bluuebunny/crossref_metadata_2025_split huggingface dataset:
AMMONIUM STIMULATION OF DARK CARBON FIXATION AS AN INDICATOR OF NITROGEN DEFICIENCY IN PHYTOPLANKTON: POTENTIAL ERRORS CAUSED BY AMMONIUM‐OXIDIZING BACTERIA1
Authors: Dodds Walter K. , Priscu John C. 
Published: October 2004

ABSTRACTStimulation of dark fixation of carbon by NH4+ is often used as an indicator of phytoplankton N deficiency. This assay is based on the influence of available NH4+ on anaplerotic CO2 fixation by algae. However, carbon fixation by chemoautotrophic NH4+‐oxidizing bacteria may also be stimulated by NH4+ enrichment, a process that can mask the algal response in natural communities. NH4+ addition enhanced dark carbon fixation up to 300%, relative to unamended controls, in organisms collected on a 0.7‐μm retention filter in oligotrophic Flathead Lake, Montana, but the effect was not detectable in the presence of nitrapyrin, an inhibitor of NH4+‐oxidizing bacteria. Dark carbon fixation was enhanced with addition of NH4+ in organisms retained on 2‐μm filters (which should allow passage of most bacteria). NH4+ stimulated dark carbon fixation in N‐deficient axenic cultures of Chlamydomonas reinhardtii Dang but not in N‐replete cultures in both the presence and absence of nitrapyrin. Application of nitrapyrin or size fractionation treatments, to separate the processes of dark carbon fixation by nitrifiers and phytoplankton, may improve the efficacy of assays using NH4+ stimulation of dark carbon fixation to specifically indicate N deficiency in natural algal communities.
IDENTIFICATION OF CYTOKININS IN SARGASSUM MUTICUM (PHAEOPHYTA) AND PORPHYRA PERFORATA (RHODOPHYTA)1
Authors: Zhang Wei , Chapman David J. , Phinney Bernard O. , Spray Clive R. , Yamane Hisakazu , Takahashi Nobutaka 
Published: October 2004

ABSTRACTCombined gas chromatography‐mass spectrometry (GCMS) was used to identify and quantify specific cytokinins from Porphyra perforate J. Ag. and Sargassum muticum (Yendo) Fensh. The level of isopentenyladenosine was estimated to be 0.6 μ·kg−1 fresh weight in Porphyra and 0.9 μ·kg−1 fresh weight in Sargassum. The level of cis‐zeatin riboside was estimated to be 0.2 μ·kg−1 fresh weight in Sargassum. This is the first definitive identification of a cytokinin from a red alga, and the second report from a brown alga.
CHARACTERIZATION OF PHOTOSYSTEM I‐ASSOCIATED POLYPEPTIDES FROM THE CHLOROPHYLLb‐RICH ALGATETRASELMISSPP. (PLEURASTROPHYCEAE) AND OTHER CHLOROPHYTE ALGAE1
Authors: Smith G. Jason , Alberts Randall S. 
Published: October 2004

