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1.
Invertebrates harbouring endosymbiotic chemoautotrophic bacteria are widely distributed in a variety of reducing marine habitats,
including deep-sea hydrothermal vents. Bathymodiolids are dominants of the biomass at geochemically distinct vent sites of
the Mid Atlantic Ridge (MAR) and thus are good candidates to study biological processes in response to site-specific conditions.
To satisfy their nutritional requirements, these organisms depend to varying extent on two types of chemoautotrophic symbionts
and on filterfeeding. The quantitative relationships of the nutritional modes are poorly understood. Using enzyme cytochemistry,
electron microscopy and X-ray microanalysis, the structural and functional aspects of the cellular equipment necessary for
lysosomal digestion was studied. We provide evidence for the following: (1) the basis of intracellular digestion of symbionts
in Bathymodiolus azoricus from two geochemically distinct vent sites was not mainly in the large lysosomal bodies as previously thought (based on the
membranous content resembling bacteria); (2) senescent bacteria are autolysed, possibly by bacterial acid phosphatase, that
is more likely a cell cycling of the symbionts rather than an active lysosomal digestion by the host; (3) the consistent absence
of hydrolases may indicate the improper use of the name “lysosome” for large vesicles at the base of the gill bacteriocytes
(4) nutrient transfer in B. azoricus, therefore, may more likely be accomplished through leaking of metabolites from the symbiont to the host, not excluding lysosomal
resorption of dead bacteria as an auxiliary strategy for organic molecule transfer; (5) evidence is provided for microvillar
transfer of substances from the seawater that may indicate filter-feeding, in non-symbiotic ciliated gill cells of mussels
from Lucky Strike; (6) two types of lysosomal vesicles can be distinguished in digestive cells based on their enzymatic content
and their elemental composition. 相似文献
2.
An autoradiographic examination of carbon fixation, transfer and utilization in the Riftia pachyptila symbiosis 总被引:4,自引:0,他引:4
Riftia pachyptila, the giant vestimentiferan tubeworm from the East Pacific Rise, harbors abundant chemolithoautotrophic, sulfide-oxidizing
bacteria in an internal organ, the trophosome. Several facts, such as the lack of a digestive system in the host, stable carbon
isotope values and net carbon dioxide uptake all suggest that the tubeworms obtain the bulk of their nutrition from their
symbionts. Using tissue autoradiography, we investigated the mode of nutritional transfer between symbionts and host, and
the site of early incorporation of symbiont fixed-carbon in the host. Fast labeling in the trophosome clearly demonstrates
that the symbionts are the primary site of carbon fixation. Appearance of label in some symbiont-free host tissues in as little
as 15 min indicates that the symbionts release a significant amount of organic carbon immediately after fixation. The organic
carbon is largely incorporated into specific, metabolically active host tissues such as fast-growing body regions in the trunk
and plume, and into tube-secreting glands. In addition to immediate release of fixed carbon by the symbionts, there is evidence
of a second possible nutritional mode, digestion of the symbionts, which is consistent with previous suggestions based on
trophosome ultrastructure. Results suggest that symbiont-containing host cells migrate in a predictable pattern within trophosome
lobules and that symbiont division occurs predominately in the center of a lobule, followed eventually by autolysis/digestion
at the periphery of the lobule.
Received: 1 July 1999 / Accepted: 30 December 1999 相似文献
3.
Until recently, the only major hydrothermal vent biogeographic province not known to include bathymodioline mussels was the spreading centers of the northeast Pacific, but deep-sea dives using DSV Alvin on the Endeavor segment of the Juan de Fuca Ridge (47°56N 129°06W; ∼2,200 m depth) in August 1999 yielded the only recorded bathymodioline mytilids from these northeastern Pacific vents. One specimen in good condition was evaluated for its relatedness to other deep-sea bathymodioline mussels and for the occurrence of chemoautotrophic and/or methanotrophic symbionts in the gills. Phylogenetic analyses of the host cytochrome oxidase I gene show this mussel shares evolutionary alliances with hydrothermal vent and cold seep mussels from the genus Bathymodiolus, and is distinct from other known species of deep-sea bathymodiolines, suggesting this mussel is a newly discovered species. Ultrastructural analyses of gill tissue revealed the presence of coccoid bacteria that lacked the intracellular membranes observed in methanotrophic symbionts. The bacteria may be extracellular but poor condition of the fixed tissue complicated conclusions regarding symbiont location. A single gamma-proteobacterial 16S rRNA sequence was amplified from gill tissue and directly sequenced from gill tissue. This sequence clusters with other mussel chemoautotrophic symbiont 16S rRNA sequences, which suggests a chemoautotrophic, rather than methanotrophic, symbiosis in this mussel. Stable carbon (δ13C = −26.6%) and nitrogen (δ15N = +5.19%) isotope ratios were also consistent with those reported for other chemoautotroph-mussel symbioses. Despite the apparent rarity of these mussels at the Juan de Fuca vent sites, this finding extends the range of the bathymodioline mussels to all hydrothermal vent biogeographic provinces studied to date. 相似文献
4.
