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991.
A biosensor for NO(inf3)(sup-) was constructed by attaching a 30- to 70-(mu)m-wide capillary with immobilized denitrifying bacteria in front of an N(inf2)O microsensor. These bacteria reduced O(inf2) so that only bacteria in the very tip of the sensor were exposed to O(inf2) whereas bacteria at a greater depth could carry out the anaerobic process of denitrification. In the presence of acetylene, which inhibits nitrous oxide reductase, bacteria reduced NO(inf3)(sup-) (or NO(inf2)(sup-)) from the surrounding medium to N(inf2)O and the concentration sensed by the N(inf2)O microsensor was directly proportional to the concentration of NO(inf3)(sup-) in the medium. By applying a 250-(mu)m-long capillary in front of the N(inf2)O microsensor, the 90% response time of the biosensor was 50 s. Biosensors may also be made with nitrous oxide-deficient strains so that acetylene inhibition can be omitted. 相似文献
992.
Four different head shapes in Daphnia hyalina (Leydig) induced by the presence of larvae of Chaoborus flavicans (Meigen) 总被引:2,自引:2,他引:0
In many species of Daphnia spines, neck teeth, and enlarged or reshaped helmets are well-known as defences against invertebrate predators. Until now, Daphnia hyalina (Leydig, 1860), a common species in many European lakes, has appeared to be an exception to this rule.Here, we provide evidence that the larvae of Chaoborus flavicans (Meigen) also can induce morphological changes in D. hyalina. Specimens react morphologically to the presence of larvae in three ways: (a) by changes in the shape of head shield, (b) by the formation of spine(s) on the head, and (c) by the elongation of the tail spine. The frequency and intensity of these morphological changes are correlated positively with midge larvae densities. The most pronounced reactions occurred in young D. hyalina.The predator kairomone also induced changes in Daphnia body size. 相似文献
993.
The aim of this study was to clarify the mechanism of isotonic fluid transport in frog skin glands. Stationary ion secretion
by the glands was studied by measuring unidirectional fluxes of 24Na+, 42K+, and carrier-free 134Cs+ in paired frog skins bathed on both sides with Ringer's solution, and with 10−5
m noradrenaline on the inside and 10−4
m amiloride on the outside. At transepithelial thermodynamic equilibrium conditions, the 134Cs+ flux ratio, J
out
Cs/J
in
Cs, varied in seven pairs of preparations from 6 to 36. Since carrier-free 134Cs+ entering the cells is irreversibly trapped in the cellular compartment (Ussing & Lind, 1996), the transepithelial net flux
of 134Cs+ indicates that a paracellular flow of water is dragging 134Cs+ in the direction from the serosal- to outside solution. From the measured flux ratios it was calculated that the force driving
the secretory flux of Cs+ varied from 30 to 61 mV among preparations. In the same experiments unidirectional Na+ fluxes were measured as well, and it was found that also Na+ was subjected to secretion. The ratio of unidirectional Na+ fluxes, however, was significantly smaller than would be predicted if the two ions were both flowing along the paracellular
route dragged by the flow of water. This result indicates that Na+ and Cs+ do not take the same pathway through the glands. The flux ratio of unidirectional K+ fluxes indicated active secretion of K+. The time it takes for steady-state K+ fluxes to be established was significantly longer than that of the simultaneously measured Cs+ fluxes. These results allow the conclusion that — in addition to being transported between cells — K+ is submitted to active transport along a cellular pathway.Based on the recirculation theory, we propose a new model which
accounts for stationary Na+, K+, Cl− and water secretion under thermodynamic equilibrium conditions. The new features of the model, as compared to the classical
Silva-model for the shark-rectal gland, are: (i) the sodium pumps in the activated gland transport Na+ into the lateral intercellular space only. (ii) A barrier at the level of the basement membrane prevents the major fraction
of Na+ entering the lateral space from returning to the serosal bath. Thus, Na+ is secreted into the outside bath. It has to be assumed then that the Na+ permeability of the basement membrane barrier (P
BM
Na) is smaller than the Na+ permeability of the junctional membrane (P
JM
Na), i.e., P
JM
Na/P
BM
Na > 1. The secretory paracellular flow of water further requires that the Na+ reflection coefficients (σNa) of the two barriers are governed by the conditions, σBM
Na > 0, and σBM
Na > σJM
Na. (iii) Na+ channels are located in the apical membrane of the activated gland cells, so that a fraction of the Na+ outflux appearing downstream the lateral intercellular space is recirculated by the gland cells. Based on measured unidirectional
fluxes, a set of equations is developed from which we estimate the ion fluxes flowing through major pathways during stationary
secretion. It is shown that 80% of the sodium ions flowing downstream the lateral intercellular space is recycled by the gland
cells. Our calculations also indicate that under the conditions prevailing in the present experiments 1.8 ATP molecule would
be hydrolyzed for every Na+ secreted to the outside bath.
