Electrophoretic and immunochemical study of the lipopolysaccharides produced by chemostat-grown Escherichia coli O157

Two chemically different O-polysaccharides, a low molecular mass form of LPS and core LPS produced by chemostat-grown E. coli O157, were analysed by SDS-PAGE, silver staining and immunoblotting. The reactivities of the different O-polysaccharides with antisera prepared against E. coli O157 grown in batch culture, Salmonella O30 or Brucella abortus were very similar, showing that the O-polysaccharides share at least some antigenic determinants. The reactions of the low molecular mass LPS with the antisera indicated it was semi-rough LPS having one repeat unit of the O-polysaccharide attached to core LPS.     

Photosynthesis and nitrogen fixation in legume plants

Plants pass through a succession of growth phases at a rate largely controlled by environmental factors. The spatial arrangement and efficiency of plant organs are influenced by the fluxes of energy and matter in their environments. Thus, the successful integration of processes, such as photosynthesis and nitrogen fixation, occurring in the very different environments of the soil and the air requires a complex functional balance. Such a balance is particularly complex for legumes in which the genetic expressions of the host plant and Rhizobium influence the nitrogen economy. Progress towards improvements in symbiotic nitrogen fixation has been severely limited by the difficulty of distinguishing between the metabolic activities of the roots and nodules in whole plant studies. Recent improvements in experimental precision have revealed processes which govern gaseous diffusion in nodules and control their carbohydrate use. Furthermore, the application of quantitative models to problems of carbon and nitrogen nutrition is improving the understanding of plant growth.     

Recovery of thrombopoietin during purification

A thrombocytopoiesis-stimulating factor (TSF or thrombopoietin) was previously purified by a six-step purification procedure. However, the exact quantity of TSF that was recovered, through the various purification procedures, was unknown because of the absence of a method for establishing a unit of measure of TSF. In the present work dose-response relationships on both the crude TSF preparations and on the more highly purified TSF were determined. TSF units were calculated from the dose-response curves. A unit of TSF is defined as the amount of material (mg) that is required to increase the percentages 35S incorporation into platelets of immunothrombocythemic mice by 50% above the baseline. The results of determining the TSF units on the crude TSF preparation indicated that 0.11 unit (U) of TSF/mg protein was present. Results showed that the specific activity of TSF can be increased to about 3.6 U/mg by a single purification procedure using Sephadex G-75 column chromatography. Increased specific activities were obtained by additional purification steps, i.e., DEAE-cellulose column chromatography, SE-HPLC, DEAE-HPLC, and SDS-PAGE. The purified product appears to have a specific activity of about 11,000 U/mg of protein with 0.00003% of the protein and 1.1% of the TSF recovered from the starting material. Establishing a unit of measure for TSF will allow calculations of its degree of purity, provide a method for quantitation of recoveries of activities after various purification procedures, and allow comparisons of results from different experiments and different laboratories.     

Behavioral interactions between three birch aphid species and Adalia bipunctata larvae

First and fourth instars of three birch aphid species were exposed to first and fourth instars of Adalia bipunctata (L.), the most common aphid predator on silver birch, Betula pendula Roth, in northern California. Defensive behavior differed by aphid species. Euceraphis betulae (Koch) (Eb), the most successful escapee, was highly mobile and frequently walked away from coccinellid larvae. Betulaphis brevipilosa Börner (Bb), a flat, sessile species, was the least successful aphid at actively escaping from A. bipunctata larvae, but could passively escape detection when coccinellid larvae walked over nymphs and did not perceive them. Active escape behavior was much safer for aphids than passive avoidance of detection. Both instars of Eb and fourth instars of Callipterinella calliptera (Hartig) (Cc) escaped from coccinellid larvae more frequently when approached from the front, apparently using vision for pre-contact detection of A. bipunctata. These aphids avoided physical contact with larger predators more often than with smaller predators. Level of predation by A. bipunctata on these three aphid species is dependent upon types of aphid defense.

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Résumé Des larves de premier et troisième stades de 3 espèces de pucerons du bouleau: Betulaphis brevipilosa, Callipterinella calliptera et Euceraphis betulae ont été exposées aux attaques des larves du premier et du quatrième stades d'Adalia bipunctata, prédateur le plus fréquent de pucerons sur Betula pendula en Californie du Nord. Le comportement défensif dépend beaucoup de l'espèce de puceron. E. betulae, qui s'échappe avec le plus de succès, est très mobile et s'écarte fréquemment des larves agressives de coccinelles. B. brevipilosa, espèce plate, sessile, a le moins de succès dans la protection active contre les attaques des larves de A. bipunctata, mais elle peut échapper passivement à la détection des larves de coccinelles qui ne peuvent pas les discerner lorsqu'elles circulent parmi les larves de pucerons. E. betulae (aux deux stades) et C. calliptera (au quatrième) échappent le plus aux larves de coccinelles qui attaquent de front, ce qui laisse supposer que la vision permet de détecter A. bipunctata avant le contact. Le succès des larves de coccinelles varie selon les stades du puceron et de la coccinelle. Les possibilités d'obtention de niveaux de prédation élevés de ces 3 pucerons par A. bipunctata dépend du type de protection du puceron.

