Differential tissue distribution of metabolites in Jacobaea vulgaris, Jacobaea aquatica and their crosses

Non-Targeted Screening of Metabolites in Aqueous-Ethanol Extract from Spiraea hypericifolia (Rosaceae) Using LC-HRMS

By means of liquid chromatography combined with high-resolution mass spectrometry, metabolite profiling was performed on an aqueous-ethanol extract from Spiraea hypericifolia (Rosaceae) collected in Siberia (Russia). Up to 140 compounds were found in the extract, of which 47 were tentatively identified. The identified compounds were amino acids, sugars, phenylpropanoids, fatty acids and their derivatives, triterpenoids, flavonoids, and others. A quantitative analysis showed the predominance of phenolcarboxylic acids and flavonoids in the studied extract, but a qualitative analysis revealed the higher structural diversity of flavonoids. Of the 23 identified flavonoids, 13 were flavonols: quercetin, hyperoside, isoquercitrin, reynoutrin, avicularin, rutin, quercetin-3-O-(6″-O-malonyl)-β-D-glucoside, 3-O-methylquercetin-3'-O-β-D-glucopyranoside, isorhamnetin, rhamnetin-3-O-β-D-xylopyranosyl-β-D-glucopyranoside, kaempferol, tiliroside, and trifolin; six were catechins: catechin, (-)-epicatechin, (+)-epicatechin, (+)-catechin-7-O-β-D-xyloside, (2S,3R)-3,5-dihydroxy-2-(4-hydroxyphenyl)-3,4-dihydro-2H-chromen-7-yl-β-D-glucopyranoside, and catechin 7-O-apiofuranoside; two are isoflavones: genistin and genistein; and one was a flavone (luteolin-4'-O-β-D-glucopyranoside) and another was an anthocyanidin (pelargonidin). The aqueous-ethanol extract from S. hypericifolia showed antioxidant activity (half-maximal inhibitory concentration 102.95 μg/mL), which was likely related to the high concentrations of phenolcarboxylic acids (229.6 mg/g), flavonoids (118.3 mg/g), and tannins (62.9 mg/g).

Metabolite profiling and bioactivity of Cicerbita alpina (L.) Wallr. (Asteraceae, Cichorieae)

Cicerbita alpina (L.) Wallr. is a perennial herbaceous plant in the tribe Cichorieae (Lactuceae), Asteraceae family, distributed in the mountainous regions in Europe. In this study, we focused on the metabolite profiling and the bioactivity of C. alpina leaves and flowering heads methanol-aqueous extracts. The antioxidant activity of extracts, as well as inhibitory potential towards selected enzymes, involving in several human diseases, including metabolic syndrome (α-glucosidase, α-amylase, and lipase), Alzheimer's disease, (cholinesterases: AChE, BchE), hyperpigmentation (tyrosinase), and cytotoxicity were assessed. The workflow comprised ultra-high-performance liquid chromatography-high-resolution mass spectrometry (UHPLC-HRMS). UHPLC-HRMS analysis revealed more than 100 secondary metabolites, including acylquinic, acyltartaric acids, flavonoids, bitter sesquiterpene lactones (STLs), such as lactucin, dihydrolactucin, their derivatives, and coumarins. Leaves showed a stronger antioxidant activity compared to flowering heads, as well as lipase (4.75 ± 0.21 mg OE/g), AchE (1.98 ± 0.02 mg GALAE/g), BchE (0.74 ± 0.06 mg GALAE/g), and tyrosinase (49.87 ± 3.19 mg KAE/g) inhibitory potential. Flowering heads showed the highest activity against α-glucosidase (1.05 ± 0.17 mmol ACAE/g) and α-amylase (0.47 ± 0.03). The obtained results highlighted C. alpina as a rich source of acylquinic, acyltartaric acids, flavonoids, and STLs with significant bioactivity, and therefore the taxon could be considered as a potential candidate for the development of health-promoting applications.

Natural or artificial: An example of topographic spatial distribution analysis of mescaline in cactus plants by matrix-assisted laser desorption/ionization mass spectrometry imaging

INTRODUCTION

Differentiating whether plant products are natural or artificial is of great importance in many practical fields, including forensic science, food safety, cosmetics, and fast-moving consumer goods. Information about the topographic distribution of compounds is an important criterion for answering this question. However, of equal importance is the likelihood that topographic spatial distribution information may provide important and valuable information for molecular mechanism study.

