Metabolic Profiling of Pyrrolizidine Alkaloids in Foliage of Two Echium spp. Invaders in Australia--A Case of Novel Weapons?

Soil pH, developmental stages and geographical origin differently influence the root metabolomic diversity and root-related microbial diversity of Echium vulgare from native habitats

Improved understanding of the complex interaction between plant metabolism, environmental conditions and the plant-associated microbiome requires an interdisciplinary approach: Our hypothesis in our multiomics study posited that several environmental and biotic factors have modulating effects on the microbiome and metabolome of the roots of wild Echium vulgare plants. Furthermore, we postulated reciprocal interactions between the root metabolome and microbiome. We investigated the metabolic content, the genetic variability, and the prokaryotic microbiome in the root systems of wild E. vulgare plants at rosette and flowering stages across six distinct locations. We incorporated the assessment of soil microbiomes and the measurement of selected soil chemical composition factors. Two distinct genetic clusters were determined based on microsatellite analysis without a consistent alignment with the geographical proximity between the locations. The microbial diversity of both the roots of E. vulgare and the surrounding bulk soil exhibited significant divergence across locations, varying soil pH characteristics, and within the identified plant genetic clusters. Notably, acidophilic bacteria were characteristic inhabitants of both soil and roots under acidic soil conditions, emphasizing the close interconnectedness between these compartments. The metabolome of E. vulgare significantly differed between root samples from different developmental stages, geographical locations, and soil pH levels. The developmental stage was the dominant driver of metabolome changes, with significantly higher concentrations of sugars, pyrrolizidine alkaloids, and some of their precursors in rosette stage plant roots. Our study featured the complex dynamics between soil pH, plant development, geographical locations, plant genetics, plant metabolome and microbiome, shedding light on existing knowledge gaps.

LC-MS/MS Evaluation of Pyrrolizidine Alkaloids Profile in Relation to Safety of Comfrey Roots and Leaves from Polish Sources

Comfrey (Symphytum officinale L.) has a long tradition of use in the treatment of musculoskeletal disorders. However, due to hepatotoxic pyrrolizidine alkaloids (PAs), the EMA restricts the use of comfrey root (CR) to external use only and for short periods of time. Recent studies indicate a low permeability of PAs across the skin, calling into question the safety of topical application of products containing comfrey preparations. The aim of our work was to develop and validate an HPLC method enabling the separation of isomeric PAs from comfrey and, on this basis, to assess the potential toxicity of CR and comfrey leaf (CL) obtained from various Polish sources. The qualitative and quantitative analysis of PAs via HPLC-MS/MS was performed in MRM mode. The results obtained confirmed a lower content of PAs in CL than in CR and showed a wide variation in the composition of PAs in CR, with a much more stable profile of PAs in CL. Factor analysis confirmed that CRs and CLs differ in PA content, which is influenced by the growth conditions and geographical origin. The determined concentrations of PAs prove that in some CRs available on the Polish herbal market, the content of PAs may exceed the daily dose considered safe.

Bioactivity of plants eaten by wild birds against laboratory models of parasites and pathogens

Plants are not only used as energy and nutrient resources for herbivores. Plants can be ingested because of their activity against host parasites and other pathogens. This so-called medicinal role of plants is well reported in ethnopharmacology and under-reported in wild animals. More studies on wild animals are needed because any plant in the world contains bioactive compounds, and probably all plants, no matter how toxic they are, experience herbivory. For example, we tested the activity of extracts and essential oils from Papaver rhoeas and Echium plantagineum against a selection of laboratory pathogens because Great bustards Otis tarda preferred these plants during the mating season, with male fecal droppings showing a higher frequency of P. rhoeas particles than the fecal droppings of females. We hypothesized that P. rhoeas could be helpful for males in the mating season if any part of this plant harbors bioactivity against parasites and other pathogens. Males’ immune system is weakened during the mating season because of their investment in secondary sexual characters and sexual display. As a first exploration of the bioactivity of these plants, we evaluated extracts of both plants against a sample of laboratory models, including a flagellated protozoon (Trichomonas gallinae), a nematode (Meloidogyne javanica) and a fungus (Aspergillus niger). Non-polar and polar extracts of the aerial parts of P. rhoeas, especially the extracts of flowers and capsules, and the extracts of leaves and flowers of E. plantagineum showed activity against nematodes and trichomonads. The bioactivity of plants against parasites could explain the foraging behavior of stressed animals. The chemical communication underpinning the capacity of fauna to recognize those plants is far less known.

