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P S Davies - One of the best experts on this subject based on the ideXlab platform.
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ammonium metabolism in the symbiotic sea anemone anemonia viridis
Hydrobiologia, 2001Co-Authors: J M Roberts, L M Fixter, P S DaviesAbstract:The temperate sea anemone Anemonia viridis (Forskal) forms an endosymbiotic association with dinoflagellate algae commonly referred to as Zooxanthellae. It is now well established that under appropriate environmental conditions, these associations can be autotrophic for carbon. Under such conditions, many of these symbioses, including A. viridis, not only retain excretory ammonium, but can take up ammonium added to the surrounding seawater. The flux from inorganic to organic nitrogen will be via the free amino acid pools and in A. viridis these were found to be markedly different between Zooxanthellae and host with glycine and taurine dominant in the latter. When anemones were maintained with 20 μM ammonium, the concentration of free amino groups increased in the Zooxanthellae but appeared not to change in the host. There was no evidence that the ratio of glutamine – glutamate in Zooxanthellae changed when anemones were maintained with 20 μM ammonium for 47 days. These ratios imply that Zooxanthellae from this temperate symbiosis may not be nitrogen-limited. GDH was detected in both Zooxanthellae and host where it was most active with the coenzyme NADPH. In addition, GDH showed activity when glutamine replaced ammonium as the substrate, indicating that the host may have alternative means to assimilate ammonium. Zooxanthellae were shown to possess GOGAT activity in the presence of a ferredoxin analogue. This suggests that in vivo Zooxanthellae could assimilate ammonium via the activity of GS linked with ferredoxin-dependent GOGAT. Given evidence from other studies of rapid ammonium assimilation and essential amino acid synthesis in symbiotic host tissue, it appears that the capacity of cnidarians to metabolise nitrogen may at present be underestimated.
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primary site and initial products of ammonium assimilation in the symbiotic sea anemone anemonia viridis
Marine Biology, 1999Co-Authors: J M Roberts, L M Fixter, P S Davies, T PrestonAbstract:Invertebrates containing endosymbiotic dinoflagellate algae (Zooxanthellae) retain excretory nitrogen, and many are able to take up ammonium from the surrounding seawater. However, the site of assimilation and role of nitrogen recycling between symbiont and host remains unclear. In the present study, ammonium uptake by the symbiotic sea anemone Anemonia viridis (Forskal) was examined by following the pathway of assimilation using 15N-enriched ammonium. Since Zooxanthellae became enriched with 15N from ammonium at up to 17 times the rate of the host, they appear to be the primary site of assimilation. In the light, the rate of Zooxanthellae enrichment at 20 M was twice that at 10 M, whereas the rate of host enrichment was not significantly affected by ammonium concentration. When anemones were incubated with [15N]ammonium in the dark, after 12 h without light the rate of enrichment was lowered in both Zooxanthellae and host. However, while the enrichment of the host was significantly reduced when the light level was lowered from 300 to 150 μmol photons m−2 s−1, Zooxanthellae enrichment was unchanged. Low molecular weight material from the Zooxanthellae became enriched at 20 times the rate of that from the host, and enrichment was detected in the amino acids glutamate, glutamine, aspartate, alanine, glycine, phenylalanine, threonine, valine, tyrosine, and leucine from Zooxanthellae. In the Zooxanthellae, amino acids accounted for 65% of the total enrichment of low molecular weight material. Of the amino acids detected in Zooxanthellae, over 90% of the enrichment was accounted for by glutamate, glutamine and aspartate. The enrichment of the amide group of glutamine was greater than that of the amine group of glutamate or glutamine, consistent with the glutamine synthetase/glutamine 2-oxoglutarate amidotransferase cycle as the mechanism of ammonium assimilation. To examine the flux of 15N from Zooxanthellae to host, anemones were pulse-labelled with [15N]ammonium and then transferred to an unlabelled chase. Over a 2 h period there was no evidence for a flux of nitrogen from Zooxanthellae to host. However, during the chase period, the enrichment of low molecular weight material declined and that of high molecular weight material increased in both Zooxanthellae and host, indicating that protein was synthesized using 15N from ammonium in both components of the symbiosis. Again by using a pulse-chase system, it was found that glutamate was metabolised most rapidly by Zooxanthellae, followed by (in order of decreasing rate of turnover) aspartate, alanine, glycine and valine (no data are available for glutamine). Unlike these amino acids, nitrogen was transferred to the essential amino acids phenylalanine and threonine, increasing their enrichment during the chase period. While recycled nitrogen is clearly important to this symbiosis, the mechanism by which it is cycled remains to be resolved.
