No description available.

Chemically mediated interactions have important ecological and evolutionary effects on populations and communities. Despite recognition that herbivory can significantly affect the biomass and composition of freshwater macrophyte communities, there are few investigations of chemical defenses among freshwater vascular plants and mosses and none of freshwater red algae. This study compares the palatability of five species of freshwater red algae (Batrachospermum helminthosum, Boldia erythrosiphon, Kumanoa sp., Paralemanea annulata, and Tuomeya americana) that occur in the southeastern United States relative to two co-occurring macrophytes (the chemically defended aquatic moss Fontinalis novae-angliae and the broadly palatable green alga Cladophora glomerata). We assessed the potential role of structural, nutritional, and chemical traits in reducing macrophyte susceptibility to generalist crayfish grazers. Both native and non-native crayfish significantly preferred the green alga C. glomerata over four of the five species of red algae. B. erythrosiphon was palatable, while the cartilaginous structure of P. annulata reduced its susceptibility to grazing, and chemical defenses of B. helminthosum, Kumanoa sp., and T. americana rendered these species as unpalatable as the moss F. novae-angliae. Extracts from these latter species reduced feeding by ~30-60% relative to solvent controls if tissues were crushed (simulating herbivore damage) prior to extraction in organic solvents. However, if algae were first soaked in organic solvents that inhibit enzymatic activity and then crushed, crude extracts stimulated or had no effect on herbivory. B. helminthosum, Kumanoa sp., and T. americana all exhibited "activated" chemical defenses in which anti-herbivore compounds are produced rapidly upon herbivore attack via enzymatic processes. In an additional accept/reject behavioral assay, B. helminthosum extracts reduced the number of crayfish willing to feed by >90%. Given that three of the five red algal taxa examined in this study yielded deterrent crude extracts, selection for defensive chemistry in freshwater rhodophytes appears to be substantial. Activated chemical defenses are thought to be an adaptation to reduce the resource allocation and ecological costs of defense. As such, activated chemical defenses may be favored in freshwater red algae, whose short-lived gametophytes must grow and reproduce rapidly. Roughly 20% of the known chemical defenses produced by marine algae are activated; further examination is needed to determine whether the frequency of activated chemistry is higher in freshwater red algae compared to their marine counterparts. Continued investigation of chemical defenses in freshwater red algae will contribute to among-system comparisons, providing new insights in the generality of plant-herbivore interactions and their evolution.

Plants produce a large number of specialized or secondary compounds that aid in their reproduction and protection against biotic and abiotic stress. In this work I investigated the metabolism and function of terpenes, the largest class of specialized metabolites, in switchgrass and carrot. Switchgrass (Panicum virgatum L.), a perennial C4 grass of the Tallgrass Prairie, represents an important species in natural and anthropogenic grasslands of North America. Its natural resilience to abiotic and biotic stress has made switchgrass a preferred bioenergy crop. I have investigated the metabolism of terpenes in switchgrass leaves and roots in response to herbivory or defense hormone treatments and the application of drought. With a focus on volatile terpene metabolites, I functionally characterized over thirty genes (terpene synthases, TPSs), of which one third could be correlated with the production and release of volatile monoterpenes and sesquiterpenes that likely function in direct chemical defense or in the attraction of insect predators or parasitoids. Drought stress application caused switchgrass roots to accumulate a larger amount of oxygenated terpenes and presumably non-volatile terpenes, the function of which in direct or indirect drought stress protection requires further investigation. I also examined the metabolic dynamics and role of the monoterpene borneol, which accumulates at high concentrations in the roots of switchgrass and to a lower extent in the roots of the close relative Setaria viridis, in root microbe interactions. Although we demonstrated a successful RNAi based knock down of the borneol terpene synthase TPS04, we found no immediate evidence that borneol significantly modifies bacterial communities in the root. Further studies on Setaria and equivalent RNAi lines in switchgrass will provide more detailed and needed insight to decipher the role of monoterpene accumulation in grasses interactions with mutualists, pathogens, and pests. In an applied project, I investigated terpene specialized metabolism in carrot (Daucus carota L.) to identify genetic determinants of carrot aroma and flavor. To determine central enzymes which contribute to the terpene component of carrot volatile blends, we first analyzed tissue specific expression patterns of carrot terpene synthase genes (TPS) in the genomic model carrot (cv. DH1) and in roots of four aromatically unique colored carrot genotypes (orange-4943B, red-R6637, yellow-Y9244A and purple-P7262). We selected nineteen key biosynthetic enzymes involved in terpene formation and compared in vitro products from recombinant proteins with native volatile profiles obtained from DH1 and colored carrot genotypes. We biochemically characterized several highly expressed TPSs with direct correlations to major compounds of carrot flavor and aroma including germacrene-D (DcTPS11), (DcTPS30) and -terpinolene (DcTPS03). Random forest analysis of colored carrot volatiles revealed that nine terpene compounds are sufficient for distinguishing the flavor and aroma of raw colored carrots. Interestingly, accumulation of specific terpene compounds rather than chemical diversity is responsible for differences in sensory quality traits in colored genotypes. As accumulations of specific terpene compounds can contribute to the undesired flavor in carrot, our report provides a detailed roadmap for future breeding efforts to enhance carrot flavor and aroma. / Doctor of Philosophy / Plants produce a large number of chemicals that are important for growth, defense, flavor, and aroma. While chemical production has been studied in some major food crops (corn, tomato, rice), knowledge of the formation and function of chemicals in switchgrass and carrot is still limited. Switchgrass (Panicum virgatum L.), a grass of the Tallgrass Prairie, represents an important species grasslands of North America. Its natural resilience to stress has made switchgrass a preferred bioenergy crop. I found that switchgrass produces many compounds in the chemical class of terpenoids in roots and leaves that likely serve as a defense against damage from pests. In addition, I found that drought stress leads to the production of terpenoid compounds that may have roles in protection when water is limited. My research also demonstrates that roots of switchgrass and the related grass Setaria maintain substantial levels of the essential oil compound borneol. This terpenoid compound can act as a nutrient source for specific bacteria and/or an antimicrobial agent. Therefore, I proposed that switchgrass and Setaria roots produce borneol to establish a distinct root microbiome by recruitment of beneficial bacteria and deterrence of harmful microorganisms. To test this hypothesis, we genetically engineered plants to reduce borneol formation and accumulation in roots. Using these plants, we evaluated changes in the root microbiome in response to altered borneol levels. We found that interfering with borneol production in Setaria roots has limited influence on the microbiome inside roots. Although a similar approach was used for switchgrass, we were unable to significantly reduce borneol V formation in roots. Results from this study provide a better understanding of belowground plant-microbe interactions, and potential for enhancing resistance traits into other crop species. I also investigated the flavor and aroma compounds produced in carrots, which are considered a key supplemental vegetable due to high nutritional value and pleasant taste. Surprisingly, little has been known about the genetic factors that control flavor and aroma traits in colored carrot varieties. Therefore, I performed a robust characterization of the biosynthesis of terpenoids, which are the predominant aroma and flavor compounds in carrot. I identified several enzymes in carrot that can produce a diverse blend of terpenoids which are associated with sweet, spicy and bitter tastes. In addition, I discovered that carrot stems and leaves also maintain a rich chemistry of terpenoids similar to that in roots. Results from this work provide a baseline for engineering enhanced flavor in carrot and provide a deeper insight into essential oil formation in root crops.