ABSTRACTThe phylogenetic distribution of photosystem I‐associated polypeptides was assessed by immunoblotting algal thylakoid membrane polypeptides with antisera generated against the P700‐chlorophyllaprotein (CC I) and a photosystem I light‐harvesting chlorophyll‐protein (LHC Ib). Polypeptides cross‐reacting with the CC I apoprotein were found in 20 species representing four classes of unicellular algae. Polypeptides sharing antigenicity with spinach LHC Ib were observed only in algal species containing chlorophyllb. Tetraselmisspp. (Pleurastrophyceae), rich in chlorophyllb(Chla:b1.2), exhibited marked heterogeneity in the composition of their CC I and LHC Ib cross‐reactive polypeptides. When immunoblotted with antisera against CC I, allTetraselmisclones examined exhibited a 25‐kD polypeptide in greater abundance than the 58‐kD CC I apoprotein characteristic of higher plants and other green algal thylakoids. ThreeTetraselmisclones (RG 6, RG 11, and RG 12) exhibited an 81‐kD polypeptide with strong antigenicity toward the LHC Ib antisera, in contrast to the 17‐ to 24‐kD cross‐reactive polypeptides found in spinach, green algae, and oneTetraselmisclone (RG 5).Associated with the unique photosystem I polypeptide composition inTetraselmisspp., Chl: P700 ratios for the group are 2–5 times greater than those observed for higher plants or other green algae. The chlorophyllbenrichment, unusual composition of photosystem I cross‐reactive polypeptides, and heterogeneity of these polypeptides within isolates ofTetraselmismight make this genus useful for investigations of the functional organization of chlorophyllbin light‐harvesting systems. These features also support the view of an alternative phyletic origin for the Pleurastrophyceae.
FURTHER STUDIES OF PRESUMEDLY PRIMITIVE GREEN ALGAE, INCLUDING THE DESCRIPTION OF PEDINOPHYCEAE CLASS. NOV. AND RESULTOR GEN. NOV.1
Authors: Moestrup Øjvind 
Published: October 2004

ABSTRACTThe tiny jumping flagellate originally described as Pedinomonas mikron Throndsen was isolated into pure culture from Australian waters and its ultrastructure critically examined. Pedinomonas mikron differs in behavior and in features of the flagellar apparatus from P. minor, the type species from freshwater, and is referred to the new genus Resultor. The two genera are closely related and form the new class Pedinophyceae, which is characterized by features of the flagellar apparatus, mitosis, and cytokinesis. The flagella show the 11/5 orientation otherwise characteristic of Ulvophyceae and Pleurastrophyceae, but they are arranged end to end as in the Chlorophyceae. The flagellar root system is asymmetric and includes a rhizoplast that emerges from the base of one flagellum but subsequently associates with a microtubular root from the second basal body. Mitosis studied previously by Pickett‐Heaps and Ott in Pedinomonas is closed, unlike in other green algae, and the spindle is persistent. No phycoplast or phragmoplast is formed during cytokinesis. The eyespot of the Pedinophyceae is located at the opposite end of the cell from the flagella and adjacent to the pyrenoid, as in the most primitive members of the Prasinophyceae. Members of the Pedinophyceae lack prasinoxanthin and Mg 2,4D, characteristic of certain other primitive green algae.The primitive green algae include the classes Prasinophyceae and Pedinophyceae. Micromonadophyceae Mattox et Stewart is considered a synonym of Prasinophyceae.Two new orders are established, Pedinomonadales, containing all known members of the Pedinophyceae, and Scourfieldiales, with the single family Scourfieldiaceae fam. nov. and the single genus Scourfieldia.
SURVIVAL OF FUCOID EMBRYOS IN THE INTERTIDAL ZONE DEPENDS UPON DEVELOPMENTAL STAGE AND MICROHABITAT1
Authors: Brawley Susan H. , Johnson Ladd E. 
Published: October 2004

ABSTRACTEmbryos of the fucoid alga Pelvetia fastigiata (J. Ag.) DeToni were outplanted into the intertidal zone to assess survival during the physical stress brought about by emersion during a single low tide. Survival varied among microhabitats. Under the adult Pelvetia canopy, survival of 6‐h‐, 24‐h‐, 48‐h‐, and 1‐wk‐old embryos was nearly 100%. Almost all embryos of all ages died in exposed habitats on bare rock or within habitats where the Pelvetia canopy was removed experimentally. However, within red algal turfs, where most juvenile Pelvetia occur, survival was unusually age specific: 24‐ to 48‐h‐old embryos survived poorly compared to younger (6 h old) or older embryos (1 wk old). Survival patterns reflected microhabitat temperatures during the experiments. The fate of young post‐settlement stages must be studied at these fine temporal and spatial scales to understand the organization of intertidal communities.
PLANKTONIC SARCODINES: MICROHABITAT FOR OCEANIC DINOFLAGELLATES1
Authors: Spero Howard J. , Angel Dror L. 
Published: October 2004

