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Just recently, the "horizontal natural product transfer" was unveiled: alkaloids, which have been leached out from decomposing alkaloidal donor plants, are taken up by the roots of acceptor plants. In the same manner, many other natural products, such as coumarins or stilbenes, are also taken up from the soil. Recent research outlined that alkaloids are transferred also from a living donor plant to plants growing in their vicinity. In the acceptor plants, the imported natural products might be modified by hydroxylation and glucosylation. These insights will strongly impact our understanding of contamination of plant-derived commodities as well as plant-plant interactions.

This study focuses on the elucidation of the stress-induced reverse changes of major indole alkaloids in Vinca minor, primarily on the postulated conversion of vincamine and vincadifformine to yield 9-methoxyvincamine, minovincine, and minovincinine, respectively. By applying the P450 enzyme inhibitors, naproxen and resveratrol, it was shown that the oxidative reaction involved in the postulated conversion of vincamine and vincadifformine is catalyzed by cytochrome P450 enzymes. In combination with the identification of 9-hydroxyvincamine as a postulated intermediate, this result confirms that the observed stress-induced reverse changes in the alkaloid pattern are caused by modifications of the alkaloids which regularly accumulate in the healthy Vinca minor plants. Up to now, just two main types of defense compounds are distinguished: phytoalexins, which are synthesized de novo from primary metabolites and phytoanticipins, which are constitutively present in plants - either intrinsically active or are activated after cell death by hydrolysis or oxidation of the precursors. In contrast, the results presented in this paper demonstrate that indole alkaloids, representing typical phytoanticipins, are just slightly modified in response to a stress-related elicitation. Accordingly, these modified alkaloids neither represent classical phytoalexins (being synthesized de novo), nor can they be classified as phytoanticipins, since modification does not occur postmortem. Consequently, we propose a new category for these modified alkaloids that we call phytomodificines.

Medicinal plants grown under stress conditions reveal higher concentrations of relevant specialized metabolites than well-watered plants, putatively due to an enhanced biosynthesis. Yet, stress also reduced the biomass gain. Accordingly, the concentration increase in comparison to control plants could also be due to lesser biomass employed as the reference value, whereas the rate of biosynthesis may remain unchanged. For an unequivocal proof that stress indeed enhances the biosynthesis, the total amount of the substances per plant has to be determined. In this study, we investigated the stress-induced impact on the alkaloids accumulated in Catharanthus roseus and quantified both, the changes in concentration and in the entire amount of alkaloids. At any time, all Catharanthus roseus plants grown under drought stress exhibited a markedly higher alkaloid concentration compared to the well-watered controls. However, by calculating the entire alkaloid content per plant, a corresponding increment occurred only within the first two weeks of drought stress. Thereafter, no significant differences among drought treatments and control were detected. Finally, within the last week, the alkaloid content per plant decreased markedly, although there was a meaningfully higher concentration of alkaloids in the drought-stressed plants. In contrast, when plants had been exposed to high salt concentrations, the alkaloid concentrations were quite the same in stressed and control plants. The related total contents were significantly lower in plants exposed to salt stress. These results display that both phenomena, an increased rate of biosynthesis and lesser reference values, i.e., the biomass, contribute to the stress-related increase in the concentration of natural product. Moreover, it has to be considered that the enhancement of biosynthesis could be due to either an “active” up-regulation of biosynthetic capacity or a “passive” shift caused by the over-reduced status as a result of the stress-induced stomatal closure.

Alkaloids extracted from mature Vinca minor leaves were fractionated by preparative HPLC. By means of HRMS and NMR data, the main alkaloids were identified as vincamine, strictamine, 10-hydroxycathofoline, and vincadifformine. Upon treatment with methyl jasmonate (MeJA), the pattern and composition of the indole alkaloids changed extensively. While 10-hydroxycathofoline and strictamine concentrations remained unaltered, vincamine and vincadifformine levels showed a dramatic reduction. Upon MeJA treatment, four other indole alkaloids were detected in high quantities. Three of these alkaloids have been identified as minovincinine, minovincine, and 9-methoxyvincamine. Whereas minovincinine and minovincine are known to occur in trace amounts in V. minor, 9-methoxyvincamine represents a novel natural product. Based on the high similarities of vincamine and 9-methoxyvincamine and their inverse changes in concentrations, it is postulated that vincamine is a precursor of 9-methoxyvincamine. Similarly, vincadifformine seems to be converted first to minovincinine and finally to minovincine. Because MeJA treatment greatly altered the alkaloidal composition of V. minor, it could be used as a potential elicitor of alkaloids that are not produced under normal conditions.

