Behaviour of drifting insect larvae

The larval drift behaviour of 23 species representing Ephemeroptera, Plecoptera and Trichoptera was investigated in the laboratory using different current regimes. Mayfly nymphs often performed swimming, while caddis larvae were reluctant to do so. Stonefly nymphs were intermediate. In mayflies swimming seemed to be used to reach the substrate as soon as possible. In contrast most stonefly nymphs by swimming prolonged the time spent in the water column. Modes of swimming and sinking posture differed markedly between the orders. Living passively sinking animals often reached bottom faster than dead control specimens, so consequently behaviour did not always express itself in activity. Some caddis larvae spun adherent anchor lines. Differences among taxa seemed more important in explaining swimming activity compared to preferred habitats (as stream, river and lake) in each species. However, observed differences among closely related species indicated subtle differences related to microhabitat to be of profound importance in explaining the alternative behavioural strategies used.     

Mitogenic effect of PMA + IL 2 on subpopulations of corticoresistant thymocytes

The proliferative response of subpopulations of corticoresistant thymocytes (CRT) to phorbol-12-myristate-13-acetate (PMA) + interleukin 2 (IL 2) was investigated. Thymocyte subpopulations were selected by the indirect "panning" technique, and their purity was checked by cytofluorometry. Microcultures were set up with an optimal concentration of PMA, EL4 supernatant, or pure IL 2 obtained by recombinant DNA technology (r-IL 2) in the presence or in the absence of accessory splenic adherent cells (SAC). Under these conditions, only the Lyt-2+ CRT proliferated, and this response was IL 2-dose-dependent and was increased by accessory cells. When the calcium ionophore A23187 was added to the cultures, the proliferation of L3T4+ CRT was greatly increased. These results were confirmed by cultures at limiting dilution of positively selected Lyt-2+ and L3T4+ subpopulations of CRT at optimal concentrations of PMA, r-IL 2, A23187, and accessory cells. These results are consistent with the idea that two signals are necessary to activate L3T4+ CRT, whereas only IL 2 is necessary for PMA-induced proliferation of Lyt-2+ CRT. Finally, unlike the case of lectin-induced proliferation of Lyt-2+ and L3T4+ CRT, the presence of accessory cells or cell-cell contact is important for optimal response to PMA + IL 2.     

Virulence genes are carried by a megaplasmid of the plant pathogen Pseudomonas solanacearum

Summary A class of avirulent mutants of the plant pathogenic bacterium Pseudomonas solanacearum, strain GMI1000, resistant to acridine orange (Acr^r), harbour a deletion of over 85 kb in their genome. This deletion affects, a1,000 kb megaplasmid which has previously been shown to be present in most of the strains of this species. In addition at least 11 out of 13 independent Tn5 insertions, leading to loss of virulence, are located on the megaplasmid. Nine of them are present in the region which is deleted from the Acr^r mutants. These results suggest that the majority of virulence genes identified so far are plasmid borne.     

Identification of host range determinants in the Rhizobium species MPIK3030

Summary R. meliloti primarily nodulates Medicago sativa but cannot nodulate Macroptilium atropurpureum. By introducing an 11.4 kb region into R. meliloti from the Symplasmid of Rhizobium strain MPIK3030, the host range of the R. meliloti transconjugants were shown to be extended to M. atropurpureum, one of the hosts of MPIK3030 but not normally nodulated by R. meliloti. The region responsible for host range extension was isolated by mass conjugating a clone bank from MPIK3030 into the R. meliloti wild type, and subsequent screening for nodulation on M. atropurpureum. Using deleted derivatives of a plasmid reisolated from endosymbiotic bacteria, the host range region was further narrowed down to three EcoRI fragments. Tn5 mutagenesis allowed the isolation of three discrete regions on an 11.4 kb section, which are involved in the extension of host range to M. atropurpureum. Finally, complementation experiments performed with R. meliloti common nod and hsn mutants indicated that none of the genes involved in the early steps of nodulation, including host-range functions, can be complemented by genes carried on the 11.4 kb fragment derived from MPIK3030.     

Polyester Wadding for Specimen Orientation During Embedding in Methacrylates

Polyester fibers are not dissolved by either glycol methacrylate or methyl methacrylate. Commercial polyester wadding is consequently an advantageous material to use in getting precise orientation of tissue specimens during embedding in methacrylate.     

Permanent Preservation of Whole Alizarin Red S Skeletons by Clearing and Embedding in Polyester Resins

A one-step clearing and embedding procedure for alizarin red S stained skeletons is described. Embryos are fixed in formalin, skinned and eviscerated. After staining in a 10 mg/liter solution of alizarin red S in 5% aqueous KOH, specimens are dehydrated in a graded series of acetone-polyester monomer solutions. Finally, the specimens are embedded at room temperature in the polyester resin. A special reusable metallic mold is described for embedment of large fetuses. Specimens previously cleared in glycerol can be processed with this method.     