METHODS

In this study, we took mescaline, a substance with hallucinogenic properties in cacti of the species Trichocereus pachanoi and Lophophora williamsii, as an example to characterize the spatial distribution of mescaline in plants and flowers by liquid chromatograph-mass spectrometry-matrix-assisted laser desorption/ionization mass spectrometry imaging at the macroscopic, tissue structure, and even cellular levels.

RESULTS

According to our results, the distribution of mescaline in natural plant was concentrated on the active meristems, epidermal tissues, and protruding parts of Trichocereus pachanoi and Lophophora williamsii, while artificially spiked Lophophora diffusa products showed no such difference in their topographic spatial distribution.

DISCUSSION

This difference in distribution pattern allowed us to distinguish between flowers that could synthesize mescaline on their own and those that had been artificially spiked with mescaline. The interesting topographic spatial distribution results, such as the overlap of the mescaline distribution map and micrographs of the vascular bundles, were consistent with the synthesis and transport theory of mescaline, indicating the potential for applying matrix-assisted laser desorption/ionization mass spectrometry imaging in botanical research.

Screening for Cyclotides in Sri Lankan Medicinal Plants: Discovery, Characterization, and Bioactivity Screening of Cyclotides from Geophila repens

Cyclotides are an intriguing class of structurally stable circular miniproteins of plant origin with numerous potential pharmaceutical and agricultural applications. To investigate the occurrence of cyclotides in Sri Lankan flora, 50 medicinal plants were screened, leading to the identification of a suite of new cyclotides from Geophila repens of the family Rubiaceae. Cycloviolacin O2-like (cyO2-like) gere 1 and the known cyclotide kalata B7 (kB7) were among the cyclotides characterized at the peptide and/or transcript level together with several putative enzymes, likely involved in cyclotide biosynthesis. Five of the most abundant cyclotides were isolated, sequenced, structurally characterized, and screened in antimicrobial and cytotoxicity assays. All gere cyclotides showed cytotoxicity (IC50 of 2.0-10.2 μM), but only gere 1 inhibited standard microbial strains at a minimum inhibitory concentration of 4-16 μM. As shown by immunohistochemistry, large quantities of the cyclotides were localized in the epidermis of the leaves and petioles of G. repens. Taken together with the cytotoxicity and membrane permeabilizing activities, this implicates gere cyclotides as potential plant defense molecules. The presence of cyO2-like gere 1 in a plant in the Rubiaceae supports the notion that phylogenetically distant plants may have coevolved to express similar cytotoxic cyclotides for a specific functional role, most likely involving host defense.

Spatial Distribution and Stability of Cholinesterase Inhibitory Protoberberine Alkaloids from Papaver setiferum

During a research program to identify new cholinesterase inhibitors of natural origin, two new 7,8-didehydroprotoberberine alkaloids (1 and 2) and nine known compounds (3-11) were isolated from the capsules of the common ornamental poppy, Papaver setiferum (previously P. pseudo-orientale). Despite their reported instability, the 7,8-didehydroprotoberberines isolated herein appeared relatively stable, particularly as their trifluoroacetic acid salts. The spatial distributions of the isolated alkaloids were also analyzed using desorption electrospray ionization imaging mass spectrometry. The alkaloids were localized predominantly within the walls and vascular bundles of the capsules, with the highest relative abundances occurring in the lower half of the capsules toward the peduncle. The relative abundances of the alkaloids were also compared across plant development stages. Although most alkaloids did not show clear patterns in their concentration across development stages, the concentration of suspected oxidation products clearly spiked upon plant death. Finally, all isolated natural products were screened for inhibitory activities against a panel of cholinesterases, from both human and animal sources. These studies identified several competitive inhibitors of cholinesterases with potency in the low micromolar range (1-4, 6, 7), offering new lead compounds for the development of cholinesterase inhibitory drugs.

Effect of spray drying on the polyphenolic compounds present in purple sweet potato roots: Identification of new cinnamoylquinic acids

The effect of spray drying on the different polyphenolic compounds present in the root of a purple-fleshed sweet potato variety of Ipomoea batatas native from Peru was performed by HPLC-QTOF-MSMS. Nine anthocyanins, including four peonidin, three cyanidin and two pelargonidin derivatives glycosylated with sophorose and/or glucose and acylated with caffeic, ferulic and p-hydroxybenzoic acid were identified. Twenty nine cinnamoylquinic acids (CiQA), including eight mono-CiQA, fourteen di-CiQA, and five tri-CiQA, were identified on the base of their MS fragmentation profile. Relevant amounts of feruloylquinic acid derivatives were identified. Among them, some di and tri-CiQAs containing feruloyl and caffeoyl moieties in their structures, and di-feruloylquinic acids were reported here, for the first time, in Ipomoea. Spray drying process negatively affected the different phenolic groups, with polyphenol losses representing around 90% of the initial amounts. Mono-CiQAs presenting feruloyl moieties and mono acylated peonidin derivatives with p-hydroxybenzoic acid were the less affected compounds.

