Constitutive Defense Research Articles

MOS6 and TN13 in plant immunity

ABSTRACTThe Arabidopsis nuclear transport receptor IMPORTIN-α3/MOS6 (MODIFIER OF SNC1, 6) is required for constitutive defense responses of the auto-immune mutant snc1 (suppressor of npr1-1, constitutive 1) and contributes to basal disease resistance, suggesting a role in nuclear import of defense-regulatory cargo proteins. We recently showed that MOS6 selectively interacts with TN13, a TIR-NBS protein involved in basal resistance to Pseudomonas syringae pv. tomato (Pst) DC3000 lacking the effectors AvrPto and AvrPtoB. Consistent with a predicted N-terminal transmembrane domain, TN13 localizes to the endoplasmic reticulum (ER) and the nuclear envelope (NE) where it interacts with MOS6 in a transient expression assay. Here, we propose a model that summarizes the subcellular localization, association and function of TN13 and MOS6 in plant defense signaling.

No place to run

Plants never had it easy. When their ancestors colonized the land about 460 M years ago during the Ordovician period, they were immediately followed by crustaceans—which eventually developed into insects—that found plants a ready source of food. Ever since plants have been at the bottom of the food chain for pathogens and predators from viruses to mammalian herbivores. Unlike animals, plants cannot run away, having given up motility to maximize their surface exposed to sunlight. In lieu, they became masters in chemical warfare and communication to recognize and fend off pathogens and herbivores. Their “claws and teeth” are a dazzling arsenal of chemicals, metabolic and regulatory pathways, producing sensing and communication molecules that attract increasing interest from chemists and biologists for their potential use in medicine and agriculture. > Humans have also learned to use toxic compounds such as digitalis, atropine, opium or nicotine for medicinal, cosmetic or recreational use. Among these molecules are many spices, including the pungent piperine and capsaicin from peppers, or the glucosinolates from mustard and horseradish, and the bitter polyphenols, flavonoids or terpenes from red grapes, coffee beans, tea or cabbage. Humans have long come to appreciate these tastes—that originally evolved as a warning signal to herbivores—for centuries, spices were the most valuable commodity in global trade. Humans have also learned to use toxic compounds such as digitalis, atropine, opium or nicotine for medicinal, cosmetic or recreational use. The alkaloid taxol from the bark of the Pacific yew is a potent chemotherapeutic drug for cancer treatment; artemisinin, isolated from the plant Artemisia annua, or sweet wormwood, has long been employed in Chinese herbal medicine and been refined into a treatment for malaria. The metabolic pathways of plant compounds with medicinal value are therefore an active field of research with the objective of engineering these into E. coli or …

Population differentiation related to climate of origin affects the intensity of plant–herbivore interactions in a clonal grass

With ongoing climate change, it is likely that shifts in species distribution ranges will lead to changes in the type and intensity of plant–herbivore interactions. Plants currently exposed to lower levels of herbivory could have less developed defensive mechanisms and therefore could suffer in case of increased herbivore pressure.We performed a common garden experiment using clones of Festuca rubra originating from four populations experiencing contrasting temperature and precipitation regimes. Clones of identical genotype were subjected to both the control and the herbivory treatment using larvae of the nymphalid butterfly Coenonympha pamphilus, a generalist herbivore feeding on several grass species. Various measures of constitutive and induced defence as well as growth response to herbivory were assessed, compared between populations of different climatic origin and related to herbivore performance (larval survival).The four F. rubra populations significantly differed in constitutive defence (content of Si and total phenols), nutritional quality (content of C) and inducibility of defence (change in total phenols), but not in growth response to herbivory. Herbivores survived better on populations from colder climate and better survival was generally related to lower Si content and lower initial plant size.We demonstrated population differentiation in both constitutive and induced defence against insect herbivory, which directly affected survival of a generalist herbivore. Our findings confirmed the expectation that plants from higher elevations are more prone to herbivory. Moreover, differences in various aspects of plant defence between populations from the same altitude stresses the need of considering multiple factors when assessing the effect of climate on plant–herbivore interactions.

