Constitutive Chemical Defences Research Articles

Trade-offs among leaf toughness, constitutive chemical defense, and growth rates in oaks are influenced by the level of leaf mass per area

Key messageAmong the variety of leaf defensive strategies to counteract herbivory attacks, the oak species analyzed in this study maximize investment in no more than one, with high-LMA oaks developing very tough leaves and low-LMA oaks favoring between high concentrations of condensed tannins or high growth rates.ContextPlants develop a variety of defense strategies to counteract herbivory attacks, from physical and chemical defenses to tolerance strategies. Tradeoffs between strategies have been widely assessed from a resource allocation perspective, but there is a need to consider eventual interactions among them.AimWe evaluate the among-species tradeoff between three main constitutive plant defense traits, while considering the leaf mass per area ratio (LMA) as a proxy of leaf construction investment on area basis.MethodsLeaf toughness measured as work of fracture, condensed tannins, and relative growth rate (RGR) were analyzed in a set of 19 Quercus L. species with contrasting LMA.ResultsMost species had low values either in two or in the three traits analyzed. Moreover, the highest values of work of fracture appeared in the species with high LMA; the highest values of condensed tannins were found in the species with the lowest LMA; and high values of RGR were measured in species with intermediate or lower values of LMA.ConclusionOaks showed a trade-off among leaf defensive strategies influenced by LMA. Oaks with high LMA developed very tough leaves while oaks with low LMA presented lower values of toughness but favored between one of the two other strategies.

The effects of provenance, climate, and chemical defense on the resistance of Pinus pinaster Aiton to Bursaphelenchus xylophilus (Steiner and Buhrer)

Key messageThe resistance of Pinus pinaster Aiton to pinewood nematode Bursaphelenchus xylophilus (Steiner and Buhrer) varied among populations from the Iberian Peninsula, with survival rates for inoculated seedlings ranging from 5 to 100%. These differences in resistance were paralleled by differences in some constitutive chemical defenses. Populations from the southeastern Iberian Peninsula displayed higher resistance than northern populations.ContextThe presence of the pinewood nematode (PWN), Bursaphelenchus xylophilus (Steiner and Buhrer), in Portugal threatens Mediterranean pine species such as Pinus pinaster Aiton.AimsWe have focused on assessing the resistance of P. pinaster populations to B. xylophilus, looking for any relationship between the PWN resistance and some constitutive chemical defenses and geoclimatic parameters.MethodsTwo-year-old seedlings from 32 provenances and two seed orchards were evaluated in an experiment of artificial inoculation following a randomized complete block design under greenhouse conditions. We measured growth-related traits, response to B. xylophilus inoculations, and constitutive chemical compounds in needles of the evaluated seedlings and compiled geoclimatic data for each population. Mixed models, nonparametric tests, correlations, and PCA were used to analyze the data.ResultsSurvival, wilting symptoms, morphological traits, and nematode density varied significantly among populations. Lower concentrations of constitutive polyphenols, lipid-soluble substances, and tannins were related to higher PWN resistance. Populations from the southeast of the Iberian Peninsula showed higher survival rates than those from further north. Additionally, we observed that populations to warm, dry climates showed higher resistance to B. xylophilus than populations originating from humid, temperate climates.ConclusionHigher susceptibility to PWN is related to lower growth traits, to lower levels of certain constitutive chemical compounds, and to adaptations to harsher climate.

Pathogen-triggered changes in plant development: Virulence strategies or host defense mechanism?

Plants, as sessile organisms, are constantly exposed to pathogens in nature. Plants rely on physical barriers, constitutive chemical defenses, and sophisticated inducible immunity to fight against pathogens. The output of these defense strategies is highly associated with host development and morphology. Successful pathogens utilize various virulence strategies to colonize, retrieve nutrients, and cause disease. In addition to the overall defense-growth balance, the host-pathogen interactions often lead to changes in the development of specific tissues/organs. In this review, we focus on recent advances in understanding the molecular mechanisms of pathogen-induced changes in plants' development. We discuss that changes in host development could be a target of pathogen virulence strategies or an active defense strategy of plants. Current and ongoing research about how pathogens shape plant development to increase their virulence and causes diseases could give us novel views on plant disease control.