Background It was recently shown that nicotine and pyrrolizidine alkaloids that leach out from decomposing plant material (donor plants) are subsequently taken up by the roots of acceptor plants and translocated into their leaves. Furthermore, it is well established that plant roots take up xenobiotics, generally by simple diffusion, and that this passive import depends on the physico-chemical properties of the substances. Hypothesis Based on the well-known uptake of xenobiotics, we assumed that in analogy, the uptake of alkaloids, which are leached out from plant material (donor plants) represents a quite general feature of plant biology. Methods Using barley as a model plant, we analyzed the uptake of alkaloids by applying them to Hordeum vulgare seedlings. Based on HPLC analyses, the presence of the particular alkaloids in the acceptor plants was determined. Results We demonstrated that numerous alkaloids of different structural types are able to diffuse through biomembranes and are taken up by acceptor plants. In contrast, an uptake of quaternary alkaloids, with a permanent positive charge, could not be detected. Conclusion As most alkaloidal plants generally die back afield, and the corresponding natural products are leached out into the soil. Our findings have substantial relevance for all plant-derived commodities, especially for the production of phytopharmaceuticals and the related safety issues. Moreover, the evidence that plants are inherently able to take up alkaloids from the soil, which are derived from other plants, will alter our appraisal of plant–plant interactions. In this context, the classical definition of xenobiotics, which are considered as “non-natural” substances, might be also extended by including natural products leached out into the soil.

Many global problems threaten our life on the Planet including climate changes, environmental pollution, food and soil security, energy crisis, etc. This environmental pollution has not only mainly serious risks and stress involving the human health and the entire ecosystem safety but also the quantity and quality of crop productivity worldwide. Due to the great gap between the global food production and the global consumption, there is a crucial need to cultivate these contaminated lands sooner or later. Therefore, the removing of pollutants from soils and waters should be performed in frame of sustainable remediation and sustainable energy production. Depending on many factors (source and kind of pollutants, land use and the economics of water and soil resources, etc) many strategies should be addressed for the sustainable and integrated management of polluted lands. Nanoremediation is a promising strategy in controlling pollution and management. Three major applications of nanoremediation could be characterized including detection of pollution using nanosensors, prevention of pollution, purification and remediation of contamination. Further studies also concerning the impact of changing climate on the nanoremediation process in the agroecosystems should be considered. Thus, this review will focus on the evaluation of environmental nanoremediation and its strategy in polluted lands under climate changes. Using of nanotechnology in pollution control as well as the environmental pollution and its sustainable management also will be highlighted.

Many plant derived commodities contain traces of toxic pyrrolizidine alkaloids (PAs). The main source of these contaminations seems to be the accidental co-harvest of PA-containing weeds. Yet, based on the insights of the newly described phenomenon of the horizontal transfer of natural products, it is very likely that the PA-contaminations may also be due to an uptake of the alkaloids from the soil, previously being leached out from rotting PA-plants. The transfer of PAs was investigated using various herbs, which had been mulched with dried plant material from Senecio jacobaea. All of the acceptor plants exhibited marked concentrations of PAs. The extent and the composition of the imported PAs was dependent on the acceptor plant species. These results demonstrate that PAs indeed are leached out from dried Senecio material into the soil and confirm their uptake by the roots of the acceptor plants and the translocation into the leaves.

The physico-chemical background of alkaloid allocation within plants is outlined and discussed exemplarily for pyrrolizidine alkaloids (PAs) and nicotine. The trigger for this discourse is the finding that, for example, PAs, which are taken up from the soil, are translocated in the xylem, whereas - when genuinely present in plants - they are allocated as N-oxides via phloem. Special emphasis is put on the impact of different pH values in certain compartments, as this entails significant changes in the relative lipophilic character of alkaloids: tertiary alkaloids diffuse readily through biomembranes, while the corresponding protonated alkaloids are retained in acidic compartments, i.e. vacuoles or xylem. Therefore, this phenomenon, well known as the 'ion trap mechanism', is also relevant for long-distance transport of alkaloids. Any efficient allocation of typical tertiary alkaloids within the phloem can thus be excluded. In contrast, due to their strongly increased hydrophilic properties, alkaloid-N-oxides or quarternary alkaloids cannot diffuse through biomembranes and, consequently, would be retained in the acidic xylem during translocation. The major aim of this paper is to sharpen the mind for the chemical peculiarities of alkaloids and to consider them adequately in forthcoming investigations on allocation of alkaloids.

A tremendous high number of herbal products such as spices, herbal teas, or phytopharmaceuticals, contain significant amounts of toxic alkaloids. These widespread contaminations are mainly due to the uptake of alkaloids from the soil. Due to their alkalinity, it is obvious that the import of alkaloids is strongly affected by the pH of the rhizosphere. This so far unconsidered issue was analyzed in a model study by applying various alkaloids to hydroponically grown barley seedlings, adjusted to several pH values, i.e., 5, 6, 7, and 8. In most cases, the resulting concentration of the alkaloids imported into the barley leaves ranged from about 0.8 to 7.7 μmol/g d.w. However, caffeine was imported to a higher extent, resulting in concentration up to 19 μmol/g d.w. In contrast, the uptake of monocrotaline (0.04–0.13 μmol/g d.w.) and atropine (just traces) was quite lower. For sparteine, no uptake was recorded. Apart from caffeine, the uptake of alkaloids strongly depends on the pH in the medium. Accordingly, these experiments demonstrated the significance of the rhizosphere pH for the alkaloid uptake. Both parameters, the overall concentration of alkaloids as well as the share of the unprotonated alkaloids, are determined by the pH. Accordingly, for the first time, it became obvious that the alkaloidal contaminations of plant derived commodities significantly depend on the pH of the rhizosphere during the cultivation of the crop plants. Moreover, the extent of alkaloid accumulation in acceptor plants is also influenced by the rate of transpiration. In consequence, the uptake of the various alkaloids and its pH-dependency might be quite different and no general prediction on the extent of alkaloid uptake can be made.

