A tracer study of ingestion and metabolic cycling of iron in Daphnia magna

1970 ◽  
Vol 48 (4) ◽  
pp. 873-878 ◽  
Author(s):  
J. W. Mcmahon
Keyword(s):  
Daphnia Magna ◽  
Half Life ◽  
Extended Period ◽  
Dry Weight ◽  
Radioactive Tracer ◽  
Gut Contents ◽  
Feeding Time ◽  
Tracer Study ◽  
65 H ◽  
Time Required

Radioactive tracer studies of the ingestion and cycling of iron by Daphnia magna showed that about 60% of the iron was present as gut contents. Daphnia assimilated iron at the rate of 3.8 × 10−3 μg per milligram dry weight per hour. After feeding on 59Fe-labeled Chlorella for an extended period the animals assimilated only 1.3% of the ingested iron. Excretion and assimilation rates were similar.The feeding time required to pack the animal's gut was 2.5 h. The use of the time of initial loss of radioactive gut contents through defecation as an indicator of a full gut is questioned.The biological half-life of 59Fe in Daphnia is divisible into two components, a short-lived fraction (2.5 h) caused by replacement of gut contents and a longer lived component with a half-life of about 65 h.

Effect of Mercury on the Survival of Daphnia Magna

1990 ◽  
Vol 22 (5) ◽  
pp. 241-246 ◽  
Author(s):  
I. Brković-Popović
Keyword(s):  
Life Span ◽  
Daphnia Magna ◽  
Abiotic Factors ◽  
Total Hardness ◽  
Chemical Characteristics ◽  
Effect Concentration ◽  
Test Organisms ◽  
Lethal Time ◽  
Two Temperatures ◽  
Time Required

The median lethal time (LT) for each concentration of mercury was determined on the basis of mortality curves. Toxicity curves (i.e., the median life-span of Daphniamagna, LT 50, versus the concentration of mercury) for four tested conditions are shown. The experiments were carried out using two diluents of different total hardness (46 and 119 mg/l as CaCO3), at two temperatures (20°C and 25°C). A comparison of the LT 50s of the control organisms with the LT 50s of the test organisms at mercury concentrations of 0.0075 and 0.0050 mg. l-1 showed that the chemical characteristics and temperatures of the mediums tested did not affect the range of the ‘no effect' concentration. However, the incipient LC 50, and the time required for its appearance, did depend on the combination of the abiotic factors tested.

Radioactive Tracer Study Performed in a Dipole Geometry in a Highly Conductive Fracture Zone

1990 ◽  
Vol 212 ◽  
Author(s):  
Johan Byegård ◽  
Gunnar Skarnemark ◽  
Mats Skålberg
Keyword(s):  
Metal Ions ◽  
Metal Complexes ◽  
Fracture Zone ◽  
Radioactive Tracer ◽  
Tracer Experiment ◽  
Tracer Study ◽  
Redox Potentials ◽  
Chemical Analogue

ABSTRACTA radioactive tracer experiment has been performed in a highly conductive fracture zone, using a dipole geometry. Anions (131I− and 82Br−) and complexed metal ions (51Cr-EDTA, 58Co-EDTA, 111In-EDTA, 140La-DOTA, 160Tb-EDTA, 169Yb-EDTA and 177Lu-DOTA) have been injected and their properties as non-sorbing tracers were evaluated. Besides, studies of slightlysorbing cations (24Na+, 58Co2+, 86Rb+ and 201T1+) were performed. 99mTcO4 and its chemical analogue 186ReO4 were also injected to study the behaviour of Tc at low redox-potentials. Breakthrough was obtained for Re and for all metal complexes and anions. Some differences in the recovery yields could be seen. No transport of cations, except for Na, could be measured. No breakthrough of Tc could be observed. This indicates that TcO4− was reduced and sorbed.

scholarly journals Quantifying the Feeding Periods Required by Corn Flea Beetles to Acquire and Transmit Pantoea stewartii

Plant Disease ◽  
2006 ◽  
Vol 90 (3) ◽  
pp. 319-324 ◽  
Author(s):  
B. Menelas ◽  
C. C. Block ◽  
P. D. Esker ◽  
F. W. Nutter
Keyword(s):  
Nalidixic Acid ◽  
Growth Models ◽  
Flea Beetle ◽  
Feeding Time ◽  
Feeding Period ◽  
Selective Media ◽  
Pantoea Stewartii ◽  
Flea Beetles ◽  
Time Required ◽  
The Relationship

