Concentrations Of Plant Secondary Metabolites Research Articles

Does spatial variation in insect herbivory match variations in plant quality? A meta-analysis.

Variation in herbivore pressure has often been predicted from patterns in plant traits considered as antiherbivore defences. Here, we tested whether spatial variation in field insect herbivory is associated with the variation in plant quality by conducting a meta-analysis of 223 correlation coefficients between herbivory levels and the expression of selected plant traits. We found no overall correlation between herbivory and either concentrations of plant secondary metabolites or values of physical leaf traits. This result was due to both the large number of low correlations and the opposing directions of high correlations in individual studies. Field herbivory demonstrated a significant association only with nitrogen: herbivore pressure increased with an increase in nitrogen concentration in plant tissues. Thus, our meta-analysis does not support either theoretical prediction, i.e., that plants possess high antiherbivore defences in localities with high herbivore pressure or that herbivory is low in localities where plant defences are high. We conclude that information about putative plant defences is insufficient to predict plant losses to insects in field conditions and that the only bottom-up factor shaping spatial variation in insect herbivory is plant nutritive value. Our findings stress the need to improve a theory linking plant putative defences and herbivory.

Concentration-dependent effect of plant secondary metabolites on bacterial and fungal microbiomes in caterpillar guts.

The caterpillar gut is an excellent model system for studying host-microbiome interactions, as it represents an extreme environment for microbial life that usually has low diversity and considerable variability in community composition. Our study design combines feeding caterpillars on a natural and artificial diet with controlled levels of plant secondary metabolites and uses metabarcoding and quantitative PCR to simultaneously profile bacterial and fungal assemblages, which has never been performed. Moreover, we focus on multiple caterpillar species and consider diet breadth. Contrary to many previous studies, our study suggested the functional importance of certain microbial taxa, especially bacteria, and confirmed the previously proposed lower importance of fungi for caterpillar holobiont. Our study revealed the lack of differences between monophagous and polyphagous species in the responses of microbial assemblages to plant secondary metabolites, suggesting the limited role of the microbiome in the plasticity of the herbivore diet.

51 Use of Plant Secondary Metabolites and Impact on Beef Cattle Production

Abstract The objective of the presentation is to describe the beneficial roles of plant secondary metabolites in beef production with special attention to mode of delivery. Plant and fungal secondary metabolites are responsible for many well-known problems in beef cattle production, such as acute or chronic intoxication. Fescue toxicosis is an example of the latter. However, there are also beneficial effects of secondary metabolites. Plant extracts (e.g., essential oils) that are rich in phenolic compounds and other secondary metabolites have been explored as alternatives to veterinary prophylactic antibiotics, growth promoting antibiotics, and enteric methane suppressants. An example of extracted botanicals is beta-acid from the hops plant. Beta-acid could be considered a model rumen-active phytochemical because of a similar mechanism of action to ionophores, which allows direct comparison with well-studied, microbially produced drugs. The route of delivery of extracted phytochemicals can also be similar to that of other commercial products. In contrast, other beneficial plant secondary metabolites can be delivered without extraction. Anthelmintic forages have been extensively studied for use in small ruminants. These forages contain concentrations of plant secondary metabolites, such as condensed tannins or sesquiterpene lactones, that reduce parasite load without processing the plant. Similarly, health and production benefits were shown in cattle consuming isoflavones by grazing forage legumes (red clover) or by supplementation with hay or other minimally processed legumes (red clover, white clover, soybean meal). The term, functional feeds, borrows from the idea of functional foods in human nutrition, this is, foods that have a benefit traditionally ascribed to medicine. Functional feeds may have advantages over commercially extracted and processed phytochemicals, not the least of which is the ability of cattlemen to produce their own feed. However, to fully take advantage of beneficial forage plant secondary metabolites more research is needed in animal nutrition, plant sciences, and chemical analysis.

Optimal chemical defence allocation in roots: where, why and how?

