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Plant genotypes often exhibit varying resistance levels to herbivores. However, the impact of this genotypic variation on resistance against multiple herbivores remains poorly understood, especially in crops undergoing recent process of domestication. To address this gap, we studied the magnitude and mechanism of resistance in 12 cranberry (Vaccinium macrocarpon) genotypes to three leaf-chewing herbivores - Sparganothis fruitworm (Sparganothis sulfureana), spotted fireworm (Choristoneura parallela), and spongy moth (Lymantria dispar) - along a domestication gradient (native 'wild' genotypes, 'early hybrid' genotypes, and 'modern hybrid' genotypes). Like cranberries, S. sulfureana and C. parallela are native to the United Sates, while L. dispar is an invasive pest. We measured the survival and growth of larvae on each genotype, as well as variation in plant performance (height and biomass) and leaf defensive chemical traits (C/N ratio, total phenolics, total proanthocyanidins, and flavonols levels) in these genotypes to elucidate potential resistance mechanisms. We found differences in C. parallela and L. dispar larval performance across genotypes, with larvae performing better on the modern hybrid genotypes, while S. sulfureana showed no differences. Morphological and chemical traits varied among genotypes, with total phenolics being the only trait correlated with C. parallela and L. dispar larval performance. Notably, the wild genotypes 'McFarlin' and 'Potter' had higher total phenolics and were more resistant to both herbivores than the modern hybrids 'Demoranville' and 'Mullica Queen.' This research contributes to a comprehensive understanding of the impact of crop domestication on multiple insect herbivores, offering insights for future breeding efforts to enhance host-plant resistance against agricultural pests., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

White fringetree is a host for the invasive emerald ash borer (EAB) but is of lower quality than the related and highly susceptible black ash. Field observations suggest that host trees grown in full sun are more resistant to EAB than those in shade, however the impact of light limitation on chemical defenses has not been assessed. We quantified constitutive and jasmonate-induced phloem defenses and growth patterns of white fringetree and black ash under differential light conditions and related them to EAB larval performance. White fringetree had significantly lower constitutive and induced activities of peroxidase, polyphenol oxidase, β-glucosidase, chitinase and lignin content, but significantly higher gallic acid equivalent soluble phenolic, soluble sugar, and oleuropein concentrations compared to black ash. Multivariate analyses based on tissue chemical attributes displayed clear separation of species and induced defense responses. Further, EAB performed significantly worse on white fringetree than black ash, consistent with previous studies. Light limitation did not impact measured defenses or EAB larval performance, but it did decrease current year growth and increase photosynthetic efficiency. Overall our results suggest that phenolic profiles, metabolite abundance, and growth traits are important in mediating white fringetree resistance to EAB, and that short-term light limitation does not influence phloem chemistry or larval success. [ABSTRACT FROM AUTHOR]

Despite active research, antiherbivore activity of specific plant phenolics remains largely unresolved. We constructed silver birch (Betula pendula) lines with modified phenolic metabolism to study the effects of foliar flavonoids and condensed tannins on consumption and growth of larvae of a generalist herbivore, the autumnal moth (Epirrita autumnata). We conducted a feeding experiment using birch lines in which expression of dihydroflavonol reductase (DFR), anthocyanidin synthase (ANS) or anthocyanidin reductase (ANR) had been decreased by RNA interference. Modification-specific effects on plant phenolics, nutrients and phenotype, and on larval consumption and growth were analyzed using uni- and multivariate methods. Inhibiting DFR expression increased the concentration of flavonoids at the expense of condensed tannins, and silencing DFR and ANR decreased leaf and plant size. E. autumnata larvae consumed on average 82% less of DFRi plants than of unmodified controls, suggesting that flavonoids or glandular trichomes deter larval feeding. However, larval growth efficiency was highest on low-tannin DFRi plants, indicating that condensed tannins (or their monomers) are physiologically more harmful than non-tannin flavonoids for E. autumnata larvae. Our results show that genetic manipulation of the flavonoid pathway in plants can effectively be used to produce altered phenolic profiles required for elucidating the roles of low-molecular weight phenolics and condensed tannins in plant–herbivore relationships, and suggest that phenolic secondary metabolites participate in regulation of plant growth. [ABSTRACT FROM AUTHOR]

Phenolics have a role in defenses against herbivores, but the defensive functions of specific groups of phenolics are still poorly understood. For example, ellagitannins (a type of hydrolyzable tannin) are predicted to decrease insect herbivore performance, but the effect of different types of ellagitannins on generalist and specialist herbivores has rarely been assessed. Here, we test the effects of the dominant oligomeric ellagitannins of Oenothera biennis and other Onagraceae on herbivore performance. We fed artificial diets containing between 1 and 100 mg/g of polyphenol fractions comprised of varying amounts and compositions of dimeric oenothein B, the trimeric oenothein A and larger oligomers, to one generalist (Spodoptera exigua) and one specialist (Schinia florida) insect herbivore species. We compared the effects of these ellagitannin fractions on herbivore performance to the effects of artificial diet containing total phenolic extracts from O. biennis, which contained these ellagitannins as well as many additional phenolic metabolites including flavonoid glycosides and caffeic acid derivatives. Both the ellagitannin fractions and O. biennis phenolic extracts had strong negative effects on S. exigua and S. florida performance, with stronger effects on the generalist herbivore. Differences between the effects of the various ellagitannin fractions were small and depended on insect life stage. The defensive effects of these ellagitannins were large, with lethal concentrations as low as 0.1% of the diet. These results highlight the important defensive function of ellagitannins against specialist and generalist herbivores and the need to characterize the effects of these understudied phenolics. [ABSTRACT FROM AUTHOR]

Conifer trees resist pest and pathogen attacks by complex defense responses involving different classes of defense compounds. However, it is unknown whether prior infection by biotrophic pathogens can lead to subsequent resistance to necrotrophic pathogens in conifers. We used the infection of jack pine, Pinus banksiana, by a common biotrophic pathogen dwarf mistletoe, Arceuthobium americanum, to investigate induced resistance to a necrotrophic fungus, Grosmannia clavigera, associated with the mountain pine beetle, Dendroctonus ponderosae. Dwarf mistletoe infection had a non-linear, systemic effect on monoterpene production, with increasing concentrations at moderate infection levels and decreasing concentrations at high infection levels. Inoculation with G. clavigera resulted in 33 times higher monoterpene concentrations and half the level of phenolics in the necrotic lesions compared to uninoculated control trees. Monoterpene production following dwarf mistletoe infection seemed to result in systemic induced resistance, as trees with moderate disease severity were most resistant to G. clavigera, as evident from shorter lesion lengths . Furthermore, trees with moderate disease severity had the highest systemic but lowest local induction of α-pinene after G. clavigera inoculation, suggesting a possible tradeoff between systemically- and locally-induced defenses. The opposing effects to inoculation by G. clavigera on monoterpene and phenolic levels may indicate the potential for biosynthetic tradeoffs by the tree between these two major defense classes. Our results demonstrate that interactions between a biotrophic parasitic plant and a necrotrophic fungus may impact mountain pine beetle establishment in novel jack pine forests through systemic effects mediated by the coordination of jack pine defense chemicals. [ABSTRACT FROM AUTHOR]

Plants are dependent on their root systems for survival, and thus are defended from belowground enemies by a range of strategies, including plant secondary metabolites (PSMs). These compounds vary among species, and an understanding of this variation may provide generality in predicting the susceptibility of forest trees to belowground enemies and the quality of their organic matter input to soil. Here, we investigated phylogenetic patterns in the root chemistry of species within the genus Eucalyptus. Given the known diversity of PSMs in eucalypt foliage, we hypothesized that (i) the range and concentrations of PSMs and carbohydrates in roots vary among Eucalyptus species, and (ii) that phylogenetic relationships explain a significant component of this variation. To test for interspecific variation in root chemistry and the influence of tree phylogeny, we grew 24 Eucalyptus species representing two subgenera ( Eucalyptus and Symphyomyrtus) in a common garden for two years. Fine root samples were collected from each species and analyzed for total phenolics, condensed tannins, carbohydrates, terpenes, and formylated phloroglucinol compounds. Compounds displaying significant interspecific variation were mapped onto a molecular phylogeny and tested for phylogenetic signal. Although all targeted groups of compounds were present, we found that phenolics dominated root defenses and that all phenolic traits displayed significant interspecific variation. Further, these compounds displayed a significant phylogenetic signal. Overall, our results suggest that within these representatives of genus Eucalyptus, more closely related species have more similar root chemistry, which may influence their susceptibility to belowground enemies and soil organic matter accrual. [ABSTRACT FROM AUTHOR]