J M Roberts - One of the best experts on this subject based on the ideXlab platform.
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ammonium metabolism in the symbiotic sea anemone anemonia viridis
Hydrobiologia, 2001Co-Authors: J M Roberts, L M Fixter, P S DaviesAbstract:The temperate sea anemone Anemonia viridis (Forskal) forms an endosymbiotic association with dinoflagellate algae commonly referred to as Zooxanthellae. It is now well established that under appropriate environmental conditions, these associations can be autotrophic for carbon. Under such conditions, many of these symbioses, including A. viridis, not only retain excretory ammonium, but can take up ammonium added to the surrounding seawater. The flux from inorganic to organic nitrogen will be via the free amino acid pools and in A. viridis these were found to be markedly different between Zooxanthellae and host with glycine and taurine dominant in the latter. When anemones were maintained with 20 μM ammonium, the concentration of free amino groups increased in the Zooxanthellae but appeared not to change in the host. There was no evidence that the ratio of glutamine – glutamate in Zooxanthellae changed when anemones were maintained with 20 μM ammonium for 47 days. These ratios imply that Zooxanthellae from this temperate symbiosis may not be nitrogen-limited. GDH was detected in both Zooxanthellae and host where it was most active with the coenzyme NADPH. In addition, GDH showed activity when glutamine replaced ammonium as the substrate, indicating that the host may have alternative means to assimilate ammonium. Zooxanthellae were shown to possess GOGAT activity in the presence of a ferredoxin analogue. This suggests that in vivo Zooxanthellae could assimilate ammonium via the activity of GS linked with ferredoxin-dependent GOGAT. Given evidence from other studies of rapid ammonium assimilation and essential amino acid synthesis in symbiotic host tissue, it appears that the capacity of cnidarians to metabolise nitrogen may at present be underestimated.
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primary site and initial products of ammonium assimilation in the symbiotic sea anemone anemonia viridis
Marine Biology, 1999Co-Authors: J M Roberts, L M Fixter, P S Davies, T PrestonAbstract:Invertebrates containing endosymbiotic dinoflagellate algae (Zooxanthellae) retain excretory nitrogen, and many are able to take up ammonium from the surrounding seawater. However, the site of assimilation and role of nitrogen recycling between symbiont and host remains unclear. In the present study, ammonium uptake by the symbiotic sea anemone Anemonia viridis (Forskal) was examined by following the pathway of assimilation using 15N-enriched ammonium. Since Zooxanthellae became enriched with 15N from ammonium at up to 17 times the rate of the host, they appear to be the primary site of assimilation. In the light, the rate of Zooxanthellae enrichment at 20 M was twice that at 10 M, whereas the rate of host enrichment was not significantly affected by ammonium concentration. When anemones were incubated with [15N]ammonium in the dark, after 12 h without light the rate of enrichment was lowered in both Zooxanthellae and host. However, while the enrichment of the host was significantly reduced when the light level was lowered from 300 to 150 μmol photons m−2 s−1, Zooxanthellae enrichment was unchanged. Low molecular weight material from the Zooxanthellae became enriched at 20 times the rate of that from the host, and enrichment was detected in the amino acids glutamate, glutamine, aspartate, alanine, glycine, phenylalanine, threonine, valine, tyrosine, and leucine from Zooxanthellae. In the Zooxanthellae, amino acids accounted for 65% of the