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71.
Synopsis Juvenile salmonids,Oncorhynchus spp., commonly encounter conditions (e.g., during hatchery release and dam passage) that result in damage to the skin, scale, and slime complex. We conducted laboratory experiments to determine if descaling of juvenile chinook salmon,O. tshawytscha, increased their vulnerability to predation, and to assess the physiological stress responses elicited by descaling. Salmon were experimentally descaled on either 10% or 20% of their total body area. When offered equal numbers of control and descaled juvenile chinook salmon, northern squawfish,Ptychocheilus oregonensis, did not consume significantly more of either prey type (48–60% of consumed prey were descaled). Juvenile chinook salmon descaled on 10% of their body area did show significant physiological stress responses, however. Mean concentrations of plasma cortisol peaked 1 h after descaling, and returned to control levels by 12 h. Plasma glucose peaked 3 h post-treatment and remained elevated for 24 h. Plasma lactate increased immediately following treatment and returned to undisturbed control levels by 3 h. The osmoregulatory response of plasma potassium was highly variable, but plasma sodium decreased immediately and remained low for 24 h. The observed physiological responses suggest that descaling of juvenile chinook salmon could result in decreased resistance to disease and other stressors encountered in the field, possibly leading to reduced performance capacity and lowered survival.  相似文献   
72.
The energetics of ubiquitin unfolding have been studied using differential scanning microcalorimetry. For the first time it has been shown directly that the enthalpy of protein unfolding is a nonlinear function of temperature. Thermodynamic parameters of ubiquitin unfolding were correlated with the structure of the protein. The enthalpy of hydrogen bonding in ubiquitin was calculated and compared to that obtained for other proteins. It appears that the energy of hydrogen bonding correlates with the average length of the hydrogen bond in a given protein structure. © 1994 John Wiley & Sons, Inc.  相似文献   
73.
A suite of functionally-related characters and demography of three species of Neotropical shadeadapted understory shrubs (Psychotria, Rubiaceae) were studied in the field over five years. Plants were growing in large-scale irrigated and control treatments in gaps and shade in old-growth moist forest at Barro Colorado Island, Panama. Irrigation demonstrated that dry-season drought limited stomatal conductance, light saturated photosynthesis, and leaf longevity in all three species. Drought increased mortality of P. furcata. In contrast, irrigation did not affect measures of photosynthetic capacity determined with an oxygen electrode or from photosynthesis-CO2 response curves in the field. Drought stress limited field photosynthesis and leaf and plant survivorship without affecting photosynthetic capacity during late dry season. Leaves grown in high light in naturally occurring treefall gaps had higher photosynthetic capacity, dark respiration and mass per unit area than leaves grown in the shaded understory. P. furcata had the lowest acclimation to high light for all of these characters, and plant mortality was greater in gaps than in shaded understory for this species. The higher photosynthetic capacity of gap-grown leaves was also apparent when photosynthetic capacity was calculated on a leaf mass basis. Acclimation to high light involved repackaging (higher mass per unit leaf area) as well as higher photosynthetic capacity per unit leaf mass in these species. The three species showed two distinct syndromes of functionally-related adaptations to low light. P. limonensis and P. marginata had high leaf longevity (3 years), high plant survivorship, low leaf nitrogen content, and high leaf mass per unit area. In contrast, P. furcata had low leaf survivorship (1 year), high plant mortality (77–96% in 39 months), low leaf mass per unit area, high leaf nitrogen content, and the highest leaf area to total plant mass; the lowest levels of shelf shading, dark respiration and light compensation; and the highest stem diameter growth rates. This suite of characters may permit higher whole-plant carbon gain and high leaf and population turnover in P. furcata. Growth in deep shade can be accomplished through alternative character syndromes, and leaf longevity may not be correlated with photosynthetic capacity in shade adapted plants.  相似文献   
74.