     

Construction of an Unstable Ring-X Chromosome Bearing the Autosomal Dopa Decarboxylase Gene in Drosophila melanogaster and Analysis of Ddc Mosaics

An unstable Ring-X chromosome, Ddc⁺- Ring-X carrying a cloned Dopa decarboxylase (Ddc) encoding segment was constructed. The construction involved a double recombination event between the unstable Ring-X, R(1)w^vC and a Rod-X chromosome which contained a P-element mediated Ddc ⁺ insert. The resulting Ddc⁺-Ring-X chromosome behaves similarly to the parent chromosome with respect to somatic instability. The Ddc⁺-Ring-X chromosome was used to generate Ddc mosaics. Analyses of Ddc mosaics revealed that while there was no absolute requirement for the Ddc ⁺ expression in either the epidermis or the nervous system, very large mutant clones did affect the viability of the mosaic.     

Diminished steroidogenic response of hamster granulosa cells to estrogen in vitro

Summary We have previously demonstrated that estrogen can exert inhibitory or atretogenic effects on the ovaries of both rats and rhesus monkeys in vivo. This study was designed to test whether the hamster (Mesocricetus auratus) is an appropriate model in which to test the effects of estrogens (diethylstilbestrol and estradiol-17) on steroid accumulation by ovarian granulosa cells in vitro, and whether the effects are similar to those demonstrated for other species in vivo. Immature female hamsters were injected with pregnant mare's serum gonadotropin at 28 to 30 days of age. Animals were sacrificed and follicular contents aspirated three days later. Granulosa cells were either left untreated or treated with diethylstilbestrol or estradiol (1×10^-7 M) in vitro for 72 h in the presence of androstenedione (1×10^-7 M), and in the presence or absence of serum (10%) or human follicle-stimulating hormone (20 ng/ml), and long-term accumulation of estrogen and progesterone was determined. Diethylstilbestrol inhibited accumulation of estrogen regardless of the presence or absence of follicle-stimulating hormone. In contrast, only estradiol plus follicle-stimulating hormone augmented accumulation of progesterone by granulosa cells. These findings that estrogen can be non-stimulatory or inhibitory to function of granulosa cells in vitro parallel those shown in vivo. Our experimental approach may therefore represent an appropriate model for study of the direct effects of estradiol on the function of granulosa cells.     

Interaction between nitrogen and photon flux density in birch seedlings at steady-state nutrition

Birch ( Betula pendula Roth.) was investigated under steady-state nutrition and growth at different incident photon flux densities (PFD) and different relative addition rates of nitrogen. PFD had a strong influence on the relative growth rate at optimum nutrition and on the nitrogen productivity (growth rate per unit of nitrogen) but little effect on the formal relationships between nitrogen and growth, i.e. PFD and nitrogen nutrition are orthogonal growth factors. At a given suboptimum nitrogen (the same distance from optimum), increased PFD increased the relative growth rate and, therefore, the relative uptake rate and the required relative addition rate in accordance with the theoretical equality between these three parameters at steady-state nutrition. Correspondingly, at a given suboptimum relative addition rate, increased PFD decreased nitrogen status (larger distance from optimum) at an unchanged relative growth rate. Nutrient uptake rate, dry matter content, and partitioning of biomass and nutrients are strongly influenced by nitrogen status. PFD influences these characteristics, but only to an extent corresponding to its effect on the nitrogen status. The influence of PDF on the relative growth rate at optimum and on nitrogen productivity is well described by hyperbolic relationships, similar to reported PFD/photosynthesis relationships. These expressions for plant growth as well as the productivities of leaf area and quantum appear to be valuable characteristics of plant responses to light and nutrition. Although the calculated PFD/growth relationships indicate saturation at high values of PFD, a more realistic estimate of PFD at which saturation occurs is about 30 mol m⁻² day⁻¹, where the highest relative growth rate and nitrogen productivity were experimentally determined. No significant effect was observed because of day length differences between the present and previous experiments.