total enrichment of low molecular weight material. Of the amino acids detected in Zooxanthellae, over 90% of the enrichment was accounted for by glutamate, glutamine and aspartate. The enrichment of the amide group of glutamine was greater than that of the amine group of glutamate or glutamine, consistent with the glutamine synthetase/glutamine 2-oxoglutarate amidotransferase cycle as the mechanism of ammonium assimilation. To examine the flux of 15N from Zooxanthellae to host, anemones were pulse-labelled with [15N]ammonium and then transferred to an unlabelled chase. Over a 2 h period there was no evidence for a flux of nitrogen from Zooxanthellae to host. However, during the chase period, the enrichment of low molecular weight material declined and that of high molecular weight material increased in both Zooxanthellae and host, indicating that protein was synthesized using 15N from ammonium in both components of the symbiosis. Again by using a pulse-chase system, it was found that glutamate was metabolised most rapidly by Zooxanthellae, followed by (in order of decreasing rate of turnover) aspartate, alanine, glycine and valine (no data are available for glutamine). Unlike these amino acids, nitrogen was transferred to the essential amino acids phenylalanine and threonine, increasing their enrichment during the chase period. While recycled nitrogen is clearly important to this symbiosis, the mechanism by which it is cycled remains to be resolved.
Shit F Chew - One of the best experts on this subject based on the ideXlab platform.
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using glutamine synthetase 1 to evaluate the symbionts potential of ammonia assimilation and their responses to illumination in five organs of the giant clam tridacna squamosa
Comparative Biochemistry and Physiology A-molecular & Integrative Physiology, 2021Co-Authors: Leanne S X Teh, Mel V Boo, Jeslyn Shi Ting Poo, Shit F ChewAbstract:Abstract Nitrogen-deficient symbiotic dinoflagellates (Zooxanthellae) living inside the fluted giant clam, Tridacna squamosa, need to obtain nitrogen from the host. Glutamine synthetase 1 (GS1) is a cytosolic enzyme that assimilates ammonia into glutamine. We determined the transcript levels of Zooxanthellal GS1 (Zoox-GS1), which represented comprehensively GS1 transcripts of Symbiodinium, Cladocopium and Durusdinium, in five organs of T. squamosa. The outer mantle had significantly higher transcript level of Zoox-GS1 than the inner mantle, foot muscle, hepatopancreas and ctenidium, but the transcript ratios of Zoox-GS1 to Zooxanthellal form II ribulose-1,5-bisphosphate carboxylase/oxygenase (Zoox-rbcII), which represented the potential of ammonia assimilation relative to the phototrophic potential, were comparable among these five organs. Based on transcript ratios of Zoox-GS1 to Zooxanthellal Urease (Zoox-URE), the outer mantle had the highest potential of urea degradation relative to ammonia assimilation among the five organs, probably because urea degradation could furnish CO2 and NH3 for photosynthesis and amino acid synthesis, respectively, in the symbionts therein. The protein abundance of Zoox-GS1 was upregulated in the outer mantle and the inner mantle during illumination. Zoox-GS1 could catalyze light-enhanced glutamine formation using ammonia absorbed from the host or ammonia released through urea degradation in the cytoplasm. The glutamine produced could be used to synthesize other nitrogenous compounds, including amino acids in the cytoplasm or in the plastid of the dinoflagellates. Some of the amino acids synthesized by the symbionts in the inner mantle and foot muscle could be donated to the host to support shell organic matrix formation and muscle production, respectively.