Plant defense under Arctic light conditions: Can plants withstand invading pests?

Global warming is predicted to change the growth conditions for plants and crops in regions at high latitudes (>60° N), including the Arctic. This will be accompanied by alterations in the composition of natural plant and pest communities, as herbivorous arthropods will invade these regions as well. Interactions between previously non-overlapping species may occur and cause new challenges to herbivore attack. However, plants growing at high latitudes experience less herbivory compared to plants grown at lower latitudes. We hypothesize that this finding is due to a gradient of constitutive chemical defense towards the Northern regions. We further hypothesize that higher level of defensive compounds is mediated by higher level of the defense-related phytohormone jasmonate. Because its biosynthesis is light dependent, Arctic summer day light conditions can promote jasmonate accumulation and, hence, downstream physiological responses. A pilot study with bilberry (Vaccinium myrtillus) plants grown under different light regimes supports the hypothesis.

Susceptibility to Phytophthora cinnamomi of six holm oak (Quercus ilex) provenances: are results under controlled vs. natural conditions consistent?

Aim of study: Quercus forests are being affected by severe decline and mortality. The oak decline is associated with the soilborne pathogen Phytophthora cinnamomi (Pc), among others. This work aims to determine if Quercus ilex growing in Pc-infested soils show mortality differences according to their provenance in the field. It also evaluates whether the most tolerant provenances are those with the greatest constitutive chemical defences.
 Area of study: Acorns from six Spanish National Parks with natural presence of Q. ilex were collected for sowing in the greenhouse and later be planted on soils naturally infested by Pc in the surroundings of Plasencia, western Spain.
 Materials and methods: Seedlings were planted in four field plots located in two areas with oak decline: 153, 156, 157 and 155 plants in plot I, II, III and IV, respectively. The presence and infection of Pc was confirmed before their installation and during the experiment. Symptoms, regrowth, mortality and development was recorded for four years.
 Main results: There was a high mortality (56.0-80.5%) with differences among provenances. The most tolerant provenances in the field coincided with those identified under greenhouse conditions in a previous test. Provenances with higher constitutive condensed tannins better tolerate the pathogen under both conditions. In the southern provenances, some families with higher tolerance and, therefore, candidates for use in reforestation programs in areas infected by Pc, were identified.
 Research highlights: The restoration of Pc-affected areas would be possible through the use of Q. ilex plant material with high constitutive defences, more tolerant to the pathogen.

European oak chemical diversity - from ecotypes to herbivore resistance.

Climate change is increasing insect pressure and forcing plants to adapt. Although chemotypic differentiation and phenotypic plasticity in spatially separated tree populations are known for decades, understanding their importance in herbivory resistance across forests remains challenging. We studied four oak forest stands in Germany using nontarget metabolomics, elemental analysis, and chemometrics and mapped the leaf metabolome of herbivore-resistant (T-) and herbivore-susceptible (S-) European oaks (Quercus robur) to Tortrix viridana, an oak pest that causes severe forest defoliation. Among the detected metabolites, we identified reliable metabolic biomarkers to distinguish S- and T-oak trees. Chemotypic differentiation resulted in metabolic shifts of primary and secondary leaf metabolism. Across forests, T-oaks allocate resources towards constitutive chemical defense enriched of polyphenolic compounds, e.g. the flavonoids kaempferol, kaempferol and quercetin glucosides, while S-oaks towards growth-promoting substances such as carbohydrates and amino-acid derivatives. This extensive work across natural forests shows that oaks' resistance and susceptibility to herbivory are linked to growth-defense trade-offs of leaf metabolism. The discovery of biomarkers and the developed predictive model pave the way to understand Quercus robur's susceptibility to herbivore attack and to support forest management, contributing to the preservation of oak forests in Europe.