The existence of endosymbiotic sulfur-oxidizing chemoautotrophic and methanotrophic bacteria associating with marine mytilid
mussels has previously been inferred by 16S rDNA analysis in Bathymodiolus puteoserpentis Von Cosel et al. 1994, a hydrothermal vent mussel from a site on the Mid-Atlantic Ridge. In mussels collected in June 1993,
we found evidence of enzymes diagnostic of two distinct C1 assimilation pathways in this symbiosis. Assays for the utilization of radiolabelled methane and for immunodetection of methanol
dehydrogenase were positive, indicating that oxidation and incorporation of this substrate are occurring in this symbiosis.
Sulfide or thiosulfate had no detectable stimulatory effect on CO2 incorporation, and assays for the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO), an enzyme diagnostic
for the Calvin–Benson cycle, were negative. RubisCO was detected in all samples examined by immunoblot analysis, indicating
this enzyme is expressed in the B. puteoserpentis symbiosis. Stable isotope data showed that carbon isotope values were in agreement with previously reported values, and nitrogen
isotope values were among the most depleted ever reported for bivalve symbioses. The carbon isotope values do not preclude
the utilization of vent-derived methane. These data could be explained by the presence of two metabolically distinct bacterial
symbionts or a Type X methanotrophic symbiont.
Received: 3 October 1997 / Accepted: 23 July 1998 相似文献
5.
When symbiotic dinoflagellate algae (Symbiodinium sp., isolated from the coral Plesiastrea versipora) were incubated with NaH14CO3 in the light in seawater, they released 22.69±9.16 nmol carbon/106 algae. Release of photosynthetically fixed carbon was stimulated more than six-fold for algae incubated in host-tissue homogenate
(148.54±97.03 nmol C/106 algae) and more than four-fold (102.00±49.16 nmol C/106 algae) for algae incubated in a low molecular weight fraction (≤1 000 M
r
) prepared from host homogenate. Soluble released 14C-labelled products, as determined by chromatography and autoradiography, were the same when algae were incubated in either
host homogenate or the low molecular weight fraction. After 4 h incubation in the light (300 mol photons m−2 s−1),␣intracellular␣glycerol increased in algae incubated with the low molecular weight fraction (an increase of 0.39 to␣0.67 nmol glycerol/106 algae) compared with little or no increase in algae incubated in seawater (0 to 0.12 nmol glycerol/106 algae). Partial inhibition of triglyceride synthesis (up to 51%) was also observed when algae were incubated in the low molecular
weight fraction. All these effects are the same as those observed when algae were incubated in host homogenate. These data
indicate that the “host release-factor” activity of P.␣versipora is a compound of low molecular weight.
Received: 13 February 1997 / Accepted: 24 October 1997 相似文献
6.
Undescribed hydrocarbon-seep mussels were collected from the Louisiana Slope, Gulf of Mexico, during March 1986, and the ultrastructure of their gills was examined and compared to Bathymodiolus thermophilus, a mussel collected from the deep-sea hydrothermal vents on the Galápagos Rift in March 1985. These closely related mytilids both contain abundant symbiotic bacteria in their gills. However, the bacteria from the two species are distinctly different in both morphology and biochemistry, and are housed differently within the gills of the two mussels. The symbionts from the seep mussel are larger than the symbionts from B. thermophilus and, unlike the latter, contain stacked intracytoplasmic membranes. In the seep mussel three or fewer symbionts appear to be contained in each host-cell vacuole, while in B. thermophilus there are often more than twenty bacteria visible in a single section through a vacuole. The methanotrophic nature of the seep-mussel symbionts was confirmed in 14C-methane uptake experiments by the appearance of label in both CO2 and acid-stable, non-volatile, organic compounds after a 3 h incubation of isolated gill tissue. Furthermore, methane consumption was correlated with methanol dehydrogenase activity in isolated gill tissue. Activity of ribulose-1,5-biphosphate (RuBP) carboxylase and 14CO2 assimilation studies indicate the presence of either a second type of symbiont or contaminating bacteria on the gills of freshly captured seep mussels. A reevaluation of the nutrition of the symbionts in B. thermophilus indicates that while the major symbiont is not a methanotroph, its status as a sulfur-oxidizing chemoautotroph, as has been suggested previously, is far from proven. 相似文献
7.