AbstractPlants produce a range of volatile and non-volatile plant secondary metabolites (PSMs) to increase their resistance to biotic threats. The optimal defence allocation theory (ODT) states that the most valuable and vulnerable plant organs should be best defended against herbivory and therefore contain high concentrations of PSMs. However, the production of PSMs can come with metabolic and ecological costs and should be adjusted to the predictability and nature of biotic interactions to minimise interference with the ecological functions of the tissue. The ODT has recently been extended to explain PSM allocation patterns over root organs. Recent research has revealed that valuable but vulnerable root classes, such as taproots or adventitious roots, indeed have higher levels of anti-herbivory PSMs than lateral or fine roots. In this perspective, we analyse how interactions with soil organisms, including insect herbivores and microorganisms, may shape PSM allocation patterns in roots. We thereby focus on the Brassicaceae family and the glucosinolate-myrosinase defence system, but also highlight relevant studies in other species. We summarise the state-of-the-art knowledge of GSL distribution patterns over the plant body, discuss potential drivers of PSM allocation and discuss which mechanisms might regulate constitutive and induced PSM allocation patterns. Finally, we argue that implementing microbial interactions into ODT will improve our understanding of the eco-evolutionary drivers of plant–insect interactions.

Toxicity, Antioxidant Activity, and Phytochemicals of Basil (Ocimum basilicum L.) Leaves Cultivated in Southern Punjab, Pakistan.

Basil (Ocimum basilicum L.) is one of the most common aromatic herbs, a rich source of bioactive compounds, and is used extensively to add aroma and flavor to food. The leaves, both in fresh and dried form, are used as a culinary ingredient in different cultures. O. basilicum is also famous for its therapeutic potential and preservation effects. The present study investigated the cytotoxicity of basil at three different growth stages (GS), i.e., GS-1 (58 days of growth), GS-2 (69 days of growth), and GS-3 (93 days of growth) using the brine shrimp lethality assay. The results revealed that cytotoxicity was influenced by GS and the concentration of extracts. Aqueous extracts of basil at a concentration of 10 to 1000 µg/mL did not show notable toxicity. The lowest mortality rate, i.e., 8.9%, was recorded for GS-2 at the highest tested dose of basil extracts. The mortality rate at GS-1, GS-2, and GS-3 was found to be 26.7 ± 3.34%, 8.91 ± 0.10%, and 16.7 ± 0.34%, respectively, at 1000 µg/mL. GS-2 basil powder with the lowest toxicological risk was extracted with different solvents, viz., n-hexane, dichloromethane, ethanol, and water. The highest concentration of plant secondary metabolites including total phenolic acid, flavonoids, and tannin content was observed in ethanol extracts. Ethanol extracts also exhibited the highest antioxidant activity in DPPH, FRAP and H2O2 assays. LC-ESI-MS/MS analysis presented ethanol extracts of basil as a promising source of known health-promoting and therapeutic compounds such as rosmarinic acid, ellagic acid, catechin, liquiritigenin, and umbelliferone. The results suggest basil, a culinary ingredient, as a potential source of bioactive compounds which may offer an array of health promoting and therapeutic properties.

The nutritional condition of moose co‐varies with climate, but not with density, predation risk or diet composition

A fundamental question about the ecology of herbivore populations pertains to the relative influence of biotic and abiotic processes on nutritional condition. Nutritional condition is influenced in important, yet poorly understood, ways by plant secondary metabolites (PSMs) which can adversely affect a herbivore's physiology and energetics. Here we assess the relative influence of various abiotic (weather) and biotic (intraspecific competition, predation risk and diet composition) factors on indicators of nutritional condition and the energetic costs of detoxifying PSMs for the moose population in Isle Royale National Park (USA). Specifically, we observed interannual variation in the ratio of urea nitrogen to creatinine (UN:C), an indicator of nutritional restriction, over 29 years and the ratio of glucuronic acid to creatinine (GA:C), an indicator of energetic investment in detoxifying PSMs, over 19‐years. Both UN:C and GA:C were measured in samples of urine‐soaked snow. Most importantly, climatic factors explained 66% of the interannual variation in UN:C, with moose being more nutritionally stressed during winters with deep snow and during winters that followed warm summers. None of the biotic factors (density, predation, diet composition) were useful predictors of UN:C or GA:C. The absence of a relationship between diet composition and either UN:C or GA:C suggests that the nutritional ecology of wild herbivores is probably complicated by fine‐scale variation in protein content and concentrations of PSMs amongst plants of the same species. UN:C increased with GA:C at both the individual and population‐level. That result is consistent with detoxification being energetically costly, such that it impairs nutritional condition and also highlights how spatio‐temporal variation in the intake and detoxification of PSMs may influence population dynamics. Lastly, because we observed interannual variation in nutritional condition over three decades and detoxification over two decades these findings are relevant to concerns about how herbivore populations respond to climate change.

