bluuebunny/crossref_metadata_2025_split huggingface dataset:
WAVELENGTH DEPENDENCY OF THE MAXIMUM QUANTUM YIELD OF CARBON FIXATION FOR TWO RED TIDE DINOFLAGELLATES, HETEROCAPSA PYGMAEA AND PROROCENTRUM MINIMUM (PYRROPHYTA): IMPLICATIONS FOR MEASURING PHOTOSYNTHETIC RATES1
Authors: Schofield Oscar , Prézelin Barbara , Johnsen Geir 
Published: October 2004

ABSTRACTThe influence of photoadaptive state on the spectral dependency of the maximum quantum yield for carbon fixation was determined for two red tide dinoflagellates, Heterocapsa pygmaea Loeblich, Schmidt, et Sherley and Prorocentrum minimum Pavillard. Cultures were acclimated to green, blue, red, and white light. The spectral dependency in the light‐limited slope of the photosynthesis–irradiance curves (α) was measured with carbon action spectra that, when divided by the spectrally weighted absorption coefficient, provided estimates of the maximum quantum yield (φmax) for carbon fixation. Values of φmax varied with wavelength within each culture condition as well as between different culture conditions. The degree to which the spectral dependency in φmax was influenced by the presence of photoprotective carotenoids and/or energy imbalances between photosystems I and II was assessed for both dinoflagellates. The impact of photoprotective pigmentation on the spectral dependency of φmax was most significant for cells grown under high light conditions reflecting the enrichment of diadinoxanthin. Energy imbalances between the photosystems was assessed by quantifying enhancement effects on spectral φmax in the presence of background illumination. Under our experimental conditions, enhancement effects on carbon action spectra were evident for H. pygmaea under nearly all growth conditions but were not detectable for P. minimum under any growth condition. We hypothesize that sensitivity to enhancement effects reflected differences in the structure of the photosynthetic machinery of these two peridinin‐containing dinoflagellates. While measurements of φmax are sensitive to the color of the light within an incubator, the relative impact on the spectral dependency of a was less than the wavelength dependency associated with the cellular absorption properties. Finally we used our data to validate an approach proposed by others to aid in the correction of photosynthetic measurements where the in situ spectral light field cannot be easily mimicked. The average error using this approach was 8%, which was significantly less than the error associated with ignoring the spectral dependency in α.
INFLUENCE OF CELL WALL COMPOSITION ON THE RESISTANCE OF TWO CHLORELLA SPECIES (CHLOROPHYTA) TO DETERGENTS1
Authors: Corre Gwenael , Templier Joëlle , Largeau Claude , Rousseau Bernard , Berkaloff Claire 
Published: October 2004

ABSTRACTThe influence of dodecylbenzene sulfonate (DBS) and Triton X‐100 (TX‐100) was examined on two species of Chlorella exhibiting conspicuous differences in cell wall composition. Chlorella emersonii has both a classical polysaccharidic wall and a thin trilaminar outer wall (TLS) composed of nonhydrolyzable macromolecules. Chlorella vulgaris lacks a TLS. Photosynthetic capacity was measured following short exposures (1 h) of the algae at different physiological stages to high DBS and TX‐100 concentrations, up to 1 g·L−1. Comparisons with untreated controls indicated that 1) the presence of a TLS in C. emersonii was associated with a very high resistance to the anionic (DBS) and nonionic (TX‐100) detergents at all growth stages, and net photosynthesis was not significantly affected in that species, 2) a high toxicity, particularly pronounced with TX‐100, was observed for actively growing cells of the TLS‐devoid species, C. vulgaris, and 3) aging exerted a protective influence, especially efficient against DBS, on the latter species. Additional observations, including fluorescence spectra and high‐performance liquid chromatography pigment analyses, were conducted following short exposures of actively growing cells. Fluorescence emission spectra revealed that the chlorophyll a‐protein complexes in thylakoid membranes were not substantially affected by DBS and TX‐100, even in the case of C. vulgaris. In sharp contrast, fluorescence excitation spectra on the latter species showed 1) that excitation transfer from antenna pigments to chlorophyll a in reaction centers was substantially altered with both detergents and 2) that the two detergents affected different parts of the photosynthetic system of the TLS‐devoid species. Analyses of C. vulgaris extracts indicated significant decreases in pigment content following exposure to DBS and, to a lesser extent, to TX‐100. Longer exposure experiments (1 day) were conducted with actively growing algae. The TLS‐containing species still showed a very high resistance and no important changes in photosynthetic capacity compared to cells exposed for 1 h. For the sensitive TLS‐devoid species, the detrimental influence of TX‐100, already very high after 1 h, was not increased. DBS toxicity was markedly increased and may reflect a lower uptake rate of DBS by C. vulgaris.Taken together, these observations confirm the important protective role of TLS against detergents. They also provide information on the factors controlling detergent toxicity in the sensitive, TLS‐devoid species and on the different modes of action of DBS and TX‐100 on its photosynthetic system. Such large differences in microalgal sensitivity to detergents, related to TLS occurrence, should have important consequences for the selection of suitable species in toxicity tests.
EVIDENCE THAT MICROCYSTIN IS A THIO‐TEMPLATE PRODUCT1
Authors: Arment Anthony R. , Carmichael Wayne W. 
Published: October 2004