Specialized metabolites from Ageratina adenophora and their inhibitory activities against pathogenic fungi

The Asteraceae plant Ageratina adenophora (also called Eupatorium adenophorum) has became the most destructive invasive species in China, especially the southwestern region, and is gravely threatening the native biodiversity. Its high reproductive capacity is partly due to the developed root system. From the roots of A. adenophora, ten compounds including three previously undescribed benzofuran derivatives (7-hydroxy-dehydrotremetone, 7,10,11-trihydroxy dehydrotremetone, 10-oxo-7-hydroxy-nordehydrotremetone), a previously undescribed chromene derivative (5-β-glucosyl-7-demethoxy-encecalin) and a previously undescribed monoterpene glucoside (8-hydroxy-8-β-glucosyl-2-carene) were isolated and identified. The previously undescribed structures were established by spectroscopic studies including 1D and 2D-NMR and HR-MS analyses. Antifungal activity of six compounds against one strain of pathogenic fungus of A. adenophora, Alternaria alternata, and other four strains of agricultural pathogenic fungi, Colletotrichum gloeosporioides, C. musae, Rhizoctonia solani and Fusarium oxysporum f. sp. niveum were investigated. The most abundant compound we isolated from A. adenophora roots was 7-hydroxy-dehydrotremetone, which showed significant broad-spectral inhibitory activity against the growth of all tested fungal strains, with diameter of inhibitory zones ranging from 13.90 ± 1.05 mm to 17.28 ± 0.46 mm at 50 μg/disk (nystatin: 24.76 ± 1.19 mm to 36.64 ± 0.85 mm). Encecalin also showed weak inhibitory activity against F. oxysporum f. sp. niveum, while other compounds were not active. Our results suggested that 7-hydroxy-dehydrotremetone might function as a constitutive defense compound in the roots of A. adenophora against pathogenic fungi.

Pisatin involvement in the variation of inhibition of Fusarium oxysporum f. sp. pisi spore germination by root exudates of Pisum spp. germplasm

Fusarium wilt caused by Fusarium oxysporum f. sp. pisi (Fop) is one of the major constraints of pea worldwide. Its control is difficult and is mainly based on the use of resistant cultivars. This study aimed to identify and characterize resistance mechanisms interfering with Fop spore germination, as an additional pre‐penetration resistance mechanism little explored so far. For this, root exudates were collected from 12 pea accessions with differential responses to the disease, from resistant to susceptible, and their effects on Fop germination and growth were determined. While root exudates from most accessions stimulated Fop germination, the root exudates of three accessions, JI 1412, JI 2480 and P42, did not stimulate, or even inhibited, Fop germination. Although some additional compounds might be involved, the analysis showed that the most active metabolite was the pea phytoalexin pisatin. Pisatin was identified in the active fraction of pea root exudate extracts and its amount in the root exudates was negatively correlated with the extent of Fop germination. This suggests an important role of pisatin in the constitutive defence of pea against F. oxysporum.

Development of an aggressive bark beetle on novel hosts: Implications for outbreaks in an invaded range

Abstract Some subcortical insects have devastating effects on native tree communities in new ranges, despite benign interactions with their historical hosts. Examples of how insects, aggressive in their native habitat might respond in novel host environs are less common. One aggressive tree‐killing insect undergoing a dramatic range shift is the mountain pine beetle (Dendroctonus ponderosae Hopkins). Ongoing eastward expansion by the mountain pine beetle through the previously climatically unsuitable Canadian boreal forest may have large‐scale impacts on north eastern North American pine forests. No systematic studies have been conducted on potential reproduction of mountain pine beetle on pines common to north eastern North America. We report reproduction of mountain pine beetle in logs of novel pine species (jack, Pinus banksiana Lamb; red, Pinus resinosa Ait.; eastern white, Pinus strobus L.; and Scots Pinus sylvestris L.) compared to the two most common pine hosts in its historical range (ponderosa, Pinus ponderosa Dougl. ex. Laws. var. scopulorum Engelm. and lodgepole Pinus contorta Dougl. var. latifolia Engelm.) in a two year study. Successful reproduction of mountain pine beetle occurred in all novel hosts, demonstrating that constitutive defences pose no barrier to further range expansion. Despite the number of progeny in novel hosts on par with that of historical hosts, a greater number of adult brood in novel hosts died prior to emergence. Brood mortality was correlated with the number of brood that developed to adulthood prior to winter, particularly in red pine. Brood developed more rapidly in novel vs. historical pine hosts and, the summer after a warm fall, exhibited less synchronized emergence in novel hosts. Synthesis and applications. Outbreaks by an aggressive bark beetle may be possible outside its historical host range, but constrained by an interaction between host and seasonality. Our results suggest that pines common to north eastern North America are suitable hosts for mountain pine beetle and highlight the value of monitoring efforts and response preparations as the insect moves eastward.

