Pollinator-attracting semiochemicals of the wasp-flower Epipactis helleborine

The orchid genus Epipactis is represented by 25 species in Europe (Richards 1982). Epipactis helleborine (L.) Crantz is the most common and widely distributed species of the genus (Wiefelspütz 1970), and is a prime example for wasp-flowers, because it is mainly pollinated by social wasps (Hymenoptera: Vespidae), like Vespula vulgaris and V. germanica (Müller 1873). Darwin (1888) already noticed that E. helleborine is almost exclusively ignored by bees and bumblebees, an observation that was confirmed in recent investigations (Keppert 2001). The flowers of E. helleborine show morphological, physiological and phenological adaptations to the visit and the pollination by Vespidae (Keppert 2001). They possess a reddish-brown or dirty purple coloration of the inflorescence (Keppert 2001), have relatively small, mostly bulbous blossoms with a broad entrance and bulbous widened, nectar-rich juice holders (Müller 1873, 1881; Schremmer 1962). Although there is much reported about wasp-pollinated flowers there is little known about the signals that are responsible for the attraction of wasps. Wiefelspütz (1970) proclaimed the statement that only the visual stimulus is responsible for the wasp attraction. Recently studies, however, assumed that odour is involved in the wasp attraction (Keppert 2001). Hölzler (2003) showed that the main attraction of the wasp-flower Epipactis for pollinators is its olfactory stimulus. It remains an unanswered question why E. helleborine flowers almost exclusively attracts social wasps, as opposed to bees and bumblebees. In this study we analysed the role of floral volatiles which are responsible for the specific attraction of social wasps. We supposed a mimicry-system in E. helleborine for the specific attraction of pollinators for the following reasons. So-called “green leaf volatiles” (GLVs) are emitted by plants while herbivorous insects, for example caterpillars, feed on them. GLVs thereby attract predators or parasitoids of the herbivorous insects (Dicke & Sabelis 1988; Turlings & al. 1990, 1995; Dicke & Vet 1999). Among the GLVs so far identified in former studies there are aldehydes, compounds that were also found in flower extracts of E. helleborine (Hölzler 2003). Therefore, we postulated that E. helleborine flowers produce GLVs in order to attract prey hunting social wasps for pollination. We performed bioassays and analysed flower odour gained to headspace-sampling using gas chromatography (GC), mass spectrometry (GC-MS) and gas chromatography coupled with electrophysiological analysis (GC-EAD) to investigate the hypothesis that E. helleborine flowers mimic “green leaf volatiles” (GLVs) to attract their pollinators.Die Orchideenart Epipactis helleborine gilt als typische Wespenblume. Die Blüten weisen Anpassungen an den Besuch und die Bestäubung durch soziale Faltenwespen (Hymenoptera: Vespidae) auf und werden häufig durch Vespula vulgaris und V. germanica bestäubt. In früheren Untersuchungen konnte gezeigt werden, dass olfaktorische Reize bei der Bestäuberanlockung eine übergeordnete Bedeutung vor optischen Reizen haben (Hölzler 2003). Die Frage, warum E. helleborine fast ausschließlich ihren optimalen Bestäuber, die soziale Faltenwespe, zur Bestäubung anlockt, und nicht auch auf andere Blütenbesucher attraktiv wirkt, ist noch unbeantwortet. Wir untersuchten die Hypothese, dass E. helleborine Blüten GLVs, die von Herbivoren befallenen Pflanzen abgegeben werden, nachahmen, um Beute jagende Wespen zur Bestäubung anzulocken. Dazu sammelten und analysierten wir Duftstoffe von Epipactis Blüten und mit Pieris-Raupen befallenen Kohl und identifizierten vier gemeinsam vorkommende GLVs. In Y-Rohrtests konnte die wespenanlockende Wirkung dieser Verbindungen nachgewiesen werden

High turnover in electro-oxidation of alcohols and ethers with a glassy carbon-supported phenanthroimidazole mediator.

