Studies on optimal conditions for polysaccharide production byPorphyridium cruentum

Summary Exocellular polysaccharide production byPorphyridium cruentum was studied in fed-batch cultures. Growth of the culture was characterized by a brief log phase, followed by a lineartype phase. The duration and the slope of the latter phase are largely dependent on culture conditions. The presence of polysaccharide in the culture medium was observed as soon as the log phase was over but the quantity did not become significant until the end of growth. Polysaccharide production depended on the cell number and the specific productivity. The cell number was affected mainly by the initial nitrogen and phosphorus concentrations and the specific productivity by the aeration and agitation systems. Other environmental conditions had no significant effect on polysaccharide production. Under photoperiodic illumination the oscillations in cell volume observed after the log phase may indicate a synchronization of polysaccharide synthesis and/or excretion with the light period and the solubilization with the dark period.

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Estudios sobre las condiciones óptimas de crecimiento para la produccióin de polisaccáridos por Porphyridium cruentum

Resumen La producción de polisaccáridos exocelulares porPorphiridium cruentum se estudió en cultivos fed-batch. El crecimiento del cultivo se caracterizó por una breve fase log seguida por una fase de tipo linear. La duración y la pendiente de esta última fase son en gran parte dependientes de las condiciones de cultivo. La presencia de polisaccáridos se observó tan pronto como se hubo terminado la fase log, sin embargo cantidades significativas de éstos no se obtuvieron hasta el final del crecimiento. La producción de polisaccáridos dependió del número de células y de la producción específica. El número de células se vió afectado principalmente por la concentración inicial de fósforo y de nitrógeno. La productividad específica lo fue por los sistemas de aeración y de agitación. No se observó que otras condiciones del medio tuvieran efecto significativo alguno sobre la producción de polisaccáridos.

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Etudes sur les conditions optimales de croissance pour la production de polysaccharides par Porphyridium cruentum

Résumé La production de polysaccharide parPorphyridium cruentum a été étudiée au cours de cultures fed-batch. La croissance d'une culture est caractérisée par une courte phase log suivie d'une phase de type linéaire. La durée et la pente de cette dernière phase dépendant beaucoup des conditions de culture. La présence de polysaccharide dans le milieu de culture a été observée dès la fin de la phase log mais elle ne devient importante qu'à la fin de la croissance. La production de polysaccharide parait être fonction du nombre de cellules et de la productivité spécifique: le nombre de cellules est essentiellement affecté par les concentrations en nitrates et phosphates du milieu de culture, la productivité spécifique par les systèmes d'aération et d'agitation. Les autres conditions testées n'ont pas eu d'influence significative sur la production de polysaccharide.

     

Microlocating lithium in the mouse embryo by use of a (n, α) nuclear reaction

Summary The quantitative imaging of lithium distribution, in histological sections of 15-days old mouse embryos (whose mother had been submitted to Li-treatment), was performed using⁶Li isotope as tracer,⁶Li(n,)³H nuclear reaction for detection, and dielectric track detectors. Despite the particular difficulties of cryosectioning the embryos without disturbing the lithium distribution, the Li regionalization appeared to be very clear-cut. The ectomesodermic tissues were significantly more loaded with lithium than the endodermic ones. This is probably related to the ectomesodermic tissues being also those most sensitive to the teratogenic effect of lithium. The Li-distribution in the embryo brain was almost homogeneous, instead of being heterogeneous as in adult brain. The mean Li-concentration in the embryo brain was not much below the Li concentration in the grey matter of the mother brain, but it was significantly larger than that in the white matter of the mother brain. Our results are discussed in the context of teratogenic effects observed in situ during mammalian development.     