ABSTRACTTwo morphologically distinct species of free‐swimming dinoflagellates belonging to the genusGyrodiniumutilize the spine and rhizopodial environments of planktonic foraminifera and colonial radiolaria as microhabitats. Up to 84% of the sarcodines examined in a given population were associated with these dinoflagellates at densities up to 20,000 cells per sarcodine in some radiolarian colonies. Both dinoflagellate species possess chloroplasts, indicating they are capable of autotrophy.14C‐labelling experiments with the radiolarian‐associated dinoflagellate demonstrate that it can take up inorganic carbon under both light and dark conditions. Ultrastructural evidence suggests the foraminiferal dinoflagellate may be capable of phagotrophy. Hence, these algae should be considered mixotrophs. An unusual cytoplasmic extension used for attachment and possibly feeding occurs in the foraminiferal‐associatedGyrodiniumand is documented with electron microscopy. Ultrastructural examination suggests this organelle may be hydrostatically controlled and may be an extension of the sac pusule.
A COMPARISON OF PERIPHYTIC ALGAL BIOMASS AND COMMUNITY STRUCTURE ON SCIRPUS VALIDUS AND ON A MORPHOLOGICALLY SIMILAR ARTIFICIAL SUBSTRATUM1
Authors: Goldsborough L. Gordon , Hickman Michael 
Published: October 2004

ABSTRACTChemically inert, cylindrical rods positioned in the littoral of two eutrophic Alberta lakes supported higher periphytic algal biomass (measured as total chlorophyll a) than nearby morphologically similar culms of Scirpus validus Vahl. during most of the summer. Upon initiation of macrophyte senescence, biomass on the two substrata became more similar. Experiments were conducted to investigate the basis for these observations. Whole extracts of intact vegetative Scirpus culms had no effect on periphyton photosynthesis, suggesting that the natural substrata do not produce water‐soluble allelochemicals. Various modifications of the rod surfaces (roughening, wax coating, wax color) were used to test whether surficial properties of Scirpus culms influenced periphyton accumulation. Roughened rods supported levels of biomass similar to those of smooth rods, and both substrata developed structurally complex periphyton communities. Rods covered with paraffin wax had periphyton communities that were lower in biomass and structurally more simple than those on un‐coated rods or on Scirpus culms. Coloring of the wax coating had no consistent effect on periphyton accumulation. We hypothesize that the hydrophobic cuticle on actively growing Scirpus culms retards the development of precursors for attachment by periphytic algae. Upon senescence of the culm and loss of epidermal integrity, colonization of culm surfaces by periphytic algae may occur in a manner similar to that on artificial substrata.
CELL DIVISION IN GLOEOTILOPSIS PLANCTONICA, A NEWLY IDENTIFIED ULVOPHYCEAN ALGA (CHLOROPHYTA) STUDIED BY FREEZE FIXATION AND FREEZE SUBSTITUTION1
Authors: Sluiman Hans J. 
Published: October 2004

ABSTRACTGloeotilopsis planctonica Iyengar & Philipose, a soil isolate, was cultured for the first time since its description in 1956. Cell division was investigated ultrastructurally by using rapid freeze fixation and freeze substitution. Vegetative interphase cells contain a persisting basal apparatus (centrioles) in which the absolute configuration of the basal body pair is identical to that in ulvophycean flagellated cells. Basal apparatus replication and segregation occurs shortly before prophase. Also before mitosis, a shallow plasma membrane indentation is formed, subtended by 2–3 cortical microtubules, in the forthcoming division plane. Daughter basal body pairs are located lateral to the mitotic spindle poles. A Golgi stack occupies each polar position of the mitotic spindle. During mitosis, which is structurally identical to that described previously for members of the Ulotrichales sensu Sluiman (Ulvophyceae), an extensive network of tubular membranes (trans Golgi reticulum, TGR) develops from each polar Golgi stack to the incipient cleavage furrow. A microtubular system, possibly organized by the basal apparatus, is associated with both the TGR and the cytokinetic septum. The TGR appears to be involved in the further development of the furrow after mitosis is completed. I conclude on the basis of this ultrastructural study that the genus Gloeotilopsis, which includes G. planctonica Iyengar & Philipose (type species) and G. sterilis Deason, should be classified in the Ulotrichales sensu Sluiman, class Ulvophyceae.
ISOZYME ANALYSIS OF MATING POPULATIONS OFGONIUM PECTORALE(CHLOROPHYTA)1
Authors: Sako Yoshihiko , Shrestha Keshab , Uchida Aritsune , Ishida Yuzaburo , Saito Shoichi 
Published: October 2004