Thesis (M.S. in Bio.)--School of Biology, Georgia Institute of Technology, 2004. Directed by Julia Kubanek. / Includes bibliographical references (leaves 42-48).

Orientador: Anita Jocelyne Marsaioli / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-19T18:09:49Z (GMT). No. of bitstreams: 1 Wouters_FelipeChristoff_M.pdf: 4919215 bytes, checksum: c2fb1e5605f041d7b55cee18189002ca (MD5) Previous issue date: 2011 / Resumo: Este trabalho consiste no estudo de secreções defensivas de 18 espécies de opiliões da família Gonyleptidae. A composição química das secreções dessas espécies foi investigada por cromatografia gasosa acoplada à espectrometria de massas (CG-EM). Os compostos encontrados nas espécies estudadas se dividem em três classes principais: cetonas, quinonas e fenóis. Análises de ressonância magnética nuclear (RMN) das secreções de três dessas espécies (Gonyleptes saprophilus, Magnispina neptunus e Progonyleptoidellus striatus) permitiram a caracterização de cinco compostos: 4-metilex-1-en-3-ona, 2-metil-1,4-benzoquinona, 2-etil-1,4-benzoquinona, 2,5-dimetilfenol e 2,3,6-trimetilfenol. Foram sintetizadas duas vinil cetonas encontradas nas secreções estudadas: 4-metilex-1-en-3-ona e 5-metilex-1-en-3-ona. Essas cetonas foram caracterizadas e confirmou-se sua presença nas secreções de seis das espécies estudadas. Os demais compostos tiveram suas estruturas sugeridas baseando-se nos dados de espectrometria de massas e/ou coinjeção em CG-EM com padrões. Além disso, foram realizados ensaios de atividade inibitória frente a diversos micro-organismos usando padrões sintéticos de compostos presentes nas secreções, representativos das três classes químicas encontradas / Abstract: This work consists on the study of defensive secretions from 18 harvestmen species belonging to the family Gonyleptidae. The chemical composition of these secretions was investigated by gas chromatography coupled to mass spectrometry (GC-MS). The identified compounds can be divided in three main classes: ketones, quinones and phenols. Nuclear Magnetic Resonance (NMR) analyses of secretions from three species (Gonyleptes saprophilus, Magnispina neptunus and Progonyleptoidellus striatus) allowed the characterization of five compounds: 4-methylhex-1-en-3-one, 2-methyl-1,4-benzoquinone, 2-ethyl-1,4-benzoquinone, 2,5-dimethylphenol, and 2,3,6-trimethylphenol. Two vinyl ketones found in the studied secretions were synthesized: 4-methylhex-1-en-3-one and 5-methylhex-1-en-3-one. These ketones were characterized and their presence in secretions of six species was confirmed. The other compounds had their structures suggested based on mass spectrometry data and/or GC-MS coinjection with standart samples. Moreover, inhibitory activity assays against microorganisms were performed with synthetic standarts of compounds found in the secretions, representatives of the three identified chemical classes / Mestrado / Quimica Organica / Mestre em Química

No description available.

