bluuebunny/crossref_metadata_2025 huggingface dataset:
NITROGEN UTILIZATION AND METABOLISM RELATIVE TO PATTERNS OF N2 FIXATION IN CULTURES OF TRICHODESMIUM NIBB1067
Authors: Mulholland Margaret R. , Ohki Kaori , Capone Douglas G.
Published: March 2003

We measured uptake kinetics for four combined N sources, ambient rates of N uptake and N2 fixation, glutamine synthetase activity (transferase and biosynthetic), and concentrations of intracellular pools of glutamate (glu) and glutamine (gln) in cultures of Trichodesmium NIBB1067. N dynamics and metabolism were examined to assess the relative importance of N2 fixation and N uptake to Trichodesmium nutrition. Comparisons were made between cultures grown on medium without added N, with excess NO, or with excess urea. Of the combined N sources tested, Trichodesmium NIBB1067 had the highest affinity for NH; high uptake capacities for NH, urea, and glu; and little capacity for NO uptake. In cultures grown on medium without added N, NH accumulated in the medium during growth, resulting in high NH uptake rates relative to rates of N2 fixation. Glu uptake rates were low but consistent throughout the diel period. In cultures grown on excess NO or urea, uptake of these compounds supplied the majority of the daily N demand, although some N2 fixation occurred during the light period. NO uptake rates were reduced when N2‐fixation rates were high. In all of the cultures, the highest gln/glu ratios and the lowest glutamine synthetase transferase/biosynthetic ratios were observed during the period when rates of total N uptake were highest.  In cultures growing exponentially on medium without added N, N2 fixation accounted for 14%– 16% of the total daily N uptake. Uptake of NH and glu, presumably regenerated within the culture vessels, represented 84%–86% of the daily N uptake. Because these systems were closed, net growth was constrained by the rate at which N2 could be fixed into the system. However, total daily N turnover was greater than that necessary to accommodate the observed increase in culture biomass. The rapid N turnover rates observed in these cultures may support gross productivity and balance the high rates of C fixation observed in natural populations of Trichodesmium.
INTERACTIONS BETWEEN IRON, LIGHT, AMMONIUM, AND NITRATE: INSIGHTS FROM THE CONSTRUCTION OF A DYNAMIC MODEL OF ALGAL PHYSIOLOGY
Authors: Flynn Kevin J. , Hipkin Charles R.
Published: March 2003

A dynamic mechanistic mathematical model (FeLANIM) is described, capable of simulating the major documented interactions between iron, light, ammonium, and nitrate in phytoplankton. There are various points in the model where species‐ or group‐specific (e.g. eukaryote vs. prokaryote) details may be altered. Cellular Fe‐containing processes accounted for in the model are photosynthesis, oxidative phosphorylation, and nitrate assimilation; synthesis of photosystems and nitrate and nitrite reductase (NNiR) are functions of the surplus Fe quota (i.e. total Fe quota minus Fe in functional components). Model simulations were run using a range of different physiological parameters for Fe‐dependent processes and contrasting ammonium–nitrate interaction scenarios. Model output indicated the following interactions. Because the proportion of Fe in photosystems varies with irradiance, it is not possible to have a single Fe cost for nitrate assimilation. Fe stress can affect the relationship between ammonium and nitrate assimilations (the f‐ratio), with a more rapid depression of nitrate use at lower concentrations of ammonium. However, depending on the degree of the repression of nitrate assimilation at high N:C, such a result may not be universal, and further experimental studies are required to clarify this issue. Fe refeeding results in a rapid recovery of growth rate accompanied by a proportionately greater increase in the amount of chl a within 24– 48 h. Estimates of enhanced production in iron fertilization experiments based only on increases in pigment may thus be exaggerated. Stimulation of NNiR activity on Fe refeeding appears indirect, through enhancement of photosynthesis rather than relief of nitrate stress. During Fe refeeding at high light, N nutrient transport increases proportionately more in nitrate‐fed cells than in ammonium‐fed cells. Changing the N source supplied to simulated Fe‐stressed cells from nitrate to ammonium results in a rapid increase in growth rate and iron use efficiency with an increase in pigment content as NNiR content declines. When nitrate replaces ammonium, acclimation is slower because of the redirection of Fe formerly associated in photosystems to NNiR. Manipulation of the model may prove useful as an indicator for new research, by revealing elements of physiology that may be most significantin determining competitive advantage between species.
RESPONSE OF GRACILARIA CONFERTA (RHODOPHYTA) TO OLIGOAGARS RESULTS IN DEFENSE AGAINST AGAR‐DEGRADING EPIPHYTES
Authors: Weinberger Florian , Friedlander Michael
Published: March 2003

