Development of chicken embryos in a pulsed magnetic field

Six independent experiments of common design were performed in laboratories in Canada, Spain, Sweden, and the United States of America. Fertilized eggs of domestic chickens were incubated as controls or in a pulsed magnetic field (PMF); embryos were then examined for developmental anomalies. Identical equipment in each laboratory consisted of two incubators, each containing a Helmholtz coil and electronic devices to develop, control, and monitor the pulsed field and to monitor temperature, relative humidity, and vibrations. A unipolar, pulsed, magnetic field (500-microseconds pulse duration, 100 pulses per s, 1-microT peak density, and 2-microseconds rise and fall time) was applied to experimental eggs during 48 h of incubation. In each laboratory, ten eggs were simultaneously sham exposed in a control incubator (pulse generator not activated) while the PMF was applied to ten eggs in the other incubator. The procedure was repeated ten times in each laboratory, and incubators were alternately used as a control device or as an active source of the PMF. After a 48-h exposure, the eggs were evaluated for fertility. All embryos were then assayed in the blind for development, morphology, and stage of maturity. In five of six laboratories, more exposed embryos exhibited structural anomalies than did controls, although putatively significant differences were observed in only two laboratories (two-tailed Ps of .03 and less than .001), and the significance of the difference in a third laboratory was only marginal (two-tailed P = .08). When the data from all six laboratories are pooled, the difference in incidence of abnormalities in PMF-exposed embryos (approximately 25 percent) and that of controls (approximately 19 percent), although small, is highly significant, as is the interaction between incidence of abnormalities and laboratory site (both Ps less than .001). The factor or factors responsible for the marked variability of inter-laboratory differences are unknown.     

Mitogens and hepatocyte growth control in vivo and in vitro

The online version of the original article can be found at     

Full-length sequence and mosaic structure of a human immunodeficiency virus type 1 isolate from Thailand.

Human immunodeficiency virus type 1 isolates of envelope genotype E are contributing substantially to the global pandemic. These strains appear to be mosaics, with the gag gene from clade A and the envelope from clade E; the parental clade E strain has not been found. Here we report the first full genomic sequence of one such mosaic virus, isolate CM240 from Thailand. Multiple breakpoints between the two parental genotypes have been found in a CM240 virus. The entire gag-pol region and most, if not all, of the accessory genes vif, vpr, tat, rev, and vpu appear to derive from clade A. The genotype switches to E shortly after the signal peptide of the envelope and back to clade A near the middle of gp41; thus, the portion of the envelope that lies on the cytoplasmic side of the membrane appears to be principally derived not from clade E, as previously thought, but from clade A. Another small segment not belonging to any recognized clade and presumably also contributed by the parental E strain has been found in the long terminal repeat. It may be significant that the implied virion structure resembles a pseudotype virus with the matrix and core from one clade and the outer envelope from another. In the long terminal repeat, differences were observed between CM240 and other clades in the number of NF-kappa B binding sites, the sequence of the TATA box, and the putative secondary structure of the transactivation response region stem-loop. The mosaic structure of a CM240 virion is suggestive of phenotypic differences which might have contributed to the emergence of this variant.     

Gliding motility in slide cultures of Myxococcus xanthus in stable and steep chemical gradients.

A method was devised to construct stable and steep chemical gradients in slide cultures to study the movements of gliding cells. The movement of Myxococcus xanthus individual cells and small swarms was studied in these gradients. There was no response to gradients of Casitone and yeast extract that were previously reported to stimulate a positive chemotactic response with M. xanthus.     

Functional coupling of a Ca2+/calmodulin-dependent nitric oxide synthase and a soluble guanylyl cyclase in vertebrate photoreceptor cells.

Electrophysiological recordings on retinal rod cells, horizontal cells and on-bipolar cells indicate that exogenous nitric oxide (NO) has neuromodulatory effects in the vertebrate retina. We report here endogenous NO formation in mammalian photoreceptor cells. Photoreceptor NO synthase resembled the neuronal NOS type I from mammalian brain. NOS activity utilized the substrate L-arginine (Km = 4 microM) and the cofactors NADPH, FAD, FMN and tetrahydrobiopterin. The activity showed a complete dependence on the free calcium concentration ([Ca2+]) and was mediated by calmodulin. NO synthase activity was sufficient to activate an endogenous soluble guanylyl cyclase that copurified in photoreceptor preparations. This functional coupling was strictly controlled by the free [Ca2+] (EC50 = 0.84 microM). Activation of the soluble guanylyl cyclase by endogenous NO was up to 100% of the maximal activation of this enzyme observed with the exogenous NO donor compound sodium nitroprusside. This NO/cGMP pathway was predominantly localized in inner and not in outer segments of photoreceptors. Immunocytochemically, we localized NO synthase type I mainly in the ellipsoid region of the inner segments and a soluble guanylyl cyclase in cell bodies of cone photoreceptor cells. We conclude that in photoreceptors endogenous NO is functionally coupled to a soluble guanylyl cyclase and suggest that it has a neuromodulatory role in visual transduction and in synaptic transmission in the outer retina.     

