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Chemical Defence (chemical + defence)
Selected AbstractsNatural hybridization between Senecio jacobaea and Senecio aquaticus: molecular and chemical evidenceMOLECULAR ECOLOGY, Issue 8 2004HEATHER KIRK Abstract Hybridization is known to be involved in a number of evolutionary processes, including species formation, and the generation of novel defence characteristics in plants. The genus Senecio of the Asteraceae family is highly speciose and has historically demonstrated significant levels of interspecific hybridization. The evolution of novel chemical defence characteristics may have contributed to the success of Senecio hybrids. Chemical defence against pathogens and herbivores has been studied extensively in the model species Senecio jacobaea, which is thought to hybridize in nature with Senecio aquaticus. Here, we use amplified fragment length polymorphisms (AFLPs) and pyrrolizidine alkaloid (PA) composition to confirm that natural hybridization occurs between S. jacobaea and the closely related species S. aquaticus. AFLPs are also used to estimate the ancestry of hybrids. We also demonstrate that even highly back-crossed hybrids can possess a unique mixture of defence chemicals specific to each of the parental species. This hybrid system may therefore prove to be useful in further studies of the role of hybridization in the evolution of plant defence and resistance. [source] Morphological and Chemical Changes Induced by Herbivory in Three Common Aquatic MacrophytesINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 3 2009Damien G. Lemoine Abstract The Dry Matter Content (DMC), the total phenolic content, the production of new branches and the plant fragmentation were compared in three macrophyte species (Elodea canadensis, Elodea nuttallii and Myriophyllum spicatum) exposed or not to snail herbivory. Grazing significantly reduced the DMC of M. spicatum and E. canadensis, but had no effect on the DMC of E. nuttallii. The phenolic contents of Elodea species were not modified by snail herbivory, whereas that of M. spicatum significantly increased when exposed to grazers. The number of new branches produced by M. spicatum and E. canadensis plants, and the fragmentation of E. canadensis also increased in response to herbivory. Chemical defences are therefore probably constitutive in Elodea and induced in M. spicatum, and morphological changes can be related to species growth form and synthesis of phenolic compounds. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Top-down and bottom-up regulation of herbivores: Spodoptera frugiperda turns tables on endophyte-mediated plant defence and virulence of an entomopathogenic nematodeECOLOGICAL ENTOMOLOGY, Issue 3 2004Douglas S. Richmond Abstract., 1. The fungus Neotyphodium lolii forms a symbiotic relationship with its grass host Lolium perenne (perennial ryegrass). The fungus benefits from access to plant nutrients and photosynthate, whereas the plant benefits from acquired chemical defence against herbivory. 2. This study examined the potential for endophyte-mediated plant defences to influence interactions between fall armyworm Spodoptera frugiperda, and the entomopathogenic nematode Steinernema carpocapsae and clarified biological mechanisms underlying the observations made. 3. In laboratory and greenhouse experiments, S. frugiperda larvae were fed endophytic or non-endophytic L. perenne then exposed to S. carpocapsae or injected with the nematodes' symbiotic bacteria Xenorhabdus nematophila. 4. In all instances, S. frugiperda larvae fed endophyte-infected grass suffered significantly lower mortality than those fed non-endophytic plants. Although larvae fed endophyte-infected grass often had significantly lower biomass than those fed uninfected grass, these differences did not account for altered susceptibility to S. carpocapsae. 5. Endophyte-mediated reductions in herbivore susceptibility to the nematode pathogen represent a herbivore adaptation that effectively turns the tables on both plant and natural enemy by reducing the virulence of the nematodes' symbiotic bacteria while expanding the temporal window of herbivory. [source] Nitrogen fertilization effects on Myzus persicae aphid dynamics on peach: vegetative growth allocation or chemical defence?ENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 2 2010Marie-Hélène Sauge Abstract Plant nitrogen (N) fertilization is a common cropping practice that is expected to serve as a pest management tool. Its effects on the dynamics of the aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae) were examined on young peach [Prunus persica (L.) Batsch (Rosaceae)] trees grown