ABSTRACTIntraspecific variation among 36 strains of the freshwater algaGonium pectoraleMüller (Chlorophyceae) isolated from three geographically different locations in Tibet, Nepal, and Japan was investigated by isozyme analysis. Variation in isozyme patterns of eight enzyme systems (malate dehydrogenase, glutamate dehydrogenase, tetrazolium oxidase, lactate dehydrogenase, octanol dehydrogenase, xanthine dehydrogenase, phosphoglucomutase, and malic enzyme) of axenic and clonal cultures was revealed by polyacrylamide gel electrophoresis. Unweighted average linkage clustering, based on Jaccard's similarity coefficient, illustrated the high similarity between most strains from Nepal and all strains from the Ryukyu Islands (Japan). However, there was relatively low similarity between strains from Tibet and those from Nepal and Japan. Strains from the Ryukyu Islands (Japan) grouped into two clusters, and most Nepalese strains formed a single cluster, but Tibetan strains were heterogenous.
CELL SURVIVAL CHARACTERISTICS AND MOLECULAR RESPONSES OF ANTARCTIC PHYTOPLANKTON TO ULTRAVIOLET‐B RADIATION1
Authors: Karentz Deneb , Cleaver James E. , Mitchell David L. 
Published: October 2004

ABSTRACTTwelve species of Antarctic diatoms were studied to assess UV sensitivity in relation to cellular and molecular aspects of DNA damage and repair. Responses of cell survival, induction of DNA damage, and DNA repair capacity were determined. There was a wide range of interspecific UV‐sensitivity among diatoms. D37 values (average fluence to kill one cell) ranged from 681 J · m−2 (most sensitive) to 25,338 J · m−2 (most resistant). Molecular analysis (by radioimmunoassay) of UV‐induced DNA damage [induction of cys‐syn cyclobutane dimers and pyrimidine (6‐4) pyrimidone photoproducts] also revealed considerable variability among species [0.98–84 lesions · (108 daltons DNA)−1 induced by exposure to 2500 J · m−2]. Repair of DNA damage ranged from 0.18 to 2.72 lesions removed · (108 daltons DNA)−1 in 6 h; removal represented 0.72–73.5% of initial damage. Comparison of cellular responses associated with photoenhanced repair and nucleotide excision (“dark”) repair indicated that light‐mediated correction of UV damage was an important factor in cell survival. There was a relationship between the number of photoproducts induced and cell survival, but not between repair efficiency and survival. The data also indicate a general dependence of photoproduct induction and D37 values on cell size and shape (expressed as the surface area: volume ratio which ranged from 0.07 to 0.66 between species) and suggest that these factors are indicators of UV sensitivity. Smaller cells with greater surface area: volume ratios sustained more damage per unit of DNA, had lower D37 values, and were more sensitive to UV exposure. The wide species variations observed in molecular and cellular responses to UV exposure emphasize the ecological implications of changes in natural UV regimes. These changes can act as determinants of cell size and taxonomic structure within phytoplankton communities and have as yet unknown effects on trophic interactions within the Antarctic ecosystem.
CIRCANNUAL GROWTH RHYTHM AND PHOTOPERIODIC SORUS INDUCTION IN THE KELPLAMINARIA SETCHELLII(PHAEOPHYTA)1
Authors: tom Dieck Inka 
Published: October 2004