The Defence of Constitutionalism: The Czech Question in Post-national Europe. By Jiří Přibáň. Trans. Stuart Hoskins. Vaclav Havel Series. Prague: Karolinum Press, 2017. xvi, 312 pp. $20.00, paper.

The Defence of Constitutionalism: The Czech Question in Post-national Europe. By Jiří Přibáň. Trans. Stuart Hoskins. Vaclav Havel Series. Prague: Karolinum Press, 2017. xvi, 312 pp. $20.00, paper. - Volume 77 Issue 4

Protective Role of Carbonic Anhydrases III and VII in Cellular Defense Mechanisms upon Redox Unbalance.

Under oxidative stress conditions, several constitutive cellular defense systems are activated, which involve both enzymatic systems and molecules with antioxidant properties such as glutathione and vitamins. In addition, proteins containing reactive sulfhydryl groups may eventually undergo reversible redox modifications whose products act as protective shields able to avoid further permanent molecular oxidative damage either in stressful conditions or under pathological circumstances. After the recovery of normal redox conditions, the reduced state of protein sulfhydryl groups is restored. In this context, carbonic anhydrases (CAs) III and VII, which are human metalloenzymes catalyzing the reversible hydration of carbon dioxide to bicarbonate and proton, have been identified to play an antioxidant role in cells where oxidative damage occurs. Both proteins are mainly localized in tissues characterized by a high rate of oxygen consumption, and contain on their molecular surface two reactive cysteine residues eventually undergoing S-glutathionylation. Here, we will provide an overview on the molecular and functional features of these proteins highlighting their implications into molecular processes occurring during oxidative stress conditions.

Batson for Judges, Police Officers & Teachers: Lessons in Democracy From the Jury Box

In our representative democracy we guarantee equal participation for all, but we fall short of this promise in so many domains of our civic life. From the schoolhouse, to the jailhouse, to the courthouse, racial minorities are underrepresented among key public decision-makers, such as judges, police officers, and teachers. This gap between our aspirations for representative democracy and the reality that our judges, police officers, and teachers are often woefully under-representative of the racially diverse communities they serve leaves many citizens of color wanting for the democratic guarantee of equal participation. This critical failure of our democracy threatens to undermine the legitimacy of these important civic institutions. It deepens mistrust between minority communities and the justice system and exacerbates the failures of a public education system already lacking accountability to minority students. But there is hope for rebuilding the trust, accountability and legitimacy of these civic institutions on behalf of minority citizens. There is one place where we have demonstrated a deeper commitment to our guarantee of democratic equality on behalf of minority citizens and exerted greater effort to that end than perhaps in any other domain of our civic life—the jury box. This paper recounts this important history and explores the political theory underlying the equal protection jurisprudence of jury selection. It then applies these lessons gleaned from the jury context to the constitutional defense of efforts to achieve greater racial diversity within the judiciary, law enforcement, and public education, all of which are as important to the legitimacy of our democracy today as the jury has been throughout American history.

Perception of Salicylic Acid in Physcomitrella patens.

Salicylic acid (SA) is a key signaling molecule in plant immunity. Two types of SA receptors, NPR1 and NPR3/NPR4, were reported to be involved in the perception of SA in Arabidopsis. SA is also synthesized in the non-vascular moss Physcomitrella patens following pathogen infection. Sequence analysis revealed that there is only one NPR1/NPR3/NPR4-like protein in P. patens. This agrees with the phylogenetic study that showed the divergence of NPR1 and NPR3/NPR4 from the same ancestor during the evolution of higher plants. Intriguingly, expression of the P. patens NPR1/NPR3/NPR4-like gene in Arabidopsis does not complement the constitutive defense phenotype of the npr3 npr4 double mutant, but can partially rescue the mutant phenotypes of npr1-1, suggesting that it functions as an NPR1-like positive regulator of SA-mediated immunity and P. patens does not have an SA receptor functioning similarly as NPR3/NPR4. Future characterization of the P. patens NPR1-like protein and analysis of its functions through knockout and biochemical approaches will help us better understand how SA is perceived and what its functions are in P. patens.

Límites al poder de reforma, modificaciones y alteraciones a la Constitución

The Political Constitution of a State can be defined as a political juridical act that establishes the structure of the State, its principles and essential purposes, its model of State and Government, its constitutional rights, duties and defense mechanisms, among others, and is summarized in the expression Navigation Chart of that State. Although constitutions are the most important legal text in a constitutional legal system, this should adapt themselves and be dynamic in order to respond to the needs of the collective that governs them. To this end, the degree of rigidity in the constitutional reform procedure must be defined, which must be different from that of an ordinary norm. This document will study the different ways how the Constitution can be reformed in Colombia, both formal and informal modifications, and the alterations that such reforms or modifications produce in the legal system, based on both normative and jurisprudential analysis, which allowed us to establish the various ways in which the original charter can be altered by a subsequent one.