Constitutive and inducible chemical defences in nursery-grown and naturally regenerated Norway spruce (Picea abies) plants

Nursery-grown Norway spruce Picea abies seedlings are often heavily attacked by the pine weevil Hylobius abietis on clear-cuts the first years after planting. Because the seedlings are not resource-limited during the growing phase in the nursery they are expected to invest less in defence than naturally regenerated seedlings already present on the clear-cuts. The latter have had to cope with various environmental stressors that could make them invest more in defence. We tested if naturally regenerated plants have stronger chemical defences than nursery-grown plants. Nursery-grown plants were planted in-between naturally regenerated plants on fresh clear cuts, and phenolic and terpene compounds in the stem bark were measured after one growing season. To test both constitutive and inducible defences, plants were either wounded, painted with methyl jasmonate (MeJA) to induce defences, or given a combination of both treatments. Growth and pine weevil attacks of the plants were registered.Nursery-grown plants had higher total concentrations of phenolic compounds and lower concentrations of terpenes than naturally regenerated plants. These opposite responses were reflected in very different compound profiles in the two plant types. We suggest the differences between plant types to be results of differences in plant age, stress level, genetic origin or possibly a combination of these factors. Most compounds showed no response to wounding, MeJA-treatment or wounding and MeJA-treatment combined, but the terpenes 3-carene, eucalyptol, limonene and para-cymene had higher concentrations in MeJA-treated nursery-grown plants than in control plants. These compounds are known to be effective in conifer resistance against weevils and bark beetles. Overall, 27% of our 400 study plants had signs of pine weevil damage after 3 ½ months in the field. However, treatment or plant type had no significant effect on whether plants were attacked or not and this might have been a result of the relatively low overall level of attacks in this study. Further studies are needed to disentangle the importance of plant age, stress level, genetic origin and resource availability for chemical defence mechanisms of young Norway spruce plants, as strengthening the natural resistance of nursery plants may be increasingly important in a future with less pesticide use.

Geographical and within-population variation of constitutive chemical defences in a Mediterranean oak (Quercus ilex)

Aim of study: to assess whether constitutive levels of total phenols and condensed tannins acting as chemical defences in Quercus ilex vary across regions, populations and genotypes.Area of study: acorns from six Spanish regions with natural presence of Q. ilex were collected for later sowing in the greenhouse of the University of Extremadura at Plasencia, western Spain.Materials and methods: 1176 acorns from 12 populations (2 per region) were sown according to a nested design (6 regions x 2 populations/region x 7 genotypes/population). After five months, 588 emerged seedlings were harvested for phenol extraction from their leaves. Quantification of total phenols through the Folin-Ciocalteu method and condensed tannins by Porter's reagent method was carried out.Main results: total phenolics and condensed tannins correlated positively. Significant differences were found for the concentration of total phenolics and condensed tannins among regions and among genotypes, but not among populations within regions. The lowest levels of constitutive defences were found in the northern Iberian Peninsula. Also, the defensive phenolic content was significantly higher in regions with acidic soils. Heritability values (total phenols 0.37±0.08 and condensed tannins 0.48±0.36) were lower than those obtained of total tannins in a previous study.Research highlights: constitutive levels of heritable chemical defences in holm oak significantly depend on their geographical origin and genotype.Keywords: condensed tannins, genetic and latitudinal variability, heritability, total phenolics.

Canditate metabolites for ash dieback tolerance in Fraxinus excelsior.

Ash dieback, a forest epidemic caused by the invasive fungus Hymenoscyphus fraxineus, threatens ash trees throughout Europe. Within Fraxinus excelsior populations, a small proportion of genotypes show a low susceptibility to the pathogen. We compared the metabolomes from a cohort of low-susceptibility ash genotypes with a cohort of high-susceptibility ash genotypes. This revealed two significantly different chemotypes. A total of 64 candidate metabolites associated with reduced or increased susceptibility in the chemical families secoiridoids, coumarins, flavonoids, phenylethanoids, and lignans. Increased levels of two coumarins, fraxetin and esculetin, were strongly associated with reduced susceptibility to ash dieback. Both coumarins inhibited the growth of H. fraxineus in vitro when supplied at physiological concentrations, thereby validating their role as markers for low susceptibility to ash dieback. Similarly, fungal growth inhibition was observed when the methanolic bark extract of low-susceptibility ash genotypes was supplied. Our findings indicate the presence of constitutive chemical defense barriers against ash dieback in ash.