Phenolic compounds play a role in plant defense against herbivores. For some herbivorous insects, particularly root herbivores, host plants with high phenolic concentrations promote insect performance and tissue consumption. This positive relationship between some insects and phenolics, however, could reflect a negative correlation with other plant defenses acting against insects. Silicon is an important element for plant growth and defense, particularly in grasses, as many grass species take up large amounts of silicon. Negative impact of a high silicon diet on insect herbivore performance has been reported aboveground, but is unreported for belowground herbivores. It has been hypothesized that some silicon accumulating plants exhibit a trade-off between carbon-based defense compounds, such as phenolics, and silicon-based defenses. Here, we investigated the impact of silicon concentrations and total phenolic concentrations in sugarcane roots on the performance of the root-feeding greyback canegrub ( Dermolepida albohirtum). Canegrub performance was positively correlated with root phenolics, but negatively correlated with root silicon. We found a negative relationship in the roots between total phenolics and silicon concentrations. This suggests the positive impact of phenolic compounds on some insects may be the effect of lower concentrations of silicon compounds in plant tissue. This is the first demonstration of plant silicon negatively affecting a belowground herbivore. [ABSTRACT FROM AUTHOR]

Non-native plants introduced to new habitats can have significant ecological impact. In many cases, even though they interact with the same community of potential herbivores as their new native competitors, they regularly receive less damage. Plants produce secondary metabolites in their leaves that serve a range of defensive functions, including resistance to herbivores and pathogens. Abiotic factors such as nutrient availability can influence the expression of defensive traits, with some species exhibiting increased chemical defense in low-nutrient conditions. Plants in the genus Lonicera are known to produce a diverse array of these secondary metabolites, yet non-native Lonicera species sustain lower amounts of herbivore damage than co-occurring native Lonicera species in North America. In this study, we searched for evidence of biochemical novelty in non-native species, and quantified its association with resistance to herbivores. In order to achieve this, we evaluated the phenolic and iridoid glycoside profiles in leaves of native and non-native Lonicera species grown under high and low fertilization treatments in a common garden. We then related these profiles to naturally occurring herbivore damage on whole plants in the garden. Herbivore damage was greater on native Lonicera, and chemical profiles and concentrations of selected putative defense compounds varied by species. Geographic origin was an inconsistent predictor of chemical variation in detected phenolics and iridoid glycosides (IGs). Overall, fertilization did not affect herbivore damage or measures of phenolics or IGs, but there were some fertilization effects within species. While we cannot conclude that non-natives were more chemically novel than native Lonicera species, chemical defense profiles and concentrations of specific compounds varied by species. Reduced attraction or deterrence of oviposition, specific direct resistance traits, or a combination of both may contribute to reduced herbivory and competitive advantages for non-native Lonicera in North America. [ABSTRACT FROM AUTHOR]

Floral nectar often contains chemicals that are deterrent to pollinators, presenting potential challenges to outcrossing plant species. Plants may be able to co-opt pollinator chemical signals to mitigate the negative effects of nectar deterrent compounds on pollination services. We found that buckwheat ( Fagopyrum esculentum) and Mexican sunflower ( Tithonia diversifolia) produce nectar with abundant phenolics, including three components of the Apis honeybee queen mandibular pheromone (QMP). In addition, these nectars contain a non-pheromonal phenolic, chlorogenic acid (CA), which was toxic to honeybees, and T. diversifolia nectar also contained isochlorogenic acid (IA). Fresh nectar or solutions containing nectar phenolics reduced Apis individual feeding compared to sucrose solutions. However, freely foraging bees preferred solutions with QMP components to control solutions, and QMP components over-rode or reversed avoidance of CA and IA. Furthermore, prior exposure to the presence or just the odor of QMP components removed the deterrent effects of CA and IA. By mimicking the honey bee pheromone blend, nectar may maintain pollinator attraction in spite of deterrent nectar compounds. [ABSTRACT FROM AUTHOR]

Field voles ( Microtus agrestis) cause severe damage to young Norway spruce ( Picea abies) plantations during wintertime in Fennoscandia. We experimentally investigated vole preference for winter-dormant, naturally regenerated seedlings; spring-planted seedlings; or autumn-planted seedlings; and how preference corresponds with seedling chemistry. Voles showed the highest preference for autumn-planted seedlings and the second highest for spring-planted seedlings, while naturally regenerated seedlings were avoided. The stems of the autumn-planted seedlings contained higher concentrations of nitrogen and piperidine alkaloids and lower concentrations of stilbenes than did the other groups. In addition to differences between naturally regenerated and planted seedlings, we investigated seasonal differences in naturally regenerated P. abies needle and bark secondary chemistry. While piperidine alkaloid concentrations did not vary with season, the soluble non-tannin phenolics of needles and the condensed tannins of bark were lower in May than in November or January. At the time of planting, the concentration of bark piperidine alkaloids was higher in autumn-planted than in spring-planted seedlings. We detected two alkaloids not previously found in P. abies, 2-methyl-6-propyl-1,6-piperideine and a tentatively identified pinidine-isomer. Our results demonstrate that vole choice of spruce seedlings is promoted by high nitrogen and low stilbene content, both associated with seedlings planted late in the season. As vole damage is linked to seedling chemistry, damage potentially could be mitigated by advancing planting or by manipulating plant chemistry in nurseries. [ABSTRACT FROM AUTHOR]

The genotype of the plant determines, through the expression of the phenotype, how well it is suited as food for herbivores. Since hybridization often results in profound genomic alterations with subsequent changes in phenotypic traits, it has the potential to significantly affect plant-herbivore interactions. In this study, we used a population of F2 hybrids that originated from a cross between a Salix viminalis and a Salix dasyclados genotype, which differed in both phenolic content and resistance to the herbivorous leaf beetle Phratora vulgatissima. We screened for plants that showed a great variability in leaf beetle performance (i.e., oviposition and survival). By correlating leaf phenolics to the response of the herbivores, we evaluated the importance of different phenolic compounds for Salix resistance to the targeted insect species. The performance of P. vulgatissima varied among the F2 hybrids, and two patterns of resistance emerged: leaf beetle oviposition was intermediate on the F2 hybrids compared to the parental genotypes, whereas leaf beetle survival demonstrated similarities to one of the parents. The findings indicate that these life history traits are controlled by different resistance mechanisms that are inherited differently in the hybrids. Salicylates and a methylated luteolin derivative seem to play major roles in hybrid resistance to Phratora vulgatissima. Synergistic effects of these compounds, as well as potential threshold concentrations, are plausible. In addition, we found considerable variation in both distributions and concentrations of different phenolics in the F2 hybrids. The phenolic profiles of parental genotypes and F2 hybrids differed significantly (e.g., novel compounds appeared in the hybrids) suggesting genomic alterations with subsequent changes in biosynthetic pathways in the hybrids. [ABSTRACT FROM AUTHOR]

We conducted a greenhouse study to assess the effects of cogongrass ( Imperata cylindrica) rhizochemicals on a suite of plants native to southeastern US pine savanna ecosystems. Our results indicated a possible allelopathic effect, although it varied by species. A ruderal grass ( Andropogon arctatus) and ericaceous shrub ( Lyonia ferruginea) were unaffected by irrigation with cogongrass soil 'leachate' (relative to leachate from mixed native species), while a mid-successional grass ( Aristida stricta Michx. var. beyrichiana) and tree ( Pinus elliottii) were negatively affected. For A. stricta, we observed a 35.7 % reduction in aboveground biomass, a 21.9 % reduction in total root length, a 24.6 % reduction in specific root length and a 23.5 % reduction in total mycorrhizal root length, relative to the native leachate treatment. For P. elliottii, there was a 19.5 % reduction in percent mycorrhizal colonization and a 20.1 % reduction in total mycorrhizal root length. Comparisons with a DI water control in year two support the possibility that the treatment effects were due to the negative effects of cogongrass leachate, rather than a facilitative effect from the mixed natives. Chemical analyses identified 12 putative allelopathic compounds (mostly phenolics) in cogongrass leachate. The concentrations of most compounds were significantly lower, if they were present at all, in the native leachate. One compound was an alkaloid with a speculated structure of hexadecahydro-1-azachrysen-8-yl ester (CHNO). This compound was not found in the native leachate. We hypothesize that the observed treatment effects may be attributable, at least partially, to these qualitative and quantitative differences in leachate chemistry. [ABSTRACT FROM AUTHOR]

