Leptodictya tabida (Hemiptera: Tingidae): a potential threat to sugarcane production in Lower Rio Grande Valley of Texas

Areawide surveys and replicated cultivar trials were conducted in 2001 and 2002 in sugarcane (Saccharum spp.) fields in the Lower Rio Grande Valley of Texas to assess the distribution and incidence of the sugarcane tingid Leptodictya tabida (Herrich-Schaeffer). L. tabida was found in all fields surveyed during both years, infesting 60 and 68% of the plants, respectively. The average percentage of leaves infested was 11% in 2001 and 15% in 2002. In 2001, 'CP70-1133' was the most infested, 'CP72-1210' was the least infested, and intermediate infestation levels were evident in 'CP70-321' and 'TCP87-3388'. In 2002, however, TCP87-3388 and CP70-321 were more heavily infested, and CP71-1240 and CP71-1405 were the least infested. Mean densities of L. tabida recovered per plant varied between 1.2 bugs on CP72-1210 and 5.1 on CP70-1133 in 2001, and in 2002, from zero bugs on CP71-1240 and CP71-1405 to 5.3 on CP72-1210. In the cultivar trials, cultivar differences also were evident in both plant and leaf infestation levels, and the proportion of immatures to total L. tabida populations; 'HoCP91-555' had the lowest L. tabida infestations and 'NCo-310' had the greatest levels in both years. Although >5000 L. tabida from the field were collected and kept in the laboratory, no parasitoids were found. The distribution of the infestations during the surveys and in the field trial evaluations suggested that L. tabida populations have been spreading in sugarcane across the Lower Rio Grande Valley. Potential varietal resistance mechanisms are discussed.     

Characteristics of rhizobia nodulating beans in the central region of Minnesota

Until recently, beans (Phaseolus vulgaris L.) grown in Minnesota were rarely inoculated. Because of this, we hypothesized that bean rhizobia collected in Minnesota would either share characteristics identifiable with Rhizobium etli of Mesoamerican or Andean origin, introduced into the region as seed-borne contaminants, or be indigenous rhizobia from prairie species, such as Dalea spp. The latter organisms have been shown to nodulate and fix N2 with Phaseolus vulgaris. Rhizobia recovered from the Staples, Verndale, and Park Rapids areas of Minnesota were grouped according to the results of BOXA1R-PCR fingerprint analysis into 5 groups, with only one of these having banding patterns similar to 2 of 4 R. etli reference strains. When representative isolates were subject to fatty acid - methyl ester analysis and 16S rRNA gene sequence analysis, the results obtained differed. 16S rRNA gene sequences of half the organisms tested were most similar to Rhizobium leguminosarum. Rhizobia from Dalea spp., an important legume in the prairie ecosystem, did not play a significant role as the microsymbiont of beans in this area. This appears to be due to the longer time needed for them to initiate infection in Phaseolus vulgaris. Strains of Rhizobium tropici IIB, including UMR1899, proved tolerant to streptomycin and captan, which are commonly applied as seed treatments for beans. Local rhizobia appeared to have very limited tolerance to these compounds.     

Insertion of Epicatechin Gallate into the Cytoplasmic Membrane of Methicillin-resistant Staphylococcus aureus Disrupts Penicillin-binding Protein (PBP) 2a-mediated ��-Lactam Resistance by Delocalizing PBP2

Epicatechin gallate (ECg) sensitizes methicillin-resistant Staphylococcus aureus (MRSA) to oxacillin and other β-lactam agents; it also reduces the secretion of virulence-associated proteins, prevents biofilm formation, and induces gross morphological changes in MRSA cells without compromising the growth rate. MRSA is resistant to oxacillin because of the presence of penicillin-binding protein 2a (PBP2a), which allows peptidoglycan synthesis to continue after oxacillin-mediated acylation of native PBPs. We show that ECg binds predominantly to the cytoplasmic membrane (CM), initially decreasing the fluidity of the bilayer, and induces changes in gene expression indicative of an attempt to preserve and repair a compromised cell wall. On further incubation, the CM is reorganized; the amount of lysylphosphatidylglycerol is markedly reduced, with a concomitant increase in phosphatidylglycerol, and the proportion of branched chain fatty acids increases, resulting in a more fluid structure. We found no evidence that ECg modulates the enzymatic activity of PBP2a through direct binding to the protein but determined that PBP2 is delocalized from the FtsZ-anchored cell wall biosynthetic machinery at the septal division site following intercalation into the CM. We argue that many features of the ECg-induced phenotype can be explained by changes in the fluid dynamics of the CM.     