Seasonal variation in defence compounds: A case study on pyrrolizidine alkaloids of clones of Jacobaea vulgaris, Jacobaea aquatica and their hybrids

Concentration of plant secondary metabolites (SMs) show seasonal variations. However, it is still not well understood how these abiotic and biotic factors influence the seasonal variations of SMs. In addition, it is of interest to know if and how SMs are reallocated to the different plant organs, in particular whether SMs are reallocated to the remaining tissues when biomass is lost, e.g., during winter. Here we used Jacobaea vulgaris, Jacobaea aquatica, two F1 and four F2 hybrids that differed in their pyrrolizidine alkaloids (PAs) bouquet as a study system. A series of clones of these genotypes were investigated during their vegetative stage spanning 14 months in a semi-natural environment. We found that the total PA concentration in roots and shoots showed a gradual increase until the spring of the second year, whereafter it dropped substantially in shoots. The variation in PA composition due to seasonal changes was significant but relatively small. Senecionine-like PAs were the dominant PAs in roots, while jacobine-/erucifoline-like PAs were dominant in shoots. The variation of PA concentration was significantly correlated with temperature, day length, and plant age. A correlation analysis showed that PAs were not reallocated when biomass was lost in winter. Overall, our study showed that PA composition of each genotype changed over seasons in a different manner but seasonal variation did not overrule the differences in PA composition among genotypes.

Seasonal Variation in the Content of Condensed Tannins in Leaves of Xylopia emarginata Mart. (Annonaceae) in Response to Phenology and Climate

Variations in the concentrations of plant secondary metabolites can occur due to the phenological stages of the plants, combined with environmental variations. Plants rich in tannins are used in folk medicine for different purposes. Xylopia emarginata Mart. (Anonaceae)-“Pindaíba” has been used to treat skin edema, bronchitis and malaria. We evaluated variations in condensed tannin (CTs) contents in relation to phenological variables in leaves of Xylopia emarginata during one year. The study took place in a Vereda in northern Minas Gerais State, Brazil. Monthly phenological observations as well as quantifications of the contents of condensed leaf tannins in ethanol and aqueous extracts were performed. The production of X. emarginata leaves occurred throughout the study, with greater budding and leaf fall in the dry season. Phenological observations were correlated with CT levels and climatic data of precipitation and temperature. There was a significant correlation (p < 0.05) between fruiting and CT levels in the extracts, which were higher during the dry season, 13.2% in the ethanol extract and 7.8% in the aqueous extract.