A change in a single gene of Salmonella typhimurium can dramatically change its buoyant density.

The growth rates and buoyant densities of a Salmonella typhimurium mutant, TL126 (proB74A+), with enhanced osmotolerance caused by proline overproduction were measured and compared with the growth rates and buoyant densities of an isogenic (wild-type) strain, TL128 (proB+ A+), with normal control of proline production. Growth rates were determined in a rich medium (Luria broth) with added NaCl to produce various osmotic strengths ranging from 300 to 2,000 mosM. At low concentrations of NaCl, there was little variation in doubling times between the two strains. However, as the osmotic strength of the medium approached and exceeded 1,300 mosM, the doubling times of TL126 (osmotolerant) were 1.5 to 2 times faster than those of TL128 (wild type), confirming the osmotolerance of TL126. Buoyant densities were determined by equilibrium sedimentation in a Percoll gradient of osmotic strength equal to that of the growth medium. The osmolarity of the Percoll gradient was adjusted by the addition of NaCl. At low osmolarities (300 to 500 mosM), the buoyant density of TL126 (osmotolerant) was slightly but consistently lower than that of TL128 (wild type). As the osmotic strength was increased, the buoyant density of TL126 (osmotolerant) increased in proportion to the osmotic strength. In contrast, the buoyant density of strain TL128 (wild type) did not increase as much. At high osmolarities (1,600 to 2,000 mosM), the buoyant density of TL126 (osmotolerant) was consistently higher than that of TL128 (wild type). These results suggest that the intracellular accumulation of proline by TL126, the osmotolerant strain, increases both the growth rates and buoyant densities at osmolarities of 1,300 mosM and above.     

Molecular and genetic characterisation of German families with paramyotonia congenita and demonstration of founder effect in the Ravensberg families

Eighteen German families with a history of paramyotonia congenita (PC) were characterised by genetic und mutational analysis at the SCN4A locus, which encodes the -subunit of the adult skeletal muscle sodium channel. We concentrated our analysis primarily on these families to test the hypothesis that a predominance of one common mutation occurs in all German PC families and that this mutation arose in a common ancestor originating in the North-West of the country. The present eighteen PC families exhibit two different mutations (R1448C and R1448H) on various SCN4A dinucleotide repeat haplotypes and therefore the majority of the mutations probably occurred independently. However, the R1448H mutation is extremely frequent in the North-West of Germany (Ravensberger Land) on a specific SCN4A microsatellite haplotype, indicating a founder effect within this subpopulation. Our results suggest that the R1448C/R1448H mutations are by far the most common to be associated with the PC phenotype in the German population.This paper is dedicated to Professor Dr. Dr. Peter Emil Becker on the occasion of this 85th birthday     

Heterogeneity of soil and soil solution chemistry under Norway spruce (Picea abies Karst.) and European beech (Fagus silvatica L.) as influenced by distance from the stem basis

The present study aims at characterizing plant water status under field conditions on a daily basis, in order to improve operational predictions of plant water stress. Ohm's law analog serves as a basis for establishing daily soil-plant relationships, using experimental data from a water-limited soybean crop: 227-1. The daily transpiration flux, T, is estimated from experimental evapotranspiration data and simulated soil evaporation values. The difference, 227-2, named the effective potential gradient, is derived from i) the midday leaf potential of the uppermost expanded leaves and ii) an effective soil potential accounting for soil potential profile and an effectiveness factor of roots competing for water uptake. This factor is experimentally estimated from field observation of roots. G is an apparent hydraulic conductance of water flow from the soil to the leaves. The value of the lower potential limit for water extraction, required to assess the effective soil potential, is calculated with respect to the plant using the predawn leaf potential. It is found to be equal to –1.2 MPa. It appears that over the range of soil and climatic conditions experienced, the daily effective potential gradient remains constant (1.2 MPa), implying that, on a daily basis, transpiration only depends on the hydraulic conductance. The authors explain this behaviour by diurnal variation of osmotic potential, relying on Morgan's theory (1984). Possible generalization of the results to other crop species is suggested, providing a framework for reasoning plant water behaviour at a daily time step.     

The effect of water flow on photosynthetic processes of the alga Ulva lactuca L.

Photosynthetic rates of aquatic macrophytes are affected by the diffusion of carbon through the boundary layer which decreases with increasing flow velocities. This is shown by a significant increase in photosynthetic rates of Ulva lactuca fronds exposed to friction velocities (u _*) between 0.0 and 0.3 cm s^–1. No further increase in photosynthetic rates is observed at u _* values between 0.3 and 1.0 cm s^–1. Stagnating flow conditions at saturating light levels caused a 29% reduction in photosynthetic rates. Experiments in a closed system indicate that Ulva may utilize internal carbon sources during periods of stagnation. On a subtidal rock directly exposed to wave action, Ulva lactuca is not exposed to such conditions while in a wave flushed intertidal pool stagnation occurs during very short time intervals based on in situ measurements of u _* levels on fronds of this species using a microprocessor-controlled, autonomous recorder and hot-film sensors.