Assessment of Distribution and Diversity of Pyrrolizidine Alkaloids in the Most Prevalent Boraginaceae Species in Macedonia

Systematic study of extraction efficiency of pyrrolizidine alkaloids (PAs) and corresponding pyrrolizidine alkaloid N-oxides (PANOs) from plant material for subsequent LC/MS analysis was carried out. The optimal extraction was achieved with methanol and one clean up step using SPE C18 column. With the optimized LC-ESI-MS/MS method using ion trap, the distribution and diversity of PAs and PANOs in plant material (leaves, flowers and stems) obtained from wild-growing E. vulgare, E. italicum, S. officinale L., C. creticum and O. heterophylla species from Macedonia was assessed. These widespread Boraginaceae species contain various PAs and PANOs and 25 of them were identified. Based on these qualitative and quantitative analyses, the profiles of 1,2-unsaturated PAs for each sample were obtained and their toxic potential was estimated. The toxic potential of O. heterophylla and C. creticum were assumed to be highest (containing up to 4753 mg/kg and 3507 mg/kg), followed by E. vulgare (up to 1340 mg/kg), S. officinale L. (up to 479 mg/kg) and E. italicum (up to 16 mg/kg). This method can be used for monitoring the inclusion of these secondary metabolites in the food chain in order to contribute in their risk management.

Comparative analysis of the main medicinal substances and applications of Echium vulgare L. and Echium plantagineum L.: A review

ETHNOPHARMACOLOGICAL RELEVANCE

Echium vulgare L. and Echium plantagineum L. originated in the Mediterranean, and were later domesticated in Africa, America, Asia, Europe and Oceania, where they were widely used to treat many diseases including cough, urinary tract infection, fever, inflammation and muscle strain.

AIM OF THE STUDY

The purpose of this review is to provide scientific literature on the traditional uses, bioactive chemical components and pharmacological activities of two species of Echium, and to critically analyze the information provided, so as to understand the current work on these two species and explore the possible prospect of this plant in pharmaceutical research.

METHODS

Systematic review and meta-analysis were conducted according to Prisma guidelines, and the related literatures searched on Google Academic, Science Direct, Baidu Scholars and China National Knowledge Infrastructure (CNKI) up to June 2021 were reviewed. The key words used are: Echium, E.vulgare, E.plantagineum, plant components, chemical components, pharmacological activities, pharmaceutical products and applications. Thereafter all eligible studies are analyzed and summarized in this review. The selection of manuscripts is based on the following inclusion criteria: the article has years of research or publication, is published in English, Portuguese or Spanish and Chinese, and there are keywords in the title, abstract, keywords or full text of the article. For the selection of manuscripts, first, select articles according to titles, then summarize them, and finally, analyze the full text of the publication. Elimination criteria: 1. Duplicate reports; 2. There are research design defects and poor quality; 3. Incomplete data and unclear ending effect; 4. The statistical method is wrong and cannot be corrected.

RESULTS

The pharmacological characteristics of E.vulgare and E.plantagineum can basically support their traditional use, but the medicinal substances contained in them are quite different in composition and content, and the development and application of corresponding products are also different.

CONCLUSIONS

At present, there is little clinical data about drugs related to the two species, and more research is needed in the future, especially human experiments and clinical trials, to evaluate the cellular and molecular mechanisms based on pharmacological, biological activity and safety studies, and to provide more powerful scientific basis for their traditional medicinal properties. In addition, the further application and development of the medicinal products of E.vulgare and E.plantagineum still need to be precise and identified, so as to give full play to their medicinal potential.

