The zoospore of Pseudoperonospora cubensis, the causal agent of cucurbit downy mildew

The zoospore of Pseudosporonospora cubensis is typical of the secondary zoospore of the Peronosporales. The reniform zoospore contains a central nucleus with a prominent beak-like extension to the kinetosomes on the lateral side of the spore in the groove region. "Fuzzy" vesicles derived from dictyosomes surround and fuse with the contractile vacuole. Mitochondria and microbodies are located in the peripheral cytoplasm of the zoospore but the latter are confined to the groove region of the spore. The microbodies usually contain a laminate inclusion and the microbodies are not in a fixed position in relation to the peripheral cisternae. Neither a microbody-lipid body complex nor a "U-body" were observed.
The kinetosomes of the spore are almost perpendicular to each other at the distal end of the beak-like extension of the nucleus. A complex system of cytoplasmic microtu-bules flare out from the kinetosomes to surround the nucleus and bundles of cytoplasmic microtubules extend under the plasmalemma of the spore. The zoospore contain numerous vesicles with osmiophilic inclusions which are finely striated; these are the so-called finger-print vesicles.     

Hormone metabolism by the fish gill

The fish gill, like the mammalian lung, is ideally situated to process circulating biomolecules because: 1) the gill is the only organ perfused by the entire cardiac output, 2) the in-series positioning of branchial and systemic circulations permits "conditioning" of blood immediately before systemic perfusion and 3) gill microcirculation is extensive, providing substantial endothelial/pillar cell surface in contact with plasma. In addition, two or three distinct circulatory pathways within the gill may differentially affect plasma substrates, raising the possibility of vasoactive control of hormone titers. Hormones may be activated or inactivated by the gill, the latter involving extraction (uptake) from the plasma, metabolism by enzymes on the endothelial surface without uptake or uptake plus intracellular metabolism. Over 60% of angiotensin I (ANG I) is activated to angiotensin II (ANG II) in a single transit through the gill lamellae by pillar cell angiotensin-converting enzyme, whereas both ANG I and II are inactivated by the non-lamellar filamental vasculature. Gills may accumulate and store (uptake 1) or degrade (uptake 2) catecholamines via intracellular monoamine oxidase and catechol-O-methyl transferase enzymes, and they show substrate preference for norepinephrine over epinephrine. Similar processes may exist for serotonin. Atrial natriuretic peptides are efficiently (60-90%) extracted from plasma in vivo by C-type clearance receptors. Fifty percent of an endothelin-1 bolus is removed in a single transit through the gill circulation, arginine vasotocin extraction is modest and bradykinin is virtually unaffected. Arachidonic acid is completely extracted by the gill, whereas extraction of prostaglandins I2 and E2 is only 13 and 5%, respectively. Intense cytochrome P450 immunofluorescence in the pillar cells suggests that the gill vasculature may be an important site of detoxification and production of biologically active epoxides. Thus, gills appear to be potent and selective effectors of hormonal signals.     

Oviposition and offspring survival within eggs of European corn borer: discrimination of the host embryo by female Trichogramma nubilale

Oviposition preference and offspring survival relative to the location of the host embryo was tested in the egg parasitoid Trichogramma nubilale on European corn borer host eggs. Females preferentially oviposited near to the embryo on hosts about 24 h old. Survival of Trichogramma was lower when females oviposited far from the embryo, and a higher proportion of host embryos hatched. Females did not show preferences for drilling or oviposition within very young hosts relative to where the embryo would develop, and these eggs did not produce wasps or host larvae. Female behavior was apparently adaptive in day-old hosts, not to very young hosts.     

A new rheophytic species of Euceraea (Flacourtiaceae) from Sierra de la Neblina, Venezuela

Euceraea rheophytica is newly described and illustrated. It differs from the two other species in the genus, E. nitida and E. sleumeriana, in its much smaller and narrower leaves and in its smaller, spicate (vs. branched) inflorescences. It is known only from frequently flash-flooded riverbanks in the large, central canyon of the Sierra de la Neblina massif in southernmost Venezuela.     

Synthesis and antiplatelet effects of an isoxazole series of glycoprotein IIb/IIIa antagonists

Despite the excellent in vitro potency of a series of benzamide glycoprotein IIb/IIIa antagonists, which have been reported previously, poor in vivo potency in the inhibition of platelet aggregation was observed when the most potent inhibitor XU057 was dosed intravenously to dogs. In this communication, we report that replacement of the benzamide in XU057 with an isoxazolecarboxamide resulted in significant improvement in in vivo potency. More importantly, the analogue XU065 showed an excellent oral antiplatelet effect in dogs.     