Lucina
pectinata is a large tropical clam living deeply burrowed in the black, reducing mud of mangrove swamps. It is known to possess hemoglobin
in the cytoplasmic areas of its bacteriocytes, which harbor sulfide-oxidizing bacteria. The bacteriocytes also possess lysosome-like
microbodies containing either membrane whorls or electron-dense granules in which free heme compounds have been identified.
The cytochemical detection of acid phosphatase and arylsulphatase through EDX (energy-dispersive X-ray) microanalysis strongly
suggests that the bacteriocytes of L.
pectinata contain, in fact, two different types of microbodies. Some of these (devoid of dense granules) possess a variable amount
of lysosomal enzymes and occasionally a limited quantity of iron, which may result from a recycling process of hemoglobin.
Their main function seems to be the digestion of a limited proportion of symbiotic bacteria. They represent genuine secondary
lysosomes with a functionally acidic pH. The second type of microbodies is characterized by dense granules containing sulfur
and iron hemes but no lysosomal enzymes. Their sulfide-oxidizing activity was substantiated by benzyl viologen assay, with
Na2S as a substrate. These microbodies appear to be similar to the sulfide-oxidizing bodies (SOBs) described in the bacteriocytes
of other bivalve species with symbiotic thioautotrophic bacteria; however, their sulfide-oxidizing activity appears to be
non-enzymatic. They are discrete organelles, characterized by a functionally basic pH and pseudoperoxidasic activity, and
have been termed SOBs. Therefore, the bacteriocytes of L.
pectinata possess at the same time functional lysosomes and functional SOBs.
Received: 17 August 2000 / Accepted: 20 December 2000 相似文献
8.
The marine bivalve Lucinoma aequizonata (Lucinidae) maintains a population of sulfide-oxidizing chemoautotrophic bacteria in its gill tissue. These are housed in
large numbers intracellularly in specialized host cells, termed bacteriocytes. In a natural population of L. aequizonata, striking variations of the gill colors occur, ranging from yellow to grey, brown and black. The aim of the present study
was to investigate how this phenomenon relates to the physiology and numbers of the symbiont population. Our results show
that in aquarium-maintained animals, black gills contained fewer numbers of bacteria as well as lower concentrations of sulfur
and total protein. Nitrate respiration was stimulated by sulfide (but not by thiosulfate) 33-fold in homogenates of black
gills and threefold in yellow gill homogenates. The total rates of sulfide-stimulated nitrate respiration were the same. Oxygen
respiration could be measured in animals with yellow gills but not in animals with black gills. The cumulative data suggest
that black-gilled clams maintained in the aquarium represent a starvation state. When collected from their natural habitat
black gills contain the same number of bacteria as yellow gills. Also, no significant difference in glycogen concentrations
of the host tissues was observed. Therefore, starvation is unlikely the cause of black gill color in a natural population.
Alternative sources of nutrition to sulfur-based metabolism are discussed. Denaturing gradient gel electrophoresis (DGGE)
performed on the different gill tissues, as well as on isolated symbionts, resulted in a single gill symbiont amplification
product, the sequence of which is identical to published data. These findings provide molecular evidence that one dominant
phylotype is present in the morphologically different gill tissues. Nevertheless, the presence of other phylotypes cannot
formally be excluded. The implications of this study are that the gill of L. aequizonata is a highly dynamic organ which lends itself to more detailed studies regarding the molecular and cellular processes underlying
nutrient transfer, regulation of bacterial numbers and host–symbiont communication.
Received: 1 September 1999 / Accepted: 1 February 2000 相似文献
9.