ABSTRACTThe hepatotoxic cyclic heptapeptide toxins of cyanobacteria, collectively termed microcystins, are potent inhibitors of protein phosphatases PP1 and PP2A. The structure of microcystins resembles small, cyclic peptide secondary metabolites from fungi and eubacteria. Many of these metabolites are manufactured via a nonribosomal thio‐template mechanism. We submit evidence that microcystin is synthesized by a similar mechanism. The organism used in this study was Microcystis aeruginosa PCC7820.Using the traditional ATP‐32PPi exchange assay for thio‐template activity, we found activity in the presence of the substrate d‐amino acids occurring in microcystin. Thio‐template mechanisms are known to be unaffected by protein synthesis inhibitors such as chloramphenicol. We subjected cultures in exponential and stationary growth to chloramphenicol and monitored culture health versus toxicity. Although the health of the treated cultures declined, the toxicity of the remaining cells increased. We developed an in vitro assay to measure microcystin synthesis in cell lysates in the presence of chloramphenicol. By supplementing the lysates with ATP and the substrate amino acids present in microcystin, we detected a fourfold increase in total microcystins over the course of 20 min.
FATTY ACID AND LIPID COMPOSITION OF THE ACIDOPHILIC GREEN ALGA CHLAMYDOMONAS SP.1
Authors: Tatsuzawa Hidetaka , Takizawa Etsuko , Wada Masayuki , Yamamoto Yoko 
Published: October 2004

ABSTRACTThe lipid and fatty acid compositions of Chlamydomonas sp. isolated from a volcanic acidic lake and C. reinhardtii were compared, and the effects of pH of the medium on lipid and fatty acid components of Chlamydomonas sp. were studied. The fatty acids in polar lipids from Chlamydomonas sp. were more saturated than those of C. reinhardtii. The relative percentage of triacylglycerol to the total lipid content in Chlamydomonas sp. grown in medium at pH 1 was higher than that in other cells grown at higher pH. A probable explanation might be that Chlamydomonas sp. has two low pH adaptation mechanisms. One mechanism is the saturation of fatty acids in membrane lipids to decrease membrane lipid fluidity, and the other is the accumulation of triacylglycerol, as a storage lipid, to prevent the osmotic imbalance caused by high concentrations of H2SO4.
IMMUNOLOGICAL IDENTIFICATION OF THE ALTERNATIVE OXIDASE IN CHLAMYDOMONAS REINHARDTII (CHLOROPHYTA)1
Authors: Derzaph Tina L. M. , Weger Harold G. 
Published: October 2004

ABSTRACTUsing a monoclonal antibody to the alternative oxidase from voodoo lily, we provide evidence that the green alga Chlamydomonas reinhardtii Dang, possesses a protein that is immunologically related to the higher plant alternative oxidase. Mitochondria were isolated from a cell wall‐less mutant strain (CW‐15), and the presence of cyanide‐resistant oxygen consumption was confirmed in these mitochondria. The voodoo lily antibody was used as a probe for immunoblotting of sodium dodecyl sulphate‐polyacrylamide gel electrophoresis gels of mitochondrial proteins of C. reinhardtii. The antibody reacted with a protein from C. reinhardtii with the same molecular mass (36 kDa) as the alternative oxidase from voodoo lily and tobacco mitochondria. These results suggest that cyanide‐resistant respiration in C. reinhardtii is mediated by a higher plant‐type alternative oxidase.
IMMUNOLOCALIZATION OF NITRATE REDUCTASE IN THE MARINE DINOFLAGELLATE GONYAULAX POLYEDRA (PYRROPHYTA)1
Authors: Fritz Lawrence , Stringher Claudia Gadni , Colepicolo Pio 
Published: October 2004