under five N treatments, ranging from N shortage to supra-optimal supply for growth. Aphid population increased over time at the three intermediate N levels. It remained stable at the lowest N level and decreased at the highest N level. Four weeks after the start of infestation, the number of aphids displayed a parabolic response to N level. The relationships between N status and parameters of plant vegetative growth (stem diameter) or biomass allocation (lateral-total leaf area and root-shoot ratio) were consistent with responses proposed by models of adaptive plasticity in resource allocation patterns. However, the variation in plant growth predicted aphid population dynamics only partially. Whereas aphid number was positively correlated with plant N status and vegetative growth up to the intermediate N level, it was negatively correlated with plant N status above this level, but not with vegetative growth. The concentrations of primary and secondary (plant defence-related) metabolites in the plant shoots were modified by N treatments: amino acids (main nutritional resource of aphids) and prunasin increased, whereas chlorogenic acid decreased with increasing N availability. Constitutive changes in plant chemistry in response to N fertilization could not directly explain the reduced aphid performance for the highest N level. Nevertheless, the indirect effect of N on the induction of plant defence compounds by aphid feeding warrants further investigation. The study focuses on the feasibility of handling N fertilization to control M. persicae in orchards, but findings may also be relevant for our understanding of the physiological relationships between the host's nutritional status and the requirements of the insect. [source] Cloning and expression of a geranylgeranyl diphosphate synthase gene: insights into the synthesis of termite defence secretionINSECT MOLECULAR BIOLOGY, Issue 1 2007Masaru Hojo Abstract In Nasutitermes takasagoensis, a termite in which soldiers perform specialized chemical defence, Nts19-1 gene is highly expressed exclusively in soldier head. In this study, two types of transcripts for this gene were obtained, and the full-length cDNAs were determined by rapid amplification of cDNA ends (RACE). These transcripts were putative homologues of the geranylgeranyl diphosphate (GGPP) synthase gene, involved in the condensation of dimethylallyl diphosphate with isopentenyl diphosphate in the isoprenoid biosynthetic pathway. The genes were thus termed NtGGPPS1. GGPP is a precursor of diterpenes in plants. In situ hybridization localized NtGGPPS1 expression to the epidermal secretory cells of the frontal gland reservoir where many kinds of diterpenes are produced, suggesting that NtGGPPS1 is involved in the biosynthesis of defence secretion. [source] Root herbivores and detritivores shape above-ground multitrophic assemblage through plant-mediated effectsJOURNAL OF ANIMAL ECOLOGY, Issue 4 2010Adela González Megías Summary 1.,Indirect effects mediated by changes in plant traits are the main mechanism by which above- and below-ground herbivores affect each other and their enemies. Only recently the role of decomposers in the regulation of such plant-based systems has been considered. We hypothesized that: (i) below-ground organisms, both herbivores (negative effect on plants) and detritivores (positive effect on plants), will have a profound effect on the interactions among above-ground arthropods; (ii) floral herbivores will negatively affect other above-ground herbivores associated with the plant; and (iii) not only above- and below-ground herbivores, but also detritivores will affect the production of secondary metabolites, i.e. glucosinolates, in the plants. 2.,We manipulated the presence of above-ground herbivores, below-ground herbivores and below-ground detritivores on the Brassicaceae Moricandia moricandioides in the field to disentangle their individual and combined effects on other organism groups. We also investigated their effects on the plant's chemical defence to evaluate potential mechanisms. 3.,Our results show that not only above- and below-ground herbivores, but also detritivores affected other herbivores and parasitoids associated with the host plant. Most effects were not additive because their strength changed when other organisms belonging to different functional groups or food web compartments were present. Moreover, below-ground herbivore and detritivore effects on above-ground fauna were related to changes in glucosinolate concentrations and in quantity of resources. 