Symbiotic dinoflagellate algae (Symbiodinium sp.) isolated from the scleractinian coral Plesiastrea versipora and incubated in homogenized host tissue released 4 to 7 times as much glycerol (14 to 46 nmol glycerol/106 algae) as those incubated in seawater (3 to 6 nmol glycerol/106 algae) after 4 h incubation in the light. During this period, no release of triglycerides was detected. Intracellular glycerol
increased 2- to 3-fold in algae incubated in host homogenate, but remained unchanged in algae incubated in seawater at a concentration
of 0.82 ± 0.47 nmol glycerol/106 algae. In each incubation condition, intracellular triglyceride levels increased. However, in algae incubated in host homogenate,
the intracellular levels of triglycerides reached only about 75% of the amount reached in algae incubated in seawater (max.
18.55 ± 2.40 nmol glycerol/106 cells). Host homogenate did not stimulate the release of glycerol from algae during dark incubation. These data show that
the glycerol released by algae incubated in host-tissue homogenate was derived from increased synthesis of glycerol or from
diversion of some glycerol or other photosynthetic intermediates from incorporation into algal triglyceride stores, and did
not come from existing stores.
Received: 20 December 1996 / Accepted: 9 January 1997 相似文献
10.
The ability of endosymbioses between anthozoans and dinoflagellate algae (zooxanthellae) to retain excretory nitrogen and
take up ammonium from seawater has been well documented. However, the quantitative importance of these processes to the nitrogen
budget of such symbioses is poorly understood. When starved symbiotic Anemonia viridis were incubated in a flow-through system in seawater supplemented with 20 μM ammonium for 91 d under a light regime of 12 h light at 150 μmol photons m−2 s−1 and 12 h darkness, they showed a mean net growth of 0.197% of their initial weight per day. Control anemones in unsupplemented
seawater with an ammonium concentration of <1 μM lost weight by a mean of 0.263% of their initial weight per day. Attempts to construct a nitrogen budget showed that, over
a 14 d period, ≃40% of the ammonium taken up could be accounted for by growth of zooxanthellae. It was assumed that the remainder
was translocated from zooxanthellae to host. However, since the budget does not balance, only 60% of the growth of host tissue
was accounted for by this translocation. The value for host excretory nitrogen which was recycled to the symbionts equalled
that taken in by ammonium uptake from the supplemented seawater, indicating the importance of nitrogen retention to the symbiotic
association.
Received: 23 December 1997 / Accepted: 12 September 1998 相似文献
11.
The concentration of glutamine in Tridacna gigas haemolymph increased >35-fold following exposure to sea water supplemented with ammonium (20 μM), but no increase was observed with nitrate (20 μM). Lack of a diel cycle, no decrease in haemolymph glucose levels, the expression patterns of glutamine synthetase in zooxanthellae
and host, and the lack of glutamine release in response to nitrate supplementation all support the proposition that the increase
in haemolymph glutamine is a product of the host and not the zooxanthellae. Unlike ammonium, nitrate accumulates rapidly in
the haemolymph. It has no effect on the concentration of glutamine in the haemolymph, but there is an increase in arginine,
histidine and lysine in the haemolymph, suggesting the release of these essential amino acids from zooxanthellae. Glutamine
synthetase (GS) activity decreased markedly in the gill and less so in the mantle over a period of 6 d exposure to elevated
ammonium (20 μM). In contrast, GS activity in zooxan- thellae doubled. The response of zooxanthellae in situ was confirmed by incubating
freshly isolated zooxanthellae for 4 d in ammonium, which resulted in a ten-fold increase in GS activity. Comparison of the
in situ response of zooxanthellae with that obtained in vitro indicates that the symbionts are likely to be exposed to ammonium
concentrations lower than that found in the haemolymph.
Received: 14 November 1997 / Accepted: 28 April 1998 相似文献
12.
The hydrothermal vent vestimentiferans Riftia pachyptila Jones, 1981 and Ridgeia piscesae Jones, 1985 live in habitats with different abundances of external CO2. R. pachyptila is found in areas with a high input of hydrothermal fluid, and therefore with a high [CO2]. R. piscesae is found in a range of habitats with low to high levels of hydrothermal fluid input, with a correspondingly broad range of
CO2 concentrations. We examined the strategies for dissolved inorganic carbon (DIC) use by the symbionts from these two species.