Substances which have been leached out from decomposing plant parts or exuded from vital plants (donor plants), are taken up by acceptor plants and subsequently modified. This phenomenon was likewise established for harmala alkaloids. Employing hydroponically grown barley seedlings, it becomes evident that harmaline and harmine are taken up by the roots of the acceptor plants. Furthermore, based on HPLC and GC-MS analyses, it was demonstrated that these alkaloids also are present in Setaria viridis plants, which grew in the direct vicinity of the alkaloid containing Peganum harmala plants. Since harmaline exhibits a bright green fluorescence, this alkaloid was employed to visualize the uptake into the acceptor plants by feeding it to roots of barley seedlings. In the further course, the imported harmaline was converted in the leaves to yield harmine, which exhibits a dark blue fluorescence. This conversion was also verified by HPLC and GC-MS analyses. Based on the massive differences in the fluorescence properties, both processes, uptake and modification in the acceptor plants, could be monitored by macroscopical studies as well as by confocal laser scanning microscopical analyses. As result, for the first time, the phenomenon of ”Horizontal Natural Product Transfer” is visualized vividly.

To elucidate the origin of the wide-spread contaminations of plant derived commodities with various alkaloids, we employed co-cultures of pyrrolizidine alkaloid (PA) containing Senecio jacobaea plants with various alkaloid free acceptor plants. Our analyses revealed that all plants grown in the vicinity of the Senecio donor plants indeed contain significant amounts of the PAs, which previously had been synthesized in the Senecio plants. These findings illustrate that typical secondary metabolites, such as pyrrolizidine alkaloids, are commonly transferred and exchanged between living plants. In contrast to the broad spectrum of alkaloids in Senecio, in the acceptor plants nearly exclusively jacobine is accumulated. This indicates that this alkaloid is exuded specifically by the Senecio roots. Although the path of alkaloid transfer from living donor plants is not yet fully elucidated, these novel insights will extend and change our understanding of plant-plant interactions and reveal a high relevance with respect to the widespread alkaloidal contaminations of plant-derived commodities. Moreover, they could be the basis for the understanding of various so far not fully understood phenomena in cultivation of various crops, e.g. the beneficial effects of crop rotations or the co-cultivation of certain vegetables.

Inspired by the recently discovered phenomenon of "horizontal natural product transfer" we investigated the putative uptake of phenolic specialized metabolites. Umbelliferone was chosen for this case study, since this coumarin as well as its derivatives can easily be determined by HPLC analyses. Barley (Hordeum vulgare L.), radish (Raphanus sativus L.), pea (Pisum sativum L.), flax (Linum usitatissimum L.), and garden cress (Lepidium sativum L.) were cultivated in hydroponic media, to which the coumarin was applied. Uptake of umbelliferone was verified by corresponding HPLC analyses of extracts obtained from the aerial parts of the seedlings. In all cases, a tremendous uptake of umbelliferone was observed. In plants that genuinely contain coumarins, the umbelliferone taken up was modified: in garden cress, it was hydroxylated and glucosylated to yield esculin, while in barley seedlings, the imported umbelliferone was modified by methoxylation to yield scopoletin. Corresponding reactions are known from modifications of xenobiotics to be catalyzed by cytochrome P450 enzymes. Accordingly, in an additional approach, umbelliferone was applied together with naproxen, which is reported to reduce enzyme activity of P450 enzymes. As predicted, the conversion of umbelliferone to scopoletin in barley as well as the modification to esculin in garden cress was strongly reduced by the addition of naproxen. These data for the first time demonstrate that - in addition to alkaloids - also phenolic compounds are taken up by various acceptor plants. Apart from the leaching of rotting plants, coumarins are known to be exuded by many plants. Accordingly, these compounds are frequently present in soils and will be taken up. These coherences imply that the horizontal natural product transfer might represent a more general phenomenon in plant ecology. Moreover, this study outlines that - in analogy to the modification of xenobiotics - also natural products taken up are modified in the acceptor plants.