Pyrrolizidine alkaloids in bee pollen identified by LC-MS/MS analysis and colour parameters using multivariate class modeling

Toxic pyrrolizidine alkaloids (PAs) and their N-oxides (PANOs) can be present in bee pollen depending on the plants visited by bees. A liquid chromatography-mass spectrometry (LC-MS/MS) method was developed and validated to monitor 17 PAs/PANOs in 44 bee pollens. The CIE-L∗a∗b∗ colour coordinates with the specular component either included or excluded were recorded in pellets and ground aliquots. Lightness (L∗) and yellowness (b∗) of ground bee pollen were significantly correlated to PAs/PANOs content. The L∗ and b∗ cut-offs sorted by a receiver operating characteristic analysis to predict PAs/PANOs presence showed a significant increase in the relative risk to detect amounts higher than 84 μg kg-1. Two supervised canonical discriminant analyses confirmed that pollen without PAs could be distinguished from those containing PAs/PANOs. The data suggest that instrumental colour coupled with supervised models could be used as a screening test for PAs/PANOs in bee pollen, before the confirmatory LC-MS/MS analysis.

Stable Isotope-Assisted Plant Metabolomics: Investigation of Phenylalanine-Related Metabolic Response in Wheat Upon Treatment With the Fusarium Virulence Factor Deoxynivalenol

The major Fusarium mycotoxin deoxynivalenol (DON) is a virulence factor in wheat and has also been shown to induce defense responses in host plant tissue. In this study, global and tracer labeling with 13C were combined to annotate the overall metabolome of wheat spikes and to evaluate the response of phenylalanine-related pathways upon treatment with DON. At anthesis, spikes of resistant and susceptible cultivars as well as two related near isogenic wheat lines (NILs) differing in the presence/absence of the major resistance QTL Fhb1 were treated with 1 mg DON or water (control), and samples were collected at 0, 12, 24, 48, and 96 h after treatment (hat). A total of 172 Phe-derived wheat constituents were detected with our untargeted approach employing 13C-labeled phenylalanine and subsequently annotated as flavonoids, lignans, coumarins, benzoic acid derivatives, hydroxycinnamic acid amides (HCAAs), as well as peptides. Ninety-six hours after the DON treatment, up to 30% of the metabolites biosynthesized from Phe showed significantly increased levels compared to the control samples. Major metabolic changes included the formation of precursors of compounds implicated in cell wall reinforcement and presumed antifungal compounds. In addition, also dipeptides, which presumably are products of proteolytic degradation of truncated proteins generated in the presence of the toxin, were significantly more abundant upon DON treatment. An in-depth comparison of the two NILs with correlation clustering of time course profiles revealed some 70 DON-responsive Phe derivatives. While several flavonoids had constitutively different abundance levels between the two NILs differing in resistance, other Phe-derived metabolites such as HCAAs and hydroxycinnamoyl quinates were affected differently in the two NILs after treatment with DON. Our results suggest a strong activation of the general phenylpropanoid pathway and that coumaroyl-CoA is mainly diverted towards HCAAs in the presence of Fhb1, whereas the metabolic route to monolignol(-conjugates), lignans, and lignin seems to be favored in the absence of the Fhb1 resistance quantitative trait loci.

How Does the Sweet Violet (Viola odorata L.) Fight Pathogens and Pests - Cyclotides as a Comprehensive Plant Host Defense System