Geographic variation in male courtship acoustics and genetic divergence of populations of the Cotesia flavipes species complex

Courtship behaviors of insect populations can vary across the range of a species. Populations exhibiting divergent courtship behavior may indicate genetic divergence or cryptic species. Courtship acoustic signals produced by male wing fanning and genetic structure (using amplified fragment length polymorphisms) were examined for seven allopatric populations of the Cotesia flavipes (Hymenoptera: Braconidae) species complex, using four C. sesamiae (Cameron) and three C. flavipes Cameron populations. Members of this species complex parasitize lepidopteran pests in gramineous crops including sugarcane, maize, and rice . Significant variation was detected in courtship acoustic signals and genetic structure among populations of both species. For C. sesamiae, courtship acoustic signals varied more between populations of two biotypes that were collected near an area of sympatry. The two biotypes of C. sesamiae were also genetically divergent. For C. flavipes, significant differences in acoustic signals and genetic structure occurred among allopatric populations; these differences support the recent designation of one population as a new species. Courtship acoustics play a role in reproductive isolation in this species complex, and are likely used in conjunction with chemical signals. Ecological factors such as host range and host plant use may also influence the divergence of both courtship acoustic signals and genetic structure among populations in the C. flavipes complex.     

Internalization and desensitization of the oxytocin receptor is inhibited by Dynamin and clathrin mutants in human embryonic kidney 293 cells

Oxytocin (OT) has long been used as an uterotonic during labor management in women, and yet responses to OT infusion remain variable and unpredictable among patients. The investigation of oxytocin receptor (OTR) regulation will benefit labor management, because the clinical practice of continuous iv infusion of OT is not optimal. As with other G protein-coupled receptors, it is likely that the OTR internalizes and/or desensitizes upon continuous agonist exposure. The mechanisms by which this might occur, however, are unclear. Here we explore OTR internalization and desensitization in human embryonic kidney cells by utilizing inhibitors of heterologous second messenger systems and recently available mutant cDNA constructs. We report rapid and extensive internalization and desensitization of the OTR upon agonist exposure. Internalization was unaffected by inhibitors of protein kinase C or Ca(2+) calmodulin-dependant kinase II but was significantly reduced after transfection with dominant-negative mutant cDNAs of G protein-coupled receptor kinase 2, beta-Arrestin2, Dynamin, and Eps15 (a component of clathrin-coated pits). Moreover, desensitization of the OTR, measured by a calcium mobilization assay, was also inhibited by the aforementioned cDNA constructs. Thus, our data demonstrate, for the first time, the importance of the classical clathrin-mediated pathway during agonist-induced OTR internalization and desensitization.     

Biological and biochemical quality of the Artemia (Anostraca: Artemiidae) population from Real de Salinas saltworks, Calkiní, Campeche, Mexico

Cysts of Artemia spp. collected from February 1997 to February 2000 in the Real de Salinas solar saltworks, Campeche, Mexico, were compared with Artemia franciscana (batch number 8,131 Microfeast Artemia Cysts, Texas, USA). The variables determined in these two populations were: number of cysts per gram, hatching percentage, hatching efficiency, hatching rate, hatching synchrony and hatching biomass, as well as diameter of the cysts and length of the nauplii (instar I). For Salinas, the average diameters of the encapsulated and decapsulated cysts were 230.5 +/- 4.14 and 221.8 +/- 3.39 microm, respectively. The thickness of the cyst shell was 4.35 +/- 0.68 microm and the length of the nauplii was 388.11 +/- 4.39 microm, this last value is among the smallest reported in the literature. For the commercial population of A. franciscana, the average diameters of the encapsulated and decapsulated cysts were 230.21 +/- 12.49 and 216.96 +/- 13.71, respectively. With respect to the corion thickness and length of the nauplii the values were 6.62 +/- 2.72 and 424.70 +/- 30.08, respectively. The protein value of the cysts (47.91 %) and nauplii (50.5 %) of Artemia population from Real de Salinas, are considered adequate to be used as food in aquaculture. The results indicate that the population from Real de Salinas presents positive features for its use in aquaculture in the region.     