The global agriculture is facing many challenges including sustainable use and conservation of natural resources, climate change, urbanization, and pollution resulting from agrochemicals (e.g., fertilizers and pesticides). So, the sustainable agriculture is an urgent issue and hence the suitable agro-technological interventions are essential (e.g., nano- and bio-technology) for ensuring the safety and sustainability of relevant production system. Biotechnology and nanotechnology also can be considered emerging solutions to resolve the global food crisis. Nanoparticles or nanomaterials can be used in delivering different nutrients for plant growth. These nanoparticles as nanofertilizers have positive and negative effects on soils, soil-biota and plants. These effects mainly depend on multiple factors including nanofertilizer properties, plant species, soil fate and dynamics as well as soil microbial communities. Nanofertilizers could improve the nutrient use efficiencies through releasing of nutrients slowly and steadily for more than 30 days as well as reducing the loss of nutrients in agroecosystems and sustaining farm productivity. Here we review the plant nano-nutrition including the response of plants and soils to nanonutrients and their fate, dynamic, bioavailability, phytotoxicity, etc. Concerning the effects of nanonutrients on terrestrial environments are still an ongoing processes and it demands further researches as well as a knowledge gap towards different changes in shape, texture, color, taste and nutritional aspects on nanonutrients exposed plants as a major component in the food chain. Moreover, the interaction between nanonutrients and plants, soils, soil biota and the entire agroecosystem will be also highlighted.

Medicinal plants grown under semi-arid conditions generally reveal significantly higher concentrations of relevant natural products than identical plants of the same species, which are cultivated in moderate climates. So far, there is very limited information on this well-known phenomenon. In the present study, corresponding data are compiled and relevant aspects are discussed. It turns out that metabolic reactions triggered by drought stress are responsible for the higher natural product accumulation in plants grown in semi-arid regions. The related plant physiological and biochemical background can be summarized as follows: In plants suffering drought stress, the water shortage caused by limited water supply triggers stomata closure. As a result, the uptake of CO2 is markedly decreased and the consumption of reduction equivalents (NADPH+H + ) consumed in the course of CO2-fixation via Calvin cycle declines considerably, generating a massive oversupply of NADPH+H + . Consequently, all metabolic processes are pushed towards the synthesis of highly reduced compounds, such as isoprenoids, phenols or alkaloids. Based on these considerations, impulses for novel practical approaches for enhancing the product quality by deliberately applying drought stress during the cultivation of medicinal plants are outlined. However, as drought stress concomitantly also leads to massive reductions in biomass production, special emphasis must be put on the interference of these stress related effects.

This study was aimed to analyze the impact of moderate drought stress and stress signal transducers (methyl jasmonate and salicylic acid) on the concentration and overall content of secondary metabolites in Thymus vulgaris (monoterpenes), Chelidonium majus (alkaloids) and Petroselinum crispum (flavones and essential oils). Short-term exposure to moderate drought stress increased concentrations as well as overall contents of the relevant secondary metabolites in T. vulgaris (+40% and +15%, respectively) and C. majus (+33% and +8%, respectively). Biosynthetic activity was clearly enhanced by the stress related over-reduced states. However, longer drought phases led to marked decreases in the overall contents of relevant natural products due to greater reductions in growth. P. crispum was very sensitive to drought, and even short-term stress caused considerable reductions in growth. SA treatments did not cause any positive effects, but the impact of MeJa applications varied depending on plant species. The application of this stress signal transducer strongly enhanced the concentrations of benzyl isoquinoline alkaloids in C. majus (+46%) and flavones in P. crispum (+70%). The main outcome was that concentrations as well as overall contents of relevant natural compounds in spice and medicinal plants could be enhanced by stress treatments, such as drought stress and signal transducer applications (MeJa and SA). Based on the results of this greenhouse study, corresponding cultivation recommendations for agricultural production of quality-enhanced spice and medicinal plants should be elaborated.