4.,This study indicates that multitrophic interactions in plant-based food webs can dramatically change by the action of below-ground organisms. One of the most important and novel results is that detritivores induced changes in plant metabolites, modifying the quality and attractiveness of plants to herbivores and parasitoids under field conditions. [source] Dry season ecology of riverine tiger beetles in Kruger National Park, South AfricaAFRICAN JOURNAL OF ECOLOGY, Issue 2 2008Jonathan R. Mawdsley Abstract The life cycles of many African species of tiger beetles (Insecta: Coleoptera: Cicindelidae) exhibit pronounced seasonality, with adult emergence and reproductive activity closely associated with seasonal rains. Anecdotal reports have suggested that adults of certain riverine tiger beetle species may be active during the dry season near perennial water sources. To test this hypothesis, fifteen sites along three perennial rivers in Kruger National Park, South Africa, were surveyed for tiger beetles in early September, 2006. Thirteen sites yielded adult beetles, with six species represented [Chaetodera regalis (Dejean), Cylindera disjuncta (Dejean), Habrodera nilotica (Dejean), Lophyra neglecta intermediola (Horn), Lophyridia fimbriata imperatrix (Srnka), and Myriochile melancholica (Fabricius)]. Microhabitat associations of adults of all six species and ovipositional/larval substrates of five of the six species are reported, along with observations on predatory and reproductive behaviours and the possible presence of an anti-predator chemical defence in C. regalis and L. fimbriata imperatrix. Résumé Le cycle vital de nombreuses espèces de Cicindèles (colépotères) africains présente une saisonnalité prononcée, l'émergence des adultes et l'activité reproductrice étant étroitement liées aux pluies saisonnières. Quelques rapports ont suggéré que les adultes de certaines espèces riveraines de cicindèles pourraient être actives en saison sèche à proximité de sources d'eau permanentes. Pour tester cette hypothèse, on a surveillé 15 sites le long de trois rivières permanentes dans le Parc National Kruger, en Afrique du Sud, au cours du mois de septembre 2006. Treize sites abritaient des cicindèles adultes, avec six espèces représentées, (Chaetodera regalis (Dejean), Cylindera disjuncta (Dejean), Habrodera nilotica (Dejean), Lophyra neglecta intermediola (Horn), Lophyridia fimbriata imperatrix (Srnka), and Myriochile melancholica (Fabricius). On a rapporté les associations d'adultes des six espèces et les substrats oviposition/larves pour cinq des six espèces dans les microhabitats, de même que des observations sur les comportements prédateur et reproducteur et sur la présence possible d'une défense chimique anti-prédateur chez C. regalis et L. fimbriata imperatrix. [source] Plant ontogeny and chemical defence: older seedlings are better defendedOIKOS, Issue 5 2009Arnaud Elger Although patterns of seedling selection by herbivores are strongly influenced by plant age and the expression of anti-herbivore defence, it is unclear how these characteristics interact to influence seedling susceptibility to herbivory. We tracked ontogenetic changes in a range of secondary metabolites (total phenolics, alkaloids and cyanogenic glycosides) commonly associated with seedling defence for nine sympatric British grassland species. Although there was marked variation in concentrations of secondary metabolites between different species, we found a consistent increase in the deployment of phenolics, alkaloids and cyanogenics with seedling age for six of the seven dicotyledonous species examined. The two grass species by contrast exhibited low levels of secondary metabolites across all developmental stages, possibly due to an investment in structural (silica phytoliths) defence. Our results corroborate species-specific patterns of seedling herbivory observed in field studies, and offer some explanation for the relatively high sensitivity to herbivore attack frequently observed for relatively young seedlings compared with their older conspecifics. Our results also support predictions made by the growth,differentiation balance hypothesis regarding ontogenetic changes in resource allocation to anti-herbivore defence for a range of potential chemical defences and across a range of sympatric plant species presumably subject to broadly similar selective pressures at the regeneration stage. [source] AGGREGATION BEHAVIOUR IN JUVENILE MILLIPEDES FROM THE UPPER CARBONIFEROUS OF MAZON CREEK, ILLINOISPALAEONTOLOGY, Issue 4 2006HEATHER M. WILSON Abstract:, Two ironstone nodules are described from the Braidwood Biota of the Upper Carboniferous Mazon Creek Lagerstätte, Illinois, each preserving numerous juvenile millipedes referred to Euphoberia sp. The millipedes belong to different stadia, as