Growth and chemical responses of balsam fir saplings released from intense browsing pressure in the boreal forests of western Newfoundland, Canada

For ungulates, balsam fir (Abies balsamea (L.) Mill.) is thought to be a low quality forage due to high levels of indigestible fiber and secondary metabolites. Regardless, intensive browsing of fir saplings by overabundant moose (Alces alces L.) populations has led to the failure of fir-dominated forests in Newfoundland, Canada to regenerate following disturbance. The construction of moose exclosures in Gros Morne National Park (GMNP), western Newfoundland, presented an opportunity to compare levels of secondary metabolites (e.g. phenols and tannins), thought to act as anti-herbivore allelochemicals in balsam fir, under extremes of moose browsing pressure. We examined browsing damage to fir saplings and compared levels of carbon (C), nitrogen (N), total phenols and condensed tannins in current-year foliage outside and inside of eight moose exclosures. Outside of exclosures, 74% of fir saplings showed apical browsing while 97% were browsed laterally. At five exclosures, exposed saplings had significantly greater total phenol concentrations than inside exclosures. Such trends for condensed tannins were observed at only two exclosures, both locations having relatively high moose density and browsing damage. Unlike condensed tannins, total phenols were responsive to different patterns and levels of browsing. Foliar phenol concentration was negatively related to canopy closure, and to height and diameter of saplings, and positively related to the foliar C level. Foliar tannin level was unrelated to canopy or growth characteristics but positively related to the foliar N concentration. Moose browsing affected the defense chemistry of balsam fir; however, phenols and tannins responded differently, this likely being influenced by time of year. Foliar nitrogen levels were greater for inside saplings at only the two exclosures having highest moose density and browsing damage. Our data suggest that balsam fir employs constitutive chemical defense; however, this investment appears to be ineffective in deterring moose browsing.

Correlated Induction of Phytohormones and Glucosinolates Shapes Insect Herbivore Resistance of Cardamine Species Along Elevational Gradients.

Although the production of phytohormones has been commonly associated with production of plant defence and stress-related traits, few studies have simultaneously investigated this phenomenon across several plant species that grow along large-scale ecological gradients. To address these knowledge gaps, we performed a common garden experiment with six Cardamine species, which collectively encompass an elevational gradient of 2000m. We quantified constitutive and Pieris brassicae caterpillars-induced phytohormones and chemical defences in leaves. We found a correlated expression of phytohormone production and the subsequent induction of chemical defences, and this correlated expression reduced herbivore performance. Furthermore, we found that abiotic conditions associated with the optimal elevation range of each species influenced the production of phytohormones and chemical defences, as well as plant growth and productivity. In particular, we found that plant species adapted to milder abiotic conditions at low elevations grew faster, were more productive and produced greater levels of chemical defences. In contrast, plant species adapted to harsher abiotic conditions at high elevations tended to produce greater levels of defence-related oxylipins. Overall, these findings highlight the importance of disentangling the role of phytohormones in mediating plant adaptations to shifting biotic and abiotic conditions.

Oak genotype and phenolic compounds differently affect the performance of two insect herbivores with contrasting diet breadth.