Glassy carbon electrodes covalently modified with a phenanthroimidazole mediator promote electrochemical alcohol and ether oxidation: three orders of magnitude increase in TON, to ∼15 000 in each case, was observed compared with homogeneous mediated reactions. We propose the deactivation pathways in homogeneous solution are prevented by the immobilization: modified electrode reversibility is increased for a one-electron oxidation reaction. The modified electrodes were used to catalytically oxidize p-anisyl alcohol and 1-((benzyloxy)methyl)-4-methoxybenzene, selectively, to the corresponding benzaldehyde and benzyl ester, respectively

Azolylborates for Electrochemical Double Layer Capacitor Electrolytes

Asymmetric tetraalkylammonium salts of azolylborates were synthesized and studied with respect to their suitability as supporting electrolytes in electrochemical double layer capacitors. In contrast to current conducting salts used in this device, azolylborates exhibit an excellent stability towards thermal load and moisture. In addition to good conductivity and stability towards cathodic reduction we found certain limitations when more positive potentials were applie

The role of pollinator attracting scent in the sexually deceptive orchids Ophrys chestermanii, O. normanii and O. tenthredinifera

Sexual deception of male bees is one of the most remarkable mechanisms of pollination (Ackermann 1986, Proctor & al. 1996). Flowers of the orchid genus Ophrys mimic females of their pollinator species, usually bees and wasps, to attract males, which try to copulate with the flowers. During this so-called “pseudocopulation” the male removes the pollinia and transfers them to another flower to ensure pollination. Apart from visual and tactile cues, floral scent was shown to be most important for eliciting mating behaviour in males (Kullenberg 1961, Schiestl & al. 1999, Ayasse & al. 2003). Pollination in Ophrys is highly specific and usually each Ophrys species attracts only one pollinator species (Paulus & Gack 1990). The high degree of specialization provides the means of reproductive isolation between the intercrossable Ophrys-species (Ehrendorfer 1980). The complex odour-bouquets released by the flowers are species-specific and often consist of more than 100 different chemical compounds (Borg-Karlson & al. 1985, Ayasse 2006). Speciation in Ophrys-orchids may be brought about by changes in the pollinator attracting floral scent. The attraction of a new pollinator may act as a pre-zygotic isolation barrier (Stebbins 1970, Paulus & Gack 1990, Soliva & al. 2001). We investigated three sympatrically occuring Ophrys-species on Sardinia. O. chestermanii and O. normanii are endemic and are both pollinated by males of the bumblebee B. vestalis. O. tenthredinifera is pollinated by Eucera nigrilabris. There are different opinions concerning the taxonomic status of O. normanii. It has been described as an actual hybrid between O. chestermanii and O. tenthredinifera (Wood 1983). Paulus & Gack (1995) suggested that it is an own species, that either has developed from a hybrid between O. chestermanii and O. normanii or that has evolved by radiation from O. tenthredinifera. By conducting behavioural-tests with B. vestalis males, performing gas chromatographic analyses and electrophysiological studies we wanted to identify pollinator attracting scent and to clarify the taxonomic status of O. normanii.Sexualtäuschorchideen der Gattung Ophrys (Orchidaceae) imitieren die Weibchen ihrer Bestäuber in Duft, Form und Farbe. Insektenmännchen versuchen mit dem Labellum der Blüte zu kopulieren und transportieren den Pollen von Blüte zu Blüte, wodurch die Orchidee bestäubt wird. In dieser Arbeit untersuchten wir die Bestäuber anlockenden Duftstoffe der beiden endemisch auf Sardinien vorkommenden Arten O. normanii und O. chestermanii, die beide von Bombus vestalis Männchen (Hymenoptera: Apidae) bestäubt werden und von O. tenthredinifera, die Eucera nigrilabris (Hymenoptera: Apidae) zur Bestäubung anlockt. O. normanii wurde von Wood (1983) als Primärhybride beschrieben. Nach Paulus und Gack (1995) handelt es sich um eine hybridogene Art oder um eine Art die durch Abspaltung von O. tenthredinifera entstanden ist. Das Ziel der Untersuchungen war die Identifizierung Männchen-anlockender Verbindungen. Die Attraktivität der drei Arten für B. vestalis Männchen sollte Hinweise auf den Artstatus von O. normanii geben. In Biotests mit B. vestalis-Männchen lösten Blütenextrakte von O. normanii und O. chestermanii ebenso wie B. vestalis-Weibchen Kopulationsverhalten der Männchen aus, nicht jedoch Extrakte von O. tenthredinifera. Folglich handelt es sich bei O. normanii nicht um einen aktuellen Hybriden zwischen O. chestermanii und O. tenthredinifera. Ein Vergleich der GC-EAD-aktiven Duftbouquets mittels Diskriminanzanalyse ergab große Ähnlichkeiten zwischen O. normanii und O. chestermanii für die Substanzklassen der Ester, Alkohole und Fettsäuren, die daher vermutlich eine Schlüsselfunktion bei der Bestäuberanlockung haben

