The Site Specificity of Two Species of Gregarina in Tenebrio molitor Larvae

The site specificity of the apicomplexans Gregarina cuneata and Gregarina sleini , in larval Tenebrio molitor was investigated. Gregarina cuneata was found to inhabit the anteriormost region of the larval midgut, while G. steini was restricted to the posterior portion of the intestine. The site specificity of the pair was conserved in single and concurrent infections. Interspecific interactions do not seem to be presently responsible for the resource partitioning by the 2 gregarine species. Key words. Gregarina, site specificity, Tenebrio molitor.     

Effect of aortic balloon inflation on ventilation and brain stem blood flow in piglets

Increases in brain stem blood flow (BBF) during hypoxia may decrease tissue PCO2/[H+], causing minute ventilation (VE) to decrease. To determine whether an increase in BBF, isolated from changes in arterial PO2 and PCO2, can affect respiration, we obstructed the thoracic aorta with a balloon in 31 intact and 24 peripherally chemobarodenervated, anesthetized, spontaneously breathing newborn piglets. Continuous measurements of cardiorespiratory variables were made before and during 2 min of aortic obstruction. Radiolabeled microspheres were used to measure BBF before and approximately 30 s after balloon inflation in eight intact and five denervated animals. After balloon inflation, there was a rapid increase in mean blood pressure in both the intact and denervated animals, followed within 10 s by a decrease in tidal volume and VE. In the intact animals, the decrease in VE after acute hypertension can be ascribed to a baroreceptor-mediated reflex. After peripheral chemobarodenervation, however, acute hypertension continued to produce a decrease in VE, which cannot be explained by baroreceptor stimulation. In these denervated animals, aortic balloon inflation was associated with an increase in BBF (13.1 +/- 2.7%; P less than 0.05). We speculate that the increase in BBF during hypoxia may contribute to the decrease in ventilation observed after carotid body denervation.     

GENETIC RELATEDNESS OF TWO POPULATIONS OF THE SOUTHERN ELEPHANT SEAL, MIROUNGA LEONINA

Blood samples from southern elephant seals ( Mirounga leonina ) from Heard and Macquarie Islands were surveyed electrophoretically for protein variation. Thirty proteins encoded by a minimum of 35 loci were screened, four of which were found to be polymorphic. Statistically significant differences in allele frequencies were found between the two populations at three loci. Heterozygosity estimates for the Heard and Macquarie island populations were 0.034 ± 0.020 (mean ± standard error) and O.029 ± 0.017 respectively, with a Nei distance of 0.007. The findings suggest that the two populations may have diverged genetically and very limited gene flow exists between the islands, a finding consistent with limited information from mark-recapture studies.     

Gustatory sensitivity of the herbivore Tilapia zillii to amino acids

The gustatory sensitivity of the herbivorous fish Tilapia zillii was investigated using electrophysiological techniques. Integrated responses from facial taste nerves were recorded during stimulation by l l amino acids. All compounds proved to be effective stimuli. The relative stimulatory efficacy (RSE) determined at 1 × 10 ⁻³ m indicated that stimuli can be organized into three groups on the basis of similarity of efficacy. Effects of pH which altered the RSE of some amino acids are documented. Amino acid RSE differed to some extent from those of previously studied carnivorous fish. There was concordance between the composition of preferred food, effective feeding stimuli and the peripheral receptor responses. These observations support the hypothesis that peripheral chemosensitivity might serve as a mechanism of feeding specialization in some fish.     

Cyclic Variations in Nitrogen Uptake Rate in Soybean Plants: Uptake During Reproductive Growth

Net uptake of by non-nodulated soybean plants [Glycme max(L ) Merr cv Ransom] growing in flowing hydroponicculture was measured daily during a 63 d period of reproductivedevelopment between the first florally inductive photopenodand late seed growth Removal of from a replenished solution containing 10 mol m^– was determined by ion chromatography Uptake of continued throughout reproductive development The net uptakerate of cycled between maxima and minima with a periodicity of oscillation of 3 to 7 d during the floralstage and about 6 d during the fruiting stage. Coupled withincreasing concentrations of carbon and C:N ratios in tissues,the oscillations in net uptake rates of are evidence that the demand for carbohydrate by reproductiveorgans is contingent on the availability of nitrogen in theshoot pool rather than that the demand for nitrogen followsthe flux of carbohydrate into reproductive tissues. Key words: Nitrate uptake rate, carbon-nitrogen partitioning, Glycme max (L ) Merrill     

Carbon Dioxide Effects on Carbohydrate Status and Partitioning in Rice

The atmospheric carbon dioxide (CO₂) concentration has beenrising and is predicted to reach double the present concentrationsometime during the next century. The objective of this investigationwas to determine the long-term effects of different CO₂ concentrationson carbohydrate status and partitioning in rice (Oryza sativaL cv. IR-30). Rice plants were grown season-long in outdoor,naturally sunlit, environmentally controlled growth chamberswith CO₂ concentrations of 160, 250, 330, 500, 660, and 900µmolCO₂ mol¹ air. In leaf blades, the priority between the partitioningof carbon into storage carbohydrates or into export changedwith developmental stage and CO₂ concentration. During vegetativegrowth, leaf sucrose and starch concentrations increased withincreasing CO₂ concentration but tended to level off above 500µmolmol^–1 CO₂. Similarly, photosynthesis also increased withCO2 concentrations up to 500µmol mol^–1 and thenreached a plateau at higher concentrations. The ratio of starchto sucrose concentration was positively correlated with theCO₂ concentration. At maturity, increasing CO₂ concentrationresulted in an increase in total non-structural carbohydrate(TNC) concentration in leaf blades, leaf sheaths and culms.Carbohydrates that were stored in vegetative plant parts beforeheading made a smaller contribution to grain dry weight at CO₂concentrations below 330µmol mol^–1 than for treatmentsat concentrations above ambient Increasing CO₂ concentrationhad no effect on the carbohydrate concentration in the grainat maturity Key words: CO₂ enrichment, starch, sucrose     