Pyrrolizidine alkaloids and beehive products: A review

Pyrrolizidine alkaloids (PA) are secondary metabolites of plants, which are mostly found in the genus Senecio, Echium, Crotalaria, and Eupatorium. The presence of 1,2-unsaturated PA in foods is a concern to food regulators around the world because these compounds have been associated to acute and chronic toxicity, mainly in the liver. The intake foods with PA/PANO usually occur through accidental ingestion of plants and their derivatives, besides to products of vegetal-animal origin, such as honey. PA/PANO are transferred to honey by their presence in nectar, honeydew, and pollen, which are collected from the flora by bees. In addition to honey, other beekeeping products, such as pollen, royal jelly, propolis, and beeswax, are also vulnerable to PA contamination. In this context, this review provides information about chemical characteristics, regulation, and toxicity, as well as summarizes and critically discusses scientific publications that evaluated PA in honeys, pollens, royal jelly, and propolis.

Analysis of Pyrrolizidine Alkaloids in Queensland Honey: Using Low Temperature Chromatography to Resolve Stereoisomers and Identify Botanical Sources by UHPLC-MS/MS

Pyrrolizidine alkaloids (PAs) are a diverse group of plant secondary metabolites with known varied toxicity. Consumption of 1,2-unsaturated PAs has been linked to acute and chronic liver damage, carcinogenicity and death, in livestock and humans, making their presence in food of concern to food regulators in Australia and internationally. In this survey, honey samples sourced from markets and shops in Queensland (Australia), were analysed by high-resolution Orbitrap UHPLC-MS/MS for 30 common PAs. Relationships between the occurrence of pyrrolizidine alkaloids and the botanical origin of the honey are essential as pyrrolizidine alkaloid contamination at up to 3300 ng/g were detected. In this study, the predominant alkaloids detected were isomeric PAs, lycopsamine, indicine and intermedine, exhibiting identical MS/MS spectra, along with lesser amounts of each of their N-oxides. Crucially, chromatographic UHPLC conditions were optimised by operation at low temperature (5 °C) to resolve these key isomeric PAs. Such separation of these isomers by UHPLC, enabled the relative proportions of these PAs present in honey to be compared to alkaloid levels in suspect source plants. Overall plant pyrrolizidine alkaloid profiles were compared to those found in honey samples to help identify the most important plants responsible for honey contamination. The native Australian vines of Parsonsia spp. are proposed as a likely contributor to high levels of lycopsamine in many of the honeys surveyed. Botanical origin information such as this, gained via low temperature chromatographic resolution of isomeric PAs, will be very valuable in identifying region of origin for honey samples.

Genetic evidence for plural introduction pathways of the invasive weed Paterson's curse (Echium plantagineum L.) to southern Australia

Paterson’s curse (Echium plantagineum L. (Boraginaceae)), is an herbaceous annual native to Western Europe and northwest Africa. It has been recorded in Australia since the 1800’s and is now a major weed in pastures and rangelands, but its introduction history is poorly understood. An understanding of its invasion pathway and subsequent genetic structure is critical to the successful introduction of biological control agents and for provision of informed decisions for plant biosecurity efforts. We sampled E. plantagineum in its native (Iberian Peninsula), non-native (UK) and invaded ranges (Australia and South Africa) and analysed three chloroplast gene regions. Considerable genetic diversity was found among E. plantagineum in Australia, suggesting a complex introduction history. Fourteen haplotypes were identified globally, 10 of which were co-present in Australia and South Africa, indicating South Africa as an important source population, likely through contamination of traded goods or livestock. Haplotype 4 was most abundant in Australia (43%), and in historical and contemporary UK populations (80%), but scarce elsewhere (< 17%), suggesting that ornamental and/or other introductions from genetically impoverished UK sources were also important. Collectively, genetic evidence and historical records indicate E. plantagineum in southern Australia exists as an admixture that is likely derived from introduced source populations in both the UK and South Africa.