R. pachyptila were collected from the East Pacific Rise (9°50′N; 104°20′W) in March 1996, and R. piscesae were collected from the Juan de Fuca Ridge (47°57′N; 129°07′W) during September of 1996 and 1997. The differences in the
hosts' habitats were reflected by the internal pools of DIC in these organisms. The concentrations of DIC in coelomic fluid
from R. piscesae were 3.1 to 10.5 mM, lower than those previously reported for R. pachyptila, which often exceed 30 mM. When symbionts from both hosts were incubated at in situ pressures, their carbon fixation rates increased with the extracellular
concentration of CO2, and not HCO3
−, and symbionts from R. piscesae had a higher affinity for CO2 than those from R. pachyptila (K
1/2 of 7.6 μM versus 49 μM). Transmission electron micrographs showed that symbionts from R. piscesae lack carboxysomes, irrespective of the coelomic fluid [DIC] of their host. This suggests that the higher affinity for CO2 of R. piscesae symbionts may be their sole means of compensating for lower DIC concentrations. The δ13C values of tissues from R. piscesae with higher [DIC] in the coelomic fluid were more positive, opposite to the trend previously described for other autotrophs.
Factors which may contribute to this trend are discussed.
Received: 24 September 1998 / Accepted: 12 May 1999 相似文献
13.
Trophic ecology of Rimicaris exoculata : a combined lipid abundance/stable isotope approach 总被引:1,自引:0,他引:1
The alvinocaridid shrimp Rimicaris exoculata is an abundant component of the biota of Mid-Atlantic Ridge hydrothermal vents. To determine the nutritional strategy of
this organism, we analysed the molecular abundance and carbon isotopic composition of its phospholipid fatty acids. High abundances
of n-7 fatty acids (>40% total fatty acids) were observed in R. exoculata muscle tissues, in bacterial epibionts scraped from its gill bailers, and from the bacterially infested metal sulphides that
the shrimp ingest. The phospholipid fatty acid abundance data indicates that the bacteria in the sulphides are closely related
to the bacterial epibiota inhabiting the shrimp gill bailers, carapace and other body parts. Compound specific δ13C analyses of the phospholipid fatty acids gave average values of −12‰ for the epibiont bacteria and −21‰ for the sulphide
bacteria. This difference may be largely due to the expression of different forms of RuBisCO (Forms I and II) which fractionate
against 13C to different extents. Carbon limitation within the shrimp epibiont population may be an additional factor. The δ13C values (mean = −13‰) of the saturated and monounsaturated fatty acids isolated from the muscle tissues of R. exoculata were very close to those of the epibionts, indicating that the predominant source of dietary carbon for the shrimp is their
epibionts, with a lesser contribution from free-living bacteria. The δ13C values (−26‰) of shrimp cholesterol were much more negative than those of the fatty acids, and this cholesterol is likely
to have derived from the oceanic photic zone.
Received: 26 June 1997 / Accepted: 6 November 1998 相似文献
14.
Microsensor studies of photosynthesis and respiration in the symbiotic foraminifer Orbulina universa 总被引:1,自引:0,他引:1
Oxygen and pH microelectrodes were used to investigate the microenvironment of the planktonic foraminifer Orbulina universa and its dinoflagellate endosymbionts. A diffusive boundary layer surrounds the foraminiferal shell and limits the O2 and proton transport from the shell to the ambient seawater and vice versa. Due to symbiont photosynthesis, high O2 concentrations of up to 206% air saturation and a pH of up to 8.8, i.e. 0.5 pH units above ambient seawater, were measured
at the shell surface of the foraminifer at saturating irradiances. The respiration of the host–symbiont system in darkness
decreased the O2 concentration at the shell surface to <70% of the oxygen content in the surrounding air-saturated water. The pH at the shell
surface dropped to 7.9 in darkness. We measured a mean gross photosynthetic rate of 8.5 ± 4.0 nmol O2 h−1 foraminifer−1. The net photosynthesis averaged 5.3 ± 2.7 nmol O2 h−1. In the light, the calculated respiration rates reached 3.9 ± 1.9 nmol O2 h−1, whereas the dark respiration rates were significantly lower (1.7 ± 0.7 nmol O2 h−1). Experimental light–dark cycles demonstrated a very dynamic response of the symbionts to changing light conditions. Gross
photosynthesis versus scalar irradiance curves (P vs E
o curves) showed light saturation irradiances (E
k) of 75 and 137 μmol photons m−2 s−1 in two O. universa specimens, respectively. No inhibition of photosynthesis was observed at irradiance levels up to 700 μmol photons m−2 s−1. The light compensation point of the symbiotic association was 50 μmol photons m−2 s−1. Radial profile measurements of scalar irradiance (E
o) inside the foraminifera showed a slight increase at the shell surface up to 105% of the incident irradiance (E
d).