Elicitation of Gracilaria conferta (Schousboe ex Montagne) J. et G. Feldmann with oligoagars resulted in a defense response that was strong enough to kill epiphytic bacteria associated with the alga. Up to 60% of the resident bacterial flora of healthy plants was eliminated within 60 min after addition of neoagarohexaose to the algal medium. Single isolates of agar‐degrading bacteria that had been isolated previously from healthy or decaying algal tissues proved to be more sensitive. Some of them were generally unable to survive on healthy G. conferta. Others survived on unelicited plants. Approximately 90% of these more resistant agar degraders were eliminated within 15 min after elicitation. The bacterial degradation of dead tissue of G. conferta resulted in a release of elicitors. The elicitors accumulated in the medium and reached high enough concentrations within 24 h to induce a hypersensitive response in healthy algae. The eliciting agent could be destroyed with β‐agarase and was thus probably oligoagar. Application of antibiotics prevented the accumulation of the elicitor, which indicated that bacteria were responsible for its release from the algal biomass. The hypersensitive response of G. conferta after contact with oligoagars is thus a true defense response, because it enables the plant to protect itself efficiently from enzymatic attacks on its cell wall.
ISOLATION OF A SULFOQUINOVOSYL MONOACYLGLYCEROL FROM BRYOPSIS SP. (CHLOROPHYTA): IDENTIFICATION OF A FACTOR CAUSING A POSSIBLE SPECIES‐SPECIFIC ECDYSIS RESPONSE IN GAMBIERDISCUS TOXICUS (DINOPHYCEAE)1,
Authors: Sakamoto Bryan , Hokama Yoshitsugi , Horgen F. David , Scheuer Paul J. , Kan Yukiko , Nagai Hiroshi
Published: March 2003

A bioactive compound that induced ecdysis (thecal loss) in Gambierdiscus toxicus Adachi et Fukuyo (Dinophyceae) cultures was isolated from a host macroalga, Bryopsis sp. (Chlorophyta). The ecdysis factor was identified by spectroscopic methods as 1‐O‐palmitoyl‐3‐O‐(6′‐sulfo‐α‐d‐quinovopyranosyl)‐sn‐glycerol (PSQG). From our results, PSQG induced ecdysis at a high frequency and appeared not to inhibit the growth of G. toxicus cultures. The induction of ecdysis followed a dose‐dependent saturation curve from 4 to 8 μM PSQG. To determine specificity of PSQG, the effects of palmitoyl‐l‐α‐lysophosphatidylcholine (PLPC) were observed. Because PLPC contains a lipophilic palmitoyl moiety and hydrophilic phosphatidyl choline group, the compound possesses a detergent‐like amphiphathic property similar to PSQG. Our results demonstrate that PLPC induced ecdysis at a high frequency in G. toxicus cultures and generated a similar dose–response curve as PSQG. The ecdysis activity observed in PSQG and PLPC may correlate with the detergent‐like amphiphathic property of both compounds. Although PLPC induced a similar ecdysis response as PSQG, PLPC appeared to inhibit the growth of G. toxicus cultures. Preliminary results on the effects of PSQG on the dinoflagellates Prorocentrum lima (Ehrenberg) Dodge and Coolia monotis Meunier did not parallel the results observed in G. toxicus. This study demonstrated the existence of a factor from Bryopsis sp. that elicited a possible species‐specific ecdysis response in G. toxicus cultures. This is the first report of a compound that induced ecdysis in G. toxicus or in any dinoflagellate.
Effects of non‐steady‐state iron limitation on nitrogen assimilatory enzymes in the marine diatom thalassiosira weissflogii (BACILLARIOPHYCEAE)
Authors: Milligan Allen J. , Harrison Paul J.
Published: March 2003