Recent advances in allelopathy for weed control: from knowledge to applications

Allelopathy is the biological phenomenon of chemical interactions between living organisms in the ecosystem, and must be taken into account in addressing pest and weed problems in future sustainable agriculture. Allelopathy is a multidisciplinary science, but in some cases, aspects of its chemistry are overlooked, despite the need for a deep knowledge of the chemical structural characteristics of allelochemicals to facilitate the design of new herbicides. This review is focused on the most important advances in allelopathy, paying particular attention to the design and development of phenolic compounds, terpenoids and alkaloids as herbicides. The isolation of allelochemicals is mainly addressed, but other aspects such as the analysis and activities of derivatives or analogs are also covered. Furthermore, the use of allelopathy in the fight against parasitic plants is included. The past 12 years have been a prolific period for publications on allelopathy. This critical review discusses future research areas in this field and the state of the art is analyzed from the chemist's perspective. © 2019 Society of Chemical Industry.

Production of pyrrolizidine alkaloids and shikonins in Echium plantagineum L. in response to various plant stressors

BACKGROUND

Echium plantagineum, a native of Europe and Africa, is a noxious invasive weed in Australia forming monocultural stands in pastures and rangelands. It produces a complex mixture of bioactive secondary metabolites, including toxic pyrrolizidine alkaloids (PAs), that protect the plant from insect and livestock herbivory and naphthoquinones (NQs), which suppress competition from weeds, insects and pathogens, and also influence invasion success. However, the extent to which allelochemical production is impacted by environmental factors, thereby influencing plant defense against pests, remains unclear.

RESULTS

Following plant stress induced by drought, herbivory and high temperature, extracts of E. plantagineum shoots and roots were subjected to metabolic profiling by UPLC-MS-DAD- QToF mass spectrometry. Abundance of NQs, especially deoxyshikonin, shikonin and dimethylacrylshikonin, rapidly increased in roots exposed to elevated temperatures. Water withholding initially increased NQ abundance, but prolonged drought resulted in reduced total PAs and NQs. Intraspecific competition elevated the production of NQs, whereas simulated herbivory had no initial effect on NQs. Following herbivory, the abundance of the PA 3'-O-acetylechimidine-N-oxide in seedling shoots was increased.

CONCLUSIONS

Differential accumulation of defense metabolites by E. plantagineum following exposure to various stressors suggested stress-dependent biosynthetic regulation, particularly with respect to NQ production, which was rapidly induced following drought, intraspecific competition and high temperature treatment, thereby positively impacting resistance or defense against herbivores, weeds and pathogens. We propose that trade-offs between above- and below-ground metabolism in E. plantagineum may facilitate allelochemical production in response to stress, rendering plants with an enhanced ability to defend against other neighboring plants, insects and microbes, with allelochemical production further facilitated by catabolic recycling following lengthier exposure to stress. © 2019 Society of Chemical Industry.

Pyrrolizidine Alkaloids of Blue Heliotrope (Heliotropium amplexicaule) and Their Presence in Australian Honey

Blue heliotrope (Heliotropium amplexicaule) is an invasive environmental weed that is widely naturalized in eastern Australia and has been implicated as a source of pyrrolizidine alkaloid (PA) poisoning in livestock. Less well-documented is the potential of such carcinogenic alkaloids to contaminate honey from bees foraging on this plant species. In this study, the PA profile of H. amplexicaule plant material, determined by HRAM LC-MS/MS, revealed the presence of nine PAs and PA-N-oxides, including several PAs and PA-N-oxides of the indicine class, which have not previously been reported. The predominant alkaloid, indicine, represents 84% of the reduced PA content, with minor alkaloids identified as intermedine and the newly reported helioamplexine, constituting 7 and 9%, respectively. NMR analysis confirmed the identity of helioamplexine as a previously unreported indicine homologue. This is the first report of the isolation of intermedine, helioamplexine, and 3'-O-angelylindicine from H. amplexicaule. Also described is the identification of N-chloromethyl analogues of the major alkaloids as isolation-derived artifacts from reactions with dichloromethane. Analysis of regional-market honey samples revealed a number of honey samples with PA profiles analogous to that seen in H. amplexicaule, with measured PA contents of up to 2.0 μg of PAs per gram of honey. These results confirm the need for honey producers to be aware of H. amplexicaule as a potential PA source, most particularly in products where honey is sourced from a single location.