Brain Ion and Amino Acid Contents During Edema Development in Hepatic Encephalopathy

Abstract: Brain edema in hepatic encephalopathy has been associated with circulating ammonia that is metabolized to glutamine. We measured alterations in blood chemistry and brain regional specific gravity and ion and amino acid contents in models of simple hyperammonemia and liver failure induced by daily administrations of ammonium acetate (AAc) or thioacetamide (TAA), respectively. Serum and brain ammonia increased to similar levels (200 and 170% of control, respectively) in both experimental groups. Serum transaminase activities increased 10-fold in animals injected with TAA but were unchanged in animals given AAc injections. In both experimental groups glutamine was elevated in cerebral white matter, cerebral gray matter, and basal ganglia, whereas brain tissue specific gravity decreased in all brain regions, indicating edema formation. In the AAc group, we observed a decrease in glutamate and taurine contents concomitant with the development of brain edema. In these animals, cerebral gray matter specific gravity and taurine contents returned to control levels 24 h after the third AAc injection. TAA-injected animals demonstrated similar decreases in brain tissue specific gravity, whereas glutamine, glutamate, and taurine contents were all elevated. During hepatic encephalopathy, ammonia-induced changes in brain amino acid content may contribute to brain edema development.     

The influence of salt on the structure and energetics of supercoiled DNA.

We present a detailed computational study of the influence of salt on the configurations, energies, and dynamics of supercoiled DNA. A potential function that includes both elastic and electrostatic energy components is employed. Specifically, the electrostatic term, with salt-dependent coefficients, is modeled after Stigter's pioneering work on the effective diameter of DNA as a function of salt concentration. Because an effective charge per unit length is used, the electrostatic formulation does not require explicit modeling of phosphates and can be used to study long DNAs at any desired resolution of charge. With explicit consideration of the electrostatic energy, an elastic bending constant corresponding to the nonelectrostatic part of the bending contribution to the persistence length is used. We show, for a series of salt concentrations ranging from 0.005 to 1.0 M sodium, how configurations and energies of supercoiled DNA (1000 and 3000 base pairs) change dramatically with the simulated salt environment. At high salt, the DNA adopts highly compact and bent interwound states, with the bending energy dominating over the other components, and the electrostatic energy playing a minor role in comparison to the bending and twisting terms. At low salt, the DNA supercoils are much more open and loosely interwound, and the electrostatic components are dominant. Over the range of three decades of salt examined, the electrostatic energy changes by a factor of 10. The buckling transition between the circle and figure-8 is highly sensitive to salt concentration: this transition is delayed as salt concentration decreases, with a particularly sharp increase below 0.1 M. For example, for a bending-to-twisting force constant ratio of A/C = 1.5, the linking number difference (delta LK) corresponding to equal energies for the circle and figure-8 increases from 2.1 to 3.25 as salt decreases from 1.0 to 0.005 M. We also present in detail a family of three-lobed supercoiled DNA configurations that are predicted by elasticity theory to be stable at low delta Lk. To our knowledge, such three-dimensional structures have not been previously presented in connection with DNA supercoiling. These branched forms have a higher bending energy than the corresponding interwound configurations at the same delta Lk but, especially at low salt, this bending energy difference is relatively small in comparison with the total energy, which is dominated by the electrostatic contributions. Significantly, the electrostatic energies of the three-lobed and (straight) interwound forms are comparable at each salt environment.(ABSTRACT TRUNCATED AT 400 WORDS)     

Configurational statistics of the DNA duplex: Extended generator matrices to treat the rotations and translations of adjacent residues