In sesquioxide-rich soils of tropical and subtropical areas and volcanic-ash soils with high levels of active Al(Fe), large amounts of phosphate fertilizers are needed to overcome their high P-fixation capacity (quenching strategy). A greenhouse pot experiment has been used to evaluate the effectiveness of city refuse compost (CRC) as a P-source for these variable-charge soils, compared to inorganic P. Mature CRC and K2HPO4 were applied at rates equivalent to 125, 250, 375, 500 and 625 kg P ha–1 to a ferrallitic soils from Tenerife Island (Andeptic Paleudult) with a high content in active Al+Fe (4.82%) and a high P-fixation capacity (87%). Perennial ryegrass (Lolium perenne L.) was grown in pots and plants were harvested at regular intervals after seedling emergence. CRC increases plant P concentration and soil labile-P proportional to the applied rate. The best results were obtained from a compost application of 30 t ha–1 equivalent-rate, after a residence time of at least three months. An important residual effect in the supply capacity of P in relation to the phosphate fertilizer was also observed. The relative agronomic effectiveness (RAE) in comparison to K2HPO4 was 66% after 6 months, considering P uptake + soil labile-P. The soil P-fixation capacity was significantly reduced from a compost application of 40 t ha–1 equivalent-rate. Competition in adsorption between organic ligands and phosphate, in combination with net mineralization of organic P in compost, might account for the high RAE value obtained. The main conclusion is that the city refuse compost could be a suitable P-amendment for resquioxic soils due to its high RAE, and the residual effect on P-supply. ei]H. Lambers  相似文献   
75.
Abstract Incorporation of [ methyl -3H]thymidine into bacterial DNA was determined for a range of axenic anaerobic bacterial cultures: fermentative heterotrophs, sulphate-reducing bacteria, purple sulphur bacteria, acetogens and methanogens. Anaerobically growing Bacillus sp. and the obligate aerobe Thiobacillus ferrooxidans were also investigated. Actively growing cultures of sulphate-reducing bacteria belonging to the genera Desulfovibrio, Desulfotomaculum, Desulfobacter, Desulfobotulus and Desulfobulbus , purple sulphur bacteria ( Chromatium vinosum OP2 and Thiocapsa roseopersicina OP1), methanogens ( Methanococcus GS16 and Methanosarcina barkeri ) and an acetogen ( Acetobacterium woodii ) did not incorporate [ methyl -3H]thymidine into DNA. The only obligate anaerobes in which thymidine incorporation into DNA could be unequivocally demonstrated were members of the genus Clostridium . Anaerobically growing Bacillus sp. also incorporated thymidine. These data demonstrate that pure culture representatives of major groups of anaerobic bacteria involved in the terminal oxidation of organic carbon and anoxygenic phototrophs within sediments are unable to incorporate [ methyl -3H]thymidine into DNA, although some obligate and facultative anaerobes can. Variability in thymidine incorporation amongst pure culture isolates indicates that unless existing techniques can be calibrated to take this into consideration then productivity estimates in both aerobic and anaerobic environments may be greatly underestimated using the [ methyl -3H]thymidine technique.  相似文献   
76.
Two Pseudomonas species (designated strains B1 and X1) were isolated from an aerobic pilot-scale fluidized bed reactor treating groundwater containing benzene, toluene, and p-xylene (BTX). Strain B1 grew with benzene and toluene as the sole sources of carbon and energy, and it cometabolized p-xylene in the presence of toluene. Strain X1 grew on toluene and p-xylene, but not benzene. In single substrate experiments, the appearance of biomass lagged the consumption of growth substrates, suggesting that substrate uptake may not be growth-rate limiting for these substrates. Batch tests using paired substrates (BT, TX, or BX) revealed competitive inhibition and cometabolic degradation patterns. Competitive inhibition was modeled by adding a competitive inhibition term to the Monod expression. Cometabolic transformation of nongrowth substrate (p-xylene) by strain B1 was quantified by coupling xylene transformation to consumption of growth substrate (toluene) during growth and to loss of biomass during the decay phase. Coupling was achieved by defining two transformation capacity terms for the cometabolizing culture: one that relates consumption of growth substrate to the consumption of nongrowth substrate, and second that relates consumption of biomass to the consumption of nongrowth substrate. Cometabolism increased decay rates, and the observed yield for strain B1 decreased in the presence of p-xylene. (c) 1993 Wiley & Sons, Inc.  相似文献   
77.
