Drought stress and pathogen infection alter feeding behavior of a phytopathogen vector

The impact of drought stress on tripartite plant-pathogen-vector interactions constitutes a complex and largely understudied field of plant-insect interaction. A number of studies explored these topics using aphid vectors of plant pathogens, but few have considered the interactions between drought-stressed plants and pathogen-transmitting psyllids. The potato psyllid, Bactericera cockerelli (Šulc) (Hemiptera: Triozidae), is one of the key pests of solanaceous crops in the USA that causes direct injury as well as indirect injury through transmission of a bacterial pathogen, Candidatus Liberibacter solanacearum (Lso), the causal agent of zebra chip. Previous studies explored the impact of Lso infection and drought stress on B. cockerelli development and reproductive rate separately, but no research to date has evaluated whether drought stress and Lso infection alter feeding behavior of the insects. We explored this using the electrical penetration graph (EPG) technique and monitored feeding behavior of Lso-infected and uninfected potato psyllids on well-watered and drought-stressed tomato (Solanum lycopersicum L., Solanaceae). We found that drought stress had a significant effect on feeding behavior associated with salivation into the phloem and phloem ingestion, both linked to Lso transmission. Furthermore, infected potato psyllids in particular produced a higher number of events associated with these feeding behaviors and remained in these phases longer in well-watered plants than in plants that were under drought stress. We also reported a new and previously undescribed waveform H of unknown biological function that was produced by the psyllids. This is the first study that considered the impact of bacterial infection and concomitant drought stress on feeding behavior of an insect quantified using EPG.     

Variations in the C-unit of bedaquiline provides analogues with improved biology and pharmacology

Analogues of the anti-tuberculosis drug bedaquiline, bearing a 3,5-dimethoxy-4-pyridyl C-unit, retain high anti-bacterial potency yet exert less inhibition of the hERG potassium channel, in vitro, than the parent compound. Two of these analogues (TBAJ-587 and TBAJ-876) are now in preclinical development. The present study further explores structure-activity relationships across a range of related 3,5-disubstituted-4-pyridyl C-unit bedaquiline analogues of greatly varying lipophilicity (clogP from 8.16 to 1.89). This broader class shows similar properties to the 3,5-dimethoxy-4-pyridyl series, being substantially more potent in vitro and equally active in an in vivo (mouse) model than bedaquiline, while retaining a lower cardiovascular risk profile through greatly attenuated hERG inhibition.     

Regional permeability differences between the proximal and distal portions of the isolated salmonid posterior intestine

The objective of this study was to assess regional variations in the permeability of the salmon posterior intestine and to evaluate the effect of permeability enhancers as a basis for oral delivery of biologically active peptides. Proximal and distal portions of the posterior intestine of the chinook salmon (Oncorhynchus tshawytscha) were removed, mounted as flat sheets in Ussing chambers and superfused with trout Ringer's. Intestinal permeability was assessed under short-circuit conditions by measurement of ¹⁴C-mannitol (mucosal to serosal) flux. Tissues were treated either with the mucolytic agent dithiothreitol (10 mmol · l⁻¹), the permeability enhancer sodium deoxycholate (5.0 mmol · l⁻¹) or both and compared to untreated controls. Both proximal and distal control tissues had low permeabilities, but the distal region had a lower transepithelial electrical resistance and produced significantly less mucus. Treatment with either dithiothreitol or sodium deoxycholate alone reduced mucus adhering to tissue in both regions but did not increase permeability or change transepithelial electrical resistance. In the distal region, sequential treatment with both agents significantly reduced adhering mucus, decreased transepithelial electrical resistance, and increased tissue permeability. The salmon posterior intestine can be divided into proximal and distal regions. The distal region is more likely to have the necessary permeability and responsiveness to enhancement for the successful delivery of peptides or polar drugs. Accepted: 14 January 1997     

Purification and characterization of glutathione reductase from Scots pine needles