​Insect Plant Interaction with Reference to Secondary Metabolites: A Review

Plant and herbivorous insect share a contradictory but everlasting relationship. To cope with the herbivores, plant invested its energy in the production of various defensive chemicals which are known as plant secondary metabolites (PSMs). During coevolution with plants, insects also adapted themselves to counter plant defensive mechanisms. The secreted saliva and ovipositional fluids of insects induce the production of secondary metabolites in plants. Plants also produce compounds constitutively in the tissues that are susceptible to insect attack. These compounds reduce insect growth and development of insects through interfering with the developmental phases, acting as feeding deterrent, reducing nutritive value, affecting protein digestion and the production of substances toxic to them. On the contrary, insect’s adaptations to PSMs include the detoxification of plant toxins, conversion of the toxic compounds into conducible form for its growth and development, development of feeding choice based on the concentration of PSMs, quicker absorption and elimination as feces and obtaining the help of symbiotic intestinal microorganism to inactivate toxic materials. Furthermore, insects also utilize PSMs as chemical cues mediated through their chemoreceptive systems. The selection of host plants by monophagous insect is sometimes concentrated on the production of particular PSMs. Secondary metabolites also act as attractant to insect pollinators by exhibiting distinctive odors. Insects also store toxic PSMs which are used by them against their predators and in giving protection to eggs. However, this intrinsic capability of plants to produce defensive chemicals in response to insect attack should be explored to a wide extent to optimize the performance of PSMs.

Plant silicon application alters leaf alkaloid concentrations and impacts parasitoids more adversely than their aphid hosts.

Grasses accumulate large amounts of silicon (Si) which acts as a highly effective physical defence against insect herbivory, however recent evidence shows that Si supplementation also modifies plant secondary metabolite concetrations. Changes in plant secondary metabolites concentrations can have cascading effects on higher trophic levels, such as parasitoids, as they are dependent on the host herbivore for growth and development. However, relatively little is known about how Si application affects higher trophic levels. We examined the effects of Si addition on alkaloid content in leaves of Phalaris aquatica (Poaceae) and the effect on interactions between an aphid (Rhopalosiphum padi) and its parasitoid (Aphidius colemani). Si supplementation had no effect on aphid abundance or parasitism rate. Adult aphids, aphid mummies (parasitised aphids) and the emergent parasitoids were, however, significantly smaller on Si+ plants. Parasitoid traits (size and emergence) were correlated with aphid mummy size. Si addition reduced parasitoid emergence rate and size due to reduced host mummy size, in addition, significantly fewer females emerged from mummies on Si+ plants. Aphid infestation significantly altered alkaloids concentrations, reducing gramine by 80% while increasing tryptamine by 91% in Si- plants. Si addition reduced aphid-induced tryptamine concentrations by 64% and increased 5-MeO-tryptamine by over 800% in control and 142% in aphid infested plants. Our results show that while Si addition has modest impacts on the herbivore, it significantly alters secondary metabolites and has stronger effects on the higher trophic level through changes in the quality of the parasitised host.

Impact of genome duplication on secondary metabolite composition in non-cultivated species: a systematic meta-analysis.

Whole-genome duplication is known to influence ecological interactions and plant physiology; however, despite abundant case studies, much is still unknown about the typical impact of genome duplication on plant secondary metabolites (PSMs). In this study, we assessed the impact of polyploidy events on PSM characteristics in non-cultivated plants. We conducted a systematic review and meta-analysis to compare composition and concentration of PSMs among closely related plant species or species complexes differing in ploidy level. We assessed 53 studies that focus on PSMs among multiple cytotypes, of which only 14 studies compared concentration quantitatively among cytotypes. We found that whole-genome duplication can have a significant effect on PSM concentration; however, these effects are highly inconsistent. Overall, there was no consistent effect of whole-genome duplication on PSM concentrations or profiles.

Inducibility of Plant Secondary Metabolites in the Stem Predicts Genetic Variation in Resistance Against a Key Insect Herbivore in Maritime Pine.