TEMPO‐Modified Polymethacrylates as Mediators in Electrosynthesis – Redox Behavior and Electrocatalytic Activity toward Alcohol Substrates

Homogeneous catalysts (“mediators”) are useful for tuning selectivity in organic electrosynthesis. However, they can have a negative impact on the overall mass and energy balance if used only once or recycled inefficiently. In a previous work, we introduced the polymediator concept, in which soluble redox-active polymers catalyze the electrochemical reaction, allowing for recovery by dialysis or pressure-driven membrane filtration. Using anodic alcohol oxidation as a test case, it was shown that TEMPO-modified polymethacrylates (TPMA) can serve as efficient and reusable mediators. In the present study, the properties of a TPMA sample with well-defined molecular weight distribution were studied using cyclic voltammetry and compared to low-molecular TEMPO species. The non-catalytic profiles of TPMA are shaped by diffusive and adsorptive processes, whereby the latter only become pronounced at low mediator concentrations and high scan rates. Electrocatalytic studies suggest that under the applied conditions, TPMA-catalyzed alcohol oxidation is a predominantly homogeneous process. The homogeneous kinetics are determined rather by the mediator potential than by steric influences of the polymer backbone. © 2021 The Authors. ChemElectroChem published by Wiley-VCH Gmb

Predicting cis-acting elements of Lactobacillus plantarum by comparative genomics with different taxonomic subgroups

Cis-acting elements in Lactobacillus plantarum were predicted by comparative analysis of the upstream regions of conserved genes and predicted transcriptional units (TUs) in different bacterial genomes. TUs were predicted for two species sets, with different evolutionary distances to L.plantarum. TUs were designated ‘cluster of orthologous transcriptional units’ (COT) when >50% of the genes were orthologous in different species. Conserved DNA sequences were detected in the upstream regions of different COTs. Subsequently, conserved motifs were used to scan upstream regions of all TUs. This method revealed 18 regulatory motifs only present in lactic acid bacteria (LAB). The 18 LAB-specific candidate regulatory motifs included 13 that were not described previously. These LAB-specific different motifs were found in front of genes encoding functions varying from cold shock proteins to RNA and DNA polymerases, and many unknown functions. The best-described LAB-specific motif found was the CopR-binding site, regulating expression of copper transport ATPases. Finally, all detected motifs were used to predict co-regulated TUs (regulons) for L.plantarum, and transcriptome profiling data were analyzed to provide regulon prediction validation. It is demonstrated that phylogenetic footprinting using different species sets can identify and distinguish between general regulatory motifs and LAB-specific regulatory motifs

TEMPO-Modified Polymethacrylates as Mediators in Electrosynthesis: Influence of the Molecular Weight on Redox Properties and Electrocatalytic Activity