Nursing protects honeybee larvae from secondary metabolites of pollen

The pollen of many plants contains toxic secondary compounds, sometimes in concentrations higher than those found in the flowers or leaves. The ecological significance of these compounds remains unclear, and their impact on bees is largely unexplored. Here, we studied the impact of pyrrolizidine alkaloids (PAs) found in the pollen of Echium vulgare on honeybee adults and larvae. Echimidine, a PA present in E. vulgare pollen, was isolated and added to the honeybee diets in order to perform toxicity bioassays. While adult bees showed relatively high tolerance to PAs, larvae were much more sensitive. In contrast to other bees, the honeybee larval diet typically contains only traces of pollen and consists predominantly of hypopharyngeal and mandibular secretions produced by nurse bees, which feed on large quantities of pollen-containing bee bread. We quantified the transfer of PAs to nursing secretions produced by bees that had previously consumed bee bread supplemented with PAs. The PA concentration in these secretions was reduced by three orders of magnitude as compared to the PA content in the nurse diet and was well below the toxicity threshold for larvae. Our results suggest that larval nursing protects honeybee larvae from the toxic effect of secondary metabolites of pollen.

Quantitative and qualitative analysis of pyrrolizidine alkaloids in liqueurs, elixirs and herbal juices

Pyrrolizidine alkaloids (PAs and corresponding N-oxides (PANOs)) are known to have adverse health effects. Their toxic effects on liver cells are especially well-documented. In addition, potential carcinogenic and mutagenic effects in chronic exposure via food and/or herbal medicines have been a subject of vivid discussion in the last decade. Liqueurs and elixirs are traditionally used alcoholic extracts made from parts of plants and herbs. PA cross-contamination of the final products seems likely. Hence, this study aims to detect and quantify the PAs in such products in the light of a possible PA-contamination. The PA content was determined in the form of a single sum parameter using HPLC-ESI-MS/MS and a stable isotope-labeled internal standard. Overall, 56 products available at German pharmacies, drugstores, or internet shops were analyzed, comprising in total 38 samples of liqueurs (mainly bitters), 12 samples of plant elixirs and six different herbal juices. The results showed that 9 out of 38 liqueurs were PA-positive (24%). The total amount of PAs ranged from non-detectable to 9.5 μg/kg. Seven out of ten elixirs were PA-positive (70%) with a maximum PA-content of 3121 μg/kg. Four out of six plant juices were PA-positive (67%) with an average of 4.4 μg/kg (PA-positive samples only).The results and potential risks are discussed in the light of recommended portions for daily consumption or daily doses, in association with the detected PA amounts for individual products and product classes.

Chemometric analysis of Amaranthus retroflexus in relation to livestock toxicity in southern Australia

Amaranthus retroflexus L., an introduced invasive weed in southern Australia, has been associated with acute renal failure and/or mortality in a number of livestock species. While its leaves, flowers and stems are generally reported to contain high levels of nitrogen, few studies have fully characterised the chemical composition of A. retroflexus foliage with respect to mammalian toxicity. We performed extensive metabolic profiling of stems, leaves, roots and inflorescence tissues of A. retroflexus collected from three spatially and/or temporally distinct toxicity outbreaks, and report on the 1) composition of primary and secondary metabolites in methanolic extracts of A. retroflexus tissues using HPLC and HPLC-MS QToF and 2) chemometric analysis of A. retroflexus extracts in relation to the associated toxin(s). All tissues of A. retroflexus possessed an abundance of N-containing metabolites, particularly quaternary ammonium compounds which were identified as betaines, two of which (valine betaine and isoleucine betaine) are rarely encountered in plants. Cytotoxicity to murine fibroblasts was highest in extracts of leaf tissue and was associated with a single, a small modified peptide with high similarity to N-acetyl-L-α-aspartyl-L-alanyl-L-α-aspartyl-L-α-glutamyl-O-(carboxymethyl)-L-tyrosyl-L-leucinamide, a synthetic phosphotyrosyl mimic involved in cell signaling processes. One possible mode of action leading to acute renal failure in grazing livestock by a modified peptide such as this is proposed.