Research on plant-herbivore interactions has long recognized that plant genetic variation plays a central role in driving insect abundance and herbivory, as well as in determining plant defense. However, how plant genes influence herbivore feeding performances, and which plant defensive traits mediate these effects, remain poorly understood. Here we investigated the feeding performances of two insect leaf chewers with contrasting diet breadth (the generalist Lymantria dispar L. and the specialist Thaumetopoea processionea L.) on different genotypes of pedunculate oak (Quercus robur L.) and tested the role of leaf phenolics. We used leaves from four clones of 30 Q. robur full-sibs grown in a common garden to estimate the performance of both herbivores in laboratory feeding trials and to quantify the concentration of constitutive chemical defences (phenolic compounds). We found that tree genetics influenced leaf consumption by T. processionea but not by L. dispar. However genetic variation among trees did not explain growth rate variation in either herbivore nor in leaf phenolics. Interestingly, all phenolic compounds displayed a positive relationship with L. dispar growth rate, and leaf consumption by both herbivores displayed a positive relationship with the concentrations of condensed tannins, suggesting that highly defended leaves could induce a compensatory feeding response. While genetic variation in oaks did not explain herbivore growth rate, we found positive genetic correlations between the two herbivores for leaf consumption and digestion. Overall, we found that oak genotype and phenolic compounds partly and independently contribute to variability in herbivore performance. We challenged the current view of plant-insect interaction and provided little support to the idea that the effect of plant genotype on associated organisms is driven by plant defences. Together, our results point to the existence of genetically determined resistance traits in oaks whose effects differ between herbivores and motivate further research on mechanisms governing oak-herbivore interactions.

Divergence in Glucosinolate Profiles between High- and Low-Elevation Populations of Arabidopsis halleri Correspond to Variation in Field Herbivory and Herbivore Behavioral Preferences.

Variation in local herbivore pressure along elevation gradients is predicted to drive variation in plant defense traits. Yet, the extent of intraspecific variation in defense investment along elevation gradients, and its effects on both herbivore preference and performance, remain relatively unexplored. Using populations of Arabidopsis halleri (Brassicaceae) occurring at different elevations in the Alps, we tested for associations between elevation, herbivore damage in the field, and constitutive chemical defense traits (glucosinolates) assayed under common-garden conditions. Additionally, we examined the feeding preferences and performance of a specialist herbivore, the butterfly Pieris brassicae, on plants from different elevations in the Alps. Although we found no effect of elevation on the overall levels of constitutive glucosinolates in leaves, relative amounts of indole glucosinolates increased significantly with elevation and were negatively correlated with herbivore damage in the field. In oviposition preference assays, P. brassicae females laid fewer eggs on plants from high-elevation populations, although larval performance was similar on populations from different elevations. Taken together, these results support the prediction that species distributed along elevation gradients exhibit genetic variation in chemical defenses, which can have consequences for interactions with herbivores in the field.

Inducibility of chemical defences in young oak trees is stronger in species with high elevational ranges.

Elevational gradients have been highly useful for understanding the underlying forces driving variation in plant traits and plant-insect herbivore interactions. A widely held view from these studies has been that greater herbivory under warmer and less variable climatic conditions found at low elevations has resulted in stronger herbivore selection on plant defences. However, this prediction has been called into question by conflicting empirical evidence, which could be explained by a number of causes such as an incomplete assessment of defensive strategies (ignoring other axes of defence such as defence inducibility) or unaccounted variation in abiotic factors along elevational clines. We conducted a greenhouse experiment testing for inter-specific variation in constitutive leaf chemical defences (phenolic compounds) and their inducibility in response to feeding by gypsy moth larvae (Lymantria dispar L., Lepidoptera) using saplings of 18 oak (Quercus, Fagaceae) species. These species vary in their elevational distribution and together span >2400 m in elevation, therefore allowing us to test for among-species elevational clines in defences based on the elevational range of each species. In addition, we further tested for elevational gradients in the correlated expression of constitutive defences and their inducibility and for associations between defences and climatic factors potentially underlying elevational gradients in defences. Our results showed that oak species with high elevational ranges exhibited a greater inducibility of phenolic compounds (hydrolysable tannins), but this gradient was not accounted for by climatic predictors. In contrast, constitutive defences and the correlated expression of constitutive phenolics and their inducibility did not exhibit elevational clines. Overall, this study builds towards a more robust and integrative understanding of how multivariate plant defensive phenotypes vary along ecological gradients and their underlying abiotic drivers.