The base-to-base virtual bond treatment of nucleic acids used in statistical mechanical calculations of polynucleotide chain properties has been refined by incorporating the six parameters that relate the positions and orientations of sequential rigid bodies. The scheme allows for the sequence-dependent bending, twisting, and displacement of base pairs as well as for asymmetry in the angular and translational fluctuations of individual residues. Expressions are developed for the generator matrices required for the computation, as a function of chain length, of various parameters measuring the overall mean extension and shape of the DNA. Quantities of interest include the end-to-end vector r , the square of the end-to-end distance r², the square radius of gyration s², the center-of-gravity vector g , the second moments of inertia S ^×2, and the higher moments of r and g . The matrix expressions introduced in the 1960s by Flory and co-workers for the determination of configuration-dependent polymer chain averages are decomposed into their translational and orientational contributions so that the methods can be extended to the rigid body analysis of chemical moieties. The new expressions permit, for the first time, examination of the effects of sequence-dependent translations, such as the lateral sliding of residues in A- and B-helices and the vertical opening of base pairs in drug–DNA complexes, on the average extension and shape of the long flexible double helix. The approach is illustrated in the following paper using conformational energy estimates of the base sequence-dependent flexibility of successive B-DNA base pairs. © 1994 John Wiley & Sons, Inc.     

Spatial translational motions of base pairs in DNA molecules: Application of the extended matrix generator method

We have used the elementary generator matrices outlined in the preceding paper to examine the conformational plasticity of the nucleic acid double helix. Here we investigate kinked DNA structures made up of alternating B- and A-type helices and intrinsically curved duplexes perturbed by the intercalation of ligands. We model the B-to-A transition by the lateral translation of adjacent base pairs, and the intercalation of ligands by the vertical displacement of neighboring residues. We report a complete set of average configuration-dependent parameters, ranging from scalars (i.e., persistence lengths) to first- and second-order tensor parameters (i.e., average second moments of inertia), as well as approximations of the associated spatial distributions of the DNA and their angular correlations. The average structures of short chains (of lengths less than 100 base pairs) with local kinks or intrinsically curved sequences are essentially rigid rods. At the smallest chain lengths (10 base pairs), the kinked and curved chains exhibit similar average properties, although they are structurally perturbed compared to the standard B-DNA duplex. In contrast, at lengths of 200 base pairs, the curved and kinked chains are more compact on average and are located in a different space from the standard B- or A-DNA helix. While A-DNA is shorter and thicker than B-DNA in x-ray models, the long flexible A-DNA helix is thinner and more extended on average than its B-DNA counterpart because of more limited fluctuations in local structure. Curved polymers of 50 base pairs or longer also show significantly greater asymmetry than other DNAs (in terms of the distribution of base pairs with respect to the center of gravity of the chain). The intercalation of drugs in the curved DNA straightens and extends the smoothly deformed template. The dimensions of the average ellipsoidal boundaries defining the configurations of the intercalated polymers are roughly double those of the intrinsically curved chain. The altered proportions and orientations of these density functions reflect the changing shape and flexibility of the double helix. The calculations shed new light on the possible structural role of short A-DNA fragments in long B-type duplexes and also offer a model for understanding how GC-specific intercalative ligands can straighten naturally curved DNA. The mechanism is not immediately obvious from current models of DNA curvature, which attribute the bending of the chain to a perturbed structure in repeating tracts of A · T base pairs. © 1994 John Wiley & Sons, Inc.     

Characterization of the Binding of Gallium, Platinum, and Uranium to Pseudomonas fluorescens by Small-Angle X-Ray Scattering and Transmission Electron Microscopy

Small-angle X-ray scattering (SAXS) was used to determine the binding of Ga, U, and Pt to Pseudomonas fluorescens in aqueous buffer. Atomic absorption spectrophotometry was used to quantify the heavy metals during bulk analysis, whereas transmission electron microscopy of whole mounts and thin sections was used to determine the locations of the cell-bound metal precipitates, as well as their sizes and physical structures. Energy-dispersive X-ray spectroscopy confirmed the compositions and identities of the precipitates and helped show that they were associated primarily with the envelope layers of the bacteria. Unlike Ga and Pt, which were located only at the cell surface, U was also found intracellularly in ~ 10% of the cells. This cytoplasmic location ultimately killed and lysed the cells. Surface-bound Ga and U were spread over the entire cell envelope (outer membrane-peptidoglycan-plasma membrane complex), whereas Pt was associated only with the lipopolysaccharide-rich, external face of the outer membrane. SAXS confirmed these data and showed that the bacteria were metal-enshrouded particles that were 1.0 to 1.5 μm in diameter. SAXS also provided a statistically significant representation of the bound metal precipitates, which ranged in size from 10 nm to 1 μm. The correlation between the microscopic data and the scattering data was extremely good. Since SAXS is performed in an aqueous milieu, it yields a more representative picture of the physical state of the metal bound to cell surfaces.