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  • 1
    Electronic Resource
    Electronic Resource
    Host glutamine synthetase activities in the giant clam—zooxanthellae symbiosis: effects of clam size, elevated ammonia and continuous darkness (1994)
    Springer
    Marine biology 118 (1994), S. 681-685 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Host tissues and zooxanthellae of the giant clam Tridacna gigas contained glutamine synthetase, with the highest transferase activities present in the gill, followed by the kidney, mantle, zooxanthellae, foot, heart and adductor muscle, in that order. Synthetase activities of glutamine synthetase in host tissues and zooxanthellae were in a similar order, but the differences were not so marked. Host tissues also contained hexokinase, glucose-6-phosphate dehydrogenase and malate dehydrogenase. Highest hexokinase activities were present in the heart, followed, in order, by the gill, mantle, adductor muscle and foot. Highest glucose-6-phosphate dehydrogenase activities were present in the gill, followed by the mantle, heart, adductor muscle and foot. All tissues assayed contained high malate dehydrogenase activities. There was no detectable glutamate dehydrogenase activity. Glutamine synthetase activity in gill and mantle tissue decreased by 1.6% with every 1 cm increase in clam size. Host glutamine synthetase activity decreased by 80% in gill tissue and by 45% in mantle tissue in clams which were maintained for 8 d in continuous darkness. Similar effects were found when clams were kept in light in the presence of elevated ammonia concentrations. It is suggested that both host and symbionts are nitrogen-deficient in small clams and that host glutamine synthetase plays a role in ammonia assimilation by the intact association.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00347516
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  • 2
    Electronic Resource
    Electronic Resource
    Modification of shell formation in the giant clam Tridacna gigas at elevated nutrient levels in sea water (1993)
    Springer
    Marine biology 117 (1993), S. 251-257 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effect on shell formation of Tridacna gigas by sea water supplemented for 3 mo with ammonium (5, 10 μM, N) and phosphate (2, 5, 10 μM, P), separately or in combination, was examined. Exposure to N and N+P significantly enhanced shell-extension rates, but significantly reduced shell weights at equivalent size. Scanning-electron microscopy further revealed structural alterations in the outer shell layer, such as misshapen aragonite crystals, irregular crossed-lamellar orientation, and relatively porous shell microstructure. These observations are consistent with results of X-ray diffractometry on the shells which show distinct shifts in the positions of reflections from the (012) and (200) crystal planes relative to the control, indicating changes in crystal lattice parameters following addition of nutrients.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00345670
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  • 3
    Electronic Resource
    Electronic Resource
    Nutrient limitation in the giant clam-zooxanthellae symbiosis: effects of nutrient supplements on growth of the symbiotic partners (1993)
    Springer
    Marine biology 117 (1993), S. 655-664 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effect of ammonium (5, 10 μM N) and phosphate (2, 5, 10 μM P) on the growth of the giant clam Tridacna gigas and its symbiotic dinoflagellate Symbiodinium sp. was examined. A 3 mo exposure to these nutritients significantly increased the N or P composition of the soft tissues, as reflected in a corresponding change in C:N:P ratio. Furthermore, exposure to N or N+P markedly increased the amount of soft tissue, but P alone did not, demonstrating that increased availability of inorganic nitrogen enhances tissue growth of the clam host. With addition of N, or N+P, there was a significant increase in the total number of zooxanthellae per clam, with a corresponding decrease in chlorophyll a (chl a) content per zooxanthella. However, only with N+P was there an increase in the zooxanthellae mitotic index. The inverse relationship between zooxanthellae number and chl a per zooxanthella is consistent with phytoplankton studies indicating conditions of nutrient-limitation. Furthermore, the unaffected C:N:P composition of the zooxanthellae and their relatively low specific-growth rates (4 to 10%) also suggest that they are nutrient-limited in vivo. In particular, their high mean C:N:P ratio of 303:52:1 indicates that, relative to C, they