches are now applied to study the spatial profiles of molecules in plant systems. A range of different plant organs and tissues have been successfully analyzed by MSI, and patterns of various classes of metabolites from primary and secondary metabolism could be obtained. It can be envisaged that MSI approaches will substantially contribute to build spatially resolved biochemical networks.

Absorption and translocation of nitrogen in rhizomes of Leymus chinensis

Leymus chinensis is a dominant species in the Inner Mongolia steppe, northern China. Plant growth in northern China grassland is often limited by low soil nitrogen availability. The objective of this study is to investigate whether rhizomes of Leymus chinensis are involved in the contribution of N uptake. The N concentration, (15)N concentration and (15)N proportion in roots, rhizomes and shoots after 48 h exposure of roots (L(root)) and rhizomes (L(rhizo)) separately and roots and rhizomes together (L(r+r)) to 0.1 mM (15)NH (4)(15)NO(3) solution were measured using root-splitting equipment and stable isotope ((15)N) techniques, respectively. The N content and dry mass were not affected by the labeling treatment. In contrast, the (15)N concentration in shoots, rhizomes and roots was significantly increased by the labeling in rhizomes, indicating that the inorganic nitrogen was absorbed via rhizomes from the solution and can be transported to other tissues, with preference to shoots rather than roots. Meanwhile, the absolute N absorption and translocation among compartments were also calculated. The N absorption via rhizomes was much smaller than via roots; however, the uptake efficiency per surface unit via rhizomes was greater than via roots. The capacity and high efficiency to absorb N nutrient via rhizomes enable plants to use transient nutrient supplies in the top soil surface.