Received: 26 January 1998 / Accepted: 11 April 1998 相似文献
15.
We present a cellular automaton that simulates the interaction between a host tree and multiple potential mycorrhizal symbionts and generates testable hypotheses of how processes at the scale of individual root tips may explain mycorrhizal community composition. Existing theoretical biological market models imply that a single host is able to interact with and select from multiple symbionts to organize an optimal symbiont community. When evaluating the tree–symbiont interaction, two scales must be considered simultaneously: the scale of the entire host plant at which carbon utilization and nutrient demands operate, and the scale of the individual root tip, at which colonization and carbon-nutrient trade occurs. Three strategies that may be employed by the host tree for optimizing carbon use and nutrient acquisition through mycorrhizal symbiont communities are simulated: (1) carbon pool adjustment, in which the plant controls only the total amount of carbon to be distributed uniformly throughout the root system, (2) symbiont selection, wherein the plant opts either for or against the interaction at each fine root tip, and (3) selective carbon allocation, wherein the plant adjusts the amount of carbon allocated to each root tip based on the cost of nutrients. Strategies were tested over various nutrient availabilities (the amount of inorganically and organically bound nutrients). Success was defined on the basis of minimizing carbon expended for nutrient acquisition because this would allow more carbon to be utilized for growth and reproduction. In all cases, the symbiont selection and selective carbon allocation strategies were able to meet the nutritional requirements of the plant, but did not necessarily optimize carbon use. The carbon pool adjustment strategy is the only strategy that does not operate at the individual root tip scale, and the strategy was not successful when inorganic nutrients were scarce since there is no mechanism to exclude suboptimal symbionts. The combination of the symbiont selection strategy and the carbon pool adjustment resulted in optimal carbon use and nutrient acquisition under all environmental conditions but result in monospecific symbiont assemblages. On the other hand, the selective carbon allocation strategy is the only strategy that maintained successful, multi-symbiont communities. The simulations presented here thus imply clear hypotheses about the effect of nutrient availability on symbiont selection and mycorrhizal community richness and composition. 相似文献
16.
A recent review suggests that meiofauna are important grazers of microphytobenthic primary production as well as of bacterial
secondary production. The potential importance of meiofauna grazers may nevertheless have systematically been underestimated,
since label leakage from chemically preserved animals has hitherto not been accounted for. Furthermore, a majority of studies
have used relatively long incubation times and assumed, rather than proved, that label recycling over this period is negligible.
In the present study we tested the influence of sample preservation on label retention in the marine nematode Pellioditis marina Andrassy, 1983 fed 3H-labelled bacteria. Label loss from formaldehyde-preserved specimens averaged 40% after 1 h preservation and amounted to
a maximum of 85% after 24 h in formaldehyde, irrespective of formaldehyde concentration; no further leakage occurred beyond
24 h. Glutaraldehyde and ethanol yielded significantly better and poorer results, respectively, but the former fixative still
yielded label losses of up to 70%. A comparison of label uptake as a function of time with observations on ingestion and defecation
behaviour suggest that on time scales of hours an indication of assimilation (after correction for label leakage) rather than
of ingestion is obtained. When killed with formaldehyde at room temperature, P. marina egested a significant part of its gut contents. The sources of bias identified here may have generally led to significant
underestimations of true grazing rates. The cumulative effect of label leakage, prey egestion and long incubation times, each
at the highest rates observed in this study, may yield as much as a 15-fold underestimation of true food consumption. Cooling
samples on ice and fixation with ice-cold formaldehyde, followed by immediate freeze-preservation, and sorting of the nematodes
within 2 h after thawing, gives average values for label leakage of 50%, and hence allows the application of a proximate correction
factor for label losses of 2.
Received: 9 July 1998 / Accepted: 23 September 1998 相似文献
17.