are much more depleted in P and less in N than are free-living phytoplankton. Furthermore, polyphosphates (phosphate reserves) were undetectable, and the activity levels of acid phosphatase in the zooxanthellae were relatively high and not influenced by the host's exposure to increased P concentrations in the sea water, implicating the clam host in active regulation of P availability to its symbiotic algae. This is strong evidence that N-limitation of clam zooxanthellae is a function of the availability of ammonium to the symbiosis while, irrespective of nutrient levels in sea water, clam zooxanthellae still show characteristics of P-limitation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00349778
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  • 4
    Electronic Resource
    Electronic Resource
    Phosphate acquisition in the giant clam-zooxanthellae symbiosis (1995)
    Springer
    Marine biology 124 (1995), S. 261-266 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effect of phosphate on the giant clam Tridacna gigas and on its symbiotic dinoflagellate Symbiodinium sp. was compared with that on cultured Symbiodinium sp. originally isolated from the same clarn species. Incubation of whole clams in elevated phosphate (10 μM) reduced their capacity for phosphate uptake, but the uptake capacity of the clam's zooxanthellae population was not influenced. In addition, there was no change in the zooxanthellae density and the N:P ratio, of these algae., On the other hand, cultured zooxanthellae were influenced by the phosphate regimen of their culture medium. Compared with controls (0 μM P), addition of 10 μM phosphate to the culture medium caused an increase of 100% in cell density and decreases of 50% in the N:P ratio, and 80% in the phosphate-uptake capacity of the zooxanthellae. Zooxanthellae freshly isolated from the clams exhibited properties similar to those of zooxanthellae cultured in the absence of phosphate. These results demonstrate that the zooxanthellae population of T. gigas have limited access to the inorganic phosphate in sea water and the phosphate reserves within the animal host.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00347130
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  • 5
    Electronic Resource
    Electronic Resource
    Photosynthetic carbon dioxide fixation in zooxanthellae (1993)
    Springer
    Marine biology 115 (1993), S. 195-198 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The carbon-fixation patterns of freshly isolated zooxanthellae from the hermatypic coral Acropora formosa were examined during a 15 min exposure to sodium mosa were examined during a 15 min exposure to sodium [14C]bicarbonate. The labelling pattern during the first 60 s exposure showed that the C3 carbon-fixation pathway is the major route for photosynthetic carbon fixation in Symbiodinium sp. 3-Phosphoglyceric acid, which constituted 〉50% of the label after 5 s, steadily decreased over the first 60 s. Hexose phosphates, aspartate, malate and glucose were the other main products during the first 60 s. Over longer periods, significant amounts of the organic acids succinate, aspartate and glutamate were found in the extract along with glucose; but no glycerol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00346335
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  • 6
    Electronic Resource
    Electronic Resource
    Role of carbonic anhydrase in the supply of inorganic carbon to the giant clam—zooxanthellate symbiosis (1993)
    Springer
    Marine biology 115 (1993), S. 605-611 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The mechanism whereby inorganic carbon (Ci) is acquired by the symbiotic association between the giant clam (Tridacna derasa) and zooxanthellae (Symbiodinium sp.) has been investigated. Ci in the haemolymph of the clam is in equilibrium with the surrounding sea water. The photosynthesis rate exhibited by the intact clam varies as a function of the Ci concentration in the clam haemolymph. The gill tissue contains high carbonic anhydrase activity which may be important in adjusting the Ci equilibrium between haemolymph and sea water. Zooxanthellae (Symbiodinium sp.) isolated from the clam mantle prefer CO2 to HCO 3 - as a source of inorganic carbon. The zooxanthellae have low levels of carbonic anhydrase on the external surface of the cell; however, mantle extracts display high carbonic anhydrase activity. Carbonic anhydrase is absent from the mantle of aposymbiotic clams (T. gigas), indicating that this enzyme may be essential to the symbiosis. The enzyme is probably associated with the zooxanthellae tubes in the mantle. The results indicate that carbonic anhydrase plays an important role in the supply of carbon dioxide within the clam symbiosis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00349368