Received: 30 January 1996/Revised: 12 March 1996 相似文献
994.
Yearling, grass-fed, beef bulls at the USDA Subtropical Agricultural Research Station, Brooksville, Florida, were assessed for physical and semen traits in January, April, July and October of 1991 (Trial 1) and 1992 (Trial 2). Bulls were given a breeding soundness evaluation (BSE) using revised semen and scrotal circumference (SC) criteria. In Trial 1, the bulls consisted of Angus (n = 15), Brahman (n = 14), Hereford (n = 15) and Senepol (n = 14). In Trial 2, the breeds were Angus (n = 15), Brahman (n = 16), Romosinuano (n = 13) and Nellore x Brahman (n = 9). Trial bulls generally showed delayed growth compared with grain-fed bulls in temperate environments. Breed influenced semen traits (percentage sperm motility, normal spermatozoa and those with primary abnormalities) in both trials. Temperate Bos taurus breeds (Angus, Hereford) were generally superior to Bos indicus breeds (Brahman, Nellore x Brahman). Tropically-adapted Bos taurus breeds (Senepol, Romosinuano) were intermediate for those traits tested. In general, tropically-adapted Bos taurus breeds were more similar in reproductive development to temperate Bos taurus than to Bos indicus breeds. Breed by test period interactions occurred and were mainly influenced by delayed sexual maturity of Bos indicus bulls. Qualitative semen traits increased with bull age, particularly from 12 to 18 mo. Scrotal circumference development was slower in the Bos indicus breeds. Bulls of satisfactory BSE status at 18.1 to 22 mo of age were 73.9% in Trial 1 and 58.5% in Trial 2. Brahman bulls had the least satisfactory BSE scores in both years (Trial 1, 44.4%; Trial 2, 22.2%). Most bulls failed to achieve satisfactory BSE status due to a small SC relative to age (Trial 1, 66%; Trial 2, 72%). The most efficacious use of the BSE was > or = 15 mo in Bos taurus bulls and > 18 mo for Bos indicus bulls. Although the BSE has proven to be useful for the assessment of young, pasture-raised bulls in semi-tropical environments, use of SC thresholds linked more with growth traits than with calendar age would improve comparisons of relative reproductive development in such bulls, particularly those of Bos indicus derivation. 相似文献
995.
996.
Abstract: The combination of chromatographic separation using reverse-phase high-performance liquid chromatography and continuous monitoring of the column eluate using a diode-array spectrophotometer allowed qualitative and quantitative pigment profiling of extracts of photosynthetic material in a single run. Carotenoids and the spectrally distinct types of chlorophyll and bacteriochlorophyll can be unambiguously identified even when imperfectly separated on the column. The resulting spectrochromatogram is a fingerprint useful for the rapid characterization of pure cultures or mixed populations. We have developed software to allow recording, manipulation, and presentation of the resulting spectrochromatograms and present results from photosynthetic microbes in pure and mixed cultures. We describe a number of approaches to the presentation of the resulting data in a readily comprehensible form. 相似文献
997.