ABSTRACTA polyclonal antibody, raised against nitrate reductase (NR) purified from the photosynthetic dinoflagellate Gonyaulax polyedra Stein, was used as a probe in immunogold‐labeling experiments on thin sections prepared from cells harvested both during day and night phases. Previous experiments have shown that both NR activity and the amount of immunoreactive NR in cell extracts is greater when day‐phase cells are examined, and this property was exploited as an internal control for the cytochemical labeling. We observed that in day‐phase cells, chloroplasts contained approximately three times more gold particles than night‐phase cells (highly significant difference; P < 0.0001), whereas cytoplasmic labeling levels remained relatively level between day and night. We conclude from the diurnal difference in labeling that our antibody faithfully reflects the distribution of NR in Gonyaulax cells. Thus, as in to some other higher plants and green algae, Gonyaulax compartmentalizes active NR in its chloroplasts.
IDENTIFICATION OF CULTURED PSEUDO‐NITZSCHIA (BACILLARIOPHYCEAE) USING SPECIES‐SPECIFIC LSU rRNA‐TARGETED FLUORESCENT PROBES1
Authors: Miller Peter E. , Scholin Christopher A. 
Published: October 2004

ABSTRACTSome, but not all, marine pennate diatoms of the genus Pseudo‐nitzschia H. Peragallo are associated with the production of domoic acid, a naturally occurring amino acid responsible for amnesic shellfish poisoning. Distinguishing between potentially toxic and nontoxic representatives of this genus is time‐consuming and difficult because it demands scanning electron microscopy of cleaned frustules. The objective of this work is to speed and ease identification of these organisms by using whole‐cell (in situ) hybridization and species‐specific large‐subunit ribosomal RNA (LSU rRNA)‐targeted oligonucleotide probes. Toward that end, cultures of P. australis Frenguelli, P. pungens (Grunow) Hasle, P. multiseries (Hasle) Hasle, P. fraudulenta (P. T. Cleve) Heiden, P. heimii Manguin, P. delicatissima (P. T. Cleve) Heiden, P. pseudo‐delicatissima (Hasle) Hasle, and P. americana (Hasle) Fryxell were screened with a suite of 15 putative species‐specific probes. Of those, a subset of eight probes was found that distinguished each species tested. In addition, Pseudo‐nitzschia chloroplasts were labeled with a probe directed against a eubacterial‐conserved sequence. Identification of new cultures based on their reactivity toward a set of probes agreed with species designations as defined by morphological criteria. Whole‐cell hybridization is a rapid, simple, and cost‐effective technique for discriminating among cultured Pseudo‐nitzschia species.
TAXONOMY OF THE FLATTENED SOLIERIACEAE (RHODOPHYTA) IN BRAZIL: AGARDHIELLA AND MERISTIELLA1
Authors: Guimarães Silvia M. P. B. , Oliveira Eurico C. 
Published: October 2004

ABSTRACTTaxonomic studies of an extensive collection of flattened members of the Solieriaceae considered by many authors to be species of Agardhiella, Eucheuma, Meristotheca, and Meristiella lead us to conclude that they represent only two genera in Brazil: Agardhiella, including A. ramosissima (Harvey) Kylin and A. floridana (Kylin) Gabrielson ex Guimarães et Oliveira, and Meristiella, with only one species, M. gelidium (J. Agardh) Cheney et Gabrielson. Accordingly, we propose that 1) Meristotheca gigartinoides Joly et Ugadim be synonymized with Agardhiella floridana, and 2) Meristiella echinocarpa (Areschoug) Cheney et Gabrielson and M. schrammii (P. et H. Crouan) Cheney et Gabrielson be synonymized with Meristiella gelidium.
MORPHOLOGY AND ECOLOGY OF THE MARINE BENTHIC DINOFLAGELLATE SCRIPPSIELLA SUBSALSA (DINOPHYCEAE)1
Authors: Faust Maria A. 
Published: October 2004