The feeding periods required by corn flea beetles to acquire and transmit Pantoea stewartii were investigated in the Stewart's disease of corn pathosystem. To quantify the effect of acquisition feeding period on percentage of acquisition, field-collected corn beetles were allowed to feed for 6, 12, 24 36, 48, and 72 h on corn seedlings previously inoculated with a rifampicin- and nalidixic acid-restraint strain of P. stewartii. Acquisition of P. stewartii by corn flea beetles was considered positive if the rifampicin- and nalidixic acid-marked strain was recovered on selective media. To quantity the effect of transmission feeding period on percent transmission of P. stewartii by corn flea beetles, P. stewartii- infested corn flea beetles were allowed to feed on healthy corn seedlings for periods of 3, 6, 12, 24, 36, 48, and 72 h. After the appropriate transmission feeding period, leaf tissues surrounding the sites of feeding scars were cultured for the presence of the P. stewartii-marked strain. Transmission of P. stewartii was considered positive if the marked strain was recovered on selective media. Acquisition of P. stewartii occurred within 6 h and the percentage of corn flea beetles that had acquired P. stewartii after 72 h ranged from 68 to 94%. The change in P. stewartii acquisition by corn flea beetles (Y) with respect to acquisition feeding period (X) was best described by the Gompertz model, with R2 values ranging from 91 to 99%. The mean time for acquisition by 50% of the corn flea beetles was 36.5 ± 11.6 h. The minimum transmission feeding time required for corn flea beetles to transmit P. stewartii following a 48-h acquisition feeding period was less than 3 h. The percent transmission of P. stewartii by corn flea beetles was nearly 100% after a 48-h transmission feeding period and was 100% by 72 h. Among population growth models evaluated, the monomolecular model best described the relationship between percent transmission (Y) and transmission feeding periods (X), with R 2 values of up to 84%. However, a nonlinear form of the monomolecular model better quantified the relationship between percent transmission and transmission feeding period, because pseudo-R2 values ranged between 98.1 and 99.5%. The predicted transmission feeding time required for 50% of P. stewartii-infested corn flea beetles to transmit the pathogen was 7.6 ± 0.87 h. These results suggest that the corn flea beetle is a highly efficient vector that can quickly acquire and transmit P. stewartii, thereby requiring insecticide seed treatments and foliar insecticides that act quickly to prevent corn flea beetles from acquiring and transmitting P. stewartii to corn plants.

Carbon Dioxide Assimilation by Pineapple Plants, Ananas comosus (L.) Merr. I. Effects of Daily Irradiance

1980 ◽  
Vol 7 (4) ◽  
pp. 363 ◽  
Author(s):  
PJM Sale ◽  
TF Neales
Keyword(s):  
Leaf Area ◽  
Leaf Tissue ◽  
Extended Period ◽  
Titratable Acidity ◽  
Dry Weight ◽  
Co2 Assimilation ◽  
Co2 Exchange ◽  
Ananas Comosus ◽  
Molar Ratio ◽  
Weight Changes

Net carbon exchange over 24-h cycles was measured in well watered pineapple plants, using a 'minicrop' in field assimilation chambers and single leaves in a growth cabinet. Whole plants under natural light and a standard 30°C day/15°C night regime showed crassulacean acid metabolism, nearly all assimilation occurring in the dark period, with a net efflux of CO2 in the day. Assimilation, as measured by both CO2 exchange and changes in titratable acidity in the leaf tissue, was markedly dependent on the total photosynthetically active radiation incident in the previous photoperiod. The molar ratio of the maximum acidity change to maximum net nocturnal CO2 influx was 1.8 : 1. The rate of deacidification depended on the irradiance in the current photoperiod. Efflux in the photoperiod was largely independent of irradiance, but was greater at very low irradiances. Maximum rates of CO2 assimilation in the minicrop were about 15 ng cm-2 (leaf area) s-1 in the dark at the standard temperature regime, and 22 ng-2 s-1 when photoperiod assimilation was induced by a 20°C day/30°C night regime. Similar rates were recorded in the single-leaf experiments, and are higher than those previously found for pineapple. Over a 24-h period, mean rates of about 6 ng cm-2 (leaf area) s-1 were recorded, in good agreement with measured dry weight changes over an extended period. These data help to explain earlier discrepancies in the literature between measured rates of CO2 assimilation and of crop growth rates in pineapples.

scholarly journals Accumulation of Norfloxacin byBacteroides fragilis

2000 ◽  
Vol 44 (9) ◽  
pp. 2361-2366 ◽  
Author(s):  
Vito Ricci ◽  
Laura J. V. Piddock
Keyword(s):  
Dry Weight ◽  
Aerobic Bacteria ◽  
External Concentration ◽  
Low Concentrations ◽  
Carbonyl Cyanide ◽  
The Mean ◽  
Time Required ◽  
State Concentration ◽  
Anaerobic Environment ◽  
Burk Plot