ABSTRACTGrowth and reproduction of laboratory‐grown sporophytes ofLaminaria setchelliiSilva were investigated in a tank system with controlled conditions of daylength, temperature, and nutrients (N and P). A circannual growth rhythm of the frond was detected under constant laboratory conditions. In continuous long‐day and night‐break conditions the period τ of the free‐running rhythm varied between 11.3 and 17.3 months; in short‐day conditions the frond grew indefinitely. The growth rhythm of individual plants could be synchronized by a simulated annual cycle of day‐length with a period of T = 12 months. The four seasons of the year were simultaneously simulated by phase shifting the annual cycle of daylength by 3, 6, or 9 months in three out of four tanks. The annual growth cycle followed these phase shifts, and initiation of the new blade always started just after the winter daylength minimum. The formation of sori was induced by a genuine photoperiodic short‐day reaction in 1‐ to 2‐year‐old plants. Sori became, visible 9–14 weeks after transfer of individual plants from long‐day to short‐day conditions, whereas plants cultured in continuous long‐day or night‐break conditions remained sterile. Sporophytes with or without blades were able to continue growth or produce new blades in continuous darkness.
RATES OF PHOTOADAPTATION IN SEA ICE DIATOMS FROM MCMURDO SOUND, ANTARCTICA1
Authors: Lizotte Michael P. , Sullivan Cornelius W. 
Published: October 2004

ABSTRACTSea ice microalgae are released from their relatively stable light environment to the water column seasonally, and any subsequent growth in a vertically mixed water column may depend, in part, on their photoadaptation rates. In this study we followed the time course of photoadaptation in natural sea ice algal communities from bottom ice and surface ice by measuring their photophysiological response to an artificial shift in the ambient irradiance field. Microalgae from under‐ice habitats, were incubated under full sunlight (LL‐HL) and microalgae from surface ice habitats were incubated under artificial light to mimic under‐ice irradiance (HL‐LL). During 3‐ to 4‐day time course studies, opposite shifts in chlorophyll: carbon, α, PBm, and Ik were observed, depending on the direction of the irradiance change. First‐order rate constants (k) ranged from 0.0067 to 0.29 h−1 for photosynthetic parameters, although PBm did not always show a clear change over time. Rates of photoadaptation for ice algae are comparable to k values reported for temperate phytoplankton, suggesting that sea ice algae may be equally capable of adapting to the light conditions experienced in a vertically mixed water column. This study presents the first evidence that sea ice microalgae are physiologically capable of adapting to a planktonic life and thus could serve as a seed population for polar marine phytoplankton blooms.
RESPONSE OF PERIPHYTON COMMUNITIES TO CLAY AND PHOSPHATE LOADING IN A SHALLOW RESERVOIR1
Authors: Burkholder JoAnn M. , Cuker Benjamin E. 
Published: October 2004

ABSTRACTEnclosures in a small piedmont reservoir in the southeastern United States were used to determine the effects of loading by phosphate and two clay sediments on periphyton community structure and production during the summer growing season. The experimental design included replicated controls and the following treatments added at 2‐to 3‐day intervals: phosphate (PHOS), kaolinite (KAOL), montmorillonite (MONT), kaolinite with phosphate (K+P), and montmorillonite with phosphate (M+P). Periphyton were sampled from polyethylene strips of the same material as the enclosure walls, suspended at depths of 0.5 m and 2.0 m to assess treatment effects on shallow (epilimnetic) vs. deep (hypolimnetic) communities. Colonization after 40 days was sparse, dominated in biovolume by blue‐green algae in all but the epilimnion of controls, in which small gelatinous green algae and chrysophyte flagellates were abundant. The biovolume of shallow periphyton after 79 days was lowest in KAOL and MONT, intermediate in controls and PHOS, and greatest in clay + P. Hence, P enrichment alleviated the deleterious effects of clay on periphyton production, and clay + P appeared to act synergistically in stimulating benthic algal growth. Periphyton biovolume was comparable among shallow and deep controls, PHOS, and treatments with the rapidly settling kaolinite. Lowest biovolume occurred at depth in treatments with montmorillonite under extreme light attenuation imposed by the suspended, finely particulate clay. The relative contribution of blue‐green algae to total periphyton production was highest in clay + P treatments and lowest in controls. Heterotrophic dinoflagellates increased in the shallow periphyton under clay loading, and in the deep communities under PHOS and M + P. Periphyton contributed only 20–32% of total mesocosm productivity in controls, PHOS, and KAOL, increasing to about 40% in MONT, and to 72–91% of the total in M + P and K + P. The data indicate that benthic microalgae can represent a major proportion of the primary production in shallow reservoirs under high phosphate and sediment loading.
STIMULATION OF NITRATE NET UPTAKE AND REDUCTION BY RED AND BLUE LIGHT AND REVERSION BY FAR‐RED LIGHT IN THE GREEN ALGA ULVA RIGIDA1
Authors: López‐Figueroa Félix , Rüdiger Wolfhart 
Published: October 2004