Interactive effects of CO2 concentrations and Alternaria brassicae (Berk.) Sacc. infection on defense signalling in Brassica juncea (L.) Czern. & Coss.

Elevated CO2 is known to affect plant’s constitutive defense by bringing about changes in its structure and biochemistry. Recently, it has been seen that not only constitutive defense but also induced defense is altered by elevated concentrations of CO2. Phytohormones such as salicylic acid and jasmonic acid play an important role in modulating induced defense of plants. Concentrations of these hormones vary due to elevated CO2 that alter plant-pathogen interactions. While, most of these studies report higher levels of SA, very few have reported increase in JA. These observations have mainly been employed to explain increased susceptibility to herbivory. There are very few reports with reference to fungal pathogens and plant defense signalling under elevated CO2. Keeping this in mind, an experiment was conducted in open top chambers (OTCs) in Department of Botany, University of Delhi to assess the impact of elevated CO2 and pathogen Alternaria brassicae on the levels of JA and SA, their respective signalling pathway and subsequently defense of Brassica juncea plants. Under elevated CO2, the activity of phenylalanine ammonia lyase increased, leading to a concomitant rise in the concentration of total phenols. The constitutive levels of salicylic acid (SA) and jasmonic acid (JA) enhanced. When inoculated with Alternaria brassicae, the CO2 concentrations interacted significantly to influence the concentrations of SA and JA; and transcript levels of downstream genes of defense signalling pathways. Under elevated CO2, on pathogen infection the concentration of SA decreased while that of JA increased. Correspondingly the transcript levels of NPR-1, PR1, PR-2, PR-12 and PR-13 were affected.

Activity of the purified plant ABC transporter NtPDR1 is stimulated by diterpenes and sesquiterpenes involved in constitutive and induced defenses

Within the plant ATP-binding cassette transporter family, pleiotropic drug resistance (PDR) transporters play essential functions, such as in hormone transport or defense against biotic and abiotic stresses. NtPDR1 from Nicotiana tabacum has been shown to be involved in the constitutive defense against pathogens through the secretion of toxic cyclic diterpenes, such as the antimicrobial substrates cembrene and sclareol from the leaf hairs (trichomes). However, direct evidence of an interaction between NtPDR1 and terpenes is lacking. Here, we stably expressed NtPDR1 in N. tabacum BY-2 suspension cells. NtPDR1 was purified as an active monomer glycosylated at a single site in the third external loop. NtPDR1 reconstitution in proteoliposomes stimulated its basal ATPase activity from 21 to 38 nmol of Pi·mg-1·min-1, and ATPase activity was further stimulated by the NtPDR1 substrates cembrene and sclareol, providing direct evidence of an interaction between NtPDR1 and its two substrates. Interestingly, NtPDR1 was also stimulated by capsidiol, a sesquiterpene produced by N. tabacum upon pathogen attack. We also monitored the transcriptional activity from the NtPDR1 promoter in situ with a reporter gene and found that, although NtPDR1 expression was limited to trichomes under normal conditions, addition of methyl jasmonate, a biotic stress hormone, induced expression in all leaf tissues. This finding indicated that NtPDR1 is involved not only in constitutive but also in induced plant defenses. In conclusion, we provide direct evidence of an interaction between the NtPDR1 transporter and its substrates and that NtPDR1 transports compounds involved in both constitutive (diterpenes) and induced (sesquiterpenes) plant defenses.

How constitutive defences affect the development of postharvest anthracnose and stem-end rot in mango fruit

How constitutive defences affect the development of postharvest anthracnose and stem-end rot in mango fruit

Induction and relaxation of extrafloral nectaries in response to simulated herbivory in young Mallotus japonicus plants.