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  • 7
    Electronic Resource
    Electronic Resource
    Nitrogen flux in giant clams: size-dependency and relationship to zooxanthellae density and clam biomass in the uptake of dissolved inorganic nitrogen (1993)
    Springer
    Marine biology 117 (1993), S. 381-386 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Tridacnid clams live on coral reefs in the Indo-Pacific, in waters containing low concentrations of inorganic nitrogen. This study examined nitrogen flux in the giant clam Tridacna gigas. Adults and juveniles of this species typically occur with symbiotic dinoflagellates of the genus Symbiodinium sp., often referred to as zooxanthellae, which live in their tissues. Intact clams took up or released dissolved inorganic nitrogen (DIN), with the direction and magnitude of the fluxes dependent on clam size. Non-symbiotic larvae and newly-settled juveniles with few zooxanthellae released ammonium. Larger juveniles and adults depleted ammonium or nitrate from seawater, when offered separately. Rates of uptake of DIN, standardized to either clam wet weight or number of zooxanthellae, were highest in small clams (1 to 5 cm in length), and decreased with increasing clam size (〉5 cm). Clams maintained in seawater containing high concentrations of ammonium (ca. 20 μM) for ≥ 1 wk generally released ammonium in the dark and exhibited net uptake in the light. Freshly isolated zooxanthellae (FIZ) from small clams had higher uptake rates than FIZ from larger clams, implying that the latter may be more nitrogen-sufficient than the former. The gradient of nitrogen sufficiency in giant clams is related to zooxanthellae density, with peaks of both algal density and rates of uptake of DIN occurring in small sizes of clams, whose growth also appears to be limited by nitrogen availability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00349313
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  • 8
    Electronic Resource
    Electronic Resource
    Ammonium, but not nitrate, stimulates an increase in glutamine concentration in the haemolymph of Tridacna gigas (1999)
    Springer
    Marine biology 133 (1999), S. 45-53 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270050441
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  • 9
    Electronic Resource
    Electronic Resource
    NADP+-dependent glutamate dehydrogenase from Acropora formosa: purification and properties (1987)
    Springer
    Marine biology 95 (1987), S. 559-563 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract As an initial step in our study of nitrogen metabolism in the coral/algal symbiosis we have purified glutamate dehydrogenase (EC 1.4.1.4) to homogeneity from polyp tissue of the staghorn coral Acropora formosa collected from Magnetic Island (North Queensland) in 1985–1986. The purified enzyme had a specific activity of 78 U mg-1. The native enzyme had a relative molecular weight, M r, of 360 000 (±20 000), and appears to be a hexamer with subunits of M r=56000 (±3 000). Like the enzyme from other coelenterates, the coral glutamate dehydrogenase (GDH) was absolutely specific with respect to the coenzyme substrate (NADP+/NADPH), and was insensitive to allosteric regulation by nucleotides; unlike other coelenterate GDHs, the coral enzyme was absorlutely specific for ammonium as amino group donor in the reductive amination reaction, and major differences in kinetic properties were apparent. Linear Michaelis-Menten kinetics were observed for the substrates a-ketoglutarate, NADPH and NADP+, the K m values being 0.93, 0.11 and 0.03 mM, respectively. However glutamate dehydrogenase displayed biphasic kinetics with respect to l-glutamate and ammonium, indicating two apparent K m values (18 and 81 mM for l-glutamate and 9.2 and 416 mM for ammonium). The enzyme also exhibits Scatchard plots, Hill coefficients and cooperativity indices characteristic of enzymes displaying negative cooperativity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00393099
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  • 10
    Electronic Resource
    Electronic Resource
    Localization of two l-glutamate dehydrogenases in the coral Acropora latistella
    Amsterdam : Elsevier
    Archives of Biochemistry and Biophysics 254 (1987), S. 368-371 
    Details
    ISSN: 0003-9861
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0003-9861(87)90112-3
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