Aufgrund zahlreicher Berichte in verschiedenen Medien ist vielen Verbrauchern und auch den meisten Wissenschaftlern bewusst, dass in Nahrungsund Genussmitteln Pyrrolizidinalkaloide als Kontamination vorkommen konnen. Pyrrolizidinalkaloide (PA) sind stickstoffhaltige Naturstoffe, die in verschiedenen Pflanzenfamilien vorkommen, u.a. in Korbblutlern (Asteraceae) oder Raublattgewachsen (Boraginaceae). Insbesondere die 1,2-ungesattigten PAs gelten als genotoxische Kanzerogene. Aufgrund dieses gesundheitsschadigenden Potenzials sollten sowohl Lebensund Genussmittel als auch Futtermittel moglichst frei von diesen toxischen Alkaloiden sein. In den letzten Jahren wurde allerdings deutlich, dass eine Reihe pflanzlicher und pflanzenbasierter Produkte wie Krautertees oder Honig relativ hohe, zum Teil gesundheitlich bedenkliche Konzentrationen an PA aufweisen. Auch im aktuellen Heft des JVL prasentieren Neumann und Huckauf eine eingehende Untersuchung zum Vorkommen von PA in Honig. Eine umfassende und informative Darstellung der gesamten PA-Problematik findet sich auch in den entsprechenden Stellungnahmen des Bundesinstituts fur Risikobewertung, die in der aktuellen Arbeit von Neumann und Huckauf zitiert sind. Bei der Suche nach den Ursachen der PA-Kontaminationen in den verschiedenen pflanzlichen Produkten zeichnete sich schnell ein klares Bild ab. Die PA im Honig stammen offensichtlich aus den Pollen PA-haltiger Pflanzen, vor allem von verschiedenen Senecio-Arten sowie einiger Raublattgewachse (z.B. der Gewohnliche Wasserdost). Als eine der Hauptquellen von PA-Kontaminationen in Fruchtetees gelten die sogenannten Beikrauter, d.h. bei der Ernte der jeweiligen Nutzpflanzen werden versehentlich auch PA-haltige Unkrauter mit eingebracht, wie z.B. verschiedene Senecio-Arten. Da die Konzentration von PA in den Senecio-Pflanzen im Mittel zwischen 1.000 und 10.000 mg pro kg Trockengewicht (mg/kg TG) liegt, reicht bereits eine versehentlich mitgeerntete Senecio-Pflanze, um eine ganze Charge von mehreren zehntausend PA-freien Krauterpflanzen derart mit PA zu kontaminieren, dass die resultierende PA-Konzentration noch weit uber der Schwelle von 0,1 mg/kg TG (=100 lg/kg) liegt. Allerdings sind auch Falle dokumentiert, bei denen eine zufallige ‘‘Miternte’’ PA-haltiger Unkrauter ausgeschlossen werden kann. Hier mussen die beobachteten Kontaminationen einen anderen Ursprung haben; die PA sind offensichtlich bereits in den geernteten Pflanzen vorhanden. Dafur gibt es eigentlich nur zwei plausible Erklarungen: entweder die Pflanzen sind in der Lage, eigenstandig PA zu produzieren, oder aber diese Pflanzen haben die PA vorher von ausen aufgenommen. Wesentliche Schritte der PA-Biosynthese wurden in der letzten Dekade durch die Arbeiten von Thomas Hartmann und Dietrich Ober erfolgreich aufgeklart. Dabei wurde deutlich, dass sich das Schlusselenzym der PA-Biosynthese, die Homospermidin-Synthase, evolutionar durch Gen-Duplikation eines Primarstoffwechselenzyms (Desoxyhyposin-Synthase) entwickelt & Dirk Selmar d.selmar@tu-bs.de

When plants are exposed to various stress situations, their alkaloid concentration frequently is enhanced. This well-known phenomenon is presumably due to a passively enhanced rate of biosynthesis, caused by greatly elevated concentrations of NADPH in stressed plants. Here, we used Chelidonium majus L. plants, which accumulate high concentrations of dihydrocoptisine in their leaves, to study the impact of drought and salt stress on the biosynthesis and accumulation of alkaloids. In comparison to well-watered controls, in the transcriptome of the gene encoding the key enzyme in alkaloid biosynthesis, stylopine synthase, is enhanced in stressed C. majus plants. If we presuppose that increased transcript levels correlate with increased enzymatic activity of the gene products, these data indicate, for the first time, that stress-related increases in alkaloid concentration might not only be caused by the well-known stress-related passive shift, but may also be due to an enhancement of enzymatic capacity.

This study aimed to elucidate the origin of the widespread nicotine contamination of plant-derived commodities, by conducting field experiments with various herbs and spice plants. By scattering tobacco and cigarette butts on the field and subsequent nicotine analyses of the acceptor plants, we verified that the alkaloid is leached out into the soil and is taken up by the crop plants. This path of contamination pertains even when there is only one cigarette butt per square meter. Even such minor pollution results - at least in the case of basil and peppermint - in considerable high nicotine contaminations, which exceed the maximum residue level by more than 20-fold. The data reported here clearly outline the large practical relevance of this soil-borne contamination path and imply that unthoughtful disposal of cigarette butts in the field by farm workers may be the reason for the widespread occurrence of nicotine contamination in plant-derived commodities. Therefore, such misbehavior needs to be prevented using education and sensitization, and by including this issue into the guidelines of good agricultural practice.

The most prominent alkaloid of Chelidonium majus is dihydrocoptisine, revealing the characteristic benzophenanthridine skeleton. To date, any informationon on the enzymes responsible for its biosynthesis and the related genes in C. majus is lacking. Based on sequence similarities to the corresponding methylenedioxy bridge-forming Cyt P450 enzymes involved in isoquinoline alkaloid biosynthesis in Eschscholzia californica, genes for a cheilanthifoline synthase and a stylopine synthase from C. majus were isolated, sequenced and heterologously expressed in yeast. The activity of the heterologously expressed Cyt P450 enzymes was determined in situ as well as on the basis of microsomal fractions. It was shown that cheilanthifoline synthase (c8931) converts scoulerine into cheilanthifoline, the latter subsequently being converted to stylopine by the action of a stylopine synthase (c1128). Based on the well-known instability of stylopine, it can be assumed that in vivo-under the acidic conditions in the vacuole-this alkaloid is converted to dihydrocoptisine, which accumulates in C. majus leaves. Both methylenedioxy bridge-forming Cyt P450 enzymes from C. majus are characterized by their high substrate specificity. Apart from their genuine substrates, i.e. scoulerine and cheilanthifoline, cheilanthifoline synthase and stylopine synthase do not accept other substrates tested; the only alternative substrate identified was scoulerine, which is converted by stylopine synthase to yield minor amounts of nandinine. Quantitative real-time PCR revealed that the expression of cheilanthifoline synthase and stylopine synthase genes is very similar in both roots and leaves from C. majus, although the alkaloid accumulation patterns in these organs are quite different.

