Sexual and genotypic variation in terpene quantitative and qualitative profiles in the dioecious shrub Baccharis salicifolia.

Terpenoids are secondary metabolites produced in most plant tissues and are often considered toxic or repellent to plant enemies. Previous work has typically reported on intra-specific variation in terpene profiles, but the effects of plant sex, an important axis of genetic variation, have been less studied for chemical defences in general, and terpenes in particular. In a prior study, we found strong genetic variation (but not sexual dimorphism) in terpene amounts in leaves of the dioecious shrub Baccharis salicifolia. Here we build on these findings and provide a more in-depth analysis of terpene chemistry on these same plants from an experiment consisting of a common garden with male (N = 19) and female (N = 20) genotypes sourced from a single population. Our goal in the present study was to investigate quantitative and qualitative differences in terpene profiles associated with plant sex and genotypic variation. For this, we quantified leaf mono- and sesquiterpene amount, richness, and diversity (quantitative profile), as well as the composition of compounds (qualitative profile). We found no evidence of sexual dimorphism in monoterpene or sesquiterpene profiles. We did, however, find significant genotypic variation in amount, diversity, and composition of monoterpenes, but no effects on sesquiterpenes. These findings indicated that genotypic variation in terpene profiles largely surpassed variation due to sexual dimorphism for the studied population of this species.

Essential Oils of Five Baccharis Species: Investigations on the Chemical Composition and Biological Activities.

This paper provides a comparative account of the essential oil chemical composition and biological activities of five Brazilian species of Baccharis (Asteraceae), namely B. microdonta, B. pauciflosculosa, B. punctulata, B. reticularioides, and B. sphenophylla. The chemical compositions of three species (B. pauciflosculosa, B. reticularioides, and B. sphenophylla) are reported for the first time. Analyses by GC/MS showed notable differences in the essential oil compositions of the five species. α-Pinene was observed in the highest concentration (24.50%) in B. reticularioides. Other major compounds included α-bisabolol (23.63%) in B. punctulata, spathulenol (24.74%) and kongol (22.22%) in B. microdonta, ß-pinene (18.33%) and limonene (18.77%) in B. pauciflosculosa, and ß-pinene (15.24%), limonene (14.33%), and spathulenol (13.15%) in B. sphenophylla. In vitro analyses for antimalarial, antitrypanosomal, and insecticidal activities were conducted for all of the species. B. microdonta and B. reticularioides showed good antitrypanosomal activities; B. sphenophylla showed insecticidal activities in fumigation bioassay against bed bugs; and B. pauciflosculosa, B. reticularioides, and B. sphenophylla exhibited moderate antimalarial activities. B. microdonta and B. punctulata showed cytotoxicity. The leaves and stems of all five species showed glandular trichomes and ducts as secretory structures. DNA barcoding successfully determined the main DNA sequences of the investigated species and enabled authenticating them.

Physiological and transcriptional responses of Baccharis halimifolia to the explosive "composition B" (RDX/TNT) in amended soil.

Unexploded explosives that include royal demolition explosive (RDX) and trinitrotoluene (TNT) cause environmental concerns for surrounding ecosystems. Baccharis halimifolia is a plant species in the sunflower family that grows naturally near munitions sites on contaminated soils, indicating that it might have tolerance to explosives. B. halimifolia plants were grown on 100, 300, and 750 mg kg(-1) of soil amended with composition B (Comp B) explosive, a mixture of royal demolition explosive and trinitrotoluene. These concentrations are environmentally relevant to such munitions sites. The purpose of the experiment was to mimic contaminated sites to assess the plant's physiological response and uptake of explosives and to identify upregulated genes in response to explosives in order to better understand how this species copes with explosives. Stomatal conductance was not significantly reduced in any treatments. However, net photosynthesis, absorbed photons, and chlorophyll were significantly reduced in all treatments relative to the control plants. The dark-adapted parameter of photosynthesis was reduced only in the 750 mg kg(-1) Comp B treatment. Thus, we observed partial physiological tolerance to Comp B in B. halimifolia plants. We identified and cloned 11 B. halimifolia gene candidates that were orthologous to explosive-responsive genes previously identified in Arabidopsis and poplar. Nine of those genes showed more than 90% similarity to Conyza canadensis (horseweed), which is the closest relative with significant available genomics resources. The expression patterns of these genes were studied using quantitative real-time PCR. Three genes were transcriptionally upregulated in Comp B treatments, and the Cytb6f gene was found to be highly active in all the tested concentrations of Comp B. These three newly identified candidate genes of this explosives-tolerant plant species can be potentially exploited for uses in phytoremediation by overexpressing these genes in transgenic plants and, similarly, by using promoters or variants of promoters from these genes fused to reporter genes in transgenic plants for making phytosensors to report the localized presence of explosives in contaminated soils.