Since the recognition of iron‐limited high nitrate (or nutrient) low chlorophyll (HNLC) regions of the ocean, low iron availability has been hypothesized to limit the assimilation of nitrate by diatoms. To determine the influence of non‐steady‐state iron availability on nitrogen assimilatory enzymes, cultures of Thalassiosira weissflogii (Grunow) Fryxell et Hasle were grown under iron‐limited and iron‐replete conditions using artificial seawater medium. Iron‐limited cultures suffered from decreased efficiency of PSII as indicated by the DCMU‐induced variable fluorescence signal (Fv/Fm). Under iron‐replete conditions, in vitro nitrate reductase (NR) activity was rate limiting to nitrogen assimilation and in vitro nitrite reductase (NiR) activity was 50‐fold higher. Under iron limitation, cultures excreted up to 100 fmol NO2−·cell−1·d−1 (about 10% of incorporated N) and NiR activities declined by 50‐fold while internal NO2− pools remained relatively constant. Activities of both NR and NiR remained in excess of nitrogen incorporation rates throughout iron‐limited growth. One possible explanation is that the supply of photosynthetically derived reductant to NiR may be responsible for the limitation of nitrogen assimilation at the NO2− reduction step. Urease activity showed no response to iron limitation. Carbon:nitrogen ratios were equivalent in both iron conditions, indicating that, relative to carbon, nitrogen was assimilated at similar rates whether iron was limiting growth or not. We hypothesize that, diatoms in HNLC regions are not deficient in their ability to assimilate nitrate when they are iron limited. Rather, it appears that diatoms are limited in their ability to process photons within the photosynthetic electron transport chain which results in nitrite reduction becoming the rate‐limiting step in nitrogenassimilation.
CHARACTERIZATION OF PSYCHROPHILIC OSCILLATORIANS (CYANOBACTERIA) FROM ANTARCTIC MELTWATER PONDS
Authors: Nadeau Tracie‐Lynn , Castenholz Richard W.
Published: March 2003

Oscillatorian cyanobacteria dominate benthic microbial mat communities in many polar freshwater ecosystems. Capable of growth at low temperatures, all benthic polar oscillatorians characterized to date are psychrotolerant (growth optima > 15° C) as opposed to psychrophilic (growth optima ≤ 15° C). Here, psychrophilic oscillatorians isolated from meltwater ponds on Antarctica's McMurdo Ice Shelf are described. Growth and photosynthetic rates were investigated at multiple temperatures, and compared with those of a psychrotolerant isolate from the same region. Two isolates showed a growth maximum at 8° C, with rates of 0.12 and 0.08 doublings·d−1, respectively. Neither displayed detectable growth at 24° C. The psychrotolerant isolate showed almost imperceptible growth at 4° C and a rate of 0.9 doublings·d−1 at its optimal temperature of ∼23° C. In both photosynthesis versus irradiance and photosynthesis versus temperature experiments, exponentially growing cultures were acclimated for 14 days at 3, 8, 12, 20, and 24° C under saturating light intensity, and [14C] photoincorporation rates were measured. Psychrophilic isolates acclimated at 8° C showed greatest photosynthetic rates; those acclimated at 3° C were capable of active photosynthesis, but photoincorporation was not detected in cells acclimated at 20 and 24° C, because these isolates were not viable after 14 days at those temperatures. The psychrotolerant isolate, conversely, displayed maximum photosynthetic rates at 24° C, though photoincorporation was actively occurring at 3° C. Within acclimation temperature treatments, short‐term photosynthetic rates increased with increasing incubation temperature for both psychrophilic and psychrotolerant isolates. These results indicate the importance of temperature acclimation before assays when determining optimal physiological temperatures. All isolates displayed photosynthetic saturation at low light levels (<128 μmol·m−2·s−1) but were not photoinhibited at the highest light treatment (233 μmol·m−2·s−1). Field studies examining the impact of temperature on photosynthetic responses of intact benthic mats, under natural solar irradiance, showed the mat communities to be actively photosynthesizing from 2 to 20° C, with maximum photoincorporation at 20° C, as well as capable of a rapid response to an increase in temperature. The rarity of psychrophilic cyanobacteria, relative to psychrotolerant strains, may be due to their extremely slow growth rates and inability to take advantage of occasional excursions to higher temperatures. We suggest an evolutionary scenario in which psychrophilic strains, or their most recent common ancestor, lost the ability to grow at higher temperatures while maintaining a broad tolerance for fluctuations in other physical and chemical parameters that define shallow meltwater Antarctic ecosystems.
PHOTOSYNTHETIC BICARBONATE UTILIZATION BY A TERRESTRIAL CYANOBACTERIUM, NOSTOC FLAGELLIFORME (CYANOPHYCEAE)
Authors: Gao Kunshan , Zou Dinghui
Published: March 2003

