Ethological description of a fixed action pattern in a kissing bug (Triatominae): vision,gustation, proboscis extension and drinking of water and guava

Triatomines (Heteroptera, Reduviidae) are vectors of Trypanosoma cruzi, the etiological agent of Chagas disease in America. These true bugs have traditionally been considered to be blood suckers, although some species have been catalogued as being entomophagous. By using their highly specialized mouthparts, these insects have evolved a stereotyped habit which includes lifting up the proboscis, piercing and sucking, when the occasion arises. Most triatomines bite their sleeping and unaware vertebrate or invertebrate hosts, but they can also search for other targets, guided, in part, by visual and chemical stimuli. In this study, we observed that triatomines apparently visually identify a drop of water in the distance, then taste it with their legs, upon which proboscis extension and sucking ensues. This invariant behavior or fixed action pattern, observed in several triatomine species (Rhodnius prolixus, Triatoma infestans and Panstrongylus geniculatus), was also elicited by a dummy drop of water and guava fruit. We discuss evolutionary and ethological aspects of this innate behavior. Digital video images related to this article are available at http://www.momo-p.com/showdetail-e.php?movieid=momo180314rp01a and http://www.momo-p.com/showdetail-e.php?movieid=momo180314rp03a.     

Characterization of Protease-Activated Receptor (PAR) ligands: Parmodulins are reversible allosteric inhibitors of PAR1-driven calcium mobilization in endothelial cells

Several classes of ligands for Protease-Activated Receptors (PARs) have shown impressive anti-inflammatory and cytoprotective activities, including PAR2 antagonists and the PAR1-targeting parmodulins. In order to support medicinal chemistry studies with hundreds of compounds and to perform detailed mode-of-action studies, it became important to develop a reliable PAR assay that is operational with endothelial cells, which mediate the cytoprotective effects of interest. We report a detailed protocol for an intracellular calcium mobilization assay with adherent endothelial cells in multiwell plates that was used to study a number of known and new PAR1 and PAR2 ligands, including an alkynylated version of the PAR1 antagonist RWJ-58259 that is suitable for the preparation of tagged or conjugate compounds. Using the cell line EA.hy926, it was necessary to perform media exchanges with automated liquid handling equipment in order to obtain optimal and reproducible antagonist concentration-response curves. The assay is also suitable for study of PAR2 ligands; a peptide antagonist reported by Fairlie was synthesized and found to inhibit PAR2 in a manner consistent with reports using epithelial cells. The assay was used to confirm that vorapaxar acts as an irreversible antagonist of PAR1 in endothelium, and parmodulin 2 (ML161) and the related parmodulin RR-90 were found to inhibit PAR1 reversibly, in a manner consistent with negative allosteric modulation.     

Orchid seed removal by ants in Neotropical ant‐gardens

• Most plants that inhabit ant‐gardens (AGs) are cultivated by the ants. Some orchids occur in AGs; however, it is not known whether their seeds are dispersed by AG ants because most orchid seeds are tiny and dispersed by wind.
• We performed in situ seed removal experiments, in which we simultaneously provided Azteca gnava ants with seeds of three AG orchid species and three other AG epiphyte species (Bromeliaceae, Cactaceae and Gesneriaceae), as well as the non‐AG orchid Catasetum integerrimum.
• The seeds most removed were those of the bromeliad Aechmea tillandsioides and the gesneriad Codonanthe uleana, while seeds of AG orchids Coryanthes picturata, Epidendrum flexuosum and Epidendrum pachyrachis were less removed. The non‐AG orchid was not removed. Removal values were positively correlated with the frequency of the AG epiphytes in the AGs, and seeds of AG orchids were larger than those of non‐AG orchids, which should favour myrmecochory.
• Our data show that Azt. gnava ants discriminate and preferentially remove seeds of the AG epiphytes. We report for the first time the removal of AG orchid seeds by AG ants in Neotropical AGs.

     

Fungal endophytes associated with Ornithopus compressus growing under semiarid conditions

ABSTRACT

Background

Ornithopus compressus is an important pasture legume of Mediterranean origin that is frequently used for sown pastures under dryland conditions.     

Conformation of 4-thio- -lyxono-1,4-lactone in solution and in the crystalline state

The conformation in ²H₂O of 4-thio- -lyxono-1,4-lactone (1) was studied by nuclear magnetic resonance spectroscopy, by means of homonuclear (J_1H,1H) and heteronuclear (J_1H,13C) coupling constants. The couplings were directly measured by a two-dimensional heteronucleus-coupled ω₁ hetero-half-filtered proton-proton correlation (HETLOC) experiment, which does not require ¹³C isotopic enrichment. In solution, the thiolactone ring of 1 adopts preferentially the E₃ conformation, and its hydroxymethyl group populates mainly the gt rotamer. The X-ray diffraction data of a single crystal of 1 indicates that also in the solid state the thiolactone ring adopts an E₃ conformation, with a puckering somewhat larger than that observed for aldono-1,4-lactones and furanose rings. The molecules are linked by hydrogen bonds, which form chains. Particularly, O-5 is fully engaged as donor and acceptor in hydrogen bonding and the rotameric conformation of the hydroxymethyl group of 1 is fixed in the tg form.     