Homogeneous catalysts (“mediators”) are frequently employed in organic electrosynthesis to control selectivity. Despite their advantages, they can have a negative influence on the overall energy and mass balance if used only once or recycled inefficiently. Polymediators are soluble redox-active polymers applicable as electrocatalysts, enabling recovery by dialysis or membrane filtration. Using anodic alcohol oxidation as an example, we have demonstrated that TEMPO-modified polymethacrylates (TPMA) can act as efficient and recyclable catalysts. In the present work, the influence of the molecular size on the redox properties and the catalytic activity was carefully elaborated using a series of TPMAs with well-defined molecular weight distributions. Cyclic voltammetry studies show that the polymer chain length has a pronounced impact on the key-properties. Together with preparative-scale electrolysis experiments, an optimum size range was identified for polymediator-guided sustainable reaction control

Stereoselective synthesis of trans-fused iridoid lactones and their identification in the parasitoid wasp Alloxysta victrix, Part II: iridomyrmecins

Abstract Following our earlier approach to the synthesis of dihydronepetalactones, all eight stereoisomers of trans-fused iridomyrmecins were synthesized starting from the enantiomers of limonene. Combined gas chromatography and mass spectrometry including enantioselective gas chromatography revealed that volatiles released by the endohyperparasitoid wasp Alloxysta victrix contain (4S,4aR,7S,7aR)-iridomyrmecin of 95-97% ee and stereochemically pure (4S,4aS,7R,7aS)-iridomyrmecin as a minor component. 125

Electrochemistry and Reactivity of Chelation‐stabilized Hypervalent Bromine(III) Compounds

Hypervalent bromine(III) reagents possess a higher electrophilicity and a stronger oxidizing power compared to their iodine(III) counterparts. Despite the superior reactivity, bromine(III) reagents have a reputation of hard‐to‐control and difficult‐to‐synthesize compounds. This is partly due to their low stability, and partly because their synthesis typically relies on the use of the toxic and highly reactive BrF3 as a precursor. Recently, we proposed chelation‐stabilized hypervalent bromine(III) compounds as a possible solution to both problems. First, they can be conveniently prepared by electro‐oxidation of the corresponding bromoarenes. Second, the chelation endows bromine(III) species with increased stability while retaining sufficient reactivity, comparable to that of iodine(III) counterparts. Finally, their intrinsic reactivity can be unlocked in the presence of acids. Herein, an in‐depth mechanistic study of both the electrochemical generation and the reactivity of the bromine(III) compounds is disclosed, with implications for known applications and future developments in the field.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659European Regional Development Fund http://dx.doi.org/10.13039/501100008530HORIZON EUROPE European Research Council http://dx.doi.org/10.13039/100019180Estonian Research Competency Council http://dx.doi.org/10.13039/501100005189Peer Reviewe

Localization of the succinate receptor in the distal nephron and its signaling in polarized MDCK cells

When the succinate receptor (SUCNR1) is activated in the afferent arterioles of the glomerulus it increases renin release and induces hypertension. To study its location in other nephron segments and its role in kidney function, we performed immunohistochemical analysis and found that SUCNR1 is located in the luminal membrane of macula densa cells of the juxtaglomerular apparatus in close proximity to renin-producing granular cells, the cortical thick ascending limb, and cortical and inner medullary collecting duct cells. In order to study its signaling, SUCNR1 was stably expressed in Madin-Darby Canine Kidney (MDCK) cells, where it localized to the apical membrane. Activation of the cells by succinate caused Gq and Gi-mediated intracellular calcium mobilization, transient phosphorylation of extracellular regulated kinase (ERK)1/2 and the release of arachidonic acid along with prostaglandins E2 and I2. Signaling was desensitized without receptor internalization but rapidly resensitized upon succinate removal. Immunohistochemical evidence of phosphorylated ERK1/2 was found in cortical collecting duct cells of wild type but not SUCNR1 knockout streptozotocin-induced diabetic mice, indicating in vivo relevance. Since urinary succinate concentrations in health and disease are in the activation range of the SUCNR1, this receptor can sense succinate in the luminal fluid. Our study suggests that changes in the luminal succinate concentration may regulate several aspects of renal function