The photosynthetic characteristics of the terrestrial cyanobacterium, Nostoc flagelliforme, after complete recovery by rewetting, was investigated to see whether it could use bicarbonate as the external inorganic carbon source when submerged. The photosynthesis–pH relationship and high pH compensation point suggested that the terrestrial alga could use bicarbonate to photosynthesize when submerged. The photosynthetic oxygen evolution rates were significantly inhibited in Na+‐free and Na++ Li+ media but were not affected by the absence of Cl−, implying that the bicarbonate uptake was associated with Na+/ HCO3− symport rather than Cl−/HCO3− exchange system.
GLUTAMINE SYNTHETASE IN MARINE ALGAE: NEW SURPRISES FROM AN OLD ENZYME
Authors: Robertson Deborah L. , Smith G. Jason , Alberte Randall S.
Published: March 2003

Glutamine synthetase (GS), which catalyzes the formation of glutamine from ammonium and glutamate in the presence of ATP, is encoded by three distinct gene families: GSI, GSII, and GSIII. Genes encoding GSI are found in the Bacteria and Archaea, whereas GSII genes are found in eukaryotes and a few species of Bacteria. Members of the third family, GSIII, have been described from a limited number of bacteria; however, recent biochemical and molecular data suggest that this type of enzyme is broadly distributed among the algae. Peptide fragments obtained from GS purified from the marine diatom Skeletonema costatum (Greville) Cleve are 77% identical to a partial sequence of GSIII from Chaetoceros compressum Lauder, which permits the unambiguous assignment of the biochemically characterized enzyme to the GSIII gene family. The N‐terminal sequence was 43% identical to the GSIII‐like enzyme purified from the haptophyte Emiliania huxleyi (Lohm.) Hay et Miller and several residues were conserved among bacterial and eukaryotic GSIII enzymes. The presence of genes encoding GSIII in diatoms and haptophytes indicates that this enzyme family is more broadly distributed in eukaryotes than previously suspected.
EVOLUTION OF PHACUS (EUGLENOPHYCEAE) AS INFERRED FROM PELLICLE MORPHOLOGY AND SSU rDNA
Authors: Leander Brian S. , Farmer Mark A.
Published: March 2003