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phototrophic potential and form ii ribulose 1 5 bisphosphate carboxylase oxygenase expression in five organs of the fluted giant clam tridacna squamosa
Coral Reefs, 2020Co-Authors: Jeslyn Shi Ting Poo, Kum C Hiong, Celine Yen Ling Choo, Mel V Boo, Wai P Wong, Shit F ChewAbstract:Despite living in oligotrophic tropical waters, giant clams can grow to large sizes because they live in symbiosis with extracellular phototrophic dinoflagellates (Zooxanthellae) and receive photosynthates from them. The physical presence of Zooxanthellae in five organs (colorful outer mantle, whitish inner mantle, ctenidium, hepatopancreas and foot muscle) of Tridacna squamosa had been confirmed by microscopy, and high densities of Zooxanthellae were detected in specific regions of the inner mantle and foot muscle. Symbiotic dinoflagellates use form II ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) to fix inorganic carbon during C3 photosynthesis. Using qPCR primers that were designed comprehensively against all known Zooxanthellal form II RuBisCO gene sequences (rbcII) in existing databases, we demonstrated that the outer mantle of T. squamosa (TS) had the greatest phototrophic potential as reflected by its high Zooxanthellal rbcII (TSZrbcII) transcript level, which varied among different regions of the outer mantle. The other four organs also expressed moderate levels of TSZrbcII, despite the lack of iridophores and direct light exposure. Importantly, light exposure led to significant increases in the protein abundance of TSZRBCII in the outer mantle but not the other four organs. Taken together, these results indicate that organs inside the mantle cavity had low phototrophic potentials, but Zooxanthellae residing inside these organs might serve some unidentified functions to benefit the host.
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molecular characterization light dependent expression and cellular localization of a host vacuolar type h atpase vha subunit a in the giant clam tridacna squamosa indicate the involvement of the host vha in the uptake of inorganic carbon and its supply to the symbiotic Zooxanthellae
Gene, 2018Co-Authors: Kum C Hiong, Mel V Boo, Wai P Wong, Leon J Y Lim, Celine Y L Choo, Mei Lin Neo, Shit F ChewAbstract:Abstract The giant clam, Tridacna squamosa, represents a clam-Zooxanthellae association. In light, the host clam and the symbiotic Zooxanthellae conduct light-enhanced calcification and photosynthesis, respectively. We had cloned the cDNA coding sequence of a Vacuolar-type Proton ATPase (VHA) subunit A, ATP6V1A, from T. squamosa, whereby the VHA is an electrogenic transporter that actively ‘pumps’ H+ out of the cell. The ATP6V1A of T. squamosa comprised 1866 bp, encoding a protein of 622 amino acids and 69.9 kDa, and had a host-origin. Its gene expression was strong in the ctenidium and the colorful outer mantle, but weak in the whitish inner mantle, corroborating a previous proposition that VHA might have a trivial role in light-enhanced calcification. Light exposure led to significant increases in the gene and protein expression levels of ATP6V1A/ATP6V1A in the ctenidium and the outer mantle. In the ctenidium, the ATP6V1A was localized in the apical epithelia of the filaments and tertiary water channels, indicating that the VHA could participate in the increased excretion of H+ produced during light-enhanced calcification. Additionally, the excreted H+ would augment HCO3– dehydration in the external medium and facilitate the uptake of CO2 by the ctenidium during insolation. In the outer mantle, the ATP6V1A was detected in intracellular vesicles in a type of cells, presumably iridocytes, surrounding the Zooxanthellal tubules, and in the apical epithelium of Zooxanthellal tubules. Hence, the host VHA could participate in the transfer of inorganic carbon from the hemolymph to the luminal fluid of the tubules by increasing the supply of H+ for the dehydration of HCO3– to CO2 during insolation to benefit the photosynthesizing Zooxanthellae.