U. Postel G. Petrausch S. Riestenpatt D. Weihrauch J. Malykh W. Becker D. Siebers 《Marine Biology》1998,130(3):407-416
Inhibition of Na+/K+-ATPase from gill plasma membranes of the shore crab Carcinus maenas by cadmium was investigated and compared with inhibitory effects by known antagonists (ouabain and Ca2+). For comparative considerations the Cd2+-inhibition of the enzyme from dog kidney was also tested. Na+/K+-ATPase from dog kidney and from crab gill differed greatly in sensitivity against ouabain. The inhibition constant K
i of the dog enzyme amounted to 9.1 × 10−7 mol l−1, i.e. more than 300-fold smaller than the K
i of 2.9 × 10−4 mol l−1 determined for the crab enzyme. Ca2+ inhibited the activity of Na+/K+-ATPase from crab gill plasma membranes with a K
i of 4.3 × 10−4 mol l−1. The Na+/K+-ATPase from crab gill was inhibited by Cd2+ with a K
i of 9.1 × 10−5 mol l−1. Cd2+ inhibited the Na+/K+-ATPase from dog kidney with a K
i (6.4 × 10−5 mol l−1) comparable to that observed in the crab gill enzyme. Under experimental conditions Cd2+-inhibition of Na+/K+-ATPase was irreversible. Repeated washing, centrifugation and homogenization of the plasma membranes (four times) with Cd2+-free buffer did not restore any activity lost in the presence of 1 × 10−3 mol l−1 Cd2+. Since ouabain-insensitive (nonspecific) ATPases in the plasma membrane fraction of crab gills were inhibited by Cd2+ in the same way as Na+/K+-ATPase, the heavy metal is considered as an unspecific ATPase inhibitor. Comparing these results with literature data on
Cd2+-binding to electrophoretically separated proteins suggests that Na+/K+-ATPase is a Cd2+-binding enzyme. The results obtained on Na+/K+-ATPase were reflected by Cd2+-inhibition of the branchial ion-transport functions depending on this enzyme. The transepithelial short-circuit current of
isolated gill half lamellae, a direct measure of area-specific active ion uptake, and the transepithelial potential difference
of isolated, perfused whole gills, also indicative of active ion uptake, were inhibited by the heavy metal in a time- and
dose-dependent mode. Remarkably these inhibitions were also irreversible. These findings are ecologically and biomedically
significant: even when the actual environmental or tissue concentrations measured are low, biological microstructures such
as Na+/K+-ATPase may accumulate the heavy metal by tight binding over prolonged periods until the first inhibitory effects occur.
Received: 25 June 1997 / Accepted: 25 August 1997 相似文献
18.
Nutrients were added separately and combined to an initial concentration of 10 μM (ammonium) and/or 2 μM (phosphate) in a series of experiments carried out with the giant clam Tridacna maxima at 12 microatolls in One Tree Island lagoon, Great Barrier Reef, Australia (ENCORE Project). These nutrient concentrations
remained for 2 to 3 h before returning to natural levels. The additions were made every low tide (twice per day) over 13 and
12 mo periods for the first and second phase of the experiment, respectively. The nutrients did not change the wet tissue
weight of the clams, host C:N ratio, protein content of the mantle, calcification rates or growth rates. However, ammonium
(N) enrichment alone significantly increased the total population density of the algal symbiont (Symbiodinium sp.: C = 3.6 · 108 cell clam−1, N = 6.6 · 108 cell clam−1, P = 5.7 · 108 cell clam−1, N + P = 5.7 · 108 cell clam−1; and C = 4.1 · 108 cell clam−1, N = 5.1 · 108 cell clam−1, P = 4.7 · 108 cell clam−1, N + P = 4.5 · 108 cell clam−1, at the end of the first and second phases of the experiment, respectively), although no differences in the mitotic index
of these populations were detected. The total chlorophyll a (chl a) content per clam but not chlorophyll a per cell also increased with ammonium addition (C = 7.0 mg chl a clam−1, N = 13.1 mg chl a clam−1, P = 12.9 mg chl a clam−1, N + P = 11.8 mg chl a clam−1; and C = 8.8 mg chl a clam−1, N = 12.8 mg chl a clam−1; P = 11.2 mg chl a clam−1, N + P = 11.3 mg chl a clam−1, at the end of the first and second phases of the experiment, respectively). The response of clams to nutrient enrichment
was quantitatively small, but indicated that small changes in inorganic nutrient levels affect the clam–zooxanthellae association.