The disadvantage of induced defenses compared with constitutive defenses is the time during which a plant is vulnerable to herbivory before activation. There is obvious importance in determining the costs and benefits of induced defenses. Some plants produce extrafloral nectaries (EFNs), which attract ants that protect against herbivores, and induce EFNs and extrafloral nectar in response to leaf damage. To understand induction of indirect defense by ants, we investigated the induction and relaxation of extrafloral nectar secretion and EFN formation after artificial leaf damage in young Mallotus japonicus. Plants were grown under control or leaf damage conditions a greenhouse or in the field. Following artificial leaf damage, we assessed secretion of extrafloral nectar and the number of ant workers on plants. We measured the number of EFNs on each of seven leaves produced after leaf damage. Extrafloral nectar secretion was induced within 1day following leaf damage, resulting in the attraction of numerous ant workers, and the extrafloral nectar secretion decreased to initial levels after 7 days. The number of EFNs was largest on the first leaf and smallest on the sixth leaf produced after leaf damage, but the total number of EFNs did not differ between treatments. Thus, M. japonicus rapidly induces extrafloral nectar secretion after leaf damage, followed by relaxation. Furthermore, following induction of EFNs on newly produced leaves, it may decrease the cost of induction by reducing the number of EFNs on leaves produced later.

Is the future as tasty as the present? Elevated temperature and hyposalinity affect the quality of Fucus (Phaeophyceae, Fucales) as food for the isopod Idotea balthica

Climate change is acknowledged to affect directly macroalgal performance but its indirect effect through changes in algal interaction with herbivores remains poorly understood. To study effects of climate change on a macroalga–herbivore interaction, we exposed three range-margin Baltic Sea populations of Fucus (60°N 39°E, 61°N 21°E, 62°N 21°E) in September 2015 to current (15.1 °C; 5.2 PSU) and predicted future (17.5 °C; 2.6 PSU) environments for 7 months. After 6 weeks we tested the indirect effect of climate change through food quality on growth, survival and food consumption of the isopod Idotea balthica while after 7 months we tested the direct effect on algal inducible defenses. We predicted that future stressful conditions impair constitutive and inducible defense traits in Fucus thus resulting in a higher susceptibility to herbivores. The short-term climate stress did decrease thallus toughness of Fucus in one population but isopod food consumption and performance remained unchanged. After 7 months, throughout the populations, Fucus grown in future conditions was softer and more consumed. The grazing attack induced resistance in two populations but irrespective of climate change. Our results show that Fucus can cope with short-term (6 weeks) stress without indirect effects on the interactions with herbivores. However, long-term (7 months) stressed Fucus was consumed more by isopods likely due to a decrease in constitutive resistance traits rather than changes in inducible resistance. This suggests that in near future, marginal populations of Fucus might become more vulnerable to grazing losses, with possibly adverse effects on the abundance and persistence of these populations.

Cell-type- and tissue-specific transcriptomes of the white spruce (Picea glauca) bark unmask fine-scale spatial patterns of constitutive and induced conifer defense.

Plant defenses often involve specialized cells and tissues. In conifers, specialized cells of the bark are important for defense against insects and pathogens. Using laser microdissection, we characterized the transcriptomes of cortical resin duct cells, phenolic cells and phloem of white spruce (Picea glauca) bark under constitutive and methyl jasmonate (MeJa)-induced conditions, and we compared these transcriptomes with the transcriptome of the bark tissue complex. Overall, ~3700 bark transcripts were differentially expressed in response to MeJa. Approximately 25% of transcripts were expressed in only one cell type, revealing cell specialization at the transcriptome level. MeJa caused cell-type-specific transcriptome responses and changed the overall patterns of cell-type-specific transcript accumulation. Comparison of transcriptomes of the conifer bark tissue complex and specialized cells resolved a masking effect inherent to transcriptome analysis of complex tissues, and showed the actual cell-type-specific transcriptome signatures. Characterization of cell-type-specific transcriptomes is critical to reveal the dynamic patterns of spatial and temporal display of constitutive and induced defense systems in a complex plant tissue or organ. This was demonstrated with the improved resolution of spatially restricted expression of sets of genes of secondary metabolism in the specialized cell types.

Below‐ground nematode herbivory of resistant soybean cultivars impairs the performances of an above‐ground caterpillar and its parasitoid