Flavonoids are biologically active low molecular weight secondary metabolites that are produced by plants, with over 10,000 structural variants now reported. Due to their physical and biochemical properties, they interact with many diverse targets in subcellular locations to elicit various activities in microbes, plants, and animals. In plants, flavonoids play important roles in transport of auxin, root and shoot development, pollination, modulation of reactive oxygen species, and signalling of symbiotic bacteria in the legume Rhizobium symbiosis. In addition, they possess antibacterial, antifungal, antiviral, and anticancer activities. In the plant, flavonoids are transported within and between plant tissues and cells, and are specifically released into the rhizosphere by roots where they are involved in plant/plant interactions or allelopathy. Released by root exudation or tissue degradation over time, both aglycones and glycosides of flavonoids are found in soil solutions and root exudates. Although the relative role of flavonoids in allelopathic interference has been less well-characterized than that of some secondary metabolites, we present classic examples of their involvement in autotoxicity and allelopathy. We also describe their activity and fate in the soil rhizosphere in selected examples involving pasture legumes, cereal crops, and ferns. Potential research directions for further elucidation of the specific role of flavonoids in soil rhizosphere interactions are considered. [ABSTRACT FROM AUTHOR]

Sorghum allelopathy has been reported in a series of field experiments following sorghum establishment. In recent years, sorghum phytotoxicity and allelopathic interference also have been well-described in greenhouse and laboratory settings. Observations of allelopathy have occurred in diverse locations and with various sorghum plant parts. Phytotoxicity has been reported when sorghum was incorporated into the soil as a green manure, when residues remained on the soil surface in reduced tillage settings, or when sorghum was cultivated as a crop in managed fields. Allelochemicals present in sorghum tissues have varied with plant part, age, and cultivar evaluated. A diverse group of sorghum allelochemicals, including numerous phenolics, a cyanogenic glycoside (dhurrin), and a hydrophobic p-benzoquinone (sorgoleone) have been isolated and identified in recent years from sorghum shoots, roots, and root exudates, as our capacity to analyze and identify complex secondary products in trace quantities in the plant and in the soil rhizosphere has improved. These allelochemicals, particularly sorgoleone, have been widely investigated in terms of their mode(s) of action, specific activity and selectivity, release into the rhizosphere, and uptake and translocation into sensitive indicator species. Both genetics and environment have been shown to influence sorgoleone production and expression of genes involved in sorgoleone biosynthesis. In the soil rhizosphere, sorgoleone is released continuously by living root hairs where it accumulates in significant concentrations around its roots. Further experimentation designed to study the regulation of sorgoleone production by living sorghum root hairs may result in increased capacity to utilize sorghum cover crops more effectively for suppression of germinating weed seedlings, in a manner similar to that of soil-applied preemergent herbicides like trifluralin. [ABSTRACT FROM AUTHOR]

The contents of individual phenolic compounds in the inner bark of silver birch ( Betula pendula Roth) were analyzed by HPLC-DAD. Samples from 21 mature trees originating from three micropropagated parent trees were collected six times over a 1-year period. Significant seasonal variation in the quantities of ten compounds and four chromatographically unresolved compound pairs was found. A majority of the compounds also exhibited significant quantitative variation among birch clones. There were no qualitative differences associated with the season or among the clones. However, wounding of the bark induced the production of new types of bark phenolics: several ellagitannins were detected in the callus tissues of birch for the first time. [ABSTRACT FROM AUTHOR]

Gene transfer techniques offer new possibilities to study regulation of phenolic pathways and the defensive role of phenolics. Hybrid aspen lines ( Populus tremula × tremuloides) that overexpress the PtMYB134 transcription factor were used to study the effects of condensed tannin production on plant physiology and plant defenses. The MYB134 protein activates all the known genes of the biosynthetic pathway for condensed tannins (CTs), so overexpression of MYB134 was expected to increase CT concentration in all tissues of the plants. Two out of three MYB134 overexpression lines (46 and 54) accumulated high levels of CTs and (+)-catechin, with a concomitant decrease in the levels of salicylates, but one transgenic line, MYB 61, failed to overproduce CTs. The concentrations of phenolic compounds generally were lower in the aspen leaves grown under elevated temperature than in those grown under ambient temperature. A specialist leaf beetle, Phratora vitellinae (Coleoptera: Chrysomelidae), was chosen to examine how over-expression of MYB134 and elevated temperature affect the food choice of a beetle adapted to feed on leaves rich in salicylates but containing little CT. Specialist beetles preferred the leaves grown at ambient temperatures possibly because these leaves had higher concentrations of salicylates, which are feeding stimulants. Beetles also preferred MYB line 61, which contained a normal level of CT but a slightly elevated level of salicylates. Our results show that transgenic plants are powerful tools, but that enhancing one secondary pathway may lead to unexpected effects on other pathways, and thus impact characteristics such as plant resistance against herbivores, especially under changing climatic conditions. [ABSTRACT FROM AUTHOR]

Studies of allelopathy in terrestrial systems have experienced tremendous growth as interest has risen in describing biochemical mechanisms responsible for structuring plant communities, determining agricultural and forest productivity, and explaining invasive behaviors in introduced organisms. While early criticisms of allelopathy involved issues with allelochemical production, stability, and degradation in soils, an understanding of the chemical ecology of soils and its microbial inhabitants has been increasingly incorporated in studies of allelopathy, and recognized as an essential predictor of the outcome of allelopathic interactions between plants. Microbes can mediate interactions in a number of ways with both positive and negative outcomes for surrounding plants and plant communities. In this review, we examine cases where soil microbes are the target of allelopathic plants leading to indirect effects on competing plants, provide examples where microbes play either a protective effect on plants against allelopathic competitors or enhance allelopathic effects, and we provide examples where soil microbial communities have changed through time in response to allelopathic plants with known or potential effects on plant communities. We focus primarily on interactions involving wild plants in natural systems, using case studies of some of the world's most notorious invasive plants, but we also provide selected examples from agriculturally managed systems. Allelopathic interactions between plants cannot be fully understood without considering microbial participants, and we conclude with suggestions for future research. [ABSTRACT FROM AUTHOR]

The defensive secretion of the ground beetle Chlaenius cordicollis is predominantly 3-methylphenol. Adult C. cordicollis were collected in Pennsylvania and Manitoba and induced to discharge defensive secretion in a vial. The headspace was sampled by solid phase microextraction, and samples were analyzed by gas chromatography-mass spectrometry. Five alkylphenolic compounds were detected: all beetles secreted 3-methlyphenol, 2,5-dimethylphenol, and 3-ethylphenol, and most beetles from each locality secreted detectable amounts of 2,3-dimethlyphenol and 3,4-dimethylphenol. In about 80% of beetles, we detected small amounts of the alkoxyphenolic compounds 2-methoxy-4-methylphenol and 2-methoxy-5-methylphenol. Multivariate compositional analysis of relative peak areas of alkylphenolic compounds revealed geographic variation and sexual dimorphism in defensive secretions. Compared with samples from Manitoba, relative peak areas of samples from Pennsylvania were lower for 2,3-dimethylphenol and higher for 3-methylphenol. Sexual dimorphism was detected only in Manitoba where, compared with samples from males, relative peak areas for samples from females were higher for 2,5-dimethylphenol and lower for 3-ethylphenol. This is the first report of geographic variation in defensive secretions of carabid beetles, and it demonstrates the need for knowledge of patterns of variation before characterizing the defensive secretions of a species as a whole. [ABSTRACT FROM AUTHOR]