Physiological responses to physical work were assessed for 29 female industrial sewing-machine operators during an 8-h working day under ordinary working conditions. During sewing-machine work, the average (left and right) static load in the trapezius muscle was 9% of the maximal electromyogram (EMG) amplitude (% EMGmax), while the average mean load was 15% EMGmax, and the average peak load was 23% EMGmax. The static load level was unrelated to the muscle strength of the sewing-machine operators, which for the group as a whole was within the normal range. The load levels remained unchanged during the working day, while changes in the EMG mean power frequency and zero crossing frequency rate occurred, both indicating the development of muscle fatigue in left and right trapezius muscle during the working day. In line with this, the rating of perceived exertion in the shoulder and neck region increased during. the working day. Dividing the group of sewing-machine operators into two groups, those with the highest frequency and those with the lowest frequency of shoulder/neck troubles showed that the former group had significantly lower muscle strength, despite the fact that no differences in the surface EMG during sewing were found between the two groups. It was concluded that industrial sewing-machine work involves a pattern of shoulder muscle activity which induces fatiguing processes in the shoulder and neck regions. Furthermore, since the static shoulder muscle load was independent of muscle strength, factors other than working posture may be of significance for the static shoulder muscle load.  相似文献   
78.
Because of its low solubility it is unlikely that elemental sulfur serves as the direct substrate for sulfur-reducing bacteria. To test the hypothesis that polysulfide may represent a soluble intermediate of sulfur reduction, the maximal polysulfide concentrations formed from elemental sulfur in aqueous sulfide solutions were measured at near neutral pH and at temperatures up to 90°C. The saturation concentrations decreased by two orders of magnitude when the pH was lowered from 7 to 6 at a given temperature, and increased about tenfold when the temperature was raised from 37°C to 90°C at a given pH. The dissolution of 0.1 mM zerovalent sulfur in 1 mM sulfide (H2S+HS) required a pH of 7.5 at 20°C and of only 6.1 at 100°C. A comparison with the growth optima of sulfur-reducers suggests that polysulfide is present at sufficient concentration at the growth conditions of the Bacteria and the moderately acidophilic Archaea. Polysulfide is apparently not available at the growth conditions of the extremely acidophilic Archaea. Alternative mechanisms for the sulfur utilization under these conditions are discussed.Abbreviations MOPS Morpholinopropanesulfonate - PIPES 1,4 piperazine-N,N-bis(2-ethanesulfonate) - HEPES N-2-hydroxy-ethylpiperazine-N-ethanesulfonate  相似文献   
79.
The methyl chloride metabolism of the homoacetogenic, methyl chloride-utilizing strain MC was investigated with cell extracts and cell suspensions of the organism. Cell extracts were found to contain all enzyme activities required for the conversion of methyl chloride or of H2 plus CO2 to acetate. They catalyzed the dechlorination of methyl chloride with tetrahydrofolate as the methyl acceptor at a rate of 20 nmol/min × mg of cell protein. Also, the O-demethylation of vanillate with tetrahydrofolate could be measured at a rate of 40 nmol/min × mg. Different enzyme systems appeared to be responsible for the dehalogenation of CH3Cl and for the O-demethylation of methoxylated aromatic compounds, since cells grown with methoxylated aromatic compounds exhibited a significantly lower activity of CH3Cl conversion than methyl chloride grown cells and vice versa. In addition, ammonium thiocyanate (5 mM) completely inhibited CH3Cl dechlorination, whereas the consumption of vanillate was not affected significantly. The data were taken to indicate, that the methyl chloride dehalogenation is catalyzed by a specific, inducible enzyme present in strain MC, and that tetrahydrofolate rather than the corrinoid-protein involved in acetate formation is the primary acceptor of the methyl group in the dechlorination reaction.  相似文献   
80.
Dimethylsulfoniopropionate, an osmolyte of marine algae, is thought to be the major precursor of dimethyl sulfide, which plays a dominant role in biogenic sulfur emission. The marine sulfate-reducing bacterium Desulfobacterium strain PM4 was found to degrade dimethylsulfoniopropionate to 3-S-methylmercaptopropionate. The oxidation of one of the methyl groups of dimethylsulfoniopropionate was coupled to the reduction of sulfate; this process is similar to the degradation betaine to dimethylglycine which was described earlier for the same strain. Desulfobacterium PM4 is the first example of an anaerobic marine bacterium that is able to demethylate dimethylsulfoniopropionate.Abbreviations DMSP dimethylsulfoniopropionate - DMS dimethyl sulfide - MMPA 3-S-methylmercaptopropionate  相似文献   
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