Coral diseases have become more prevalent and destructive over the past 20 years, possibly due to an increase in stressful environmental factors that may weaken corals defenses against disease. Aspergillosis is a disease caused by the fungus Aspergillus sydowii, which apparently infects only two species of gorgonian corals in the Caribbean Ocean (Gorgonia ventalina and G. flabellum). We hypothesized that the differential resistance to infection is caused by differences in chemical defenses among gorgonians. Freeze-dried gorgonian powders and extracts deterred fungal growth, but potencies varied among gorgonian species and among fungi. Extracts and powders generated from G. ventalina all strongly inhibited fungal growth. Since G. ventalina was predicted to have weak antifungal chemical defenses compared to gorgonians not known to suffer from aspergillosis, we concluded that gorgonian susceptibility to fungal infection is determined by factors other than, or in addition to, chemical defenses. In order to investigate specific gorgonian antifungal strategies, we attempted to use bioassay-guided fractionation to isolate antifungal compounds from four gorgonians: Gorgonia ventalina, Briareum asbestinum, Eunicea succinea, and Pseudopterogorgia americana. We succeeded in isolating two antifungal compounds, diastereomers of 9,11-seco-24-hydroxydinosterol, from the gorgonian Pseudopterogorgia americana. This compound was previously identified by other groups, but this study is the first to establish its antifungal activity. At natural concentration, one diastereomer of 9,11-seco-24-hydroxydinosterol inhibited the growth of three different fungi, suggesting that at least this diastereomer may possess broad-spectrum antifungal activity. The results from our survey of gorgonian chemical defenses indicate that susceptibility to aspergillosis cannot be explained by chemical growth inhibition alone. Further areas of investigation include induction of gorgonian chemical defenses, examination of growth-inhibiting mechanisms of antifungal metabolites, and identification of non-chemical factors affecting gorgonians vulnerability to fungal infection.

Because organisms have limited resources to allocate to multiple life history traits, the Optimal Defense Theory (ODT) and the Growth-Differentiation Balance Hypothesis (GDBH) were developed by terrestrial plant ecologists to predict intraindividual defense allocation based on the cost of defense and these life history trade-offs. However, these theories have garnered equivocal experimental support over the years and are rarely experimentally extended from predictions of plant physiology to the palatability of the tissues an herbivore experiences. We therefore examined tissue palatability, nutritional value, and defense mechanisms in multiple Dictyotalean seaweeds in two Caribbean locations, using two herbivores. Relative palatability of tissues varied greatly with algal species, grazer species, and location. Because older bases were not consistently defended, GDBH did not predict relative palatability. We could not reject ODT without intensive measures of tissue fitness value and herbivore risk, and this theory was therefore not useful in making broad predictions of tissue palatability. In testing the physiological predictions of these theories, we found the young, growing apices of these seaweeds to be generally more nutritionally valuable than the old, anchoring bases and found organic-rich apices to be more chemically deterrent, thus supporting ODT. However, the combined chemical, nutritional, and structural traits of these algae all influenced herbivore choice. As a result, these patterns of apical value and chemical defense reflected palatability of live tissues for only one of five algal species, which rendered ODT and GDBH poor predictors of relative palatability for most algae.

Plant-herbivore interactions play a significant role in the structure and functioning of ecosystems. Co-evolutionary theory suggests that plant defenses evolved due to herbivores and herbivore pressure can shape the genetic composition of their food resources. We used interactions between North American porcupines (Erethizon dorsatum) and trembling aspens ( Populus tremuloides) as a system to investigate this theory's important assumption that herbivores select food sources based on genetically controlled traits. We confirmed that porcupines exhibit intra-specific food selection and that this is linked to the genetic composition of the aspens. We also demonstrated that variation in phenolic glycosides and condensed tannins are strong components of this selection, thereby creating an important link between genetics, plant chemistry, and mammalian herbivory. We investigated potential impacts of porcupine herbivory on aspen using fluctuating asymmetry, however we did not detect any stress on heavily eaten trees, thereby questioning the validity of this tool for this study system.

This thesis investigates the possibility of using aposematic insects as guides to plants that contain pharmacologically-active compounds. Plants were monitored within national parks in the Republic of Panama over a period of six months and all insects feeding on them were collected and raised in captivity. The insects were then extracted and analyzed to determine how they were treating toxic chemical compounds in their host plant. Two principal plants were investigated with their associated insects: (1) Vismia baccifera and (2) Mikania guaco. One generalist and one specialist Lepidopteran species were found to sequester vismione B from their host plant Vismia baccifera, a cytotoxic compound active against three cancer cell lines. Two specialist Coleopterans were found to sequester the novel compound Guacanone, isolated by the primary author from the vine Mikania guaco and active against Trypanosoma cruzi, the causative agent of Chagas' disease. A generalist Coleopteran was found to not sequester this compound. (Abstract shortened by UMI.)