Cyclotides are cyclic plant polypeptides of 27-37 amino acid residues. They have been extensively studied in bioengineering and drug development contexts. However, less is known about the relevance of cyclotides for the plants producing them. The anti-insect larvae effects of kB1 and antibacterial activity of cyO2 suggest that cyclotides are a part of plant host defense. The sweet violet (Viola odorata L.) produces a wide array of cyclotides, including kB1 (kalata B1) and cyO2 (cycloviolacin O2), with distinct presumed biological roles. Here, we evaluate V. odorata cyclotides' potency against plant pathogens and their mode of action using bioassays, liposome experiments and immunogold labeling for transmission electron microscopy (TEM). We explore the link between the biological activity and distribution in plant generative, vegetative tissues and seeds, depicted by immunohistochemistry and matrix assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI). Cyclotides cyO2, cyO3, cyO13, and cyO19 are shown to have potent activity against model fungal plant pathogens (Fusarium oxysporum, F. graminearum, F. culmorum, Mycosphaerella fragariae, Botrytis cinerea) and fungi isolated from violets (Colletotrichum utrechtense and Alternaria alternata), with minimal inhibitory concentrations (MICs) ranging from 0.8 μM to 25 μM. Inhibition of phytopathogenic bacteria - Pseudomonas syringae pv. syringae, Dickeya dadantii and Pectobacterium atrosepticum - is also observed with MIC = 25-100 μM. A membrane-disrupting antifungal mode of action is shown. Finding cyO2 inside the fungal spore cells in TEM images may indicate that other, intracellular targets may be involved in the mechanism of toxicity. Fungi can not break down cyclotides in the course of days. varv A (kalata S) and kB1 show little potency against pathogenic fungi when compared with the tested cycloviolacins. cyO2, cyO3, cyO19 and kB1 are differentially distributed and found in tissues vulnerable to pathogen (epidermis, rizodermis, vascular bundles, protodermis, procambium, ovary walls, outer integuments) and pest (ground tissues of leaf and petiole) attacks, respectively, indicating a link between the cyclotides' sites of accumulation and biological role. Cyclotides emerge as a comprehensive defense system in V. odorata, in which different types of peptides have specific targets that determine their distribution in plant tissues.

Thrips advisor: exploiting thrips-induced defences to combat pests on crops

Plants have developed diverse defence mechanisms to ward off herbivorous pests. However, agriculture still faces estimated crop yield losses ranging from 25% to 40% annually. These losses arise not only because of direct feeding damage, but also because many pests serve as vectors of plant viruses. Herbivorous thrips (Thysanoptera) are important pests of vegetable and ornamental crops worldwide, and encompass virtually all general problems of pests: they are highly polyphagous, hard to control because of their complex lifestyle, and they are vectors of destructive viruses. Currently, control management of thrips mainly relies on the use of chemical pesticides. However, thrips rapidly develop resistance to these pesticides. With the rising demand for more sustainable, safer, and healthier food production systems, we urgently need to pinpoint the gaps in knowledge of plant defences against thrips to enable the future development of novel control methods. In this review, we summarize the current, rather scarce, knowledge of thrips-induced plant responses and the role of phytohormonal signalling and chemical defences in these responses. We describe concrete opportunities for breeding resistance against pests such as thrips as a prototype approach for next-generation resistance breeding.

Chlorogenic acids and the acyl-quinic acids: discovery, biosynthesis, bioavailability and bioactivity

This review is focussed upon the acyl-quinic acids, the most studied group within theca.400 chlorogenic acids so far reported.

Interactions between Plant Metabolites Affect Herbivores: A Study with Pyrrolizidine Alkaloids and Chlorogenic Acid

The high structural diversity of plant metabolites suggests that interactions among them should be common. We investigated the effects of single metabolites and combinations of plant metabolites on insect herbivores. In particular we studied the interacting effects of pyrrolizidine alkaloid (PAs), and chlorogenic acid (CGA), on a generalist herbivore, Frankliniella occidentalis. We studied both the predominantly occurring PA N-oxides and the less frequent PA free bases. We found antagonistic effects between CGA and PA free bases on thrips mortality. In contrast PA N-oxides showed synergistic interactions with CGA. PA free bases caused a higher thrips mortality than PA N-oxides while the reverse was through for PAs in combination with CGA. Our results provide an explanation for the predominate storage of PA N-oxides in plants. We propose that antagonistic interactions represent a constraint on the accumulation of plant metabolites, as we found here for Jacobaea vulgaris. The results show that the bioactivity of a given metabolite is not merely dependent upon the amount and chemical structure of that metabolite, but also on the co-occurrence metabolites in, e.g., plant cells, tissues and organs. The significance of this study is beyond the concerns of the two specific groups tested here. The current study is one of the few studies so far that experimentally support the general conception that the interactions among plant metabolites are of great importance to plant-environment interactions.