A Dynamic Growth Model of Vegetative Soya Bean Plants: Model Structure and Behaviour under Varying Root Temperature and Nitrogen Concentration

A differential equation model of vegetative growth of the soyabean plant (Glycine max (L.) Merrill cv. ‘Ransom’)was developed to account for plant growth in a phytotron systemunder variation of root temperature and nitrogen concentrationin nutrient solution. The model was tested by comparing modeloutputs with data from four different experiments. Model predictionsagreed fairly well with measured plant performance over a widerange of root temperatures and over a range of nitrogen concentrationsin nutrient solution between 0.5 and 10.0 mmol in the phytotron environment. Sensitivity analyses revealedthat the model was most sensitive to changes in parameters relatingto carbohydrate concentration in the plant and nitrogen uptakerate. Key words: Glycine max (L.) Merrill, dry matter, nitrogen uptake, partitioning, photosynthesis, respiration, sensitivity analysis     

Ribulose 1, 5-bisphosphate Carboxylase/ Oxygenase Activities in Leaves of Greenhouse Roses

An enzyme assay was developed to measure the initial and Mg²⁺–CO₂activated forms of Ribulose 1,5-bisphosphate Carboxylase/Oxygenase(Rubisco) in rose leaves. The assay was verified by co-extractionof the leaflets with partially purified spinach Rubisco andthrough correlation with net photosynthetic rates of individualleaflets (r²=0.7324). Changes in activities were measured asa function of depth of leaves in the canopy for two cultivarsof greenhouse hybrid tea roses. Initial Rubisco activity declinedwith increasing canopy depth for both cultivars. The activatedform of the enzyme, however, remained constant with canopy depthfor cv. Red Success; but increased with canopy depth, then declinedafter mid-canopy in the cv. Royalty. Rubisco activities werealso measured in the cv. Red Success grown in CO₂ enriched environments(100 mm³ dm^–3) at three humidity levels. The activitieswere not significantly affected by humidity treatment. However,there was a trend for plants grown at lower humidity to havehigher activated activities. Key words: Humidity, Rubisco, Rosa ? hybrida, Royalty, Red Success     

Characterization of envelope proteins of alcelaphine herpesvirus 1.

Alcelaphine herpesvirus 1 is a gammaherpesvirus which causes malignant catarrhal fever, an acute lymphoproliferative disorder of cattle and other susceptible Bovidae, which is almost invariably fatal. A preliminary analysis of proteins induced by the virus indicated that as many as six glycoproteins and one nonglycosylated molecule might be present in the virus envelope. Monoclonal antibodies selected for recognition of virion envelope proteins included two that recognized a complex of infected cell proteins, designated the gp115 complex, and neutralized virus infectivity in the absence of complement. The gp115 complex consisted of five glycoproteins of 115, 110, 105, 78, and 48 kilodaltons (kDa), and all except the 48-kDa species reacted with antibody in Western blots (immunoblots). Pulse-chase experiments analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing and nonreducing conditions suggested that the 110-kDa protein was the precursor molecule which was processed by addition of sugars to 115 kDa. The 115-kDa protein was cleaved to form a disulfide-linked heterodimer of 78 and 48 kDa, which was the mature form of the molecule incorporated into the virion envelope. The glycoprotein contained N-linked sugars, but little or no O-linked sugar was present. The relative abundance of the mature protein and its ability to induce neutralizing antibodies suggest that it will prove useful to studies aimed at elucidating the biology and pathogenesis of alcelaphine herpesvirus 1.     

A novel and remarkably thermostable ferredoxin from the hyperthermophilic archaebacterium Pyrococcus furiosus.

The archaebacterium Pyrococcus furiosus is a strict anaerobe that grows optimally at 100 degrees C by a fermentative-type metabolism in which H2 and CO2 are the only detectable products. A ferredoxin, which functions as the electron donor to the hydrogenase of this organism was purified under anaerobic reducing conditions. It had a molecular weight of approximately 12,000 and contained 8 iron atoms and 8 cysteine residues/mol but lacked histidine or arginine residues. Reduction and oxidation of the ferredoxin each required 2 electrons/mol, which is consistent with the presence of two [4Fe-4S] clusters. The reduced protein gave rise to a broad rhombic electronic paramagnetic resonance spectrum, with gz = 2.10, gy = 1.86, gx = 1.80, and a midpoint potential of -345 mV (at pH 8). However, this spectrum represented a minor species, since it quantitated to only approximately 0.3 spins/mol. P. furiosus ferredoxin is therefore distinct from other ferredoxins in that the bulk of its iron is not present as iron-sulfur clusters with an S = 1/2 ground state. The apoferredoxin was reconstituted with iron and sulfide to give a protein that was indistinguishable from the native ferredoxin by its iron content and electron paramagnetic resonance properties, which showed that the novel iron-sulfur clusters were not artifacts of purification. The reduced ferredoxin also functioned as an electron donor for H2 evolution catalyzed by the hydrogenase of the mesophilic eubacterium Clostridium pasteurianum. P. furiosus ferredoxin was resistant to denaturation by sodium dodecyl sulfate (20%, wt/vol) and was remarkably thermostable. Its UV-visible absorption spectrum and electron carrier activity to P. furiosus hydrogenase were unaffected by a 12-h incubation of 95 degrees C.