M. L. Grondahl M. B. Hansen I. E. Larsen E. Skadhauge 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1996,166(1):21-29
5-Hydroxytryptamine is a mediator in cholera toxin-induced hypersecretion in the small intestine. Our hypothesis is that the hypersecretion induced by 5-hydroxytryptamine in the small intestine decreases with increasing age and in an aboral direction in the small intestine. In vivo, measuring accumulated fluid in ligated loops, the apparent maximal efficacy of the 5-hydroxytryptamine-induced jejunal secretion in pig neonates was 4.8±1.1 mg·mg–1 dry loop·45 min–1. The apparent maximal efficacy decreased by 23% and 63% in young and adult pigs, respectively, compared with neonates. In vitro, measuring changes in short-circuit current in Ussing chambers, the apparent maximal efficacy was 66.7±4.8 A·cm–2 in neonates and was reduced by 30% and 57% in young and adult pigs, respectively. Young pigs were used in the segmental study. The apparent maximal efficacy in vivo was 3.7±0.5 mg·mg–1 dry loop and decreased by 22% and 56% in the mid and distal small intestine, respectively. By contrast, in vitro the apparent maximal efficacy was elevated by 56% to 72.0±5.0 A·cm–2 in the distal compared with the proximal part. In conclusion, the secretory response to 5-hydroxytryptamine in pig small intestine decreases with increasing age and in the aboral direction according to in vivo results. We suggest that the decrease in sensitivity to 5-hydroxytryptamine can explain a part of the reduced secretory response to cholera toxin with age and in the aboral direction of the small intestine.Abbreviations
ASF
pituitary peptide antisecretory factor
-
AMP
cyclic adenosine monophosphate
-
CT
cholera toxin
-
E
max
apparent maximal efficacy
-
EC
enterochromaffine ENS enteric nerve system
-
5-HT
5-hydroxytryptamine serotonin
-
LT
heat-labile
-
E. coli
enterotoxin
-
PD
electrical potential difference
-
R
tissue resistance
-
SCC
short-circuit current
-
VIP
vasoactive intestinal peptide 相似文献
998.
K. S. Larsen 《Entomologia Experimentalis et Applicata》1995,76(3):241-245
A rearing method for the fleaCeratophyllus (Monopsyllus) sciurorum sciurorum, a pest on farmed mink in Europe, has been developed. The behaviour of egg-laying and the development period are described
at 23 °C and 80% r.h. The eggs ofC. sciurorum sciurorum hatched after 4–7 days and cocoons were formed 10–12 days later. The development period from egg to newly emerged adult was
23–32 days. Females emerged, in general, earlier than males. 相似文献
999.
Growth response to different types of NPK-fertilizer in Norway spruce plantations in Western Denmark
In Norway spruce planted on former heathland and fertilized to increase production, a series of experiments (72 sample plots) was established throughout Central and Western Jutland (Denmark) during the springs of 1978 and 79. The sample plots were all fertilized with 120 kg nitrogen in each of two five-year periods. Different types of mixed nitrogen/potassim/phosphorus fertilizer were applied. According to results from fertilization trials in the 1950s and 60s a gain of 3–4 m3 · ha-1 · year-1 was expected. In contrast to these earlier findings, only 0, 76 m3 · ha-1 · year-1 was gained over the two periods as an average of all sample plots. The initial assumption that nitrogen is the main limiting factor for tree growth in Western Denmark no longer seems valid. The results might indicate that due to increasing nitrogen deposition during the 1970s and 80s, potassium and maybe phosphorus are developing into new minimum factors, limiting tree growth and devitalizing the forest ecosystem. Hence, fertilization on these soils should mainly be considered as a way to compensate such nutrient imbalances. 相似文献
1000.
Pollination-Induced Ethylene in Carnation (Role of Pollen Tube Growth and Sexual Compatibility) 总被引:5,自引:2,他引:3 下载免费PDF全文
The pollen-pistil interactions that result in the stimulation of ethylene production and petal senescence in carnation (Dianthus caryophyllus L.) flowers were investigated. Pollination of White Sim flowers with Starlight pollen elicited an increase in ethylene production by styles, leading to increased petal ethylene and premature petal senescence. In contrast, pollination with 87-29G pollen led to an early increase in ethylene production, but this was not sustained, and did not lead to petal senescence. Both Starlight and 87-29G pollen germinated on White Sim stigmas and their tubes grew at similar rates, penetrating the length of the style. Crosses between Starlight and White Sim led to the production of viable seeds, whereas 87-29G pollen was infertile on White Sim flowers. Pollination of other carnations with 87-29G elicited ethylene production and petal senescence and led to the production of viable seeds. These results suggest that physical growth of pollen tubes is insufficient to elicit a sustained increase in ethylene production or to lead to the production of signals necessary for elicitation of petal ethylene production and senescence. Rather, the cell-cell recognition reactions leading to sexual compatibility in Dianthus appear to play a role in this interorgan signaling after pollination. 相似文献