Resistance to herbivores and pathogens is considered a key plant trait with strong adaptive value in trees, usually involving high concentrations of a diverse array of plant secondary metabolites (PSM). Intraspecific genetic variation and plasticity of PSM are widely known. However, their ecology and evolution are unclear, and even the implication of PSM as traits that provide direct effective resistance against herbivores is currently questioned. We used control and methyl jasmonate (MJ) induced clonal copies of genotypes within families from ten populations of the main distribution range of maritime pine to exhaustively characterize the constitutive and induced profile and concentration of PSM in the stem phloem, and to measure insect herbivory damage as a proxy of resistance. Then, we explored whether genetic variation in resistance to herbivory may be predicted by the constitutive concentration of PSM, and the role of its inducibility to predict the increase in resistance once the plant is induced. We found large and structured genetic variation among populations but not between families within populations in resistance to herbivory. The MJ-induction treatment strongly increased resistance to the weevil in the species, and the genetic variation in the inducibility of resistance was significantly structured among populations, with greater inducibility in the Atlantic populations. Genetic variation in resistance was largely explained by the multivariate concentration and profile of PSM at the genotypic level, rather than by bivariate correlations with individual PSM, after accounting for genetic relatedness among genotypes. While the constitutive concentration of the PSM blend did not show a clear pattern of resistance to herbivory, specific changes in the chemical profile and the increase in concentration of the PSM blend after MJ induction were related to increased resistance. To date, this is the first example of a comprehensive and rigorous approach in which inducibility of PSM in trees and its implication in resistance was analyzed excluding spurious associations due to genetic relatedness, often overlooked in intraspecific studies. Here we provide evidences that multivariate analyses of PSM, rather than bivariate correlations, provide more realistic information about the potentially causal relationships between PSM and resistance to herbivory in pine trees.

Preferences of Specialist and Generalist Mammalian Herbivores for Mixtures Versus Individual Plant Secondary Metabolites.

Herbivores that forage on chemically defended plants consume complex mixtures of plant secondary metabolites (PSMs). However, the mechanisms by which herbivores tolerate mixtures of PSMs are relatively poorly understood. As such, it remains difficult to predict how PSMs, singly or as complex mixtures, influence diet selection by herbivores. Although relative rates of detoxification of PSMs have been used to explain tolerance of PSMs by dietary specialist herbivores, few studies have used the rate of detoxification of individual PSMs to understand dietary preferences of individual herbivores for individual versus mixtures of PSMs. We coupled in vivo experiments using captive feeding trials with in vitro experiments using enzymatic detoxification assays to evaluate the dietary preferences and detoxification capacities of pygmy rabbits (Brachylagus idahoensis), dietary specialists on sagebrush (Artemisia spp.), and mountain cottontails (Sylvilagus nuttallii), dietary generalists. We compared preference for five single PSMs in sagebrush compared to a mixture containing those same five PSMs. We hypothesized that relative preference for individual PSMs would coincide with faster detoxification capacity for those PSMs by specialists and generalists. Pygmy rabbits generally showed little preference among individual PSMs compared to mixed PSMs, whereas mountain cottontails exhibited stronger preferences. Pygmy rabbits had faster detoxification capacities for all PSMs and consumed higher concentrations of individual PSMs versus a mixture than cottontails. However, detoxification capacity for an individual PSM did not generally coincide with preferences or avoidance of individual PSMs by either species. Cottontails avoided, but pygmy rabbits preferred, camphor, the PSM with the slowest detoxification rate by both species. Both species avoided β-pinene despite it having one of the fastest detoxification rate. Taken together our in vivo and in vitro results add to existing evidence that detoxification capacity is higher in dietary specialist than generalist herbivores. However, results also suggest that alternative mechanisms such as absorption and the pharmacological action of individual ormixtures of PSMs may play a role in determining preference of PSMs within herbivore species.

The effect of maturity on concentration and biological activity of protein precipitating polyphenolics in ground juniper is dependent upon species