Subchronic and acute preclinic toxicity and some pharmacological effects of the water extract from leaves of Petiveria alliacea (Phytolaccaceae)

We tested the effects of the aqueous extract of Petiveria alliacea leaves on acute and sub-chronic toxicity, hematocrit and blood glucose level and intestinal motility of male albino NGP mice of 20 to 25 g mean weight. Treatments were in all cases doses of 1,000 and 2,000 mg/kg animal weight and a control treatment with 0.5 ml distilled water, using 10 animals per treatment and administered orally every day (5 days per week). Experimental periods were 18 and 70 days for acute and sub chronic toxicity, respectively. No mortality nor any toxicity signs could be observed. A slight but significant increase in the glucose levels during the first three weeks was observed with the 1,000 mg/kg dose but not for the higher 2,000 mg/kg dose. After administering the doses once after a starving period of six hours, no significant differences in intestinal motility could be found.     

Recruiting of somatotroph cells after combined somatostatin, GHRH and growth hormone (GH) secretagogue stimulation in a study of pituitary GH reserve in prepuberal female rats

Diagnostic confirmation of growth hormone (GH) deficiency in children and adults is based on stimulation tests designed to assess the pituitary reserve by measuring the amount of GH released into the bloodstream; however, the results obtained by this means cannot provide any direct indication of the amount of GH actually produced by pituitary somatotroph cells. The present paper sought to test the hypothesis that release of GH following administration of specific stimuli does not accurately reflect the somatotroph cell response, and that the amount of GH released into the bloodstream may often be greater or smaller than the amount synthesized. GH release and changes in the proportion of somatotroph cells were charted in prepuberal female Wistar rats, following administration of several different GH stimuli: GHRH (1 microg/kg), GHRP-6 (1 microg/kg), GHRELIN (1 microg/kg) and combined GHRH-based treatments, with or without SRIH pretreatment (1 microg/kg) 90 minutes earlier. Peak serum GH values were recorded 15 minutes after administration of GHRH+GHRELIN and GHRH+GHRP-6; maximum stimulation in terms of an increased proportion of somatotroph cells occurred 15 minutes after combined adminstration of GHRH + GHRELIN. SRIH pretreatment (- 90 min) inhibited GH release, with a subsequent "escape" and lack of response to stimulation which lasted at least 30 minutes except following administration of GHRH. However, combined administration of GHRH+GHRELIN maintained stimulation of the somatotroph cell population. In conclusion, the results suggest that the enhanced GH release prompted by stimulation tests used to diagnose GH deficiency in prepuberal female rats does not fully reflect somatroph cell dynamics, and that not all the GH produced and stored by somatotroph cells is released into the bloodstream.     

Improved gating of a chimeric alpha7-5HT3A receptor upon mutations at the M2-M3 extracellular loop

Acetylcholine-evoked currents of the receptor chimera alpha7-5HT3A V201 expressed in Xenopus oocytes are strikingly small when compared to the amount of alpha-bungarotoxin binding sites detected at the oocyte membrane. Since the chimeric receptor is made of the extracellular N-terminal region of the rat alpha7 nicotinic acetylcholine receptor and the C-terminal region of the mouse 5-HT3A receptor, which includes the ion channel, we hypothesized that communication between these two regions was not optimal. Here, we show that mutating to aspartate several adjacent positions in the M2-M3 extracellular linker increases current amplitudes to different extents, thus confirming the important role of this region on receptor gating.