Baccharis trimera (Less.) DC as genotoxicity indicator of exposure to coal and emissions from a thermal power plant.

During coal combustion, hazardous elements are discharged that impair environmental quality. Plant cover is the first available surface for the atmospheric pollutants in terrestrial ecosystems. The aim of this study was to evaluate genotoxicity in the aqueous extract of the native plant, Baccharis trimera, exposed to coal and emissions from a thermal power plant (coal-fired power plant in Candiota, Brazil), correlating seasonality, wind tunnel predominance, and presence of inorganic elements. The presence of inorganic elements in the aerial parts of B. trimera was analyzed by particle-induced X-ray emission (PIXE) spectrometry, and genotoxicity was evaluated by ex vivo comet assay. The genotoxic effects of aqueous extracts of B. trimera from four sites located in the area around power plant were analyzed by comet assay in peripheral human lymphocytes. Winter samples showed greater levels of metals than summer samples. Genotoxicity was detected in B. trimera extracts collected from the region exposed to extraction and burning coal. Extracts from the site impacted by the dominant wind induced more damage to DNA than those from other sites. Based on our data, we can suggest that in winter the inorganic elements from extraction and burning of coal and carried through the wind tunnel were responsible for the genotoxicity observed in aqueous extract of B. trimera.

Influence of plant genetic diversity on interactions between higher trophic levels.

While the ecological consequences of plant diversity have received much attention, the mechanisms by which intraspecific diversity affects associated communities remains understudied. We report on a field experiment documenting the effects of patch diversity in the plant Baccharis salicifolia (genotypic monocultures versus polycultures of four genotypes), ants (presence versus absence) and their interaction on ant-tended aphids, ants and parasitic wasps, and the mechanistic pathways by which diversity influences their multi-trophic interactions. Five months after planting, polycultures (versus monocultures) had increased abundances of aphids (threefold), ants (3.2-fold) and parasitoids (1.7-fold) owing to non-additive effects of genetic diversity. The effect on aphids was direct, as plant genetic diversity did not mediate ant-aphid, parasitoid-aphid or ant-parasitoid interactions. This increase in aphid abundance occurred even though plant growth (and thus aphid resources) was not higher in polycultures. The increase in ants and parasitoids was an indirect effect, due entirely to higher aphid abundance. Ants reduced parasitoid abundance by 60 per cent, but did not affect aphid abundance or plant growth, and these top-down effects were equivalent between monocultures and polycultures. In summary, intraspecific plant diversity did not increase primary productivity, but nevertheless had strong effects across multiple trophic levels, and effects on both herbivore mutualists and enemies could be predicted entirely as an extension of plant-herbivore interactions.

Genetic variation within a dominant shrub species determines plant species colonization in a coastal dune ecosystem.

The diversity and structure of plant communities is often determined by the presence and identity of competitively dominant species. Recent studies suggest that intraspecific variation within dominants may also have important community-level consequences. In a coastal dunes ecosystem of northern California, we use a decade-old common garden experiment to test the effects of a genetically based architectural dimorphism within a dominant native shrub, Baccharis pilularis, on plant colonization success and understory plant diversity. We found that erect Baccharis morphs had higher richness and cover of colonizing plant species (both native and exotic species) compared to prostrate morphs, as well as higher biomass of a dominant exotic dune grass (Ammophila arenaria). Trait differences between architectural morphs influenced the abiotic understory environment (light availability, soil surface temperature, and litter depth) and were associated with species colonization success. Taken together, our results demonstrate that incorporating within-species variation, particularly within dominant species, into community ecological research can increase the ability to predict patterns of species diversity and assembly within communities.