This review addresses the well known phenomenon that spice and medicinal plants grown under semi-arid conditions generally reveal significantly higher concentrations of relevant natural products than identical plants, which however are cultivated in moderate climates. Unfortunately, only limited information on this intriguing phenomenon is available. The corresponding data are compiled, the relevant aspects are outlined, and the metabolic background is presented. Based on these reflections, it becomes obvious that drought stress and the related metabolic changes are responsible for the higher natural product accumulation in plants grown in semi-arid regions. In principle, there are three causes: first, the effect might be a consequence of a reduced production of biomass in the stressed plants. Even without an enhancement of biosynthesis of natural products, their concentration on dry or fresh weight basis simply will be elevated. Secondly, the drought stress enhances the actual rate of biosynthesis of natural products due to a passive shift or thirdly, due to an active up-regulation of the enzymes involved in natural product biosynthesis. The latter both options are related to the strongly enhanced reduction status of the leaves exposed to drought stress. The over-reduction, which goes along with a strongly enhanced concentration of NADPH+H+, directly results in a passive increase of all processes consuming NADPH+H+, including the biosyntheses of highly reduced secondary plant products. Alternatively, the enzymes responsible for the biosynthesis of natural products could be actively up-regulated. The corresponding increment in NADPH+H+ consumption significantly contributes to the dissipation of the stress related surplus of energy and thus, is part of the machinery that prevents the generation of toxic oxygen radicals.

In this treatise, an actual overview on the newly verbalised phenomenon of “Horizontal Natural Product Transfer” is presented. This phenomenon was recently discovered when analyzing the potential sources of contaminations of plant derived commodities by nicotine and pyrrolizidine alkaloids. It turned out that these alkaloids, leached out from decomposing alkaloid containing plant parts (donor plants), are taken up by the roots of acceptor plants. In analogy to the well-known and widespread phenomenon of the uptake of xenobiotics, it can be deduced that a wide array of alkaloids and other natural products are taken up by acceptor plants either. As such uptake generally is due to a simple diffusion of the substances across the biomembranes, the physico-chemical properties of the natural products, especially their hydrophilic as well as their lipophilic character, determines the extent of a corresponding uptake. Latest findings from co-cultivation experiments revealed that natural products are not transferred exclusively from dead and rotting donor plant material, but also from living and vital plants. Yet, up to now, the exact path, i.e., in which manner the natural products are translocated from the living plants into the acceptor plants is unknown. The finding that plants inherently are able to take up most alkaloids from the soil, derived from other plants, necessitates a reconsideration of our understanding of plant-plant-interactions. In this context, also the classical definition of xenobiotics, which up to now are considered as “non-natural” substances, might be extended by including also natural products leached out into the soil.

The glucosinolate (GSL) content is an important quality parameter of crops, such as mustard, horseradish or nasturtium, which are grown for their taste as condiments or for medical purposes. Accordingly, an enhancement of the GSL content should promote the large-scale cultivation of these plants. It is well known that GSLs reveal a high significance in plant defense, and that several stress factors cause an increase in the GSL concentration. The goal of the present study was to evaluate the means to stimulate the GSL biosynthesis during plant growth by applying moderate stress. The impact of different treatments on the GSL content and on growth of Tropaeolum majus L. was investigated in a greenhouse trial. Moderate stress was induced by drought, by the addition of salt, or the application of growth regulators (methyl jasmonate, salicylic acid). Moreover, cell wall lysate was applied to the plants to mimic biotic stress, such as pathogen attack. Evapotranspiration (ETP), biomass development, specific leaf weight (SLW), plant pigments, and thiol contents had been recorded to evaluate physiological changes in response to the treatments. The glucotropaeolin (GT) content, representing the sole GSL of T. majus was measured as target compound. Drought and MeJA application increased the GT concentration on dry weight basis and impacted on ETP, dry matter content, SLW and plant pigments, too. Application of salt, SA and cell wall lysate did not affect the GT concentration in a consistent way. Moderate drought and the application of MeJA are suitable tools to increase the GT concentration in T. majus . However, in case of drought the higher GT concentration was only reached at the expense of biomass production. High GT concentrations together with reasonable yields were only achieved by MeJA application.

Using individual grain analyses, the degree of inherent biological variation in germinating barley seeds has been established. Even under homogenous laboratory conditions, the activities of the germination-related enzymes α-amylase, β-amylase and β-glucanase varied by a factor of two to three. The comparison with single grain analyses of different industrially produced malts (steeping systems without aeration, with air suction and pressurised aeration) revealed that the heterogeneity of these malts nearly tripled. This increase may be due to the gradients in O2 and CO2 that arise in large industrial steeping vessels. The most homogenous malting in the industrial systems was achieved without any aeration during steeping. Therefore, to improve homogeneity, the common practise of steep aeration should be omitted. Germination progression was quite different within the three exhaustively aerated attempts, which indicated that gaseous composition was not the only factor affecting germination progression.

