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781.
Jay Jayaraman William T. Jones Dawn Harvey Lauren M. Hemara Honour C. McCann Minsoo Yoon Suzanne L. Warring Peter C. Fineran Carl H. Mesarich Matthew D. Templeton 《Environmental microbiology》2020,22(12):5356-5372
The common polysaccharide antigen (CPA) of the lipopolysaccharide (LPS) from Pseudomonas syringae is highly variable, but the genetic basis for this is poorly understood. We have characterized the CPA locus from P. syringae pv. actinidiae (Psa). This locus has genes for l - and d -rhamnose biosynthesis and an operon coding for ABC transporter subunits, a bifunctional glycosyltransferase and an o -methyltransferase. This operon is predicted to have a role in the transport, elongation and termination of the CPA oligosaccharide and is referred to as the TET operon. Two alleles of the TET operon were present in different biovars (BV) of Psa and lineages of the closely related pathovar P. syringae pv. actinidifoliorum. This allelic variation was reflected in the electrophoretic properties of purified LPS from the different isolates. Gene knockout of the TET operon allele from BV1 and replacement with that from BV3, demonstrated the link between the genetic locus and the biochemical properties of the LPS molecules in Psa. Sequence analysis of the TET operon from a range of P. syringae and P. viridiflava isolates displayed a phylogenetic history incongruent with core gene phylogeny but correlates with previously reported tailocin sensitivity, suggesting a functional relationship between LPS structure and tailocin susceptibility. 相似文献
782.
The beta-adrenergic antagonists, propranolol and bornaprolol (FM-24), at greater than 2 mg/kg (as [-] form) significantly depressed plasma levels of luteinizing hormone (LH) in orchidectomized rats. This occurred in the absence of consistently significant changes in interpulse intervals or amplitudes of pulsatile LH release. Nadirs of plasma LH decreased significantly even at low blocker doses, with a clear dose dependence for both drugs. The highly significant decrease of plasma LH induced by blocker dosages causing greater than 93% inhibition of beta-adrenergic binding in the anterior pituitary gland was shown to occur without significant changes in binding of specific ligands at pituitary dopamine receptors and hypothalamic alpha 1-adrenergic receptors. The above evidence indicates that beta-blockers may lower LH release in vivo at the level of pituitary beta-adrenergic receptors. 相似文献
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784.
785.
Sit‐and‐wait predators use relatively simple rules for their decisions to choose and leave a patch, such as using the direct presence of prey to select a hunting site. However, the direct presence of prey can only be used when there is a highly visited patch in the proximity of the predator. Therefore, it is plausible that sit‐and‐wait predators also exploit indirect cues of prey presence and, consequently, use associative learning to select a hunting site. The present study tests for the role of associative learning in a sit‐and‐wait predator species for which the ecology is well understood: Misumena vatia Clerck crab spiders. An ecologically relevant scenario is used by selecting flower colour as the conditioned stimulus and prey presence as the unconditioned stimulus. The results provide no evidence that M. vatia crab spiders use the association between flower colour and food presence for selecting a hunting site. After a training phase of being exposed to a colourful artificial flower highly visited by bees, spiders select a hunting site independently of its colour during the testing phase. Investigations of similar scope and ecological relevance are required with other sit‐and‐wait predators to identify the conditions promoting the use of associative learning for foraging site selection when animals face an unpredictable food supply. 相似文献
786.
Characterization of a large conductance non-selective anion channel in B lymphocytes 总被引:3,自引:0,他引:3
Studies on ion channel currents in freshly isolated murine B lymphocytes with the patch clamp technique revealed the presence of a non-selective anion channel of large conductance in inside-out (i/o) patches. This channel is characterized here according to its unitary conductance, ion selectivity, regulatory factors, distribution and kinetic behaviour. With a unitary conductance of 348 +/- 4.4 pS in a normal physiological ion gradient, it exhibited an indiscriminate selectivity to cations (Na+ and K+). Selectivity to chloride over sodium was established by substitution of high concentrations of NaCl (450 mM) in the bath (i/o patches), resulting in a selectivity ratio (PCl/PNa) of 33. Selectivity to chloride over potassium was confirmed in a similar manner by substitution of TEA-Cl for KCl, yielding a selectivity ratio (PCl/Pk) greater than 80. Conductance of aspartate through the channel demonstrated the non-selective nature of this anion channel. Voltage proved to be a regulatory factor but other influences on channel activity were also present, including the configuration of the patch (channel is inactive in cell attached patches), and the enhancement of activity at negative membrane voltages by previous pulsing. Intracellular levels of calcium (i/o patches) did not appear to control channel conductances or regulate kinetic activity. Kinetic behaviour of this channel was complex, with periods of bursting and flickering activity interspersed with prolonged closed/open intervals. Multiple subconductance states were also present. The complex properties and behaviour of this channel suggest a possible role in signal transduction in B cell activation. 相似文献
787.