Increasing global atmospheric CO has been shown to affect important plant traits, including constitutive levels of defensive compounds. However, little is known about the effects of elevated CO on the inducibility of chemical defenses or on plant mechanical defenses. We grew Brassica rapa (oilseed rape) under ambient and elevated CO to determine the effects of elevated CO on constitutive levels and inducibility of carbon-based phenolic compounds, and on constitutive trichome densities. Trichome density increased by 57% under elevated CO. Constitutive levels of simple, complex, and total phenolics also increased under elevated CO, but inducibility of each decreased. Induction of simple phenolics occurred only under ambient CO. Although induction of complex and total phenolics occurred under both ambient and elevated CO, the damage-induced increases were 64% and 75% smaller, respectively, under elevated CO. Constitutive phenolic levels were positively correlated with leaf C:N ratio, and inducibility was positively correlated with leaf N and negatively correlated with leaf C:N ratio, as would be expected if inducibility were constrained by nitrogen availability under elevated CO. We conclude that B. rapa is likely to exhibit higher constitutive levels of both chemical and mechanical defenses in the future, but is also likely to be less able to respond to herbivore damage by inducing phenolic defenses. To our knowledge, this is only the second study to report a negative effect of elevated CO on the inducibility of any plant defense. [ABSTRACT FROM AUTHOR]

Lodgepole pines, Pinus contorta Douglas ex Louden var. latifolia Engelm. ex S. Watson, are encountering increased abiotic stress and pest activity due to recent increases in temperature and changes in precipitation throughout their range. This tree species counters these threats by producing secondary metabolites, including phenolics and terpenoids. We examined foliar levels of lignin, soluble phenolics, monoterpenoids, sesquiterpenoids, and diterpenoids in 12 stands in British Columbia, Canada. We used these data to assess associations among foliar secondary metabolite levels and ecosystem, geographic, and climatic variables. Regressions were also performed to observe which combinations of variables best explained secondary metabolite variance. Stands of P. c. latifolia in the Coastal Western Hemlock and Interior Cedar/Hemlock biogeoclimatic zones had consistently greater foliar levels of almost all measured secondary metabolites than did other stands. Lignin was present in greater amounts in Boreal White/Black Spruce ecosystem (i.e., northern) stands than in southern stands, suggesting a role for this metabolite in pine survival in the boreal forest. Attempts to develop regression models with geographic and climatic variables to explain foliar secondary metabolite levels resulted in multiple models with similar predictive capability. Since foliar secondary metabolite levels appeared to vary most between stand ecosystem types and not as much due to geographic and climatic variables, metabolic profiles appeared best matched to the stress levels within local environments. It is unknown if differences in secondary metabolite levels are the result of genetic adaptation or phenotypic plasticity, but results from this and other studies suggest that both are important. These results are interpreted in light of ongoing efforts to assist in the migration of certain populations of P. c. latifolia northward in an effort to counter predicted effects of climate change. [ABSTRACT FROM AUTHOR]

We examined the extent to which three Fraxinus cultivars and a wild population that vary in their resistance to Emerald Ash Borer (EAB) could be differentiated on the basis of a suite of constitutive chemical defense traits in phloem extracts. The EAB-resistant Manchurian ash ( F. mandshurica, cv. Mancana) was characterized by having a rapid rate of wound browning, a high soluble protein concentration, low trypsin inhibitor activities, and intermediate levels of peroxidase activity and total soluble phenolic concentration. The EAB-susceptible white ash ( F. americana, cv. Autumn Purple) was characterized by a slow wound browning rate and low levels of peroxidase activity and total soluble phenolic concentrations. An EAB-susceptible green ash cultivar ( F. pennsylvanica, cv. Patmore) and a wild accession were similar to each other on the basis of several chemical defense traits, and were characterized by high activities of peroxidase and trypsin inhibitor, a high total soluble phenolic concentration, and an intermediate rate of wound browning. Lignin concentration and polyphenol oxidase activities did not differentiate resistant and susceptible species. Of 33 phenolic compounds separated by HPLC and meeting a minimum criterion for analysis, nine were unique to Manchurian ash, five were shared among all species, and four were found in North American ashes and not in the Manchurian ash. Principal components analysis revealed clear separations between Manchurian, white, and green ashes on the basis of all phenolics, as well as clear separations on the basis of quantities of phenolics that all species shared. Variation in some of these constitutive chemical defense traits may contribute to variation in resistance to EAB in these species. [ABSTRACT FROM AUTHOR]

The existence of tradeoffs among plant defenses is commonly accepted, however, actual evidence for these tradeoffs is scarce. In this study, I analyzed effects of different direct defenses of wild lima bean plants ( Phaseolus lunatus) that were simultaneously exposed to a fungal pathogen ( Colletotrichum lindemuthianum) and an insect herbivore, the Mexican bean beetle ( Epilachna varivestis). Although plants were derived from spatially widely separated populations, I observed a common tradeoff between resistance to pathogens and herbivores. Plants with high levels of anti-herbivore defense (cyanogenesis) showed low levels of resistance to pathogens (polyphenol oxidase activity and phenolic compounds), and vice versa. Competition for resources generally is considered to be the basis for tradeoffs. However, I report direct inhibition of polyphenol oxidase by cyanide, making simultaneous expression of both defenses at high levels impossible. I argue that populations composed of individuals investing in one type of defense have an advantage in environments that periodically favor either pathogen or herbivore plant antagonists. [ABSTRACT FROM AUTHOR]

The emerald ash borer (EAB; Agrilus planipennis Fairmaire; Coleoptera: Buprestidae), is an exotic wood-boring beetle that has been threatening North American ash ( Fraxinus spp.) resources since its discovery in Michigan and Ontario in 2002. In this study, we investigated the phytochemical responses of the three most common North American ash species (black, green, and white ash) in northeastern USA to EAB adult feeding. Black ash was the least responsive to EAB adult feeding in terms of the induction of volatile compounds, and levels of only two (indole and benzyl cyanide) of the 11 compounds studied increased. In green ash, levels of two [( E)- β-ocimene and indole] of the 11 volatile compounds studied were elevated, while the levels of two green leaf volatiles [hexanal and ( E)-2-hexenal] decreased. White ash showed the greatest response with an increase in levels of seven of the 11 compounds studied. Qualitative differences among ash species were detected. Among the phenolic compounds detected, ligustroside was the only one detected in all three species. Oleuropein aglycone and 2 unidentified compounds were found only in black ash; coumaroylquinic acid and feruloylquinic acid were detected only in green ash; and verbascoside hexoside was detected only in white ash. EAB adult feeding did not elicit or decrease concentrations of any selected individual phenolic compounds. However, although levels of total phenolics from black and green ash foliage were not affected by EAB adult feeding, they decreased significantly in white ash. EAB adult feeding elevated chymotrypsin inhibitors in black ash. The possible ecological implications of these findings are discussed. [ABSTRACT FROM AUTHOR]

The capacity to produce carbon-based secondary compounds (CBSC), such as phenolics (including tannins) and terpenes as defensive compounds against herbivores or against neighboring competing plants can be involved in the competition between alien and native plant species. Since the Hawaiian Islands are especially vulnerable to invasions by alien species, we compared total phenolic (TP), total tannin (Tta), and total terpene (TT) leaf contents of alien and native plants on Oahu Island (Hawaii). We analyzed 35 native and 38 alien woody plant species randomly chosen among representative current Hawaiian flora. None of these CBSC exhibited phylogenetic fingerprinting. Alien species had similar leaf TP and leaf Tta contents, and 135% higher leaf TT contents compared with native species. Alien plants had 80% higher leaf TT:N leaf content ratio than native plants. The results suggest that apart from greater growth rate and greater nutrient use, alien success in Oahu also may be linked to greater contents of low cost chemical defenses, such as terpenes, as expected in faster-growing species in resource rich regions. The higher TT contents in aliens may counterbalance their lower investment in leaf structural defenses and their higher leaf nutritional quality. The higher TT provides higher effectiveness in deterring the generalist herbivores of the introduced range, where specialist herbivores are absent. In addition, higher TT contents may favor aliens conferring higher protection against abiotic and biotic stressors. The higher terpene accumulation was independent of the alien species origin, which indicates that being alien either selects for higher terpene contents post-invasion, or that species with high terpene contents are pre-adapted to invasiveness. Although less likely, an originally lower terpene accumulation in Hawaiian than in continental plants that avoids the increased attraction of specialist enemies associated to terpenes may not be discarded. [ABSTRACT FROM AUTHOR]