Assessing the influence of biogeographical region and phylogenetic history on chemical defences and herbivory in Quercus species

Biogeographical factors and phylogenetic history are key determinants of inter-specific variation in plant defences. However, few studies have conducted broad-scale geographical comparisons of plant defences while controlling for phylogenetic relationships, and, in doing so, none have separated constitutive from induced defences. This gap has limited our understanding of how historical or large-scale processes mediate biogeographical patterns in plant defences since these may be contingent upon shared evolutionary history and phylogenetic constraints. We conducted a phylogenetically-controlled experiment testing for differences in constitutive leaf chemical defences and their inducibility between Palearctic and Nearctic oak species (Quercus, total 18 species). We induced defences in one-year old plants by inflicting damage by gypsy moth larvae (Lymantria dispar), estimated the amount of leaf area consumed, and quantified various groups of phenolic compounds. There was no detectable phylogenetic signal for constitutive or induced levels of most defensive traits except for constitutive condensed tannins, as well as no phylogenetic signal in leaf herbivory. We did, however, find marked differences in defence levels between oak species from each region: Palearctic species had higher levels of constitutive condensed tannins, but less constitutive lignins and less constitutive and induced hydrolysable tannins compared with Nearctic species. Additionally, Palearctic species had lower levels of leaf damage compared with Nearctic species. These differences in leaf damage, lignins and hydrolysable (but not condensed) tannins were lost after accounting for phylogeny, suggesting that geographical structuring of phylogenetic relationships mediated biogeographical differences in defences and herbivore resistance. Together, these findings suggest that historical processes and large-scale drivers have shaped differences in allocation to constitutive defences (and in turn resistance) between Palearctic and Nearctic oaks. Moreover, although evidence of phylogenetic conservatism in the studied traits is rather weak, shared evolutionary history appears to mediate some of these biogeographical patterns in allocation to chemical defences.

Ecological Importance of Cyanogenesis and Extrafloral Nectar in Invasive English Laurel,Prunus laurocerasus

Abstract English laurel (Rosaceae: Prunus laurocerasus L.) is an evergreen shrub to small tree that is native to Asia but widely used in landscaping in temperate zones. In the Pacific Northwest this plant has become an important invasive species. However, surprisingly little is known about its ecology—in particular, its chemical defenses and interaction with herbivores and organisms of higher trophic levels. In the present field study, we quantitatively measured cyanogenesis (a constitutive direct chemical defense) and secretion of extrafloral nectar (EFN; an inducible indirect defense), and analyzed the effects of these defenses on insect herbivores (black vine weevil [Otiorhynchus sulcatus]) and predators (sugar ants [Tapinoma sessile]). To induce EFN production, English laurel leaves were mechanically damaged at different intensities and in a way to mimic feeding damage by the black vine weevil, which represents the only observed insect herbivore feeding on this plant at our study site near Portland, O...

Defensive Traits in Young Pine Trees Cluster into Two Divergent Syndromes Related to Early Growth Rate.

The combination of defensive traits leads to the evolution of ‘plant defense syndromes’ which should provide better protection against herbivores than individual traits on their own. Defense syndromes can be generally driven by plant phylogeny and/or biotic and abiotic factors. However, we lack a solid understanding of (i) the relative importance of shared evolution vs. convergence due to similar ecological conditions and (ii) the role of induced defense strategies in shaping defense syndromes. We investigate the relative roles of evolutionary and ecological factors shaping the deployment of pine defense syndromes including multiple constitutive and induced chemical defense traits. We performed a greenhouse experiment with seedlings of eighteen species of Pinaceae family, and measured plant growth rate, constitutive chemical defenses and their inducibility. Plant growth rate, but not phylogenetic relatedness, determined the deployment of two divergent syndromes. Slow-growing pine species living in harsh environments where tissue replacement is costly allocated more to constitutive defenses (energetically more costly to produce than induced). In contrast, fast-growing species living in resource-rich habitats had greater inducibility of their defenses, consistent with the theory of constitutive-induced defense trade-offs. This study contributes to a better understanding of evolutionary and ecological factors driving the deployment of defense syndromes.