ABSTRACT The accumulation of norfloxacin by Bacteroides fragilisNCTC 9343 was determined by the modified fluorescence method. The time required to achieve a steady-state concentration (SSC) after allowingB. fragilis to accumulate norfloxacin in an aerobic or an anaerobic environment was ∼2 min; the SSC achieved in air was 90.28 ± 9.32 ng of norfloxacin/mg (dry weight) of cells, and that achieved anaerobically was 98.45 ± 3.7 ng of norfloxacin/mg (dry weight) of cells. Initial rates of accumulation were determined with a range of external concentrations, as up to 8 μg/ml the concentration of norfloxacin accumulated increased proportionally to the external concentration, 12.13 ng/mg (dry weight) of cells per μg of exogenous norfloxacin per ml. At concentrations above 10 μg/ml no increase in the rate of norfloxacin accumulation was observed. From the kinetic data, a Lineweaver-Burk plot calculated a Km of 5.03 μg/ml and a V max of 25.1 ng of norfloxacin/s. With an increase in temperature of between 0 and 30°C, the concentration of norfloxacin accumulated also increased proportionally at 4.722 ng of norfloxacin/mg (dry weight) of cells/°C. At low concentrations of glucose (<0.2%; 11 mM), the concentration of norfloxacin accumulated was decreased. With the addition of 100 μM carbonyl cyanidem-chlorophenylhydrazone (CCCP) the mean SSC of norfloxacin was increased to 116 ± 7.01 ng of norfloxacin/mg (dry weight) of cells; glucose had no significant effect in the presence of CCCP. Magnesium chloride (20 mM) decreased the SSC of norfloxacin to 40.5 ± 3.76 ng of norfloxacin per mg (dry weight) of cells. These data suggest that the mechanism of accumulation of norfloxacin byB. fragilis is similar to that of aerobic bacteria and that the fluoresence procedure is suitable for use with an anaerobic bacterium.

Food of Shorthorn Sculpin, Myoxocephalus scorpius, in the Cumberland Sound Area of Baffin Island

1974 ◽  
Vol 31 (3) ◽  
pp. 355-359 ◽  
Author(s):  
I. A. Moore ◽  
J. W. Moore
Keyword(s):  
Dry Weight ◽  
Abundant Species ◽  
The Other ◽  
Gut Contents ◽  
Baffin Island ◽  
Littorina Saxatilis ◽  
Shorthorn Sculpin ◽  
Cumberland Sound ◽  
Myoxocephalus Scorpius ◽  
Benthic Prey

One hundred shorthorn sculpins, Myoxocephalus scorpius, over 15 cm in length captured from June to October, 1972, in Cumberland Sound, Baffin Island, fed almost exclusively (90% by both numbers and dry weight) on the planktonic amphipods Pseudalibrotus glacialis and Parathemisto libellula. In contrast, 140 fish captured about the same times from nearby Pangnirtung Fjord fed heavily on the benthic gastropods Littorina saxatilis and Margarites umbilicalis (each 34% by numbers and 22% by weight) and the bivalve Modiolaria discors (16% by both). Drifting ice on Cumberland Sound probably reduced the level of illumination making the detection of benthic prey difficult and causing the sculpins in this area to feed entirely on the better illuminated, brightly colored plankton. At both localities, the most abundant species in the plankton and the epifauna were also the most frequently encountered in gut contents. On the other hand, coelenterates, planktonic gastropods, copepods, and infauna, all of which were abundant in the environment, were rarely eaten.

scholarly journals Changes of tannin and nutrients during decomposition of branchlets of Casuarina equisetifolia plantation in subtropical coastal areas of China

2013 ◽  
Vol 59 (No. 2) ◽  
pp. 74-79 ◽  
Author(s):  
Zhang LH ◽  
Zhang SJ ◽  
Ye GF ◽  
Shao HB ◽  
Lin GH ◽  
...  
Keyword(s):  
Condensed Tannins ◽  
Total Phenolics ◽  
Current Knowledge ◽  
Dry Weight ◽  
Phosphorus Concentration ◽  
Casuarina Equisetifolia ◽  
Nitrogen And Phosphorus ◽  
Litterbag Experiment ◽  
Time Required

A litterbag experiment was conducted to investigate the changes of tannins and nutrients in branchlets at different decomposition stages of Casuarina equisetifolia in southern subtropical coastal zone, China, using the colorimetric assays. The time required for the loss of half of the initial dry weight (t<sub>50</sub>) was 9.13 months. Total phenolics (TP), extractable condensed tannins (ECT), protein-bound condensed tannins (PBCT), total condensed tannins (TCT) and protein precipitation capacity (PPC) of branchlets litter decreased rapidly, while fibre-bound condensed tannins (FBCT) increased during decomposition. Nitrogen and phosphorus concentration of the branchlet litter both increased gradually during decay. Negative correlations between TP and nitrogen or phosphorus, as well as TCT and nitrogen or phosphorus were found. These chemical changes enhanced the current knowledge on the potential ecological role of nutrient transformation in tannins in C. equisetifolia plantations.

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