This research integrates a large morphological data set into a molecular context. Nineteen pellicle characters and 62 states from 13 euglenid taxa were analyzed cladistically. The pellicle morphology of Euglena tripteris (Klebs), Lepocinclis ovata (Conrad), Phacus brachykentron (Pochmann), P. oscillans (Klebs), P. pyrum (Stein), and P. triqueter (Dujardin) is described comprehensively. These data are compared with new information on the pellicle morphology of Euglena acus (Ehrenberg), E. stellata (Mainx), and Peranema trichophorum (Stein) in addition to published data on Entosiphon sulcatum (Dujardin), Euglena gracilis (Klebs), Distigma proteus (Pringsheim), and Petalomonas cantuscygni (Cann and Pennick). Nuclear small subunit (SSU) rDNA sequences provided an independent test for establishing a robust organismal pedigree of the same taxa. A synthetic tree derived from the combined phylogenetic analyses of pellicle morphology and SSU rDNA enabled us to parsimoniously map morphological character states. This approach demonstrated the utility of pellicle morphology for inferring phylogenetic relationships of euglenids and establishing apomorphy‐based clade definitions. Three robust clades with unambiguous pellicle‐based apomorphies can be recognized within taxa traditionally classified as Phacus: (1) L. ovata and P. pyrum, (2) E. tripteris and P. triqueter, and (3) P. brachykentron and P. oscillans. Taxonomic concerns that emerged from these results are discussed.
POPULATION STRUCTURE AND PHYSIOLOGICAL DIFFERENTIATION OF HAPLOTYPES OF CALOGLOSSA LEPRIEURII (RHODOPHYTA) IN A MANGROVE INTERTIDAL ZONE
Authors: Zuccarello Giuseppe C. , Yeates Paul H. , Wright Jeff T. , Bartlett Jason
Published: March 2003

Zonation of macroalgae in the intertidal zone has been well documented. However, studies of zonation of macroalgae have predominantly examined the distribution of different species rather than the distribution of variants within a species. This study investigated the spatial variation of plastid haplotypes of the mangrove red alga Caloglossa leprieurii (Montagne) J. Agardh at a site in eastern Australia and tests for physiological differences (growth, photosynthesis) between those haplotypes. RUBISCO spacer plastid haplotypes were scored using single‐stranded comformational polymorphism, and the population structure at two sites was examined using a nested sampling design comparing between sites, among transects within sites, and among quadrats within transects. Growth rates at various salinities and light intensities and the photosynthesis–irradiance curves of the three main haplotypes were compared. The two sites showed a high degree of genetic differentiation across a short distance, suggesting limited gene flow. The distribution of haplotypes was patchy and did not reflect a zonation pattern along the intertidal gradient. The three haplotypes were physiologically differentiated with haplotype A, with a lower growth rate and a lower photosynthetic efficiency at higher light intensities. There is some evidence of physiological differentiation between life history phases in C. leprieurii with sporophytes having a higher growth rate than females under most conditions. Our results suggest a correlation between our culture results and our population data. Haplotypes (haplotype A) and life history phases (gametophytes) with lower performance (growth and photosynthetic efficiency) under our culture conditions were correlated with a minor representation in the field. This is the first study to integrate population‐level data with physiological parameters toward an understanding of the distribution and relative abundance of red algal genetic variants.
FIXED CARBON PARTITIONING IN THE RED MICROALGA PORPHYRIDIUM SP. (RHODOPHYTA)
Authors: Li Shi‐Yan , Lellouche Jean‐Paul , Shabtai Yossef , Arad Shoshana
Published: March 2003

The main products of carbon fixation in the red algae are sulfated cell‐wall polysaccharides, floridean starch, and low molecular weight (LMW) carbohydrates, mainly floridoside. In the red microalga Porphyridium sp., sulfated polysaccharide—cell bound and soluble—comprises up to 70% of the algal biomass. The purpose of this study was to elucidate the partitioning of fixed carbon in Porphyridium sp. toward the different products of carbon fixation. Using pulse‐chase technique with [14C]bicarbonate, we followed 14C flow into the major compounds, namely, cell‐wall polysaccharide, floridoside, starch, and protein, under various environmental conditions (i.e. carbon dioxide enrichment and nitrate starvation). 13C‐NMR and gas chromatography analysis showed the main LMW product in Porphyridium sp. to be floridoside. After the short [14C]bicarbonate pulse (20 min), 42%–53% of total 14C uptake was initially found in floridoside. The appearance of 14C in the soluble polysaccharide was evident immediately at the end of the 20‐min [14C]bicarbonate pulse. The specific radioactivity in the floridoside fraction declined by 80% after the 48‐h chase, this decline being accompanied by increased labeling of starch and the soluble polysaccharide. In cells exposed to high CO2 concentration, larger amounts of 14C (about twice as much) were channeled into starch and soluble polysaccharide than in cells under low CO2 concentration. The most significant increase (1500%) in labeling during chase was found in the soluble polysaccharide of the nitrate‐deprived cultures. It therefore seems likely that the large amounts of carbon incorporated by Porphyridium sp. cells into floridoside were subsequently used for the synthesis of macromolecular components. The data thus support the premise that floridoside serves as a dynamic carbon pool, which channels the fixed carbon toward polysaccharides and other end products according to the ambient conditions.
ALKALINE PHOSPHATASE ACTIVITIES AMONG POPULATIONS OF THE COLONY‐FORMING DIAZOTROPHIC CYANOBACTERIUM TRICHODESMIUM SPP. (CYANOBACTERIA) IN THE RED SEA
Authors: Stihl Andrea , Sommer Ulrich , Post Anton F.
Published: March 2003