Changes in the excitability of the liverwort Conocephalum conicum L. caused by inhibitors of ionic channels and phosphorylation uncouplers, were examined. Action potentials were triggered by electrical and light stimuli. Tetraethylammonium chloride, an inhibitor of K⁺ channels, completely blocked the ability to generate action potentials. Excitability also disappeared under the influence of MnCl₂ and LaCl₃, inhibitors of Ca²⁺ channels. The participation of Ca²⁺ and K⁺ in the electrogenesis of action potentials in C. conicum is discussed. Treatment with phosphorylation uncouplers induced a gradual disappearance of the metabolic component of the resting potential. It was accompanied by some series of excitations, numbering from several to over a dozen impulses characterized by decreasing amplitudes, after which the organism became totally unexcitable. Dicyclohexylcarbodiimide an inhibitor of H⁺-ATPase, also caused depolarization of the transmembrane potential and disappearance of excitability. The results indicated the participation of a metabolic component in the generation of action potentials in C. conicum .     

Leaching Soluble Salts Increases Population Densities of Tylenchulus semipenetrans

The effect of salinity on population densities of Tylenchulus semipenetrans was measured on 3-month-old salt-tolerant Rangpur lime growing on either loamy sand, sand, or organic mix and on 4-month-old salt-sensitive Sweet lime in organic mix. Salinity treatments were initiated by watering daily with 25 mol/m³ NaCl + 3.3 mol/m³ CaCl₂ for 3 days and every other day with 50 mol/m³ NaC1 + 6.6 mol/m³ CaC1₂ for one week, with no salt (NS) treatments as controls. Salinity was discontinued in one treatment (DS) by leaching with tap water prior to inoculation with nematodes, whereas the continuous salinity (CS) treatment remained unchanged. Overall, in Rangpur lime organic soil supported the highest population densities of T. semipenetrans, followed by loamy sand and sand. The DS treatment resulted in the highest (P ≤ 0.05) mean population densities of T. semipenetrans in the three soil types. Similarly, the DS treatment in Sweet lime resulted in the highest (P ≤ 0.05) nematode populations. The DS treatment predisposed citrus to nematode infection through accumulated salt stress, whereas leaching soluble salt in soil solution offered nematodes a suitable nonosmotic habitat. Nematode females under the DS treatment also had the highest (P ≤ 0.05) fecundity.     

Effect of vasoactive intestinal polypeptide on porcine gastrointestinal electrical activity

The influence of intravenous infusion of VIP, 150 and 300 pmol/kg/min, on gastrointestinal electrical activity was studied in conscious piglets with electrodes implanted in the wall of the antrum pylori, duodenum, jejunum, and ileum. Both doses resulted in a decrease in antral electrical activity. In the small intestine, only the lower dose caused a shortening of the irregular spiking activity phase in the jejunum and ileum. In the jejunum this resulted in a reduction of the MMC interval. It may be concluded that the prevailing effect of VIP is an inhibition of gastrointestinal electrical activity in the piglet.     

Correlation of receptive field position of mechanosensory neurons and the strength of their connections to AP neurons in the CNS of the leech (Whitmania pigra)

An identified neuron of unknown function in the CNS of the leech, the anterior pagoda (AP) cell, receives multiple synaptic inputs from mechanosensory neurons that innervate the skin. Impulses in touch (T), pressure (P) and nociceptive (N) sensory cells on both sides of the ganglion produced electrical coupling potentials on both AP cells. Sensory cells with receptive fields contralateral to the cell body of the AP neuron always gave rise to larger synaptic potentials. In addition sensory cells supplying dorsal skin gave rise to larger synaptic potentials than those with lateral or ventral fields. It is suggested that integration by the AP cell can provide information about the position of mechanical stimuli impinging on the body wall of the animal.     

Variety of types of cortical interneurons

A most important component of the mammalian neocortex is the system of inhibitory interneurons. It is composed of cellular elements, which differ from each other in morphological, electrophysiological, and genetical features; these cells form a complex system of synaptic connections with glutamatergic cells and with each other. Some regularities that characterize the variety of types of cortical interneurons are discussed in our study. Neirofiziologiya/Neurophysiology, Vol. 39, No. 3, pp. 260–269, May–June, 2007.