evidenced by segment number, but are similar in size so probably nearly the same age. These juvenile euphoberiids differ from adults in having shorter pleurotergal spines, a reduced number of ocelli and a series of reduced, apodous trunk rings posteriorly. These nodules provide the first evidence of aggregation behaviour in Palaeozoic millipedes. Aggregation in juvenile euphoberiids is hypothesized to serve as a defence mechanism, compensating for the reduced length of their pleurotergal spines relative to adults, possibly through a collective chemical defence. [source] Effects of climacostol on normal and tumoral mammalian cell linesTHE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 2 2005FEDERICO BUONANNO Climacostol, 1,3-dihydroxy-5-[(Z)-2,-nonenyl]benzene, is a natural toxin contained in the extrusomal cortical granules of the heterotrich ciliate Climacostomum virens. It is used for chemical defence against predators such as the raptorial ciliate Dileptus margaritifer and its cytotoxic activity has been assessed on several species of ciliates such as Didinium nasutum, Paramecium caudatum, and Blepharisma japonicum (Miyake et al. 2003, Europ. J. Protistol., 39:25,36). On the basis of its chemical structure, climacostol may be classified into the large group of natural compounds known as resorcinolic lipids, that show antimicrobial, antiparasitic, and antitumoral activities (Kozubek et al. 2003, Cell Moll. Biol. Lett., 6:351,355). To explore the possibility to use climacostol in medical applications, we examined the effects of chemically synthesized climacostol (Masaki et al. 2004, Tetrahedron, 60:7041,7048) on the growth and proliferation of tumoral and normal mammalian cell lines: (1) human promyelocytic leukaemia cells, HL60; (2) human squamous carcinoma cells, A431; and (3) non-tumoral cells derived from mice Leydig cells, TM3. It was observed that (1) a concentration of 10 ,g/ml of climacostol exerts a strong cytotoxic activity on all cell lines used; (2) at lower concentrations of 10 ng/ml and 1 ng/ml, the effect of climacostol is limited to the inhibition of the cell growth; and (3) the normal TM3 cells are more resistant to climacostol than the two tumoral HL60 and A431cell lines. The dose-dependent cytotoxic effects of climacostol encourage further investigation on the potential use of this ciliate toxin as an anti-cancer chemical. [source] Lipid and Fatty Acid Composition of Diatoms Revisited: Rapid Wound-Activated Change of Food Quality Parameters Influences Herbivorous Copepod Reproductive SuccessCHEMBIOCHEM, Issue 10 2007Thomas Wichard Dr. Abstract Lipid and fatty acid composition are considered to be key parameters that determine the nutritive quality of phytoplankton diets for zooplanktonic herbivores. The fitness, reproduction and physiology of the grazers are influenced by these factors. The trophic transfer of lipids and fatty acids from algal cells has been typically studied by using simple extraction and quantification approaches, which, as we argue here, do not reflect the actual situation in the plankton. We show that cell disruption, as it occurs during a predator's grazing on diatoms can drastically change the lipid and fatty acid content of the food. In some algae, a rapid depletion of polyunsaturated fatty acids (PUFAs) is observed within the first minutes after cell disruption. This fatty acid depletion is directly linked to the production of PUFA-derived polyunsaturated aldehydes (PUA); these are molecules that are thought to be involved in the chemical defence of the algae. PUA-releasing diatoms are even capable of transforming lipids from other sources if these are available in the vicinity of the wounded cells. Fluorescent staining reveals that the enzymes involved in lipid transformation are active in the foregut of copepods, and therefore link the depletion processes directly to food uptake. Incubation experiments with the calanoid copepod Temora longicornis showed that PUFA depletion in PUA-producing diatoms is correlated to reduced hatching success, and can be compensated for by externally added single fatty acids. [source] Palatability of macrophytes to the invasive freshwater snail Pomacea canaliculata: differential effects of multiple plant traitsFRESHWATER BIOLOGY, Issue 10 2010PAK KI WONG Summary 1.,By selective grazing, invasive grazers can alter macrophyte-herbivore relationships in shallow freshwater bodies. Evaluating the palatability of macrophytes and understanding the determinants of plant palatability can help predict grazing impact. In no-choice feeding assays, we tested the palatability of 21 species of freshwater macrophytes to the invasive freshwater apple snail Pomacea canaliculata. 