In the search for new secondary metabolites with biopesticidal properties

Secondary metabolites are involved in diverse functions in plants, including defense and protective processes. Information concerning the biosynthesis of secondary metabolites in plants points at a constitutive or induced chemical defense, generated for protection against a variety of phytopathogenic attacks. Our phytochemical studies are aimed at finding biopesticides of botanical origin. Some plant taxa of American distribution are toxic to selected insects, fungi and bacterial strains, and their effect has been associated with the presence of phenolics, phenylpropanoids and terpenes. We have isolated some diterpenes, triterpenes, sesquiterpene lactones, flavonoids, and phenylpropanoids from members of the plant families Araucariaceae, Asteraceae, Calceolariaceae, Celastraceae, and Rhamnaceae. In addition, we have identified a number of chemical derivatives of these compound classes from the plants. A major finding indicates that compounds or their derivatives that possess antioxidant, antifungal, insect growth regulator or insecticidal activity and enzymatic inhibitors are natural compounds. Insecticidal activities were assayed against strains of lepidopteran, dipteran, and coleopteran insect pests that affect many crops. Antifungal and antibacterial activities were assayed against phytopathogenic species of filamentous fungi and bacterial strains that are pests on many crops. Our results indicate that the plant-derived compounds obtained from the abovementioned plants have excellent insect growth regulatory activity and a good potency as antifungal agents. However, little is known about the effects of these natural compounds and their derivatives on insect pests. The natural compounds that we have isolated represent a valuable resource for future studies of plant chemical defense and the role of these substances in chemical ecology.

Chemical constituents and biological activities of South American Rhamnaceae

Secondary metabolites have diverse functions into plants. These functions are products of the coevolution which result in synthesis of constitutive and/or induced chemical defense generated for protection against to different phytopathogenic attack. Many phytochemical studies are biodirected with the aim of finding biopesticides of botanical origins. Some taxa of Americas such as Rhamnaceae family are toxic to insects, fungi and several bacteria strains, and these effects has been associated with the presence of alkaloids, phenolics and terpenes. The natural compounds that have been isolated represent a valuable resource for future studies of plant chemical defense and the role of these substances in chemical ecology. Here are show recent advances in the phytochemistry and biological activities of selected members of Rhamnaceae from Latin-America.

Simple Growth Patterns Can Create Complex Trajectories for the Ontogeny of Constitutive Chemical Defences in Seaweeds

All of the theory and most of the data on the ecology and evolution of chemical defences derive from terrestrial plants, which have considerable capacity for internal movement of resources. In contrast, most macroalgae – seaweeds – have no or very limited capacity for resource translocation, meaning that trade-offs between growth and defence, for example, should be localised rather than systemic. This may change the predictions of chemical defence theories for seaweeds. We developed a model that mimicked the simple growth pattern of the red seaweed Asparagopsis armata which is composed of repeating clusters of somatic cells and cells which contain deterrent secondary chemicals (gland cells). To do this we created a distinct growth curve for the somatic cells and another for the gland cells using empirical data. The somatic growth function was linked to the growth function for defence via differential equations modelling, which effectively generated a trade-off between growth and defence as these neighbouring cells develop. By treating growth and defence as separate functions we were also able to model a trade-off in growth of 2–3% under most circumstances. However, we found contrasting evidence for this trade-off in the empirical relationships between growth and defence, depending on the light level under which the alga was cultured. After developing a model that incorporated both branching and cell division rates, we formally demonstrated that positive correlations between growth and defence are predicted in many circumstances and also that allocation costs, if they exist, will be constrained by the intrinsic growth patterns of the seaweed. Growth patterns could therefore explain contrasting evidence for cost of constitutive chemical defence in many studies, highlighting the need to consider the fundamental biology and ontogeny of organisms when assessing the allocation theories for defence.