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molecular characterization of a novel algal glutamine synthetase gs and an algal glutamate synthase gogat from the colorful outer mantle of the giant clam tridacna squamosa and the putative gs gogat cycle in its symbiotic Zooxanthellae
Gene, 2018Co-Authors: Rachel R S Fam, Kum C Hiong, Wai P Wong, Celine Y L Choo, Shit F ChewAbstract:Abstract Giant clams harbor symbiotic Zooxanthellae (Symbiodinium), which are nitrogen-deficient, mainly in the fleshy and colorful outer mantle. This study aimed to sequence and characterize the algal Glutamine Synthetase (GS) and Glutamate Synthase (GLT), which constitute the glutamate synthase cycle (or GS-GOGAT cycle, whereby GOGAT is the protein acronym of GLT) of nitrogen assimilation, from the outer mantle of the fluted giant clam, Tridacna squamosa. We had identified a novel GS-like cDNA coding sequence of 2325 bp, and named it as T. squamosa Symbiodinium GS1 (TSSGS1). The deduced TSSGS1 sequence had 774 amino acids with a molecular mass of 85 kDa, and displayed the characteristics of GS1 and Nucleotide Diphosphate Kinase. The cDNA coding sequence of the algal GLT, named as T. squamosa Symbiodinium GLT (TSSGLT), comprised 6399 bp, encoding a protein of 2133 amino acids and 232.4 kDa. The Zooxanthellal origin of TSSGS1 and TSSGOGAT was confirmed by sequence comparison and phylogenetic analyses. Indeed, TSSGS1 and TSSGOGAT were expressed predominately in the outer mantle, which contained the majority of the Zooxanthellae. Immunofluorescence microscopy confirmed the expression of TSSGS1 and TSSGOGAT in the cytoplasm and the plastids, respectively, of the Zooxanthellae in the outer mantle. It can be concluded that the symbiotic Zooxanthellae of T. squamosa possesses a glutamate synthase (TSSGS1-TSSGOGAT) cycle that can assimilate endogenous ammonia produced by the host clam into glutamate, which can act as a substrate for amino acid syntheses. Thus, our results provide insights into why intact giant clam-Zooxanthellae associations do not excrete ammonia under normal circumstances.
Virginia M Weis - One of the best experts on this subject based on the ideXlab platform.
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feeding behavior and acquisition of Zooxanthellae by planula larvae of the sea anemone anthopleura elegantissima
Marine Biology, 2002Co-Authors: Jodi A Schwarz, Virginia M Weis, Donald C PottsAbstract:Symbiotic associations between cnidarians and photosynthetic dinoflagellates (i.e., Zooxanthellae) are common in the marine environment. Many symbiotic cnidarians produce offspring that are initially nonsymbiotic. These new hosts must acquire symbiotic algae from environmental sources. We examined Zooxanthella acquisition by laboratory-reared planula larvae of the temperate sea anemone Anthopleura elegantissima. Larvae ingested Zooxanthellae while they were feeding. However, the signal that prompted larval feeding behavior did not originate from the symbiotic algae; the addition of algal cells to larval cultures never elicited a feeding response. In contrast, the addition of macerated animal tissue from several sources invariably generated a strong feeding response, which resulted in the larvae indiscriminately ingesting any particulate matter that was present, including Zooxanthellae or other unicellular algae. Ingested Zooxanthellae were incorporated into endodermal cells, where they remained undigested, while all other ingested material was digested or expelled within 24 h. Our results provide evidence that one source of Zooxanthellae likely to serve as a route of infection in the natural environment is Zooxanthella-laden mucus egested by anemones. This egested material fulfilled both of the criteria necessary for successful infection: it prompted larvae to begin feeding and provided an abundant supply of Zooxanthellae that were ingested and taken up into endodermal cells of the new host.