Comparison of Strategies to Overcome Drug Resistance: Learning from Various Kingdoms

Drug resistance, especially antibiotic resistance, is a growing threat to human health. To overcome this problem, it is significant to know precisely the mechanisms of drug resistance and/or self-resistance in various kingdoms, from bacteria through plants to animals, once more. This review compares the molecular mechanisms of the resistance against phycotoxins, toxins from marine and terrestrial animals, plants and fungi, and antibiotics. The results reveal that each kingdom possesses the characteristic features. The main mechanisms in each kingdom are transporters/efflux pumps in phycotoxins, mutation and modification of targets and sequestration in marine and terrestrial animal toxins, ABC transporters and sequestration in plant toxins, transporters in fungal toxins, and various or mixed mechanisms in antibiotics. Antibiotic producers in particular make tremendous efforts for avoiding suicide, and are more flexible and adaptable to the changes of environments. With these features in mind, potential alternative strategies to overcome these resistance problems are discussed. This paper will provide clues for solving the issues of drug resistance.

Bioactivity and quantitative analysis of isohexenylnaphthazarins in root periderm of two Echium spp.: E. plantagineum and E. gaditanum

Isohexenylnaphthazarins are commonly found in the root periderm of several Boraginaceous plants and are known for their broad range of biological activities. The work described herein concerns the biological activity of compounds from the roots of Echium plantagineum L. and Echium gaditanum Boiss (Boraginaceae) collected from field sites in southern Spain and Australia. Bioactivity was assessed using etiolated wheat coleoptile bioassay and in vitro growth inhibitory activity in HeLa and IGROV-1 cells. The quantification of four isohexenylnaphthazarins (shikonin/alkannin, deoxyshikonin/deoxyalkannin, acetylshikonin/acetylalkannin and dimethylacrylshikonin/dimethylacrylalkannin) was performed by LC-MS/MS using juglone as internal standard. Correlation coefficient values for the activities and concentrations of these four analytes were in the linear range and were greater than 0.99. Acetylshikonin/acetylalkannin and dimethylacrylshikonin/dimethylacrylalkannin were present in the highest concentrations in extracts of both species. The results reveal that greatest overall inhibition was observed in both bioassays with E. gaditanum extracts. Strong correlations between time of collection, sampling location and bioactivity were identified.

Pyrrolizidine alkaloid variation in Senecio vulgaris populations from native and invasive ranges

Biological invasion is regarded as one of the greatest environmental problems facilitated by globalization. Some hypotheses about the invasive mechanisms of alien invasive plants consider the plant–herbivore interaction and the role of plant defense in this interaction. For example, the “Shift Defense Hypothesis” (SDH) argues that introduced plants evolve higher levels of qualitative defense chemicals and decreased levels of quantitative defense, as they are released of the selective pressures from specialist herbivores but still face attack from generalists. Common groundsel (Senecio vulgaris), originating from Europe, is a cosmopolitan invasive plant in temperate regions. As in other Senecio species, S. vulgaris contains pyrrolizidine alkaloids (PAs) as characteristic qualitative defense compounds. In this study, S. vulgaris plants originating from native and invasive ranges (Europe and China, respectively) were grown under identical conditions and harvested upon flowering. PA composition and concentration in shoot and root samples were determined using Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS). We investigated the differences between native and invasive S. vulgaris populations with regard to quantitative and qualitative variation of PAs. We identified 20 PAs, among which senecionine, senecionine N-oxide, integerrimine N-oxide and seneciphylline N-oxide were dominant in the roots. In the shoots, in addition to the 4 PAs dominant in roots, retrorsine N-oxide, spartioidine N-oxide and 2 non-identified PAs were also prevalent. The roots possessed a lower PA diversity but a higher total PA concentration than the shoots. Most individual PAs as well as the total PA concentration were strongly positively correlated between the roots and shoots. Both native and invasive S. vulgaris populations shared the pattern described above. However, there was a slight trend indicating lower PA diversity and lower total PA concentration in invasive S. vulgaris populations than native populations, which is not consistent with the prediction of SDH.