2.,Daily feeding rate varied greatly with plant species, ranging from 1.1 to 22% of snail body mass. We assessed six plant properties and examined their correlation with feeding rate. Total nitrogen content was positively related, and C:N ratio and dry matter content (DMC) negatively related, to snail feeding rate. There was no significant correlation between snail feeding rate and plant phenolic content, but the feeding rate on Myriophyllum aquaticum (the plant with the highest phenolic content) was very low. 3.,We repeated the feeding assays for 15 species that were not palatable as fresh leaves with reconstituted plant tissues formed by mixing ground up dried leaves with agar. The feeding rate still differed greatly among macrophyte species. Phragmites australis and Vallisneria natans (two species with the highest DMC) were eaten much more as reconstituted plant than as fresh leaves, indicating that structure (i.e. DMC) may be important in their defence against snail herbivory. For two plants (M. aquaticum and Alternanthera philoxeroides) that had moderate amounts of nitrogen/phosphorus but were consumed very little as fresh and reconstituted tissues, we incorporated their extracts into a palatable agar-based food. The extracts from both species greatly reduced snail feeding rate, indicating the presence of chemical defences in these two species. 4.,These results indicated that feeding was affected by several plant traits. The snail favoured plants with a high nitrogen content and avoided plants with a high DMC. Only a few plants possessed chemical feeding deterrents that were effective against this snail. Given the invasive spread of P. canaliculata in Asia, ecologists and managers should consider plant palatability when selecting plants for use in wetland restoration and when predicting the impact of further invasion by this species. [source] Foraging by fearful frugivores: combined effect of fruit ripening and predation riskFUNCTIONAL ECOLOGY, Issue 6 2006J. M. FEDRIANI Summary 1Plant defensive compounds and predation risk are main determinants of herbivore foraging, though empirical studies have seldom measured the combined effects of these two factors. By considering the interaction between the herb Helleborus foetidus and its main fruit and seed predator, the Wood Mouse Apodemus sylvaticus, we evaluated whether the defensive role against seed predators of compounds present in H. foetidus unripe fruits holds across a micro-landscape that differs in foraging costs (i.e. predation risk). 2First, we used standardized food patches that simulated fruiting H. foetidus plants to ascertain fruit preferences of captive mice. Then, by means of field experiments, we assessed the combined effects of fruit ripening and predation risk on foraging by free-ranging mice. 3Captive mice avoided plants with unripe fruit and avoided consuming unripe fruits within a particular plant. Free-ranging mice also avoided unripe fruits in safe microhabitats (rocky substrate), but not in risky microhabitats (bare ground) where few fruits were consumed. This unexpected result may be driven by predation risk experienced by mice foraging on H. foetidus fruits, and/or plant defensive compounds acting in a dose-dependent manner. 4Frugivorous mice responded to both chemical defences present in unripe H. foetidus fruits as well as to predation cost though such response was sequential. Plant defence compounds appeared to play a part in mouse foraging only after mice selected low predation risk microhabitats. 5Our study indicates that both digestive and ecological factors influence foraging decisions, which in turn affects pressures exerted by herbivores on plant populations. [source] Effects of simulated browsing on growth and leaf chemical properties in Colophospermum mopane saplingsAFRICAN JOURNAL OF ECOLOGY, Issue 1 2010Edward M. Kohi Abstract Browsing intensity influences a plant's response to herbivory. Plants face a trade-off between investment in the production of secondary compounds and investment in growth. To elucidate this trade-off, we simulated four browsing intensities (0%, 50%, 75% and 100%) on mopane saplings, Colophospermum mopane (J. Kirk ex Benth.) J.Léonard, in a greenhouse experiment. This showed that, with increasing defoliation intensity, plants change their investment strategy. At intermediate levels of defoliation (50%), mopane saplings increased the synthesis of condensed tannins, so that tannin concentrations followed a hump-shaped relation with defoliation intensity, with significantly higher tannin concentration at intermediate defoliation levels. When defoliated heavily (75% and 100%), tannin concentrations dropped, and