A high molecular weight humic fraction (>3,500 Da) was characterized chemically by DRIFT and 1H NMR spectroscopy, and was applied to Zea mays L. plants to evaluate its effect on phenylpropanoid metabolism. The activity and gene expression of phenylalanine (tyrosine) ammonia-lyase (PAL/TAL), and the concentrations of phenolics and their amino acid precursors phenylalanine and tyrosine were assayed. Maximum induction of PAL/TAL activity and expression was obtained when the concentration of added humic substance was 1 mg C/l hydroponic solution. Phenylalanine and tyrosine significantly decreased (−16% and −22%, respectively), and phenolic compounds increased in treated plants. The effects of the humic substance could be ascribed partly to indoleacetic acid (27 nmol/mg C) in the humic fraction. Our results suggest that this humic fraction induces changes in phenylpropanoid metabolism. This is the first study that shows a relationship between humic substances and the phenylpropanoid pathway. [ABSTRACT FROM AUTHOR]

Prominent among the many factors now affecting the sustainability of forest ecosystems are anthropogenically-generated carbon dioxide (CO2) and ozone (O3). CO2 is the substrate for photosynthesis and thus can accelerate tree growth, whereas O3 is a highly reactive oxygen species and interferes with basic physiological functions. This review summarizes the impacts of CO2 and O3 on tree chemical composition and highlights the consequences thereof for trophic interactions and ecosystem dynamics. CO2 and O3 influence phytochemical composition by altering substrate availability and biochemical/physiological processes such as photosynthesis and defense signaling pathways. Growth of trees under enriched CO2 generally leads to an increase in the C/N ratio, due to a decline in foliar nitrogen and concomitant increases in carbohydrates and phenolics. Terpenoid levels generally are not affected by atmospheric CO2 concentration. O3 triggers up-regulation of antioxidant defense pathways, leading to the production of simple phenolics and flavonoids (more so in angiosperms than gymnosperms). Tannins levels generally are unaffected, while terpenoids exhibit variable responses. In combination, CO2 and O3 exert both additive and interactive effects on tree chemical composition. CO2-and O3-mediated changes in plant chemistry influence host selection, individual performance (development, growth, reproduction), and population densities of herbivores (primarily phytophagous insects) and soil invertebrates. These changes can effect shifts in the amount and temporal pattern of forest canopy damage and organic substrate deposition. Decomposition rates of leaf litter produced under elevated CO2 and O3 may or may not be altered, and can respond to both the independent and interactive effects of the pollutants. Overall, however, CO2 and O3 effects on decomposition will be influenced more by their impacts on the quantity, rather than quality, of litter produced. A prominent theme to emerge from this and related reviews is that the effects of elevated CO2 and O3 on plant chemistry and ecological interactions are highly context- and species-specific, thus frustrating attempts to identify general, global patterns. Many of the interactions that govern above- and below-ground community and ecosystem processes are chemically mediated, ultimately influencing terrestrial carbon sequestration and feeding back to influence atmospheric composition. Thus, the discipline of chemical ecology is fundamentally important for elucidating the impacts of humans on the health and sustainability of forest ecosystems. Future research should seek to increase the diversity of natural products, species, and biomes studied; incorporate long-term, multi-factor experiments; and employ a comprehensive “genes to ecosystems” perspective that couples genetic/genomic tools with the approaches of evolutionary and ecosystem ecology. [ABSTRACT FROM AUTHOR]

Leaves of Chrysanthemum morifolium cv. Ramat were extracted sequentially with hexane, ethyl acetate, and methanol. The methanol fraction, when incorporated into artificial diet was found to reduce the growth of cabbage looper (Trichoplusia ni Hubner) larvae at concentrations between 500 and 5000 ppm of diet. Fractionation of the methanol extract on a Sephadex column yielded five fractions, three of which reduced the weight of larvae relative to the control. One fraction was analyzed using high performance liquid chromatography (HPLC) and found to contain three main constituents. These compounds were purified using a combination of gel permeation chromatography on Sephadex LH20 and HPLC, and analyzed by ¹H and 13C NMR as well as undergoing chemical and physical analyses. The compounds were identified as: 1, chlorogenic acid (5-O-caffeoylquinic acid); 2, 3,5-O-dicaffeoylquinic acid; and 3, 3', 4', 5-trihydroxyflavanone 7-O-glucuronide (eriodictyol 7-O-glucuronide). At concentrations between 100 to 1000 ppm these compounds reduced both growth and photosynthesis of Lemna gibba L. with the order of efficacy being: flavanone > chlorogenic acid > 3,5-O-dicaffeoylquinic acid. Furthermore, when incorporated separately into artificial diet these compounds, at 10 to 1000 ppm, enhanced or reduced growth of the cabbage looper (Trichoplusia ni) and gypsy moth (Lymantria dispar L.). [ABSTRACT FROM AUTHOR]

Phytotoxicity-based extraction and fractionation were employed to separate allelochemicals contained in an extract of Lethariella canariensis. Twelve phenolic substances were isolated from the phytotoxic fraction "Letharal" of the thalli. These were identified by spectroscopic methods, physicochemical constants, and HPLC chemical correlation, and determined to be atranol (2), chloroatranol (3), hematommic acid (4), chlorohematommic acid (5), methyl hematommate (6), methyl chlorohematommate (7) (new compound), ethyl hematommate (8), ethyl chlorohematommate (9), methyl β-orsellinate (10), atranorin (11), chloroatranorin (12), and (+)-usnic acid (13). Further identification and quantification of these allelochemicals in the environment were conducted by HPLC. Several phenolic compounds showed moderate antimicrobial activity. The cytostatic activity of the polyphenols was investigated on U937 and I-IL-60 cells. All compounds were assayed, with the exception of 10. The "Letharal" mixture decreased cell viability in both cell lines. Protection against lipid peroxidation was investigated using brain homogenates. Compounds 2, 3, 6, 8, 11, and Letharal decreased H[SUB2]O/Fe[SUP+2] induced lipid peroxidation in a concentration-dependent manner, while 10 and 13 were unable to protect tissue against oxidative stress. [ABSTRACT FROM AUTHOR]

High foliar phenolics are generally assumed to increase resistance to insect herbivores, but recent studies show that tobacco lines modified to over– and underexpress phenolics do not exhibit higher constitutive resistance to caterpillars. This is contrary to the expectation that ingestion of tobacco phenolics, particularly chlorogenic acid, should cause oxidative stress in herbivores. We investigated free radical production and antioxidant capacity of fresh crushed leaves of tobacco lines exhibiting over a sixfold difference in chlorogenic acid content to test whether high phenolic concentrations are associated with increased production of reactive oxygen species (ROS). The effects of in planta phenolic levels on feeding behavior, growth, biochemical markers of oxidative stress, and the antioxidant capacity of midgut fluid and hemolymph were assessed in tobacco budworm, Heliothis virescens. The experiments showed that high phenolic foliage was more prooxidant than low phenolic foliage, but the net balance in crushed tissue was antioxidant in comparison to buffer and the commercial antioxidant standard, Trolox. In H. virescens, the antioxidant capacity of midgut fluid was also powerful, and caterpillars fed high phenolic foliage did not exhibit the expected markers of oxidative stress in midgut tissues (altered ascorbate ratios, disulfides, or total hydroperoxides). Instead, hemolymph of larvae fed high phenolic foliage exhibited improved total Trolox equivalent antioxidant capacity (TEAC). These results suggest that the elevated foliar phenolics in some plants may have beneficial antioxidant properties for herbivorous insects, much as dietary phenolics do in mammals. [ABSTRACT FROM AUTHOR]