ABSTRACTThe thecal surface morphology of Scrippsiella subsalsa (Ostenfeld) Steidinger et Balech was examined using the scanning electron microscope. This species is distinguished by a number of morphological characteristics. Apical plate 1′ is wide, asymmetric, and pentagonal, and it ends at the anterior margin of the cingulum. Intercalary plates 2a and 3a are separated by apical plate 3′. The apical pore complex includes a large Po plate with a raised dome at the center and a deep canal plate with thickened margins at plates 2′, 3′, and 4′. The intercalary bands are wide and deeply striated. The cingulum is deep, formed by six cingular plates; its surface is transversely striated and aligned with a row of minute pores. The cingular list continues around postcingular plate 1′” to form a sulcal list. The sulcal list is a flexible ribbon with a rounded tip that protrudes posteriorly, partially covering the sulcal plates. The hypotheca is lobed, and the antapical plates are irregularly shaped and wide in antapical view. The thecal surface is vermiculate to reticulate. A comparison in morphology and ecology is presented between S. subsalsa and other known Scrippsiella species.
SILICEOUS SCALE PRODUCTION IN CHRYSOPHYTE AND SYNUROPHYTE ALGAE. I. EFFECTS OF SILICA‐LIMITED GROWTH ON CELL SILICA CONTENT, SCALE MORPHOLOGY, AND THE CONSTRUCTION OF THE SCALE LAYER OFSYNURA PETERSENII1
Authors: Sandgren Craig D. , Hall Shirley A. , Barlow Steven B. 
Published: October 2004

ABSTRACTThe cells of synurophyte flagellates (algal class Synurophyceae, formerly included in the Chrysophyceae) are enclosed within a regularly imbricate layer of ornamented siliceous scales. Scale morphology is of critical taxonomic importance within this group of algae, and the scales are valuable indicator microfossils in paleolimnological studies. The data presented here demonstrate that scale morphology and the integrity of the scale layer can exhibit extreme variability in culture as a function of the cellular quota of silica under silica‐limited growth. Silica‐limited, steady‐state populations of the colonial flagellateSynura peterseniiKorsh. were maintained over a range of specific growth rates (μ= 0.11–0.69 days−1) and silica cell quotas (Qsi= 0.13–2.40 pmoles Si · cell1). Scale morphology and the organization of the scale layer became increasingly aberrant as silica stress increased. Under severe stress, scale deposition was completely suppressed so that cells appeared scale‐free. This depression of scale deposition was reversible; populations of silica‐starved, scale‐free cells rapidly regenerated new scale layers when placed in batch culture and spiked with dissolved silica. During recovery from silica stress, cell division was repressed for 24 h while mean cell silica quota increased 25‐fold. The first new scales appeared within 2 h after the silica addition, and development of the new scale layer proceeded in an approximately synchronous manner, residting in normal scale layers on virtually all cells after 48 h of recovery in Sirich medium. Silica content of silica‐repleteSynuracells is comparable to freshwater diatoms of siynilar size, butSynurahas much greater potential quota variability than diatoms and no apparent threshold silica requirement. Silica‐limited growth kinetics and competition between diatoms andSynurafor silica are discussed.The results suggest that morphological variability of siliceous scales in natural populations of synurophyte flagellates may result from silica stress and that the experimental approach developed here has great potential value as a means for circumscribing ecotypic variation in scale morphology. Results also demonstrate that scale production can be uncoupled from cell division, suggesting that cell cycle regulation of silica biomineralization in the Synurophyceae may be fundamentally different from that of diatoms (algal class Bacillariophyceae). This experimental system has application in the future study of the intracellular membrane systems and the regulatory processes involved in silica biomineralization.
QUANTITATIVE METHOD FOR DETERMINING A REPRESENTATIVE ALGAL SAMPLE COUNT1
Authors: Pappas Janice L. , Stoermer Eugene F. 
Published: October 2004

ABSTRACTA method for determining a representative count of a sample dependent on number of species is presented for application to various algal communities. Constant species curves are calculated as efficiency = (number of individuals–number of species)/number of individuals and diagrammed on a plot of efficiency versus number of individuals counted. Efficiency is defined as the probability that a new species encountered is minimal. That is, as the ratio of number of species to number of individuals approaches 1, more individuals will need to be counted in order to achieve a representative count. Data and calculations of efficiency from two algal communities are presented for illustration.
PHOTOSYNTHESIS AND REGULATION OF RUBISCO ACTIVITY IN NET PHYTOPLANKTON FROM DELAWARE BAY1
Authors: MacIntyre Hugh L. , Geider Richard J. , McKay R. Michael 
Published: October 2004