plants were carbon stressed as indicated by a reduced growth rate of the stem diameter, and leaf production and mean individual leaf mass were reduced. This suggests that, at intermediate defoliation intensity, the strategy of the plants is towards induced chemical defences. With increasing defoliation, the relative costs of the secondary metabolite synthesis become too high, and therefore, the plants change their growing strategy. Hence, browsers should be able to benefit from earlier browsing by either adopting a low or a relatively high browsing pressure. Résumé La réponse d'une plante à sa consommation dépend de l'intensité de ce phénomène. Les plantes sont confrontées à un compromis entre un investissement dans la production de composants secondaires et un investissement dans leur croissance. Pour élucider ce compromis, nous avons simulé quatre intensités de consommation (0%, 50%, 75% et 100%) sur des jeunes mopanes, Colophospermum mopane (J. Kirk ex Benth.) J.Leonard, lors d'expériences sous serre. Ceci a montré que, lorsque la défoliation s'intensifie, les plantes changent leur stratégie d'investissement. À des niveaux de défoliation intermédiaires (50%), les jeunes plants de mopanes augmentaient la synthèse de tanins condensés, de sorte que les concentrations en tanins suivaient une courbe en cloche (hump-shaped) selon l'intensité de la défoliation; elles étaient significativement plus élevées aux niveaux de défoliation intermédiaires. Lorsque les plantes sont fortement défoliées (75% et 100%), leurs concentrations en tanins chutent, et elles sont en stress carbone comme le montre le taux de croissance réduit du diamètre du tronc; la production de feuilles et la masse moyenne de feuilles par individu sont aussi réduites. Cela suggère que, quand l'intensité de défoliation est intermédiaire, la stratégie des plants va vers une défense chimique induite. Lorsque la défoliation augmente, le coût relatif de la synthèse du métabolite secondaire devient trop élevé et le plant change de stratégie de croissance. Donc, les herbivores qui les consomment devraient pouvoir bénéficier d'une consommation antérieure en adoptant une pression de consommation faible ou relativement élevée. [source] Age-related changes in defensive traits of Acacia tortilis HayneAFRICAN JOURNAL OF ECOLOGY, Issue 3 2003Juan H. Gowda Abstract The theory of plant defences proposes that investments in physical and chemical defences are driven by the risk of herbivore damage, and limited by the cost of producing the particular defensive trait in terms of resources that could be directed to other sinks, such as growth and reproduction. We sampled twigs of 18 mature Acacia tortilis trees and their cohort of juveniles to test some predictions of this hypothesis. We expected a higher allocation of defensive traits to leaves and twigs in the young plants than in the mature ones as a result of a higher risk of damage by ungulates at the juvenile stage. Our results show that the juvenile plants produce more spines along their twigs, but have lower concentrations of phenolic compounds in their leaves than in the mature ones. We also expected a negative relation between the concentration of foliar nutrients and phenolic compounds, as predicted by the carbon/nutrient hypothesis. Only mature plants showed this pattern. Reproduction (in mature plants) and water stress (in juvenile plants) did not relate to allocation to secondary compounds as predicted by current hypotheses of plant defence. Résumé La théorie sur la défense des plantes propose que les investissements dans des défenses physiques et chimiques sont suscités par le risque de dommages dus aux herbivores, et limités par le coût de la production d'un caractère défensif particulier, exprimé en terme de ressources qui auraient pu être affectées à une autre destination, telle que la croissance ou la reproduction. Nous avons récolté des rameaux de 18 Acacia tortilis mâtures et de leurs cohortes de juvéniles pour tester diverses prédictions de cette théorie. Nous nous attendions à une plus forte attribution de caractères défensifs dans les feuilles et les rameaux des jeunes plants que dans ceux des arbres mâtures puisque le risque de dommages dus aux ongulés est plus grand au stade juvénile. Nos résultats montrent que les plants juvéniles produisent plus d'épines le long des branches mais que leurs feuilles ont une concentration moindre en composés phénoliques que celles des arbres mâtures. Nous nous attendions aussi à une relation négative entre la concentration des nutriments foliaires et les composés phénoliques, selon l'hypothèse carbone/nutriment. Seuls les plants mâtures reproduisaient ce schéma. La reproduction (chez les plants mâtures) et le stress hydrique (chez les plants juvéniles) n'avaient pas de relation avec l'attribution aux composés secondaires, comme le prédisaient les hypothèses actuelles sur la défense des plantes. [source] Effects of variable phytochemistry and budbreak phenology on defoliation of aspen during a forest tent caterpillar outbreakAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 4 2008Jack R. Donaldson Abstract 1,The present study assessed the relationship between clonally variable rates of defoliation in trembling aspen (Populus tremuloides Michx.) and two potential resistance traits: defensive chemistry and leaf phenology. 