An ethanolic extract of red maple ( Acer rubrum L.) leaves (RME) applied to trembling aspen ( Populus tremuloides Michx.) leaves reduced feeding in choice test assays with forest tent caterpillar larvae ( Malacosoma disstria Hbn.) (FTC), whereas a trembling aspen foliage extract, similarly applied, stimulated feeding. Compounds isolated from the RME were gallic acid, methyl gallate, ethyl gallate, m-digallate, ethyl m-digallate, 1- O-galloyl-β-D-glucose, 1- O-galloyl-α-L-rhamnose, kaempferol 3- O-β-D-glucoside, kaempferol 3- O-β-D-galactoside, kaempferol 3- O-β-L-rhamnoside, kaempferol-3- O-rhamnoglucoside, quercetin 3- O-β-D-glucoside, quercetin 3- O-β-L-rhamnoside and quercetin 3- O-rhamnoglucoside, (−)-epicatechin, (+)-catechin and ellagic acid. All of the gallates, (−)-epicatechin, and kaempferol 3- O-β-L-rhamnoside deterred feeding on trembling aspen leaf disks when applied at 0.28 mg/cm2. The two digallates deterred feeding by 90% and were the most effective. HPLC analysis indicated that ethyl m-digallate is present in amounts 10–100 × higher in RME (∼2.5–250 mg/g) than any other compound. Thus, ethyl m-digallate appears to be the major compound protecting red maple from feeding by FTC, with a minor contribution from other gallates. [ABSTRACT FROM AUTHOR]

The response of phenolic compounds as a result of long-term low open-field ozone exposure was studied in ozone-sensitive and ozone-tolerant clones of European silver birch (Betula pendula Roth). The saplings were exposed to 1.5–1.6 times the ambient (elevated) ozone and ambient air (as control) over three growing seasons from May 1996 until August 1998. Quantification by modified Folin-Ciocalteau assay showed a 16.2% increase in total phenolics in elevated ozone plants as compared to that in controls and a corresponding 9.9% increase of 10 phenolic compounds quantified by HPLC. Five nonflavonoids and five flavonoids showed 8.4% and 11.4% increases, respectively. The phenolic results indicated slightly higher ozone sensitivity of clone 5 as compared to clone 2. The most ozone-responsive phenolic compounds in clone 2 and clone 5 were (+)-catechin (CT), chlorogenic acid (CGA), 5-p-coumaroylquinic acid (5CQA), 3-p-coumaroylquinic acid (3CQA), myricetin galactopyranoside (MG), quercetin-3-O-glucuronopyranoside (QGR), and quercetin-3-O-arabinofuranoside (QA). Increased phenolic content in ozone-exposed plants was related to impaired growth and accelerated leaf senescence, indicated by enhanced autumn leaf yellowing and lower chlorophyll and Mg content. The change in carbon allocation towards defensive phenolics at the expense of growth was greater in the ozone-sensitive clone as compared to tolerant clone. [ABSTRACT FROM AUTHOR]

We examined the response of the widely used Folin-Denis assay to purified tannins from 16 woody plant species and to three commercial polyphenol preparations often used as standards. The reagent's response to these chemical mixtures differed significantly among sources (tree species, commercial preparations) and sampling dates, even though the mixtures contained the same total dry weight of tannins. Response to commercial standards usually did not resemble response to actual plant tannin and produced estimates that differed from actual concentrations by as much as twofold. Species-based and seasonal differences in polyphenol composition are evidently responsible for these variable results. Reagents that depend on redox reactions, such as the Folin-Denis, do not produce reliable absolute or relative quantification of phenolics when different species or samples from different dates are compared, and use of commercial standards does not resolve this problem. [ABSTRACT FROM AUTHOR]

Phytotoxic studies strongly depend on evaluation of germination responses, which implies the need for adequate procedures to account for distinct aspects of the germinative process. For this, indices, comparisons among treatments at various times, and model fitting have been proposed. The objective of this work is to compare the three approaches and select the one providing the greatest insight and precision. Speed of germination, speed of accumulated germination, the coefficient of the rate of germination, comparisons at each determination time, including final germination, and the parameters of the Weibull function were examined. The Weibull function proved the best approach to describe the germination process, providing not only the same type of information about the speed of germination, with greater precision, but also additional information about the initiation and shape of the germination response curve. [ABSTRACT FROM AUTHOR]

CE145–66 is an improved early-maturing grain sorghum genotype, increasingly grown by farmers in the Sahelian part of Senegal. This genotype is known to have negative effects on the following groundnut crop, because of the release of allelopathic phenolic compounds into the soil. We have assessed the synthesis of phenolics in sorghum vegetative parts and the variations in synthesis between years and sites. Total phenols and phenolic acids in the aerial parts and roots of flowering sorghum plants from 52 farmers' fields at two sites (Sagnanème and Médina) in Senegal in 1996 and 1997 were measured. Thirty-eight soil samples, collected after the sorghum harvest, from sorghum rows and interrows also were analyzed for their phenolic content. Total phenols reached 1.1–1.5% of root dry weight and 1.1–2.2% of aerial parts dry weight, with little variation between sites, and large variability between years, presumably due to climatic conditions. Eight phenolic acids and three associated aldehydes were identified by HPLC, with p-hydroxybenzoic, p-coumaric, and ferulic acids the most abundant. Their totals reached 2.9–3.2 mg/g in 1996 and 2.6–2.8 mg/g in 1997 for the aerial part; and 3.3–3.6 mg/g in 1996 and 2.8–3.3 mg/g in 1997 for roots. In soils under sorghum rows, the mean water-soluble total phenols increased from 4.6 in 1997 to 6.7 μg/g in 1998 in Sagnanème, and from 3.8 in 1997 to 5 μg/g in 1998 in Médina. The concentrations of total phenols and phenolic acids were higher in rows than in interrows. All the phenolic monomers identified in vegetative parts were recovered in associated soil samples, with vanillic and p-hydroxybenzoic acids the most abundant. Finally, variability in plant phenolic content seemed more due to climatic than to cropping or soil factors, as differences between years appear more important than differences between or within sites. [ABSTRACT FROM AUTHOR]

The aim of this work was to study how nitrogen availability affects within-plant allocation to growth and secondary metabolites and how this allocation affects host selection by herbivores. Tomato plants ( Lycopersicon esculentum) were grown at six levels of nitrogen availability. When nitrogen availability increased, plant relative growth rate increased, but tissue carbon/nitrogen ratio in the second oldest true leaf and allocation to large glandular trichomes (type VI) as well as to the defense compounds rutin and chlorogenic acid decreased. Leaf protein concentration increased. Two-spotted spider mite ( Tetranychus urticae) females responded significantly to these changes: in dual choice tests they preferred leaf disks from plants grown at high nitrogen availability, with a low C/N ratio. This preference persisted in an olfactometer in which the mites were offered only the odors released by leaves with damaged trichomes. We conclude that in a tomato leaf increased nitrogen availability leads to decreased allocation to defenses, and that repellent volatiles released by trichomes play a key role in affecting leaf selection by two-spotted spider mite females. [ABSTRACT FROM AUTHOR]

The change of total phenolic content in decomposing Chinese fir stump-roots of different ages in replant woodland and its effects was investigated. The total phenolic contents in stump-roots decreased with increasing stump-root age. The order of total phenolic content in different parts of stump-roots was, root > stump heartwood > stump sapwood. Phenolics released from Chinese fir stump-roots reduced the growth of fir seedlings. The growth of Chinese fir seedlings was negatively correlated with total phenolic content in stump-roots that had been added to the soil. Extracts of Chinese fir stump-roots inhibited fir seed germination. The results, based on paper chromatography and HPLC, revealed that eight phenolic compounds were present in the Chinese fir stump-roots. [ABSTRACT FROM AUTHOR]