Alkaline phosphatase activities of the diazotrophic marine cyanobacterium Trichodesmium were studied among natural populations in the northern Red Sea and in laboratory cultures of Trichodesmium sp. strain WH9601. Open‐water tuft‐shaped colonies of Trichodesmium showed high alkaline phosphatase activities with 2.4–11.7 μmol p‐nitrophenylphosphate (PNPP) hydrolyzed·μg chl a−1·h−1, irrespective of date or origin of the sample. Coastal populations of the Trichodesmium tuft colonies had low alkaline phosphatase activities with 0.2–0.5 μmol PNPP·μg chl a−1·h−1. An exception was the Trichodesmium fall maximum, when both tuft colonies and the plankton community (<100 μm) had alkaline phosphatase activities of 0.6–7.4 μmol PNPP·μg chl a−1·h−1. Likewise, the more rare puff and bow‐tie colonies of Trichodesmium spp. in coastal waters had elevated alkaline phosphatase activities (0.8–1.6 μmol PNPP·μg chl a−1·h−1) as compared with tuft colonies coinhabiting the same waters. Intact filaments of tuft‐forming Trichodesmium sp. strain WH9601 from phosphate‐replete cultures had a base alkaline phosphatase activity of 0.5 μmol PNPP·μg chl a−1·h−1. This activity underwent a 10‐fold increase in phosphate‐deplete cultures and in cultures supplied with glycerophosphate as the sole P source. The elevated level of alkaline phosphatase activity was sustained in P‐deplete cultures, but it declined in cultures with glycerophosphate. The decline is suggested to result from feedback repression of alkaline phosphatase synthesis by the phosphate generated in the glycerophosphate hydrolysis. The enhanced alkaline phosphatase activities of Trichodesmium spp. populations provide evidence that P stress is an important factor in the ecology of Trichodesmium in the northern Red Sea.
OXYGEN CONSUMPTION ASSOCIATED WITH FERRIC REDUCTASE ACTIVITY AND IRON UPTAKE BY IRON‐LIMITED CELLS OF CHLORELLA KESSLERI (CHLOROPHYCEAE)
Authors: Middlemiss Jocelyn K. , Anderson Andrea M. , Stratilo Chad W. , Weger Harold G.
Published: March 2003

Plasma membrane ferric reductase activity was enhanced 5‐fold under iron limitation in the unicellular green alga Chlorella kessleri Fott et Nováková. Furthermore, ferric reductase activity in iron‐limited cells was approximately 50% higher in the light than in the dark. In contrast, iron uptake rates of iron‐limited cells were unaffected by light versus dark treatments. Rates of iron uptake were much lower than rates of ferric reduction, averaging approximately 2% of the dark ferric reduction rate. Ferric reduction was associated with an increased rate of O2 consumption in both light and dark, the increase in the light being approximately 1.5 times as large as in the dark. The increased rate of O2 consumption could be decreased by half by the addition of catalase, indicating that H2O2 is the product of the O2 consumption and that the increased O2 consumption is nonrespiratory. The stimulation of O2 consumption was almost completely abolished by the addition of bathophenanthroline disulfonate, a strong chelator of Fe2+. Anaerobic conditions or the presence of exogenous superoxide dismutase affected neither ferric reduction nor iron uptake. We suggest that the O2 consumption associated with ferric reductase activity resulted from superoxide formation from the aerobic oxidation of Fe2+, which is the product of ferric reductase activity. At saturating concentrations of Fe3+ chelates, ferric reductase activity is much greater than the iron uptake rate, leading to rapid oxidation of Fe2+ and superoxide generation. Therefore, O2 consumption is not an integral part of the iron assimilation process.
PARTICULATE DIMETHYLSULFOXIDE IN ARCTIC SEA‐ICE ALGAL COMMUNITIES: THE CRYOPROTECTANT HYPOTHESIS REVISITED
Authors: Lee Peter A. , De Mora Stephen J. , Gosselin Michel , Levasseur Maurice , Bouillon René‐Christian , Nozais Christian , Michel Christine
Published: March 2003