2,In 2001, coincident with a major outbreak of the forest tent caterpillar (Malacosoma disstria Hubner) in the northcentral U.S.A., we monitored defoliation rates, phytochemical composition, and foliar development in 30 clones of trembling aspen. Leaf chemistry was also assessed in re-flushed leaves and 2 years post-outbreak. 3,Early in the season, differences in defoliation among clones were substantial but, by mid-June, all clones were completely defoliated. Leaf nitrogen, condensed tannins, and phenolic glycosides varied among clones but did not relate to defoliation levels. Budbreak phenology differed by 3 weeks among clones and clones that broke bud early or late relative to forest tent caterpillar eclosion experienced reduced rates of defoliation. 4,Defoliation led to increased tannins and slight decreases in phenolic glycoside concentrations in damaged leaf remnants, but to moderately decreased tannins and a six-fold increase in phenolic glycosides in reflushed leaves. This shift in chemical composition may significantly affect late season herbivores. 5,These results suggest that aspen chemical resistance mechanisms are ineffective during intense episodic eruptions of outbreak folivores such as the forest tent caterpillar. Variable budbreak phenology may lead to differential susceptibility during less intense outbreak years and, at peak forest tent caterpillar population densities, mechanisms affording tolerance are probably more important than chemical defences. [source] The role of plant defence proteins in fungal pathogenesisMOLECULAR PLANT PATHOLOGY, Issue 5 2007RICARDO B. FERREIRA SUMMARY It is becoming increasingly evident that a plant,pathogen interaction may be compared to an open warfare, whose major weapons are proteins synthesized by both organisms. These weapons were gradually developed in what must have been a multimillion-year evolutionary game of ping-pong. The outcome of each battle results in the establishment of resistance or pathogenesis. The plethora of resistance mechanisms exhibited by plants may be grouped into constitutive and inducible, and range from morphological to structural and chemical defences. Most of these mechanisms are defensive, exhibiting a passive role, but some are highly active against pathogens, using as major targets the fungal cell wall, the plasma membrane or intracellular targets. A considerable overlap exists between pathogenesis-related (PR) proteins and antifungal proteins. However, many of the now considered 17 families of PR proteins do not present any known role as antipathogen activity, whereas among the 13 classes of antifungal proteins, most are not PR proteins. Discovery of novel antifungal proteins and peptides continues at a rapid pace. In their long coevolution with plants, phytopathogens have evolved ways to avoid or circumvent the plant defence weaponry. These include protection of fungal structures from plant defence reactions, inhibition of elicitor-induced plant defence responses and suppression of plant defences. A detailed understanding of the molecular events that take place during a plant,pathogen interaction is an essential goal for disease control in the future. [source] Plant ontogeny and chemical defence: older seedlings are better defendedOIKOS, Issue 5 2009Arnaud Elger Although patterns of seedling selection by herbivores are strongly influenced by plant age and the expression of anti-herbivore defence, it is unclear how these characteristics interact to influence seedling susceptibility to herbivory. We tracked ontogenetic changes in a range of secondary metabolites (total phenolics, alkaloids and cyanogenic glycosides) commonly associated with seedling defence for nine sympatric British grassland species. Although there was marked variation in concentrations of secondary metabolites between different species, we found a consistent increase in the deployment of phenolics, alkaloids and cyanogenics with seedling age for six of the seven dicotyledonous species examined. The two grass species by contrast