ABSTRACTNet phytoplankton (> 20 μm) comprised 51 ± 9% of the total chlorophyll (Chl) in a Skeletonema costatum– dominated spring bloom in Delaware Bay. The net phytoplankton had low C:N and high protein: carbohydrate ratios, indicating that their growth was nutrient‐replete. Their photosynthetic responses were characterized by low specific absorption, low light‐limited and light‐saturated rates of photosynthesis, and high quantum yields, indicative of acclimation to low irradiance and internal self‐shading. High fucoxanthin: Chi ratios also indicated low light acclimation, but high photoprotective xanthophyll: Chi ratios suggested a high capacity for photoprotective energy dissipation. Ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) could be activated and deactivated in response to changes in irradiance and was fully activated at the surface of the water column and fully deactivated in aphotic deep water. Maximum Rubisco activity was correlated with Rubisco content and bulk protein content of the phytoplankton and with light‐saturated rates of photosynthesis measured in short (< 20‐min) incubations. Long (60‐min) incubations caused a decrease in the light‐saturated rate of photosynthesis, possibly because of feedback limitation. While feedback limitation is unlikely to occur in the water column, it should be considered when estimating productivity in well‐mixed waters from fixed light‐depth incubations.
A MODEL APPROACH FOR SIZE‐SELECTIVE COMPETITION OF MARINE PHYTOPLANKTON FOR FLUCTUATING NITRATE AND AMMONIUM1
Authors: Stolte Willem , Riegman Roel 
Published: October 2004

ABSTRACTPhytoplankton size‐selective competition for fluctuating nutrients was studied with the use of a numerical model, which describes nitrate and ammonium uptake, nitrate reduction to ammonium, and growth as a function of cell she under fluctuating nitrogen limitation. The only size‐dependent parameter in the model was the cell nutrient quota. Related to this, the cell surface area per biomass was negatively correlated to cell volume, and the vacuole volume per biomass ratio was positively correlated to cell volume. Simulations showed an inverse correlation between the maximum specific growth rate and cell size under steady‐state conditions. With nitrate as the limiting nitrogen source, nitrogen quotas were always higher than with ammonium at the same specific growth rate. Net passive transport of ammonium due to unspecific diffusion of ammonia across the plasma membrane decreased the affinity for ammonium, whereas the affinity for nitrate was not influenced. Transient state‐specific ammonium uptake was not dependent on cell size. However, small algae always have the highest specific growth rate in ammonium‐controlled systems according to our model. Transient state nitrate uptake rate was positively correlated to cell size because larger algae have a higher vacuole volume per biomass, in which nitrate can be stored. Despite their lower maximum growth rate, larger algae became dominant during simulations under fluctuating nitrate supply when amplitude of and the period between nitrate pulses were high enough. Results from model simulations were qualitatively validated by earlier observations that large diatoms become dominant under fluctuating conditions when nitrate is the main nitrogen source.
PHYSIOLOGICAL AND OPTICAL PROPERTIES OF RHIZOSOLENIA FORMOSA (BACILLARIOPHYCEAE) IN THE CONTEXT OF OPEN‐OCEAN VERTICAL MIGRATION1
Authors: Richardson Tammi L. , Ciotti Áurea M. , Cullen John J. , Villareal Tracy A. 
Published: October 2004

ABSTRACTCultures of Rhizosolenia formosa H. Peragallo were studied to assess whether or not physiological and optical characteristics of this large diatom were consistent with the ability to migrate vertically in the open ocean. Time‐course experiments examined changes in chemical composition and buoyancy of R. formosa during nitrate (N)–replete growth, N starvation, and recovery. Cells could maintain unbalanced growth for at least 53 h after depletion of ambient nitrate. Increases in C:N and carbohydrate: protein ratios observed during N starvation reversed within 24 h of reintroduction of nitrate to culture medium. Buoyancy was related to nutrition: Upon N depletion, the percentage of positively buoyant cells decreased to 4% from 11% but reverted to 9% within 12 h of nitrate readdition. Cells took up nitrate in the dark. Nitrogen‐specific uptake rates averaged 0.48 d−1; these rates were higher than N‐specific growth rates (0. 15 d−1), indicating the potential for luxury consumption of nitrate, which can be stored for later use. Measurements of photosynthesis vs. irradiance, chlorophyll‐specific absorption (aph*(λ)), and pigment composition showed that cells may be adapted for growth under a wide range of irradiances. Values of aph*(λ) were lower for N‐depleted cells than for N‐replete cells, and N‐depleted cells had higher ratios of total carotenoids to chlorophyll a. Aggregation of chloroplasts was more pronounced in N‐depleted cells. These are possibly photoprotective mechanisms that would be an advantage to N‐depleted cells in surface waters. Compounds that absorb in the ultraviolet region were detected in N‐replete cells but were absent in N‐depleted cultures. Overall, these results have important implications for migrations of Rhizosolenia in nature. Cells may survive fairly long periods in N‐depleted surface waters and will continue to take up carbon; then they can resume nitrate uptake and revert to positive buoyancy upon returning to deep, N‐rich water. Uncoupled uptake of carbon and nitrogen during migrations of Rhizosolenia is a form of new production that may result in the net removal of carbon from oceanic surface waters.