Metabolic Profiling and Identification of Shikonins in Root Periderm of Two Invasive Echium spp. Weeds in Australia

Metabolic profiling can be successfully implemented to analyse a living system's response to environmental conditions by providing critical information on an organism's physiological state at a particular point in time and allowing for both quantitative and qualitative assessment of a specific subset(s) of key metabolites. Shikonins are highly reactive chemicals that affect various cell signalling pathways and possess antifungal, antibacterial and allelopathic activity. Based on previous bioassay results, bioactive shikonins, are likely to play important roles in the regulation of rhizosphere interactions with neighbouring plants, microbes and herbivores. An effective platform allowing for rapid identification and accurate profiling of numerous structurally similar, difficult-to-separate bioactive isohexenylnaphthazarins (shikonins) was developed using UHPLC Q-TOF MS. Root periderm tissues of the invasive Australian weeds Echium plantagineum and its congener E. vulgare were extracted overnight in ethanol for shikonin profiling. Shikonin production was evaluated at seedling, rosette and flowering stages. Five populations of each species were compared for qualitative and quantitative differences in shikonin formation. Each species showed little populational variation in qualitative shikonin production; however, shikonin was considerably low in one population of E. plantagineum from Western New South Wales. Seedlings of all populations produced the bioactive metabolite acetylshikonin and production was upregulated over time. Mature plants of both species produced significantly higher total levels of shikonins and isovalerylshikonin > dimethylacrylshikonin > shikonin > acetylshikonin in mature E. plantagineum. Although qualitative metabolic profiles in both Echium spp. were nearly identical, shikonin abundance in mature plant periderm was approximately 2.5 times higher in perennial E. vulgare extracts in comparison to those of the annual E. plantagineum. These findings contribute to our understanding of the biosynthesis of shikonins in roots of two related invasive plants and their expression in relation to plant phenological stage.

Ecology and genetics affect relative invasion success of two Echium species in southern Australia

Echium plantagineum and E. vulgare are congeneric exotics first introduced to Australia in the early 1800 s. There, E. plantagineum is now highly invasive, whereas E. vulgare has a limited distribution. Studies were conducted to evaluate distribution, ecology, genetics and secondary chemistry to shed light on factors associated with their respective invasive success. When sampled across geographically diverse locales, E. plantagineum was widespread and exhibited a small genome size (1 C = 0.34 pg), an annual life cycle, and greater genetic diversity as assessed by DNA sequence analysis. It was found frequently in areas with temperature extremes and low rainfall. In contrast, E. vulgare exhibited a larger genome size (1 C = 0.43 pg), a perennial lifecycle, less chloroplast genetic diversity, and occurred in areas with lower temperatures and higher rainfall. Twelve chloroplast haplotypes of E. plantagineum were evident and incidence aligned well with reported historical introduction events. In contrast, E. vulgare exhibited two haplotypes and was found only sporadically at higher elevations. Echium plantagineum possessed significantly higher levels of numerous pyrrolizidine alkaloids involved in plant defence. We conclude that elevated genetic diversity, tolerance to environmental stress and capacity for producing defensive secondary metabolites have contributed to the successful invasion of E. plantagineum in Australia.

Understanding invasion history and predicting invasive niches using genetic sequencing technology in Australia: case studies from Cucurbitaceae and Boraginaceae

Part of the challenge in dealing with invasive plant species is that they seldom represent a uniform, static entity. Often, an accurate understanding of the history of plant introduction and knowledge of the real levels of genetic diversity present in species and populations of importance is lacking. Currently, the role of genetic diversity in promoting the successful establishment of invasive plants is not well defined. Genetic profiling of invasive plants should enhance our understanding of the dynamics of colonization in the invaded range. Recent advances in DNA sequencing technology have greatly facilitated the rapid and complete assessment of plant population genetics. Here, we apply our current understanding of the genetics and ecophysiology of plant invasions to recent work on Australian plant invaders from the Cucurbitaceae and Boraginaceae. The Cucurbitaceae study showed that both prickly paddy melon (Cucumis myriocarpus) and camel melon (Citrullus lanatus) were represented by only a single genotype in Australia, implying that each was probably introduced as a single introduction event. In contrast, a third invasive melon, Citrullus colocynthis, possessed a moderate level of genetic diversity in Australia and was potentially introduced to the continent at least twice. The Boraginaceae study demonstrated the value of comparing two similar congeneric species; one, Echium plantagineum, is highly invasive and genetically diverse, whereas the other, Echium vulgare, exhibits less genetic diversity and occupies a more limited ecological niche. Sequence analysis provided precise identification of invasive plant species, as well as information on genetic diversity and phylogeographic history. Improved sequencing technologies will continue to allow greater resolution of genetic relationships among invasive plant populations, thereby potentially improving our ability to predict the impact of these relationships upon future spread and better manage invaders possessing potentially diverse biotypes and exhibiting diverse breeding systems, life histories and invasion histories.