Received: 2 June 1997 / Accepted: 9 June 1997 相似文献
19.
Contribution of salps to carbon flux of marginal ice zone of the Lazarev Sea, southern ocean 总被引:3,自引:0,他引:3
In order to estimate the in situ grazing rates of Salpa thompsoni and their implications for the development of phytoplankton blooms and for the sequestration of biogenic carbon in the high
Antarctic, a repeat-grid survey and drogue study were carried out in the Lazarev Sea during austral summer of 1994/1995 (December/January).
Exceptionally high grazing rates were measured for S. thompsoni at the onset of a phytoplankton bloom (0.2 to 0.8 μg chlorophyll a l−1) in December 1994, with up to ≃160 μg of plant pigments consumed by an individual salp of 7 to 10 cm length per day. Dense
salp swarms extended throughout the marginal ice zone, consuming up to 108% of daily phytoplankton production and 21% of the
total chlorophyll a stock. Due to the much faster sinking rates and higher carbon content of salp faecal pellets, the efficiency of downward
carbon flux through salps is much higher than through the other major grazers, krill and copepods. S. thompsoni can thus export large amounts of biogenic carbon from the euphotic zone to the deep ocean. With the observed ingestion rates
during December 1994, this flux could have attained levels of up to 88 mg C m−2 d−1, accounting for the bulk of the vertical transport of carbon in the Lazarev Sea. However, in January 1995, when phytoplankton
concentrations exceeded a threshold level of 1.0 to 1.5 μg chlorophyll a l−1, salps experienced a drastic reduction in their feeding efficiency, possibly as a result of clogging of their filtering apparatus.
This triggered a dramatic reversal in the relationship, during which a dense phytoplankton bloom developed in conjunction
with the collapse of the salp population. Increases in the biomass and geographic range of the tunicate S. thompsoni have occurred in several areas of the southern ocean, often in parallel with a rise in sea-surface temperature during sub-decadal
periods of warming anomalies.
Received: 10 August 1997 / Accepted: 21 October 1997 相似文献
20.
The giant clam Tridacna crocea harbors in the mantle tissue symbiotic microalgae commonly called zooxanthellae. Isolated zooxanthellae release glycerol
into the medium in the presence of mantle tissue homogenate (MH), but it is not clear whether the cells do so in situ. In
order to determine the photosynthetic products released by zooxanthellae in the mantle of the giant clam we traced photosynthetic
fixation products from 13C- and 14C-bicarbonate both in the clam and in isolated zooxanthellae (IZ) in the presence or absence of MH. After 15 min incubation
in the absence of MH the IZ released less than 0.6% of the fixed labeled carbon, mainly as glucose. The major intracellular
photosynthates were neutral lipids, which constituted 20 to 40% of the total extractable 14C. In the presence of MH, the IZ released up to 5.6% of the total fixed 14C, mostly as glycerol, and the major intracellular photosynthate was glucose. In an intact clam incubated in sea water containing
14C-bicarbonate, 46 to 80% of the fixed 14C was translocated from the zooxanthellae to the host tissues. Most of the 14C in the hemolymph, in the isolated zooxanthellae and in intact mantle tissue (containing zooxanthellae) was recovered as
glucose. No 14C-glycerol was detected in the mantle after 1 to 30 min incubation, and, even after 60 min, far less 14C-glycerol was synthesized than by IZ in the presence of MH. The possibility that in clam tissue glycerol is converted to
glucose was examined by tracing the labeled carbon from 14C-glycerol injected into the adductor muscle. After 5 min incubation, no labeled glucose was found in the hemolymph, but after
60 min, some 20% was found as glucose. Thin slices containing zooxanthellae, cut from the surface of the mantle, fixed inorganic
carbon supplied as NaH14CO3 in the medium and mainly released 14C-glucose. The addition of MH to the surrounding medium did not affect the release rate or form of release product. When the
slices were cut into smaller pieces, however, the ratio of glycerol to glucose in the release product increased. These results
indicate that in the presence of MH the metabolism of isolated zooxan- thellae was different from that of zooxanthellae in
the mantle. In the presence of MH, isolated zooxanthellae release mostly glycerol, whereas in the mantle they release glucose.
Received: 18 February 1998 / Accepted: 4 December 1998 相似文献