Based on the occurrence of indole alkaloids in so-called "chloroform leaf surface extracts", it was previously deduced that these alkaloids are present in the cuticle at the leaf surface of Catharanthus roseus and Vinca minor. As no symplastic markers were found in these extracts this deduction seemed to be sound. However, since chloroform is known to destroy biomembranes very rapidly, these data have to be judged with scepticism. We reanalyzed the alleged apoplastic localization of indole alkaloids by employing slightly acidic aqueous surface extracts and comparing the corresponding alkaloid patterns with those of aqueous total leaf extracts. Whereas in the "chloroform leaf surface extracts" all alkaloids are present in the same manner as in the total leaf extracts, no alkaloids occur in the aqueous leaf surface extracts. These results clearly show that chloroform had rapidly destroyed cell integrity, and the related extracts also contain the alkaloids genuinely accumulated within the protoplasm. The related decompartmentation was verified by the massively enhanced concentration of amino acids in aqueous surface extracts of chloroform treated leaves. Furthermore, the chloroform-induced cell disintegration was vividly visualized by confocal laser scanning microscopical analyses, which clearly displayed a strong decrease in the chlorophyll fluorescence in chloroform treated leaves. These findings unequivocally display that the indole alkaloids are not located in the apoplastic space, but exclusively are present symplastically within the cells of V. minor and C. roseus leaves. Accordingly, we have to presume that also other leaf surface extracts employing organic solvents have to be re-investigated.

Medicinal plants grown under semi-arid conditions reveal much higher concentrations of relevant natural products than the equivalent plants, but cultivated in moderate climates. This phenomenon can be explained on the basis of general plant physiological and biochemical considerations: in semi-arid regions – due to limited water supply and much higher light intensities – the plants are exposed to a higher level of drought stress than the plants grown in moderate climates. Up to now, only limited experimental data on these coherences are available. In this section, a comprehensive survey on the relevant literature is presented. In most of the studies available, the content of secondary plant products indeed is enhanced in plants suffering drought stress. The metabolic background of the stress-induced enhancement of natural products can be explained as follows: because of the stomata closure due to the incipient water deficiency, the uptake of CO2 markedly decreases. As result, the consumption of reduction equivalents (NADPH+H+) for the CO2-fixation via Calvin cycle declines considerably, generating a massive oversupply of NADPH+H+. As consequence, metabolic processes are pushed toward the synthesis of highly reduced compounds, like isoprenoids, phenols or alkaloids. Using sage (Salvia officinalis) as model plant, the interaction of drought stress induced metabolic changes and synthesis and accumulation of secondary plant products have been investigated. When the plants had been cultivated under moderate drought stress, the overall content as well as the concentration of total monoterpenes was markedly higher than in the corresponding, well-watered control plants. When these plants had been cultivated in parallel under elevated CO2 (700 ppm), the drought stress related increase in monoterpene synthesis was totally compensated. Obviously, despite the stress related stomata closure, still large amounts of CO2 could enter the leaves. Based on these considerations, putative applications to increase the quality of medicinal plants by deliberately applying drought stress are delineated.

In previous experiments, we demonstrated that the amount of monoterpenes in sage is increased massively by drought stress. Our current study is aimed to elucidate whether this increase is due, at least in part, to elevated activity of the monoterpene synthases responsible for the biosynthesis of essential oils in sage. Accordingly, the transcription rates of the monoterpene synthases were analyzed. Salvia officinalis plants were cultivated under moderate drought stress. The concentrations of monoterpenes as well as the expression of the monoterpene synthases were analyzed. The amount of monoterpenes massively increased in response to drought stress; it doubled after just two days of drought stress. The observed changes in monoterpene content mostly match with the patterns of monoterpene synthase expressions. The expression of bornyl diphosphate synthase was strongly up-regulated; its maximum level was reached after two days. Sabinene synthase increased gradually and reached a maximum after two weeks. In contrast, the transcript level of cineole synthase continuously declined. This study revealed that the stress related increase of biosynthesis is not only due to a "passive" shift caused by the stress related over-reduced status, but also is due - at least in part-to an "active" up-regulation of the enzymes involved.