The particulate‐phase concentrations of dimethyl sulfoxide (DMSOp) and dimethylsulfoniopropionate (DMSPp) in sea‐ice algal communities from the North Water, northern Baffin Bay, were examined from April to June 1998. The concentrations of these compounds were measured in the bottom 2 cm of the ice at 36 locations throughout this region and are compared with results from water‐column samples collected for a complementary study. In general, levels of DMSPp (8.66–987 nmol·L−1, average 126 nmol·L−1) in sea‐ice algal communities were slightly less than those found in bottom sea‐ice algal communities from other polar locations but greater than those found in phytoplankton in other polar environments or at more temperate latitudes. Furthermore, DMSPp  :chl a ratios (0.02–14.8 nmol·μg−1, average 1.91 nmol·μg−1) in the sea‐ice algal community were slightly less than those found in other polar environments. DMSOp was measured for the first time in sea‐ice algal communities. DMSOp concentrations varied from 1.35 to 102 nmol·L−1 (average 13.7 nmol·L−1). DMSOp:chl a ratios varied from 0.01 to 4.5 nmol·μg−1 (average 0.22 nmol·μg−1) and were significantly lower than the DMSPp:chl a ratios observed in this study. It has been hypothesized that DMSO can act as a cryoprotector in phytoplankton cells. However, the low concentrations of DMSO observed in the ice algae during this study indicate that intracellular concentrations of DMSO are unlikely to have a significant influence on the freezing point depression of intracellular fluids.
PRIMARY PRODUCTION OF CRUSTOSE CORALLINE RED ALGAE IN A HIGH ARCTIC FJORD1
Authors: Roberts Rodney D. , Kühl Michael , Glud Ronnie Nøhr , Rysgaard Søren
Published: March 2003

Crustose coralline algae occupied ∼1%–2% (occasionally up to 7%) of the sea floor within their depth range of 15–50 m, and they were the dominant encrusting organisms and macroalgae beyond 20 m depth in Young Sound, NE Greenland. In the laboratory, oxygen microelectrodes were used to measure net photosynthesis (P) versus downwelling irradiance (Ed) and season for the two dominant corallines [Phymatolithon foecundum (Kjellman) Düwel et Wegeberg 1996 and Phymatolithon tenue (Rosenvinge) Düwel et Wegeberg 1996] representing> 90% of coralline cover. Differences in P‐Ed curves between the two species, the ice‐covered and open‐water seasons, or between specimens from 17 and 36 m depth were insignificant. The corallines were low light adapted, with compensation irradiances (Ec) averaging 0.7–1.8 μmol photons·m−2·s−1 and light adaptation (Ek) indices averaging 7–17 μmol photons·m−2·s−1. Slight photoinhibition was evident in most plants at irradiances up to 160 μmol photons·m−2·s−1. Photosynthetic capacity (Pm) was low, averaging 43–67 mmol O2·m−2 thallus·d−1 (∼250–400 g C·m−2 thallus·yr−1). Dark respiration rates averaged ∼5 mmol O2·m−2 thallus·d−1. In ice covered periods, Ed at 20 m depth averaged ∼1 μmol photons·m−2·s−1, with daily maxima of 2–3 μmol photons·m−2·s−1. During the open water season, Ed at 20 m depth averaged ∼7 μmol photons·m−2·s−1 with daily maxima of ∼30 μmol photons·m−2·s−1. Significant net primary production of corallines was apparently limited to the 2–3 months with open water, and the small contribution of corallines to primary production seems due to low Pm values, low in situ irradiance, and their relatively low abundance in Young Sound.
FACTORS AFFECTING DARK SURVIVAL OF THE BROWN TIDE ALGAAUREOCOCCUS ANOPHAGEFFERENS(PELAGOPHYCEAE)1
Authors: Popels Linda C. , Hutchins David A.
Published: March 2003