Effects of temperature and CO2 enrichment on kinetic properties of phospho-enol-pyruvate carboxylase in two ecotypes of Echinochloa crus-galli (L.) Beauv., a C4 weed grass species

Summary Two populations of Echinochloa crus-galli (Québec, Mississippi) were grown at the Duke University Phytotron under 2 thermoperiods (28°/22°C, 21°/15°C day/night) and 2 CO₂ regimes (350 and 675 l l^-1). Thermostability, energy of activation (E _a ),K _m (PEP), K _m (Mg⁺⁺), and specific activity of phospho-enol-pyruvate carboxylase (PEP_c) were analyzed in partially purified enzyme preparations of plants grown for 5 weeks. Thermostability of PEP_c from extracts (in vitro) and leaves (in situ) was significantly higher in Mississippi plants. In vitro denaturation was not appreciably modified by thermal acclimation but CO₂ enrichment elicited higher thermostability of PEP_c. In situ thermostability was significantly higher than that of in vitro assays and was higher in Mississippi plants acclimated at 28°/22°C and in plants of the two ecotypes grown at 675 l l^-1 CO₂. E _a (Q ₁₀ 30°/20°C) for PEP_c was significantly lower in Québec plants as compared to Mississippi and no acclimatory shifts were observed. Significantly higher K _m's (PEP) in 20°C assays were obtained for Mississippi as compared to Québec plants but values were similar at 30°C and 40°C assays. K _m (Mg⁺⁺) decreased at higher assay temperatures and were significantly lower for PEP_c of the Québec ecotype. No significant changes in K _m (Mg⁺⁺) values were associated with modifications in temperature on CO₂ regimes. PEP_c activity measured at 30°C was significantly higher for Québec plants when measured on a leaf fresh weight, leaf area or protein basis but not on a chlorophyll basis. Significantly higher PEP_c activity for both genotypes was observed for plants acclimated at 21°/15°C or grown at 675 l l^-1 CO₂. Net photosynthesis (Ps) and net assimilation rates (NAR) were higher in Québec plants and were enhanced by CO₂ enrichment. NAR was higher in plants acclimated at low temperature, while an opposite trend was observed for Ps. PEP_c activities were always in excess of the amounts required to support observed rates of CO₂ assimilation.     

Kinetics of cell-mediated cytotoxicity: Stochastic and deterministic multistage models

One of the body's major defenses against viral diseases and tumors is the killing of abnormal cells by host defense cells, such as T lymphocytes. The mechanism by which killing is accomplished is unknown. Here we develop both stochastic and deterministic models for the kinetics of killing in aggregates which contain a single lymphocyte and multiple target cells (LT_n conjugates), as might be seen early in an immune response, and in aggregates containing multiple lymphocytes and a single target cell (L_nT conjugates), which is characteristic of the late phase of a successful immune response. Comparing our models with data, we rule out the possibility of certain classes of lytic mechanisms and draw attention to the characteristics of likely mechanisms. Our stochastic model can be viewed as a specialized application of queueing theory to cell biology. For certain choices of arrival-time and service-time distributions, we find an exact correspondence between our stochastic and deterministic models.     

Locus determining the human sperm-specific lactate dehydrogenase,LDHC, is syntenic with LDHC

From the data presented in this report, the human LDHC gene locus is assigned to chromosome 11. Three genes determine lactate dehydrogenase (LDH) in man. LDHA and LDHB are expressed in most somatic tissues, while expression of LDHC is confined to the germinal epithelium of the testes. A human LDHC cDNA clone was used as a probe to analyze genomic DNA from rodent/human somatic cell hybrids. The pattern of bands with LDHC hybridization is easily distinguished from the pattern detected by LDHA hybridization, and the LDHC probe is specific for testis mRNA. The structural gene LDHA has been previously assigned to human chromosome 11, while LDHB maps to chromosome 12. Studies of pigeon LDH have shown tight linkage between LDHB and LDHC leading to the expectation that these genes would be syntenic in man. However, the data presented in this paper show conclusively that LDHC is syntenic with LDHA on human chromosome 11. The terminology for LDH genes LDHA, LDHB, and LDHC is equivalent to Ldhl, Ldh2, and Ldh3, respectively.     