ABSTRACTThe steady‐state levels of nitrate, nitrite, and ammonium were estimated in the green alga Ulva rigida C. Agardh in darkness after addition of 0.5 mM KNO3 and irradiation with red (R) and blue (B) light pulses of different duration (5 and 30 min). The net uptake of nitrate was very rapid. Seventy‐five percent of the nitrate added was consumed after 60 min in darkness. Although uptake was stable after R or B, efflux of nitrate occurred within 3 h in the dark control and when R or B were followed by far‐red (FR) irradiation. The internal nitrate concentration after 3 h in darkness was similar after R and B light pulses; however, the intracellular ammonium was higher after R than after B. The intracellular nitrate and ammonium decreased when FR tight pulses were applied immediately after R or B. Thus, the involvement of phytochrome in the transport of nitrate and ammonium is proposed.Nitrate reductase activity, measured by the in situ method, was increased by both R and B light pulses. The effect was partially reversed by FR light. Nitrate reductase activity was higher after 5 min of R light than after 5 min of B. However, after 30‐min light pulses, the relative increase in activity was reversed for R and B. We propose that phytochrome and a blue‐light photoreceptor are involved in regulation of nitrogen metabolism. Nitrate uptake and reduction correlates with previously detected light‐regulated accumulation of protein in Ulva rigida under the same experimental conditions.
CHARACTERIZATION AND BIOLOGICAL IMPLICATIONS OF SCYTONEMIN, A CYANOBACTERIAL SHEATH PIGMENT1
Authors: Garcia‐Pichel Ferran , Castenholz Richard W. 
Published: October 2004

ABSTRACTScytonemin, the yellow‐brown pigment of cyanobacterial (blue‐green algal) extracellular sheaths, was found in species thriving in habitats exposed to intense solar radiation. Scytonemin occurred predominantly in sheaths of the outermost parts or top layers of cyanobacterial mats, crusts, or colonies. Scytonemin appears to be a single compound identified in more than 30 species of cyanobacteria from cultures and natural populations. It is lipid soluble and has a prominent absorption maximum in the near‐ultraviolet region of the spectrum (384 nm in acetone; ca. 370 nm in vivo) with a long tail extending to the infrared region. Microspectrophotometric measurements of the transmittance of pigmented sheaths and the quenching of ultraviolet excitation of phycocyanin fluorescence demonstrate that the pigment was effective in shielding the cells from incoming near‐ultraviolet‐blue radiation, but not from green or red light. High light intensity (between 99 and 250 μmol photon · m−2· S−1, depending on species) promoted the synthesis of scytonemin in cultures of cyanobacteria. In cultures, high light intensity caused reduction in the specific content of Chl a and phycobilins, increase in the ratio of total carotenoids to Chl a, and scytonemin increase. UV‐A (320–400 nm) radiation was very effective in eliciting scytonemin synthesis. Scytonemin production was physiological and not due to a mere photochemical conversion. These results strongly suggest that scytonemin production constitutes an adaptive strategy of photoprotection against short‐wavelength solar irradiance.