Nutritional characteristics of Juniperus species are now well known and suitability as an abundant, low-cost feedstuff for ruminant animal production is a possibility. Juniperus species produce plant secondary metabolites including condensed tannins (CT) and volatile oils. Maturity of Juniperus species has been shown to affect the concentration of plant secondary metabolites produced. The objectives of this study were to determine the effects of Juniperus species (Juniperus ashei, J. monosperma, J. pinchotii and J. virginiana) and maturity on protein precipitating polyphenolic (PPP) compounds, their biological activity and relatedness of these effects to rumen digestibility characteristics. We found a species by maturity interaction for PPP (P < 0.001) and for the amount of protein bound (PB; P < 0.001) by PPP. Protein precipitable phenolic concentrations were greater (P < 0.001) for all species in the immature stage as compared to the mature stage except for J. virginiana, for which PPP were unaffected by maturity. The PB by J. pinchotii and J. monosperma was greater (P < 0.001) in the immature stage as compared to the mature stage whereas that of J. ashei and J. virginiana remained unchanged by stage of maturity. Linear regression within species and maturity of 48-h IVTDMD and total gas production on PPP suggested a positive correlation exists for immature J. virginiana (R2 = 0.71) and mature J. pinchotii (R2 = 0.68) for IVTDMD, and J. virginiana (R2 = 0.81) for total gas production. There was no relationship for PB within species and maturity of juniper and 48-h IVTDMD or total gas production, suggesting that biological activity of protein binding by PPP is unrelated to overall in vitro digestion of Juniperus species. The effect of maturity on concentration and biological activity of PPP in juniper is dependent upon species.

Effects of long-term nitrogen and phosphorus addition on plant defence compounds in a freshwater wetland

Prominent theories of plant defence have predicted that alleviating nutrient limitation will result in decreased production of defence compounds. Yet effects of nutrient addition on plant defence compounds have been found to vary, and research on plant resource allocation in different organs in response to long-term nutrient addition is limited. In this study, we aimed to elucidate effects of 12-yr nitrogen (N) addition and 10-yr phosphorus (P) addition on plant defence compounds (total polyphenols, condensed tannins, cellulose and lignin) in both leaves and stems of dominant specie Glyceria spiculosa in a freshwater wetland in the Sanjiang Plain, Northeast China. Both N addition and P addition reduced the production of defence compounds in plant leaves, but increased the production of lignin in the stems. Notably, the concentrations of plant secondary metabolites closely correlated with the plant C:N:P stoichiometric ratios. The results suggest that long-term nutrient addition can alter plant carbon allocation to C-based defence compounds, and thus potentially exert influences on nutrient cycling and ecological processes in freshwater wetlands.

Effects of Developmental Stages and Reduced UVB and Low UV Conditions on Plant Secondary Metabolite Profiles in Pak Choi (Brassica rapa subsp. chinensis).

Pak choi (Brassica rapa subsp. chinensis) is rich in secondary metabolites and contains numerous antioxidants, including flavonoids; hydroxycinnamic acids; carotenoids; chlorophylls; and glucosinolates, which can be hydrolyzed to epithionitriles, nitriles, or isothiocyanates. Here, we investigate the effect of reduced exposure to ultraviolet B (UVB) and UV (UVA and UVB) light at four different developmental stages of pak choi. We found that both the plant morphology and secondary metabolite profiles were affected by reduced exposure to UVB and UV, depending on the plant's developmental stage. In detail, mature 15- and 30-leaf plants had higher concentrations of flavonoids, hydroxycinnamic acids, carotenoids, and chlorophylls, whereas sprouts contained high concentrations of glucosinolates and their hydrolysis products. Dry weights and leaf areas increased as a result of reduced UVB and low UV. For the flavonoids and hydroxycinnamic acids in 30-leaf plants, less complex compounds were favored, for example, sinapic acid acylated kaempferol triglycoside instead of the corresponding tetraglycoside. Moreover, also in 30-leaf plants, zeaxanthin, a carotenoid linked to protection during photosynthesis, was increased under low UV conditions. Interestingly, most glucosinolates were not affected by reduced UVB and low UV conditions. However, this study underlines the importance of 4-(methylsulfinyl)butyl glucosinolate in response to UVA and UVB exposure. Further, reduced UVB and low UV conditions resulted in higher concentrations of glucosinolate-derived nitriles. In conclusion, exposure to low doses of UVB and UV from the early to late developmental stages did not result in overall lower concentrations of plant secondary metabolites.

Intraspecific Variation in Nutritional Composition Affects the Leaf Age Preferences of a Mammalian Herbivore.