Immunolocalization of cyclotides in plant cells, tissues and organ supports their role in host defense

The distribution of cyclotides was visualized in plant cells, tissues and organs using immunohistochemistry. Finding of cyclotides in tissues potentially vulnerable to pathogen attacks supports their role as defense molecules. The cyclotide family of plant peptides is characterized by the cyclic cystine knot motif and its diverse biological activities. Given their insecticidal and antimicrobial properties, the role of cyclotides in planta is probably associated with host defense. Our current understanding of the cellular compartmentalization of cyclotides in the vacuole is based on indirect studies on transgenic model plants that do not express cyclotides naturally. Matrix-assisted laser desorption ionization (MALDI) imaging has also been used to study the distribution of cyclotides, but the technique's resolution was insufficient to determine their tissue or cell distribution. To avoid the limitations of these approaches, immunohistochemical visualization methods were used. Antibodies were raised in rabbits using cycloviolacin O2 (cyO2), and their specificity was determined by Western and dot blot experiments. Slides for immunohistochemical analysis were prepared from leaf, petiole and root fragments of Viola odorata and Viola uliginosa, and specimens were visualized using indirect epifluorescence microscopy. The antibodies against cyclotides were specific against selected bracelet cyclotides with high similarity (cyO2, cyO3, cyO8, cyO13) and suitable for immunohistochemistry. The tissue distribution of the cyclotides visualized in this way is consistent with their proposed role in host defense-relatively large quantities were observed in the leaf and petiole epidermis in both Viola species. Cyclotides were also found in vascular tissue in all the assessed plant organs. The vacuole storage of cyclotides was directly shown.

Immunolocalization of cyclotides in plant cells, tissues and organ supports their role in host defense

The distribution of cyclotides was visualized in plant cells, tissues and organs using immunohistochemistry. Finding of cyclotides in tissues potentially vulnerable to pathogen attacks supports their role as defense molecules. The cyclotide family of plant peptides is characterized by the cyclic cystine knot motif and its diverse biological activities. Given their insecticidal and antimicrobial properties, the role of cyclotides in planta is probably associated with host defense. Our current understanding of the cellular compartmentalization of cyclotides in the vacuole is based on indirect studies on transgenic model plants that do not express cyclotides naturally. Matrix-assisted laser desorption ionization (MALDI) imaging has also been used to study the distribution of cyclotides, but the technique's resolution was insufficient to determine their tissue or cell distribution. To avoid the limitations of these approaches, immunohistochemical visualization methods were used. Antibodies were raised in rabbits using cycloviolacin O2 (cyO2), and their specificity was determined by Western and dot blot experiments. Slides for immunohistochemical analysis were prepared from leaf, petiole and root fragments of Viola odorata and Viola uliginosa, and specimens were visualized using indirect epifluorescence microscopy. The antibodies against cyclotides were specific against selected bracelet cyclotides with high similarity (cyO2, cyO3, cyO8, cyO13) and suitable for immunohistochemistry. The tissue distribution of the cyclotides visualized in this way is consistent with their proposed role in host defense-relatively large quantities were observed in the leaf and petiole epidermis in both Viola species. Cyclotides were also found in vascular tissue in all the assessed plant organs. The vacuole storage of cyclotides was directly shown.

Testing the generalist-specialist dilemma: the role of pyrrolizidine alkaloids in resistance to invertebrate herbivores in Jacobaea species

Plants produce a diversity of secondary metabolites (SMs) to protect them from generalist herbivores. On the other hand, specialist herbivores use SMs for host plant recognition, feeding and oviposition cues, and even sequester SMs for their own defense. Therefore, plants are assumed to face an evolutionary dilemma stemming from the contrasting effects of generalist and specialist herbivores on SMs. To test this hypothesis, bioassays were performed with F2 hybrids from Jacobaea species segregating for their pyrrolizidine alkaloids (PAs), using a specialist flea beetle (Longitarsus jacobaeae) and a generalist slug (Deroceras invadens). Our study demonstrated that while slug feeding damage was negatively correlated with the concentration of total PAs and that of senecionine-like PAs, flea beetle feeding damage was not affected by PAs. It was positively correlated though, with leaf fresh weight. The generalist slug was deterred by senecionine-like PAs but the specialist flea beetle was adapted to PAs in its host plant. Testing other herbivores in the same plant system, it was observed that the egg number of the specialist cinnabar moth was positively correlated with jacobine-like PAs, while the silver damage of generalist thrips was negatively correlated with senecionine- and jacobine-like PAs, and the pupae number of generalist leaf miner was negatively correlated with otosenine-like PAs. Therefore, while the specialist herbivores showed no correlation whatsoever with PA concentration, the generalist herbivores all showed a negative correlation with at least one type of PA. We concluded that the generalist herbivores were deterred by different structural groups of PAs while the specialist herbivores were attracted or adapted to PAs in its host plants.