1. Interactions between below‐ and above‐ground organisms have attracted interest in recent years, but less is known about the effect of root‐feeding nematodes on above‐ground trophic interactions between herbivores and their natural enemies.2. This study examined whether the presence of the soybean cyst root nematode Heterodera glycines influences the performance of the above‐ground leaf‐chewing tobacco cutworm Spodoptera litura on soybeans, Glycine max, and whether this in turn affects the success of its parasitoid, Meteorus pulchricornis. Using three soybean cultivars that varied in the level of constitutive resistance to the tobacco cutworm, the study determined whether feeding by the nematode altered the developmental and reproductive performances of the caterpillar and its parasitoid.3. Root feeding by the nematode slowed tobacco cutworm larval development time and reduced adult body weight. Root feeding by the nematode also had a negative effect on the caterpillar's parasitoid, by prolonging development time, decreasing adult body size and reducing fecundity. These effects increased in a linear trend and varied in magnitude depending on levels of soybean constitutive resistance.4. These findings demonstrate that root feeding by the nematode can prime soybean plants with negative impacts on their herbivore and its parasitoid, and that the impact may vary in magnitude depending on levels of soybean constitutive defence. The results emphasise the need to integrate soybean constitutive and root nematode‐induced defences for a better understanding of below‐ and above‐ground organism interactions, and to allow insights to be gained into the improvement of soybean integrated pest management programmes.

Potential for adaptation to climate change: family-level variation in fitness-related traits and their responses to heat waves in a snail population

BackgroundOn-going global climate change poses a serious threat for natural populations unless they are able to evolutionarily adapt to changing environmental conditions (e.g. increasing average temperatures, occurrence of extreme weather events). A prerequisite for evolutionary change is within-population heritable genetic variation in traits subject to selection. In relation to climate change, mainly phenological traits as well as heat and desiccation resistance have been examined for such variation. Therefore, it is important to investigate adaptive potential under climate change conditions across a broader range of traits. This is especially true for life-history traits and defences against natural enemies (e.g. parasites) since they influence organisms’ fitness both directly and through species interactions. We examined the adaptive potential of fitness-related traits and their responses to heat waves in a population of a freshwater snail, Lymnaea stagnalis. We estimated family-level variation and covariation in life history (size, reproduction) and constitutive immune defence traits [haemocyte concentration, phenoloxidase (PO)-like activity, antibacterial activity of haemolymph] in snails experimentally exposed to typical (15 °C) and heat wave (25 °C) temperatures. We also assessed variation in the reaction norms of these traits between the treatments.ResultsWe found that at the heat wave temperature, snails were larger and reproduced more, while their immune defence was reduced. Snails showed high family-level variation in all examined traits within both temperature treatments. The only negative genetic correlation (between reproduction and antibacterial activity) appeared at the high temperature. However, we found no family-level variation in the responses of most examined traits to the experimental heat wave (i.e. largely parallel reaction norms between the treatments). Only the reduction of PO-like activity when exposed to the high temperature showed family-level variation, suggesting that the cost of heat waves may be lower for some families and could evolve under selection.ConclusionOur results suggest that there is genetic potential for adaptation within both thermal environments and that trait evolution may not be strongly affected by trade-offs between them. However, rare differences in thermal reaction norms across families indicate limited evolutionary potential in the responses of snails to changing temperatures during extreme weather events.

Age- and environment-dependent changes in chemical defences of larval and post-metamorphic toads

BackgroundChemical defences are widespread in animals, but how their production is adjusted to ecological conditions is poorly known. Optimal defence theory predicts that inducible defences are favoured over constitutive defences when toxin production is costly and the need for it varies across environments. However, if some environmental changes occur predictably (e.g. coupled to transitions during ontogeny), whereas others are unpredictable (e.g. predation, food availability), changes in defences may have constitutive as well as plastic elements. To investigate this phenomenon, we raised common toad (Bufo bufo) tadpoles with ad libitum or limited food and in the presence or absence of chemical cues on predation risk, and measured their toxin content on 5 occasions during early ontogeny.ResultsThe number of compounds showed limited variation with age in tadpoles and was unaffected by food limitation and predator cues. The total amount of bufadienolides first increased and later decreased during development, and it was elevated in young and mid-aged tadpoles with limited food availability compared to their ad libitum fed conspecifics, whereas it did not change in response to cues on predation risk. We provide the first evidence for the active synthesis of defensive toxin compounds this early during ontogeny in amphibians. Furthermore, the observation of increased quantities of bufadienolides in food-restricted tadpoles is the first experimental demonstration of resource-dependent induction of elevated de novo toxin production, suggesting a role for bufadienolides in allelopathy.ConclusionsOur study shows that the evolution of phenotypic plasticity in chemical defences may depend on the ecological context (i.e. predation vs. competition). Our results furthermore suggest that the age-dependent changes in the diversity of toxin compounds in developing toads may be fixed (i.e., constitutive), timed for the developmental stages in which they are most reliant on their chemical arsenal, whereas inducible plasticity may prevail in the amount of synthesized compounds.