788.
Abstract. The aim of this study was to characterize the vibratory signals produced by the parasitoid Sympiesis sericeicornis Nees (Hymenoptera: Eulophidae) while foraging on apple leaves infested by one of its hosts, the spotted tentiform leafminer Phyllonorycter malella (Ger.) (Lepidoptera: Gracillariidae).This leafminer changes its behaviour as a function of the parasitoid's behaviour to escape parasitization.We propose that the leafminer uses vibrations triggered by the parasitoid to detect the presence of its enemy.We measured vibrations produced by a foraging parasitoid on a mine with a laser vibrometer.By recording concurrently the behaviour of the parasitoid on video, vibrations could be assigned to particular behaviours.Subsequently, vibrations were characterized by their dominant frequencies and intensities.The behaviours Landing and Take-off both produced strong impact-like vibrations characterized by an initial irregular phase during which frequencies up to 25 kHz occurred followed by a slow decaying regular phase.Vibrations elicited by Moving, Standing and Probing showed no clear temporal pattern.During Probing , dominant frequencies of up to 5.6 kHz were observed frequently at intensities well above the background noise (>10 dB).During Moving and Standing , vibrations were more scarce and of lower frequencies and intensities.Due to their impact-like nature, vibrations produced by Landing and Take-off are probably not specific to the parasitoid.Vibrations produced by Moving and Standing are difficult to detect and not reliable because of their non-specificity.Therefore, only Probing provides a reliable and detectable source of information for the host.The vibrations elicited during Probing could account for the evasive behaviour that is observed in this and other leafminers. 相似文献
789.
The dynamic aspects of human harvesting behaviour are often overlooked in resource management, such that models often neglect the complexities of dynamic human effort. Some researchers have recognized this, and a recent push has been made to understand how human behaviour and ecological systems interact through dynamic social-ecological systems. Here, we use a recent example of a social-ecological dynamical systems model to investigate the relationship between harvesting behaviour and the dynamics and stability of a harvested resource, and search for general rules in how relatively simple human behaviours can either stabilize or destabilize resource dynamics and yield. Our results suggest that weak to moderate behavioural and effort responses tend to stabilize dynamics by decreasing return times to equilibria or reducing the magnitude of cycles; however, relatively strong human impacts can readily lead to human-driven cycles, chaos, long transients and alternate states. Importantly, we further show that human-driven cycles are characteristically different from typical resource-driven cycles and, therefore, may be differentiated in real ecosystems. Given the potentially dramatic implications of harvesting on resource dynamics, it becomes critical to better understand how human behaviour determines harvesting effort through dynamic social-ecological systems. 相似文献
790.
Wenming Zhang Caleb W. Holyoke Thomas F. Pahutski George P. Lahm James D. Barry Daniel Cordova Robert M. Leighty Vineet Singh Daniel R. Vicent My-Hanh T. Tong Kenneth A. Hughes Stephen F. McCann Yewande T. Henry Ming Xu Twyla A. Briddell 《Bioorganic & medicinal chemistry letters》2017,27(1):16-20
A novel class of mesoionic pyrido[1,2-a]pyrimidinones has been discovered with exceptional insecticidal activity controlling a number of insect species. In this communication, we report the part of the optimization program which led to the discovery of triflumezopyrim as a highly potent insecticide controlling various hopper species. Our efforts in discovery, synthesis, structure-activity relationship elucidation, and biological activity evaluation are also presented. 相似文献