Mobilization of cloned luciferase genes into Vibrio harveyi luminescence mutants

A recombinant plasmid which carried a 5 kb fragment of Vibrio harveyi DNA containing the luxA and luxB genes was mobilized from Escherichia coli into luminescence-deficient mutants of V. harveyi. The cloned genes complemented a temperature sensitive luciferase mutation, but failed to complement lesions in two different aldehyde deficient mutants. Expression of the cloned genes was not subject to autoinduction in either E. coli or in V. harveyi.     

Community patterns of nectivorous adult parasitoids (Diptera,Bombyliidae) on their resources

Summary Highly diverse assemblages of nectivorous bee flies (Diptera: bombyliidae) occur at desert sites in California presenting an opportunity to investigate the ecology of this little-known group. This study compared communities of adult bee flies visiting flowers at two sites, one in the Mojave Desert (Darwin Plateau) and one in the Great Basin (Mono Basin), during periods of higher and lower resource abundance. The range of resources used by single species varied inversely with the number of species present, with the greatest number of species and smallest niche breadths occurring at the Darwin Plateau. Adult bee flies did not visit flower resources at random. Rather the two major divisions of the family exhibited contrasting patterns of specialization on plant species. Results of this study support the hypothesis that resources were limiting for adult bee flies in the period of lower food abundance at the Darwin Plateau and not limiting at the Mono Basin during this study. Bee flies at the Mono Basin exhibited lower densities per flower (despite higher densities per unit area), lower frequency of feeding, a lower degree of specialization, and less pronounced phenological changes than bee flies at the Darwin Plateau. The data suggest that episodes of population regulation in the non-parasitic (i.e. adult) stage, due to short supply of the adults' food, contribute to determining the structure of parasitoid communities.     

Sexual differentiation of rat liver carbonic anhydrase III

Using radioimmunoassay, the concentration of carbonic anhydrase III in the livers of adult male rats was found to be approx. 30-times greater than that observed in mature females. Castration of male rats led to a marked reduction in liver carbonic anhydrase III concentrations which could be partially restored to control levels by testosterone replacement. Administration of testosterone to ovariectomised female rats induced about a 5-fold increase in liver carbonic anhydrase III concentration. Immunoprecipitation analysis of the products of liver mRNA translation in vitro with antiserum specific for carbonic anhydrase III showed that hormonal control of the levels of carbonic anhydrase III in liver is mediated by changes in the amount of translatable carbonic anhydrase III mRNA. Marked changes in liver carbonic anhydrase III concentrations were also observed in developing and ageing male rats.     

Postoperative Depression of Tumour-directed Cell-mediated Immunity in Patients with Malignant Disease

Leucocytes from 46 melanoma patients, 45 breast carcinoma patients, and 95 control donors were tested by the leucocyte migration test against the supernatants of homogenates of malignant melanomas, breast carcinomas, simple breast tumours, and breasts showing simple cystic disease. By comparison with controls inhibition of migration occurred significantly more frequently when tumour patients'' leucocytes were exposed to extracts of histogenetically similar tumours.Cell-mediated immunity to tumour-associated antigens was measured in 12 patients with breast carcinoma and 12 with malignant melanoma immediately before surgical operation and in the postoperative period. All patients tested before operation showed significant inhibition of migration on contact with extracts of histogenetically similar tumours. Postoperatively the degree of leucocyte migration inhibition was reduced in all patients with melanoma and breast carcinoma. Significant inhibition of leucocyte migration returned in most patients 6-22 days after operation.     

The behaviour of 14C profiles in Helianthus seedlings

Summary The log. ¹⁴C activity/distance profile in the stems of Helianthus seedlings consists of two main parts: region 1, the linear advancing front and region 2, which is also linear but with a less steep slope. As the front passes down the stem, the slope of region 1 remains constant but the amplitude of the front becomes attenuated. The attenuation increases with temperature. The apparent velocity of the profile, which can be derived from the position of the front, is also temperature dependent. Small amounts of ¹⁴C occur in the stem ahead of the profile; these amounts increase with a rise of temperature. Region 2 behaves differently: its slope decreases steadily with time but it is insensitive to temperature. The behaviour of this region is dependent on the movement of tracer into an immobile fraction as well as on the longitudinal movement of tracer in the translocation stream.