Plant-produced phenolic compounds inhibit soil microbial activity and are suspected to be involved in the failure of natural regeneration of French subalpine Norway spruce ( Picea abies) forests. This work evaluated relationships between phenolic compounds and soil microorganisms in humus collected in spruce forest during winter and summer seasons. After having identified and quantified different phenolics from humus samples, we incubated another set of humus samples with 10 times the concentration of naturally occurring phenolics, and effects on the density of microorganisms were compared to humus with no addition of phenolic compounds. Furthermore, in order to follow the degradation of phenolic compounds by microbes, the concentration of phenolics in the incubated humus samples was determined by HPLC after three and six days of incubation. The results indicate that humus microorganisms use phenolics as a carbon source, since almost all phenolic compounds had disappeared after six days of incubation. Addition of phenolic compounds to the humus samples also affected the soil microbial populations so that bacteria were inhibited in the humus collected both in the winter and in the summer. However, there were differences between the experiments. Fungi and cellulose hydrolyzers were stimulated in the winter humus experiment, while fungi were unaffected and cellulose hydrolyzers were inhibited in the summer experiment. The addition of phenolic compounds stimulated ammonifiers in the summer experiment. We anticipate that the role of soil microorganisms in the problem of natural regeneration failure is probably more important than previously thought. [ABSTRACT FROM AUTHOR]

Allelopathy due to humus phenolics is a cause of natural regeneration deficiency in subalpine Norway spruce ( Picea abies) forests. If inhibition of spruce germination and seedling growth due to allelochemicals is generally accepted, in contrast there is a lack of knowledge about phenolic effects on mycorrhizal fungi. Thus, this work tested effects of a humic solution and its naturally occurring phenolics on the growth and respiration of two mycorrhizal fungi: Hymenoscyphus ericae (symbiont of Vaccinium myrtillus, the main allelochemical-producing plant) and Hebeloma crustuliniforme (symbiont of P. abies, the target plant). Growth and respiration of H. crustuliniforme were inhibited by growth medium with the original humic solution (−6% and −30%), respectively, whereas the same humic solution did not affect growth but decreased respiration of H. ericae (−55%). When naturally occurring phenolics (same chemicals and concentrations in the original humic solution) were added to the growth medium, growth of H. crustuliniforme was not affected, whereas that of H. ericae significantly increased (+10%). We conclude that H. ericae is better adapted to the allelopathic constraints of this forest soil than H. crustuliniforme and that the dominance of V. myrtillus among understory species could be explained in this way. [ABSTRACT FROM AUTHOR]

Phytotoxicity-based extraction and fractionation were employed to separate and purify the allelochemicals from an aqueous extract of vulpia ( Vulpia myuros) residues. Further analyses, identification, and quantitation of these allelochemicals were conducted by gas chromatography–mass spectrometry on the most toxic fraction. Twenty-one compounds were identified in the ether fraction from the vulpia residue aqueous extract. They were catechol, hydroquinone, 3,4-dimethoxyphenol, pyrogallol, coniferyl alcohol, and benzoic, succinic, hydrocinnamic, salicylic, protocatechuic, vanillic, gentisic, syringic, p-hydroxybenzoic, α-hydroxybenzenepropanoic, p-hydroxyphenylacetic, p-hydroxybenzenepropanoic, hydroferulic, p-coumaric, hydrocaffeic, and ferulic acids. A chromatographic internal standard method with multiple-point calibration graphs was used to quantify the identified compounds. Quantities in the vulpia residues ranged from 1.36 to 81.0 μg/g dry residue, in total accounting for 0.05% of the dry weight residue. The combined syringic and hydroferulic acids were present in the largest amount, 140.11 μg/g residue. Vanillic, succinic, p-hydroxybenzenepropanoic, and salicylic acids were next in amount, ranging from 37.24 to 81.24 μg/g residue. Catechol, hydrocinnamic acid, and hydroquinone were present in the smallest quantities, ranging from 1.36 to 1.82 μg/g residue. The remainder of the compounds were intermediate in amount, ranging from 2.33 to 18.1 μg/g residue. [ABSTRACT FROM AUTHOR]

Sorghum bicolor is an allelopathic crop that reduces the yield of succeeding crops. We have assessed its effect on the germination, emergence, and seedling growth of Arachis hypogea sown in soil that had had a prior sorghum cropping. A. hypogea was sown on rows and interrows of a previous sorghum crop in 1997 and 1998 in Senegal. Seedling establishment (germination rate and seedling weight) was better between rows than on rows of the previous crop. The highest concentrations of phenolic compounds occurred in the rows in 1998, while contents of row and interrow soils were similar in 1997. Vanillic acid was the main component of the six chemicals found in 1997 soils, whereas the 1998 soil samples contained mainly p-hydroxybenzoic acid, p-hydroxybenzaldehyde, vanillic, and p-coumaric acids (10 phenolics identified). The germination of peanut seeds in water (control), soil water extracts, and mixtures of pure phenolics (equivalent to those in 1997 and 1998 soil samples) was tested. All extracts inhibited germination compared to controls, but there was no significant difference among treatments, i.e., the inhibition was the same for seeds in soil solutions and those in the respective phenolic mixtures. Similarly, there were no significant differences among the germination rates in soil water extracts of rows and interrows or in the pure phenolic mixtures of rows and interrows. We propose a geometrical sowing pattern for peanuts between the rows of the previous sorghum crop to escape the latter's "allelopathic heritage." [ABSTRACT FROM AUTHOR]

The effects of chlorogenic acid on larval survival and growth of the tobacco budworm Heliothis virescens and larval susceptibility to Helicoverpa zea nucleopolyhedrovirus (HzSNPV) were studied with an artificial diet and transgenic tobacco Nicotiana tabacum. Survival of neonates on over- or underexpressed phenylalanine ammonia-lyase (PAL) transgenic tobacco lines was positively correlated with the level of chlorogenic acid. Larval weight was not correlated with the level of chlorogenic acid in tobacco foliage. On the other hand, larval weights on artificial diet supplemented with chlorogenic acid were negatively correlated with chlorogenic acid concentration. Second instars treated on virus-treated (10 occlusion bodies/larva) tobacco leaf disks for 24 hr and then reared on tobacco leaves showed higher survival time and increased mortality on lines with increasing levels of chlorogenic acid. However, viral-related larval mortality on artificial diet was negatively correlated with dietary chlorogenic acid. These results illustrate the inadequacy of artificial diet studies in establishing causal relationships among plant chemistry, herbivores, and natural enemies. [ABSTRACT FROM AUTHOR]

Theory predicts that mammalian herbivores detoxify different classes of plant secondary compounds via separate metabolic pathways and that generalist herbivores maintain broad diet breadth to avoid overloading individual detoxification pathways. We tested the hypothesis that a generalist marsupial herbivore, the common brushtail possum, Trichosurus vulpecula, can maintain a higher intake of food when allowed to select from two diets containing different profiles of secondary compounds (phenolics and terpenes) than when given access to the diets individually. Diets consisted of a fruit and vegetable mash to which was added ground leaves of either Eucalyptus melliodora or E. radiata. E. melliodora and E. radiata differ in their concentrations and types of secondary compounds. Brushtail possums include these eucalypt species as part of their natural diet. We measured food consumption and detoxification metabolites of possums on these diets. Consistent with the hypothesis, animals presented with a choice of both diets consumed more food than animals given diets singly. One of the two indicators of detoxification, acid load in urine, differed significantly between diets while the other, glucuronic acid, did not. These results provide partial support for the hypothesis that diet breadth is governed by detoxification abilities. [ABSTRACT FROM AUTHOR]

When adults of Porcellio scaber fed on litter prior to an artificial diet containing 5% of commercially available tannic acid, 55% of the ingested galloylglucose esters was excreted unchanged, about 25% was hydrolyzed, and 20% was oxidized during the gut passage. After reducing the counts of microorganisms in the gut of P. scaber, the data obtained indicated an important role of ingested platable microorganisms in hydrolyzing gallotannins. Oxidation of phenolics appeared to be mainly due to the endosymbiotic bacteria of the hepatopancreas. Microbial counts in the hindgut were strongly reduced by ingested galloylglucose esters, while gallic acid in the diet (2%) reduced the number of palatable fungi and bacteria less strikingly, and increased the total number of the gut microbiota. Hepatopancreatic bacteria were only slightly affected by ingested tannic acid, since the hepatopancreas contained only few galloylglucose esters. This may be due to the permeability of the hindgut cuticle: the cuticle of the anterior hindgut was freely permeable to gallic acid, while it was nearly impermeable to larger polyphenols. The cuticle of the posterior hindgut was permeable to only about 4% of the gallic acid present in the hindgut lumen. The results are discussed with respect to potentially harmful effects of ingested hydrolyzable tannins and their digestion in Porcellio scaber. [ABSTRACT FROM AUTHOR]