Metabolism and Solubilization of Cellulose by Clostridium cellulolyticum H10

When Clostridium cellulolyticum was grown with cellulose MN300 as the substrate, the rates of growth and metabolite production were found to be lower than those observed with soluble sugars as the substrate. At low cellulose concentrations, the growth yields were equal to those obtained with cellobiose. The main fermentation products from cellulose and soluble sugars were the same. Up to 15 mM of consumed hexose, a change in the metabolic pathway favoring lactate production similar to that observed with soluble sugars was found to occur concomitantly with a decrease in molar growth yield. With cellulose concentrations above 5 g/liter, accumulation of soluble sugars occurred once growth had ceased. Glucose accounted for 30% of these sugars. A kinetic analysis of cellulose solubilization revealed that cellulolysis by C. cellulolyticum involved three stages whatever cellulose concentration was used. Analysis of these kinetics showed three consecutive enzymatic activity levels having the same K_m (0.8 g of cellulose per liter, i.e., 5 mM hexose equivalent) but decreasing values of V_max. The hypothesis is suggested that each step corresponds to differences in cellulose structure.     

Physical and biotic determinants of space utilization by the Galapagos land iguana (Conolophus pallidus)

Summary Home ranges of the Galapagos land iguana (Conolophus pallidus) were examined with respect to food availability and the thermal environment. Activity patterns, the amount of space used per day, and time required to use the entire home range were also investigated. The effects of, and the relationships between, these factors vary seasonally, as do home range sizes and preferred body temperatures.Food supplementation experiments resulted in only temporary reductions in use of space. Home range sizes were not different between the seasons with the least (Fall) and the most (Hot) food availalble, but home ranges were significantly smaller in Garua when food supplies were low, but not as low as in Fall. Calculations of metabolic expenditures in each season suggests that food availability alone does not explain seasonal patterns of home range size in this species.The thermal environment within each home range was characterized by microclimatic measurements and measurements of the area of sun, shade, and semi-shade. An index with units of m²h was used to quantify the thermal quality of each home range. Iguanas exploited optimal (with respect to body temperature) conditions more than would be expected from random use of their home ranges. Thermal transients (due to large body size) and optimal conditions were exploited to the largest degree in Fall.During Garua, low metabolic rates and time constraints imposed by an abundance of stressful thermal environments may result in small home ranges. In Fall, increased temperatures cause higher metabolic rates and allow more time for exploitation of the cooler portions of the home range, hence, home range sizes increase. In the Hot season, there is abundant food and optimal thermal conditions, but home ranges remain large. Searching for preferred foods may cause the large home ranges in this season.     

Proliferative heterogeneity of vascular smooth muscle cells and its alteration by injury

This study was designed to explore the question of whether the population of morphologically similar smooth muscle cells (SMC) in the vessel wall is functionally homogeneous or heterogeneous with respect to their proliferative response to injury. Using time-lapse video recording we measured interdivision times (IDT) of primary SMC clones, sibling pairs, and mother/daughter pairs. SMC from in vivo undisturbed vessels displayed an interclonal and intraclonal heterogeneity with a wide range in IDT. In vivo balloon injury resulted in a population with homogeneously short IDT. While 80% of IDT of SMC from injured vessels were shorter than 14 h, only slightly more than half of IDT of cells from undisturbed vessels fell into this category. Longitudinal analysis of mother/daughter pairs confirmed the presence of a heterogeneous population of SMC in the undisturbed vessel wall. In vivo balloon injury not only shortened the IDT of the majority of cells, but the shorter IDT persisted much longer than in the case of the undisturbed vessel. We suggest that a morphologically homogeneous SMC population in the aorta can now be subdivided into several groups of functionally different SMC with respect to their proliferative response to injury.     

Acute effects of filipin on the plasmic, hepatic, and biliary cholesterol of the rat

Twenty-one male Wistar rats, 13 weeks old, were fed ad libitum hyperlipidic diets (28% fats) loaded with cholesterol (1.2%) for 5 weeks. One group of 11 rats was fed saturated fats (diet group "S") and another group of 10 rats was fed polyunsaturated fats (diet group "PU"). On the day they were sacrificed 10 of the rats were injected intravenously with 1 mg of filipin. Contrary to the rats in diet group "PU," the rats in diet group "S" treated with filipin presented certain characteristics that were not found in the nontreated group: They provided evidence of biliary cholestasis accompanied by a decline in the level of secretion of bile salts and phospholipids into bile. The concentrations of both free and esterified cholesterol in plasma fell and the amount of (esterified) hepatic cholesterol rose, although there was no change due to the filipin in the amounts of hepatic phospholipids. Explanatory hypotheses for these phenomena were considered, first, at the site of plasma membranes where filipin binds selectively to the cholesterol in the membrane, causing a disruption which probably disturbs the absorbance of circulating lipoproteins, especially that of hepatocyte cells, particularly in diet group "PU." Second, the effects of filipin on subcellular membranes seem to disturb the secretion of lipids and lipoproteins into bile and plasma, especially in diet group "S." Last, at the intracellular level, filipin appears to have a blocking effect on the organelles involved in biliary lipid secretion. The activity of certain enzymes such as cholesterol esterase may also be blocked, particularly in diet group "S," which would explain the accumulation of esterified cholesterol in liver.