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host symbiont specificity during onset of symbiosis between the dinoflagellates symbiodinium spp and planula larvae of the scleractinian coral fungia scutaria
Coral Reefs, 2001Co-Authors: Virginia M Weis, Wendy S Reynolds, Melissa D Deboer, Dave A KruppAbstract:Many corals which engage in symbioses with dinoflagellates from the genus Symbiodinium (Zooxanthellae) produce offspring which initially lack Zooxanthellae. These species must choose their symbionts from numerous genetically distinct strains of Zooxanthellae co-occurring in the environment. In most cases, symbiosis onset results in an association between a specific host coral and a specific strain of algal symbiont. This is the first study to examine host-symbiont specificity during symbiosis onset in a larval cnidarian, and the first to examine such events in a scleractinian of any life stage. We infected planula larvae of the solitary Hawaiian scleractinian Fungia scutaria with both homologous Zooxanthellae, freshly isolated from F. scutaria adults, and heterologous Zooxanthellae, isolated from Montipora verrucosa, Porites compressa, and Pocillopora damicornis, three species of scleractinians which co-occur with F. scutaria. We found that homologous Zooxanthellae were better able to establish symbioses with larval hosts than were heterologous isolates, by two separate measures: percent of a larval population infected, and densities of Zooxanthellae per larva. We also measured algal densities in larvae over a 4-day period until the onset of settlement and metamorphosis. We found no changes in Zooxanthella population densities, regardless of Zooxanthella type or the light environment in which they were incubated. Strong infection of host larvae with homologous algae compared to heterologous algae suggests that there is a specificity process which occurs sometime during the early stages of infection between the partners, and which results in the establishment of a specific symbiosis.
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late larval development and onset of symbiosis in the scleractinian coral fungia scutaria
The Biological Bulletin, 1999Co-Authors: Jodi A Schwarz, Dave A Krupp, Virginia M WeisAbstract:Many corals that harbor symbiotic algae (Zooxanthellae) produce offspring that initially lack Zooxanthellae. This study examined late larval development and the acquisition of Zooxanthellae in the scleractinian coral Fungia scutaria, which produces planula larvae that lack Zooxanthellae. Larvae reared under laboratory conditions developed the ability to feed 3 days after fertilization; feeding behavior was stimulated by homogenized Artemia. Larvae began to settle and metamorphose 5 days after fertilization. In laboratory experiments, larvae acquired experimentally added Zooxanthellae by ingesting them while feeding. Zooxanthellae entered the gastric cavity and were phagocytosed by endodermal cells. As early as 1 h after feeding, Zooxanthellae were observed in both endodermal and ectodermal cells. Larvae were able to form an association with three genetically distinct strains of Zooxanthellae. Both Zooxanthellate and aZooxanthellate larvae underwent metamorphosis, and aZooxanthellate polyps were able to ac...
Evgrafovich Aleksandr Titlyanov - One of the best experts on this subject based on the ideXlab platform.
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rhythmicity in division and degradation of Zooxanthellae in the hermatypic coral stylophora pistillata
Symbiosis, 2004Co-Authors: Evgrafovich Aleksandr Titlyanov, T. L. Kalita, Tamara V. Titlyanova, Irina M YakovlevaAbstract:Three types of rhythmic changes in division and degradation of symbiotic dinoflagellates-Zooxanthellae were found in the scleractinian coral Stylophora pistillata from the fringing reef of Sesoko Island, Okinawa, Japan. The first type of phased change in proliferating Zooxanthellae frequency (PZF) and degrading Zooxanthellae frequency (DZF) indices is a diurnal cycle with a period of 24 h. The second type of the phased change in PZF and DZF levels is rhythmicity with a period of 3 days. The rhythmicity of these changes was disrupted by changes in the weather conditions (from rainy to sunny days and conversely) and by the sharp changes in irradiation during the experiment. The third type of rhythmic change in the levels of Zooxanthellae division and degradation is a rhythmicity with a period of 6-7 days. Sharp changes in daily light intensity did not disrupt 6-days cycles. These changes in the PZF and DZF levels of the second and third types of rhythmicity occurred in an opposite trend. Amplitudes of changes in both processes are depended on the light intensity. Bright light (95% PAR 0 ) stimulates both the division and degradation of Zooxanthellae. We suggest that all three types of rhythmic changes in Zooxanthellae division and degradation are the reactions that regulate algal population density in symbiotic corals.