Ecologists have long been interested in how the nutritional composition of leaves changes as they age, and whether this affects herbivore feeding preferences. As a consequence, the literature abounds with reports that younger leaves contain higher concentrations of nitrogen and plant secondary metabolites (PSMs) than do older leaves. Most of these studies, however, base their conclusions on average values that often mean little to herbivores. We examined this issue in the well-studied marsupial-eucalypt system, using Eucalyptus melliodora and captive common brushtail possums (Trichosurus vulpecula) offered branches from individual trees containing both young and mature leaves. Like many plants, the concentrations of N and PSMs differed among individual E. melliodora. Although young leaves were, on average, "better defended" by the PSM sideroxylonal than were mature leaves, some trees produced leaves that were relatively undefended at both ages. In response, possums chose different proportions of young and mature leaves depending on the chemistry of the individual tree. Possums did not always prefer leaves with lower concentrations of sideroxylonal (mature leaves) or those with higher concentrations of available N (young leaves). Instead, the sideroxylonal concentration of young leaves dictated their choice: possums preferred young leaves with low sideroxylonal concentrations, but not with high concentrations. By skewing their feeding toward trees producing young leaves with low concentrations of PSMs, possums may influence plant fitness. Researchers will detect these potentially important interactions only if they are aware that measuring variation among plants discloses more information than do average relationships.

Ornamental Asteraceae Species as New Sources of Secondary Metabolites

Abstract: Objective: This paper presents the results regarding the morphological characters, the content in total phenols, the metabolites profile and the antioxidant activity of outdoor cultivated Rudbeckia hirta var. Goldilocks and Tagetes erecta plants. Material and Methods: The plant material was represented by flower buds and fully bloomed inflorescences taken from Rudbeckia hirta var. Goldilocks and Tagetes erecta. Morphological assessment was carried using microscopy, while chemical assessment used thin layer chromatography (TLC) and UHPLC methods. The total phenolic content was established with Folin- Ciocalteu method. The antioxidant activity was evaluated with DPPH radical scavenging tests. The secondary metabolites were evaluated in two different nutritional statuses. Results: The results indicated that the studied ornamental Asteraceae species represent rich sources of phenols. However, the fertilization lowers the plant’s biosynthetic capacity for polyphenols for both Rudbeckia and Tagetes flowers. Thus, by fertilizing, the flowers of Tagetes lose components such as polyphenolic acids, modifying their spectrum. Regarding the antioxidant activity, Tagetes erecta showed a promising activity against free radicals. Conclusion: The concentration of plant secondary metabolites was found to be influenced by the nutritional status. Both species represent a good source for secondary metabolites, but their biological potential remains to be established. Key words: Rudbeckia, Tagetes, Secondary metabolites, Ornamental plants, Antioxidant activity.

Phylogeny Explains Variation in The Root Chemistry of Eucalyptus Species.

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.

Effect of light intensity and wavelength on concentration of plant secondary metabolites in the leaves of Flourensia cernua

Flourensia cernua (tarbush) is a shrub that has encroached into grasslands in many areas of the northern Chihuahuan Desert and contains high levels of carbon-based secondary compounds. Concentrations of secondary compounds are affected by numerous biotic and abiotic influences, including amount and wavelength of solar radiation. However, responses to shade and ultraviolet light restriction are inconsistent among plant species and compound class. We conducted a three-year study to evaluate the effect of shade and UV light restriction on total phenolic and terpene concentrations in tarbush. Sixty plants were randomly assigned to one of three treatments (control, UV light restriction, or 50% incident light restriction). Mean concentrations of total phenolics and total volatiles in tarbush were 82.4 and 12.5 mg/g DM, respectively. Total phenolics did not differ between UV-restricted and control plants, but were lower in shaded plants than the other treatments (P < 0.05). Total volatiles tended to be greater for the UV-restricted treatment than control plants (P = 0.056), with shaded plants not different from either treatment. Treatment effects were detected for 18 individual compounds (P < 0.05). Our results partially support the hypothesis that UV restriction and shading alter carbon-based secondary chemical concentrations.