BACKGROUND: Horseradish plants (Armoracia rusticana) contain high concentrations of glucosinolates. Former studies have revealed that Armoracia plants cultivated in vitro have markedly lower glucosinolate concentrations than those grown in soils. Yet, these studies neglected that the sulfate concentration in the growth medium may have had a strong impact on glucosinolate metabolism. Accordingly, in this study horseradish in vitro plants were cultivated with differing sulfate concentrations and the glucosinolate concentrations were quantified by ion pair HPLC. RESULTS: Cultivation in 1.7 mmol L−1 sulfate (as used in the prior studies) resulted in the accumulation of 16.2 µmol g−1 DW glucosinolates, while the glucosinolate concentration increased to more than 23 µmol g−1 DW when 23.5 mmol L−1 sulfate was used in the medium. Correspondingly, the glucosinolate concentration decreased to 1.6 µmol g−1 DW when sulfate concentration was lowered to 0.2 mmol L−1. CONCLUSION: Since the glucosinolate accumulation in relation to the sulfate concentration follows a typical saturation curve, we deduce that the availability of sulfate determines the glucosinolate concentration in horseradish in vitro plants. © 2012 Society of Chemical Industry

During malting, barley (Hordeum vulgare L.) seeds are germinated to promote the mobilisation of storage compounds. Germination is strongly influenced by O2 and CO2; however, any distinction between the particular effects is missing. Since, in this study, the ambient O2 concentration was maintained when high CO2 concentrations were applied, for the first time the impacts of CO2 and of O2 deficiency could be distinguished unambiguously. Germination was inhibited by both O2 deficiency and high CO2 (80%) concentrations, documented by the lack of any growth of coleoptiles and any increase of α-amylase and β-glucanase activity. In contrast, the related impacts of O2 starvation and high CO2 on fermentation differ strongly, demonstrated by quite different patterns of ethanol emission. Additionally, the stress metabolism - monitored by the means of GABA accumulation - was also differently impacted. The elucidation of the underlying, so far unknown, mechanisms will provide novel opportunities to improve malting.

BACKGROUND AND AIMS The release of hydrogen cyanide (HCN) from injured plant tissue affects multiple ecological interactions. Plant-derived HCN can act as a defence against herbivores and also plays an important role in plant-pathogen interactions. Crucial for activity as a feeding deterrent is the amount of HCN generated per unit time, referred to as cyanogenic capacity (HCNc). Strong intraspecific variation in HCNc has been observed among cyanogenic plants. This variation, in addition to genotypic variability (e.g. in Trifolium repens), can result from modifications in the expression level of the enzymes involved in either cyanogenic precursor formation or HCN release (as seen in Sorghum bicolor and Phaseolus lunatus). Thus, a modification or modulation of HCNc in reaction to the environment can only be achieved from one to the next generation when under genetic control and within days or hours when transcriptional regulations are involved. In the present study, it is shown that in rubber tree (Hevea brasiliensis) HCNc is modulated by post-translational activity regulation of the key enzymes for cyanide release. METHODS Linamarase (LIN) and hydroxynitrile lyase (HNL) activity was determined by colorimetric assays utilizing dissociation of the substrates p-nitrophenyl-β-d-glucopyranoside and acetone cyanohydrin, respectively. KEY RESULTS In rubber tree leaves, LIN and HNL show up to ten-fold increased activity in response to tissue damage. This enzyme activation occurs within seconds and results in accelerated HCN formation. It is restricted to the damaged leaf area and depends on the severity of tissue damage. CONCLUSIONS LIN and HNL activation (in contrast to genetic and transcriptional regulations) allows an immediate, local and damage type-dependent modulation of the cyanogenic response. Accordingly, this post-translational activation plays a decisive role in the defence of H. brasiliensis against herbivores as well as pathogens and may allow more flexible reactions in response to these different antagonists.

Dehydrins are well known for being expressed in leaves during the course of developmental processes as well as under drought stress, being part of the protective machinery. Moreover, in seed physiology, dehydrins are classified as late embryogenesis-related proteins (LEA protein), where they are thought to be responsible for persistence and longevity of seeds. Although both topics are a focus of modern plant biology, a direct linkage between these both areas is generally lacking. Based on an alignment of the chain of events, this paper will help to generate understanding that the occurrence of dehydrins in maturing seeds and leaves suffering drought stress is part of the same basic principle: basic principle: dehydrins are expressed in response to water shortage. Unfortunately, the related developmental process in seeds, i.e. maturation drying, has not been adequately considered as a part of this process. As a corresponding implication, the chain of events must be adjusted: the differences in dehydrin expression in orthodox, intermediate and recalcitrant seeds could be directly attributed to the occurrence or absence of maturation drying. The differences in dehydrin expression in orthodox, intermediate and recalcitrant seeds, and thus the differences in longevity, could be attributed to the occurrence or absence of a maturation drying.

When wet processed coffee beans are dried, the resulting decrease in the water potential induces various metabolic responses. This study was aimed at elucidating the impact of these reactions on the composition of sugars, representing potential aroma precursors. Wet processed green coffees were dried under defined conditions, and the relevant sugars were analysed. Special emphasis was put on the influence of the drying regime, i.e. continuous dryings and such interrupted by pauses in order to mimic sun dryings. The contents of fructose and glucose decreased significantly within the first day of drying. This diminution for the first time proves that the lower contents of glucose and fructose generally present in wet processed coffee beans in comparison to dry processed ones are - at least in part - due to metabolic processes and are not related to the leaching of sugars into the process water in the course of wet processing.