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acclimation of the hermatypic coral stylophora pistillata to bright light
Russian Journal of Marine Biology, 2002Co-Authors: Evgrafovich Aleksandr Titlyanov, R Van Woesik, Tamara V. Titlyanova, Keisyo YamazatoAbstract:Photoacclimation dynamics to bright light was studied in the symbiotic reef-building coral Stylophora pistillata. Coral colonies were collected from shallow shaded sites (2 m, 40–20% PARs) from a fringing reef at Sesoko Island, Okinawa, Japan. Outer branches were broken off from the colonies and placed in an outdoor aquarium until the start of the experiments. After maintenance of the branches in an aquarium under a light intensity of 30% PARs for 30 days (experiment 1) or for 90 days (experiment 2), the samples were exposed to 95% PARs for 120 days in the same aquarium. The population density of Zooxanthellae, chlorophyll concentration, locations of Zooxanthellae, proliferating Zooxanthellae frequency (PZF), and degrading Zooxanthellae frequency (DZF) were examined. It was shown that after acclimation of coral branches to bright light, the population density of Zooxanthellae, chlorophyll concentration calculated per 1000 polyps, and chlorophyll concentration in Zooxanthellae decreased. The size of Zooxanthellae significantly decreased. A decrease in the population density of Zooxanthellae was detected by the eighth day of acclimation, and stabilization in the density of the symbionts occurred in the period from the 40th to the 60th day of the experiment. The chlorophyll concentration in Zooxanthellae significantly decreased by the second day of exposure to bright light and stabilized by the fourth day. The PZF level sharply dropped on the second day, while the DZF level sharply increased and was higher than the PZF level for 40 days of exposure to bright light. We conclude, therefore, that the population density of Zooxanthellae is regulated by the rates of two processes: cell division and the cell degradation.
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photo acclimation of the hermatypic coral stylophora pistillata while subjected to either starvation or food provisioning
Journal of Experimental Marine Biology and Ecology, 2001Co-Authors: Evgrafovich Aleksandr Titlyanov, Keisyo Yamazato, Tamara V. Titlyanova, R Van WoesikAbstract:This study investigated the photo-acclimation capacity of the coral Stylophora pistillata (Esper). Outer branches of coral colonies, taken from 2 m, were subjected to 90, 20, or 3% of incident surface photosynthetic active radiation (PAR0), or kept in total darkness. The corals were maintained either in filtered seawater (i.e., under starvation), or in seawater that had daily additions of zooplankton (rotifers). The experiments were maintained for 31 days. Zooxanthellae population densities and chlorophyll concentrations increased in S. pistillata fragments subjected to 20 and 3% PAR0. The Zooxanthellae densities decreased after 6 days in corals kept in total darkness, although chlorophyll concentrations remained higher. Corals that were fed and subjected to 90% PAR0 showed lower degrading Zooxanthellae frequencies, higher photosynthetic and respiration rates, and higher chlorophyll concentrations than corals in the same light regime under starvation. Complete acclimation to dim (20% PAR0) and low (3% PAR0) light was only apparent for corals fed with zooplankton. Changes in Zooxanthellae population densities occurred through differential rates of Zooxanthellae division and degradation.