Carbon allocation to shoots and roots in relation to nitrogen supply is mediated by cytokinins and sucrose: Opinion

In this paper we firstly show some general responses of biomass partitioning upon nitrogen deprivation. Secondly, these responses are explained in terms of allocation of carbon and nitrogen, photosynthesis and respiration, using a simulation model. Thirdly, we present a hypothesis for the regulation of biomass partitioning to shoots and roots.Shortly after nitrogen deprivation, the relative growth rate (RGR) of the roots generally increases and thereafter decreases, whereas that of the shoot decreases immediately. The increased RGR of the root and decreased RGR of the shoot shortly after a reduction in the nitrogen supply, cause the root weight ratio (root weight per unit plant weight) to increase rapidly.We showed previously that allocation of carbon and nitrogen to shoots and roots can satisfactorily be described as a function of the internal organic plant nitrogen concentration. Using these functions in a simulation model, we analyzed why the relative growth rate of the roots increases shortly after a reduction in nitrogen supply. The model predicts that upon nitrogen deprivation, the plant nitrogen concentration and the rate of photosynthesis per unit plant weight rapidly decrease, and the allocation of recently assimilated carbon and nitrogen to roots rapidly increases. Simulations show that the increased relative growth rate of the root upon nitrogen deprivation is explained by decreased use of carbon for root respiration, due to decreased carbon costs for nitrogen uptake. The stimulation of the relative growth rate of the root is further amplified by the increased allocation of carbon and nitrogen to roots. Using the simple relation between the plant nitrogen concentration and allocation, the model describes plant responses quite realistically.Based on information in the literature and on our own experiments we hypothesize that allocation of carbon is mediated by sucrose and cytokinins. We propose that nitrogen deprivation leads to a reduced cytokinin production, a decreased rate of cytokinin export from the roots to the shoot, and decreased cytokinin concentrations. A reduced cytokinin concentration in the shoot represses cell division in leaves, whereas a low cytokinin concentration in roots neutralizes the inhibitory effect of cytokinins on cell division. A reduced rate of cell division in the leaves leads to a reduced unloading of sucrose from the phloem into the expanding cells. Consequently, the sucrose concentration in the phloem nearby the expanding cells increases, leading to an increase in turgor pressure in the phloem nearby the leaf's division zone. In the roots, cell division continues and no accumulation of sugars occurs in dividing cells, leading to only marginal changes in osmotic potential and turgor pressure in the phloem nearby the root's cell division zone. These changes in turgor pressure in the phloem of roots and sink leaves affect the turgor pressure gradients between source leaf-sink leaf and source leaf-root in such a way that relatively more carbohydrates are exported to the roots. As a consequence RWR increases after nitrogen deprivation. This hypothesis also explains the strong relationship between allocation and the plant nitrogen status.     

Localization of an Ataxia-Telangiectasia Gene to an −500-kb Interval on Chromosome 11q23.1: Linkage Analysis of 176 Families by an International Consortium

We describe a 20-point linkage analysis map of chromosome 11q22-23 that is based on genotyping 249 families (59 CEPH and 190 A-T). Monte Carlo linkage analyses of 176 ataxia-telangiectasia (A-T) families localizes the major A-T locus to the region between S1819(A4) and S1818(A2). When seven nonlinking families were excluded from subsequent analyses, a 2-lod support interval of ~500 kb was identified between S1819(A4) and S1294. No recombinants were observed between A-T and markers S384, B7, S535, or S1294. Only 17 of the international consortium families have been assigned to complementation groups. The available evidence favors either a cluster of A-T genes on chromosome 11 or intragenic defects in a single gene.     

Proton pumping and the internal pH of yeast cells, measured with pyranine introduced by electroporation.

The internal pH of yeast cells was determined by measuring the fluorescence changes of pyranine (8-hydroxy-1,3,6-pyrene-trisulfonic acid), which was introduced into the cells by electroporation. This may be a suitable procedure for the following reasons. (i) Only minor changes in the physiological status of the cells seemed to be produced. (ii) The dye did not seem to leak at a significant rate from the cells. (iii) Different incubation conditions produced large fluorescence changes in the dye, which in general agree with present knowledge of the proton movements of the yeast cell under different conditions. (iv) Pyranine introduced by electroporation seemed to be located in the cytoplasm and to avoid the vacuole, and therefore it probably measured actual cytoplasmic pH. (v) Correction factors to obtain a more precise estimation of the internal pH are not difficult to apply, and the procedure may be useful for other yeasts and microorganisms, as well as for the introduction of other substances into cells. Values for the cytoplasmic pHs of yeast cells that were higher than those reported previously were obtained, probably because this fluorescent indicator did not seem to penetrate into the cell vacuole.