A 28-day oral toxicity study of echimidine and lasiocarpine in Wistar rats

Pyrrolizidine alkaloids (PAs) are a class of naturally-occurring plant toxins. Echimidine is one of the predominant PAs found in honeys produced in Australia and New Zealand. There is a lack of information on the oral toxicity of echimidine on which to base regulatory decisions concerning the risk to humans of these honeys. This GLP study was conducted to assess the subchronic dietary toxicity of echimidine to rats compared to that of lasiocarpine as a positive control. Wistar rats, 10/sex, were fed diets containing 0, 0.6, 1.2 or 2.5 mg/kg bw echimidine. Positive control groups, 10/sex, were fed diets containing 0.6, 1.2 or 2.5 mg/kg bw lasiocarpine. Neither PA had any effect on survival, food consumption, clinical signs, gross lesions, or histopathology. Consumption of lasiocarpine, but not echimidine, decreased bodyweight gain in males at ≥ 1.2 mg/kg bw, and in females at 2.5 mg/kg bw. Slight alterations in white cell counts and serum ALT concentrations at 2.5 mg/kg bw of both PAs were not clinically significant, had no histological correlates, and were considered to be of equivocal relevance. In conclusion, the subchronic No Observed Adverse Effect Level (NOAEL) for echimidine is 2.5 mg/kg bw/day, whereas, on the basis of a treatment-related decrease in bodyweight gain in males at 1.2 mg/kg bodyweight, the NOAEL for lasiocarpine is 0.6 mg/kg bw/day.

Identification and localization of bioactive naphthoquinones in the roots and rhizosphere of Paterson's curse (Echium plantagineum), a noxious invader

Bioactive plant secondary products are frequently the drivers of complex rhizosphere interactions, including those with other plants, herbivores and microbiota. These chemically diverse molecules typically accumulate in a highly regulated manner in specialized plant tissues and organelles. We studied the production and localization of bioactive naphthoquinones (NQs) in the roots of Echium plantagineum, an invasive endemic weed in Australia. Roots of E. plantagineum produced red-coloured NQs in the periderm of primary and secondary roots, while seedling root hairs exuded NQs in copious quantities. Confocal imaging and microspectrofluorimetry confirmed that bioactive NQs were deposited in the outer layer of periderm cells in mature roots, resulting in red colouration. Intracellular examination revealed that periderm cells contained numerous small red vesicles for storage and intracellular transport of shikonins, followed by subsequent extracellular deposition. Periderm and root hair extracts of field- and phytotron-grown plants were analysed by UHPLC/Q-ToF MS (ultra high pressure liquid chromatography coupled to quadrupole time of flight mass spectrometry) and contained more than nine individual NQs, with dimethylacrylshikonin, and phytotoxic shikonin, deoxyshikonin and acetylshikonin predominating. In seedlings, shikonins were first found 48h following germination in the root-hypocotyl junction, as well as in root hair exudates. In contrast, the root cortices of both seedling and mature root tissues were devoid of NQs. SPRE (solid phase root zone extraction) microprobes strategically placed in soil surrounding living E. plantagineum plants successfully extracted significant levels of bioactive shikonins from living roots, rhizosphere and bulk soil surrounding roots. These findings suggest important roles for accumulation of shikonins in the root periderm and subsequent rhizodeposition in plant defence, interference, and invasion success.