exhibited low levels of secondary metabolites across all developmental stages, possibly due to an investment in structural (silica phytoliths) defence. Our results corroborate species-specific patterns of seedling herbivory observed in field studies, and offer some explanation for the relatively high sensitivity to herbivore attack frequently observed for relatively young seedlings compared with their older conspecifics. Our results also support predictions made by the growth,differentiation balance hypothesis regarding ontogenetic changes in resource allocation to anti-herbivore defence for a range of potential chemical defences and across a range of sympatric plant species presumably subject to broadly similar selective pressures at the regeneration stage. [source] Silicon-augmented resistance of plants to herbivorous insects: a reviewANNALS OF APPLIED BIOLOGY, Issue 2 2009O.L. Reynolds Abstract Silicon (Si) is one of the most abundant elements in the earth's crust, although its essentiality in plant growth is not clearly established. However, the importance of Si as an element that is particularly beneficial for plants under a range of abiotic and biotic stresses is now beyond doubt. This paper reviews progress in exploring the benefits at two- and three-trophic levels and the underlying mechanism of Si in enhancing the resistance of host plants to herbivorous insects. Numerous studies have shown an enhanced resistance of plants to insect herbivores including folivores, borers, and phloem and xylem feeders. Silicon may act directly on insect herbivores leading to a reduction in insect performance and plant damage. Various indirect effects may also be caused, for example, by delaying herbivore establishment and thus an increased chance of exposure to natural enemies, adverse weather events or control measures that target exposed insects. A further indirect effect of Si may be to increase tolerance of plants to abiotic stresses, notably water stress, which can in turn lead to a reduction in insect numbers and plant damage. There are two mechanisms by which Si is likely to increase resistance to herbivore feeding. Increased physical resistance (constitutive), based on solid amorphous silica, has long been considered the major mechanism of Si-mediated defences of plants, although there is recent evidence for induced physical defence. Physical resistance involves reduced digestibility and/or increased hardness and abrasiveness of plant tissues because of silica deposition, mainly as opaline phytoliths, in various tissues, including epidermal silica cells. Further, there is now evidence that soluble Si is involved in induced chemical defences to insect herbivore attack through the enhanced production of defensive enzymes or possibly the enhanced release of plant volatiles. However, only two studies have tested for the effect of Si on an insect herbivore and third trophic level effects on the herbivore's predators and parasitoids. One study showed no effect of Si on natural enemies, but the methods used were not favourable for the detection of semiochemical-mediated effects. Work recently commenced in Australia is methodologically and conceptually more advanced and an effect of Si on the plants' ability to generate an induced response by acting at the third trophic level was observed. This paper provides the first overview of Si in insect herbivore resistance studies, and highlights novel, recent hypotheses and findings in this area of research. Finally, we make suggestions for future research efforts in the use of Si to enhance plant resistance to insect herbivores. [source] Sublethal costs associated with the consumption of toxic prey by snakesAUSTRAL ECOLOGY, Issue 2 2009JOHN S. LLEWELYN Abstract Costs of plant defences to herbivores have been extensively studied, but costs of chemical defences to carnivores are less well understood. We examine the costs to Australian keelback snakes (Tropidonophis mairii, Gray 1841) of consuming cane toads (Bufo[Rhinella]marinus Linnaeus 1758). Cane toads (an invasive species in Australia) are highly toxic. Although keelbacks can consume toads without dying (unlike most Australian snakes), we show that cane toads are poor quality prey for keelbacks. Toads are of low net nutritional value, take longer to consume than do native frogs and reduce the snake's locomotor performance for up to 6 h after ingestion of a meal. These latter effects may increase a snake's vulnerability to predation. Nutritional content of vertebrate prey is not the only factor driving the evolution of foraging behaviour; other more subtle costs, such as risk of predation, may be widespread. [source] | ||||||||||||||||||||||||||||