Acacia confusa (an endemic species) and other introduced species, namely A. aulacocarpa, A. auricumiformis, A. cincinnata, A. crassicarpa, A. leptocarpa, A. margium, A. polystachya, and A. torfilis were evaluated for allelopathic potential. Among these, A. confusa is widely distributed on the hills and lowlands of Taiwn and often exhibits a unique pattern of weed exclusion under stands. Four study sites were selected. Field observations and measurements were carried out at sites that exhibited relatively pure stands of A. confusa. Although the diversity of understory species was comparatively higher in Acacia stands than in adjacent weedy sites, the total coverage and biomass of understory plants was significantly lower than in control sites. Aqueous extracts (0.5%, 1%, 2%, 3%, 4%, and 5%) of dry leaves and litter of Acacia confusa and other species collected from various sites and dates were bioassayed using lettuce, alfalfa, and Chinese cabbage to examine their phytotoxicity. Most extracts exhibited phytotoxicity even at a concentration as low as 0.5%. Inhibition of radicle growth of test plants varied with sampling sites and dates. Bioassay with 5% extracts or above produced more than 85% inhibition of test plants regardless of habitat. In addition, surface soils collected from the upper 20 cm layer of Acacia stands revealed significant inhibition as compared with adjacent grassland control soils. The most inhibitory compounds isolated from the ether fraction of aqueous extracts were identified as: ferulic, vanillic, caffeic, gallic, m-hydroxybenzoic, and m-hydroxyphenylacetic acids. Unidentified flavonoids were also found. Chromatographic bioassays of compounds isolated from both ethyl acetate and water fractions of methanolic extracts of Acacia leaves also showed significant phytotoxicity but none was found in the fractions of chloroform and hexane, suggesting the phytotoxic compounds present in Acacia plants are water soluble. [ABSTRACT FROM AUTHOR]

Young tomato plants ( Lycopersicon esculentum) grown in sand in a greenhouse and subjected to different fertilization regimes were used to test the effects of nitrogen availability on constitutive levels of phenolics and on constitutive and inducible activities of polyphenol oxidase and proteinase inhibitors. Theories that emphasize physiological constraints on the expression of phytochemicals predict an increase in levels of carbon-based allelochemicals under moderate nitrogen stress but predict, under the same conditions, an attenuation of chemical responses involving nitrogen-containing compounds such as proteinase inhibitors and polyphenol oxidase. We found that nitrogen availability had a strong effect on constitutive levels of phenolics; weaker effects on constitutive polyphenol oxidase activity, constitutive proteinase inhibitor activity, and inducible polyphenol oxidase activity; and no effect on inducible proteinase inhibitor activity. These results point to a need for the integration of theories that emphasize physiological influences on secondary metabolism with those that emphasize ecological influences on secondary metabolism and suggest that current theories of plant defense do not adequately account for enzymatic and proteinaceous defenses against arthropods. [ABSTRACT FROM AUTHOR]

In previous studies, we reported the existence of a high concentration of free glycine in the digestive juice of several Lepidoptera larvae, particularly in the digestive juice of species that feed on the privet tree, Ligustrum oblusifolium. The water extract of privet leaves showed very strong protein-denaturing activity and lysine-decreasing activity, which closely resembled activity of oxidized polyphenolics. Addition of 1% glycine to the extract could completely inhibit these activities. Free glycine may be secreted into the digestive juice by larvae as an adaptive mechanism for chemical defense against its host plants. The protein-denaturing compound in privet leaves is present in the cytosol or in the vacuoles of the leaf cells. The compound does not show protein-denaturing activity without oxidation, but when mixed with intact organelles under low osmotic conditions to give an osmotic shock, a very high protein-denaturing activity is produced. Our results suggest that the privet tree is endowed with a defense mechanism in which a stable compound in the cytosol or in the vacuoles is activated into a chemically active denaturant by an enzyme present in the organelles (including chloroplasts) after the leaves are eaten by insects and the organelles are broken by osmotic shock or by digestive mechanisms. Based upon HPLC and NMR data, we conclude that the denaturing compound is oleuropein, an o-dihydroxyphenolic compound. This compound makes up 3% of the wet weight of privet leaves. The protein-denaturing activity of purified oleuropein activated by the leaf enzyme is high enough to account for all the denaturing activity in a water extract of privet leaves. The denaturing reaction is completely inhibited by free glycine. Our results suggest that the protein-denaturing activity and lysine-decreasing activity of privet leaves are caused by oxidized polyphenolics, and that some insects secrete free glycine to counter the denaturing activity of oxidized phenolics. The chemical mechanism of counteraction by glycine is also considered. Free glycine in the midgut of insects probably protects proteins from denaturation by competing with proteins for oxidized phenolics. [ABSTRACT FROM AUTHOR]

Baculoviruses are arthropod-specific, dsDNA viruses primarily used to control lepidopteran pests. A limitation of the use of baculoviruses for pest control is that their efficacy is modifiable by host-plant chemicals. The levels of phenolic substrates and two foliar oxidative enzymes, peroxidase (POD) and polyphenol oxidase (PTO), were significant predictors of disease caused by a baculovirus in Heliothis virescens fed on either cotton or lettuce; POD was the more influential of the two enzymes. The higher the plant phenolase activity, the lower the percent mortality and the slower the insects died from viral infection. Whether a particular class of phenolic substrates was correlated with enhanced or attenuated baculoviral disease depended upon context, i.e., admixture. Diminution of viral efficacy by plant oxidative activity may compromise the compatibility of baculoviruses with other components of an integrated pest management system such as host plant resistance. [ABSTRACT FROM AUTHOR]

Monoterpenes, sesquiterpenes, and phenolic and flavonoid glycosides typical of the current year's foliage of Douglas fir ( Pseudotsuga menziesii) were bioassayed using agar diets to determine the effect of these compounds on natural and colony populations of western spruce budworm ( Choristoneura occidentalis). Several terpenes adversely affected budworm larval growth, supporting previous field and laboratory studies. However, larvae collected from a population in southeastern Idaho were significantly more tolerant of the monoterpenes than those from a Montana population. For the Montana population, agar diet studies showed that camphene, myrcene, terpinolene, bornyl acetate, and tricyclene adversely affected larval growth rate and pupal weight. For the Idaho population, agar diet studies showed that only terpinolene and bornyl acetate adversely affected larval growth and pupal weights. For both populations bornyl acetate was the most toxic, and this compound in addition to other monoterpenes represent defensive mechanisms in the current year's growth of Douglas fir. Sesquiterpene and phenolic-flavonoid glycoside fractions extracted from Douglas fir current year's growth also were bioassayed using agar diets. The sesquiterpene fraction showed a significant negative effect on budworm larval growth, but phenolics and flavonoid glycosides had no effect. Sesquiterpenes, in combination with tricyclene, camphene, myrcene, limonene, terpinolene, and the acetate fraction appear to represent an effective mixture of defensive compounds against the budworm. [ABSTRACT FROM AUTHOR]

The effects of the application of 0.25 or 1.0 mM p-coumaric acid, p-hydroxybenzoic acid, or quercetin on growth and colonization of clover ( Trifolium repens L. cv. Ladino) and sorghum ( Sorghum bicolor L.) roots by the arbuscular mycorrhizal (AM) fungus Glomus intraradices Schenck and Smith were studied. In general, soil application of these compounds at 0.25 mM stimulated plant growth and AM colonization, whereas at 1.0 mM these phenolics were inhibitory to both growth and colonization. Such effects were noted for both clover and sorghum. The results suggest that phenolic compounds, commonly found in many soils, influence the establishment of AM symbioses, and these compounds may have immediate effects on host growth. Studies involving these chemicals and their effects on mycorrhizal associations may provide new insights concerning the importance of the AM symbiosis in agricultural systems. These phenolic compounds may be used as potential soil amendments to enhance AM fungal colonization, and thus, exploit indigenous populations of AM fungi. [ABSTRACT FROM AUTHOR]