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effects of dissolved ammonium addition and host feeding with artemia salina on photoacclimation of the hermatypic coral stylophora pistillata
Marine Biology, 2000Co-Authors: Evgrafovich Aleksandr Titlyanov, Alexander Malkin, Irina R. Fomina, V. Leletkin, N Eden, Tamara V. Titlyanova, Zvy DubinskyAbstract:Effects of nutrient treatments on photoacclimation of the hermatypic coral Stylophora pistillata (Esper) were studied. Studies on photoacclimation of colonies from different light regimes in the field were evaluated and used to design laboratory experiments. Coral colonies were collected in the Gulf of Eilat (Israel) from January to March 1993. Exterior branches of colonies from different depths (1 to 40 m) displayed different trends in production characteristics at reduced and very low levels of illumination. From 24 ± 3% to 12 ± 2% of incident surface photosynthetic active radiation (PARo), Zooxanthella population density and chlorophyll a+c per 106 Zooxanthellae increased, a trend seen in the range of light levels optimal for coral growth (90 to 30% PARo). The P max of CO2 per 106 Zooxanthellae decreased, while P max of CO2 per 103 polyps increased, indicating an increase in Zooxanthella population density at low light levels. Proliferous Zooxanthella frequency (PZF, a measure of Zooxanthella division) declined significantly at light levels <18 ± 3% PARo. At the lowest levels of illumination (<5% PARo), Zooxanthella population density decreased, as did the PZF; chl a+c per 106 Zooxanthellae was unchanged. In 28-d experiments, exterior coral branches from the upper surfaces of colonies from 3 m depth (65 ± 4% PARo) were incubated in aquaria under bright (80 to 90% PARo), reduced (20 to 30% PARo), and extremely low (2 to 4% PARo) light intensities. At each light intensity, the corals were maintained in three feeding treatments: sea water (SW); ammonium enriched SW (SW + N); SW with Artemia salina nauplii (SW + A). An increase in P max of CO2 per 103 polyps was found in corals acclimated to reduced light (20 to 30% PARo) in nutrient-enriched SW, while in SW, where the increase in Zooxanthella population density was smaller, it did not occur. Nutrient enrichments (SW + N at 2 to 4% PARo and SW + A at 20 to 30% PARo) increased Zooxanthella population density, but had no effect on chl a+c per 106 Zooxanthellae. Acclimation for 14 d to reduced (10 to 20% PARo) and extremely low (1 to 3% PARo) light intensities shifted 14C photoassimilation into glycerol and other compounds (probably glycerides), rather than sugars. Both ammonium addition and feeding with Artemia salina nauplii resulted in an increase in photosynthetic assimilation of 14C into amino acids. We conclude that acclimation to reduced light consists of two processes: an increase in photosynthetic pigments and in Zooxanthella population density. Both processes require nitrogen, the increase in Zooxanthella population density needing more; this adaptation is therefore limited in nitrogen-poor sea water.
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autotrophy and predation in the hermatypic coral stylophora pistillata in different light habitats
Symbiosis, 2000Co-Authors: Evgrafovich Aleksandr Titlyanov, V. Leletkin, Zvy DubinskyAbstract:The influence of light conditions in natural habitats on autotrophic function and also effects of light intensities, ammonium additions and feeding with zooplankton on predation of the coral Stylophora pistillata in aquaria experiments were studied. Coral colonies were collected in the Gulf of Eilat (Israel) from depths 2 m, 20 m and 40 m. Some branches were maintained in aquaria during two weeks under different light regimes from 5% to 90% of PAR 0 and with different feeding treatments: seawater; seawater enriched with (NH 4 ) 2 SO 4 ; and seawater with the Artemia salina nauplii additions. It was shown that in exterior branches of the colonies Zooxanthella population density and chlorophyll concentration (calculated as per polyp as per 10 6 Zooxanthellae) increased with gradual reducing light intensity from 90% to 5% PARE, while the level of dividing Zooxanthella frequency declined. With reducing light intensity from 20% to 5% PAR 0 an average volume of Zooxanthellae and the ratio of values of maximal gross photosynthesis and dark respiration of corals decreased. It was elucidated that ingestion rates as well as killing rates increased with reducing light intensity in the field and in the experimental aquaria. In most cases the value of the ratio of ingestion rate to killing rate was increased. Feeding of corals with inorganic nitrogen as well as with zooplankton stimulated the ingestion rate. When corals incubated under 90% and 20% PAR 0 in all feeding treatments the highest daily rate of predation observed at morning hours and lesser - at evening hours. Under light intensity 5% PAR 0 the rate of predation was high during the day in all feeding variants of the experiments. We conclude that with reducing light intensity in habitat the production capacities of autotrophic function of corals increased by accumulation of algal-symbionts in exterior branches of corals and by increasing photosynthetic pigment concentration in the algae. In all probabilities, it depended on intensification of predation under shade. We assume that corals are capable of adapting to dim light not only by maximization of light absorption and its effective use, but also by intensification of heterotrophic function, at least predation.