Aureococcus anophagefferensHargraves et Sieburth is a pelagophyte responsible for the harmful brown tides in New York, New Jersey, and Rhode Island, USA. Recent reports of blooms in new areas, Maryland, USA, and Saldanha Bay, South Africa, suggest that the alga may be expanding its range, possibly through anthropogenic transport. Experiments tested the ability ofA. anophagefferensto survive dark conditions, such as those that might be encountered during transport in ballast tanks or recreational boats. Laboratory cultures were stored in complete darkness for various lengths of time under different conditions. After returning cultures to optimal light and growth conditions, we recorded the time until growth resumed. CulturedA. anophagefferenswas able to survive for at least 30 days in the dark. Temperature played a major role in dark survival, because cultures stored at 6° C and 12° C recovered faster than those stored at 18° C or 24° C. Growth phase at the time of storage had a minor effect on recovery, with exponential phase cultures resuming growth more quickly than stationary phase cells. Although the alga is known to have heterotrophic capabilities, the addition of low levels (1–3 μM) of organic nutrients did not appear to increase dark survival. Salinities within normal estuarine and oceanic ranges also did not affect survival. The ability ofA. anophagefferensto survive dark periods could allow it to be transported by anthropogenic means to new regions, and temperature and length of storage appear to be key factors determining cell viability during prolonged darkness.
NUCLEAR HISTONE PROTEINS OF GAMETES IN AN OOGAMOUS AND TWO ISOGAMOUS BROWN ALGAE1
Authors: Yoshikawa Shinya , Nagasato Chikako , Makino Yumiko , Murakami Akio , Kawai Hiroshi , Ichimura Terunobu , Motomura Taizo
Published: March 2003

Nuclear basic proteins (histones) were studied in male and female gametes of the isogamous brown algae, Colpomenia bullosa (Saunders) Yamada and Analipus japonicus (Harvey) Wynne and sperm of the oogamous Cystoseira hakodatensis (Yendo) Fensholt by using SDS‐ and AUT‐PAGE. Four major core histones and several linker histone H1s were detected by electrophoresis. Each of the core histones was identified by amino acid sequence analysis and peptide mapping. Electrophoresis patterns of histones were the same in male and female gametes and quite similar between the two species. The composition of histone H1s in conspicuously condensed sperm nuclei of C. hakodatensis was different from that in isogamous gametes. Electrophoresis after micrococcal nuclease digestion of chromatin in male and female gamete nuclei of C. bullosa and A. japonicus and sperm of C. hakodatensis resulted in regular ladder patterns of DNA fragments (ca. 200 base pair). The chromatin of the brown algal gametes thus has the typical nucleosome structure. These results showed that chromatin condensation in sperm nuclei of C. hakodatensis was associated with a modification of linker histone H1 but not by change of core histones, replacement by other basic proteins, changes of repeating patterns, or disappearance of nucleosomes.
ARE CYTOPLASMIC POCKETS (MTR/POCKET) PRESENT IN ALL PHOTOSYNTHETIC EUGLENOID GENERA?1
Authors: Shin Woongghi , Brosnan Stacy , Triemer Richard E.
Published: March 2003

In 1985, the existence of a cytoplasmic pocket formed from the reservoir membrane in the photosynthetic euglenoid Colacium was described. A band of reinforcing microtubules (MTR) derived from the ventral flagellar root lined the pocket, and a dense fibrillar mesh was associated with the membrane. A comparison of bodonid cytostomes, colorless euglenoid cytostomes, and the reservoir pocket found in Colacium suggested that the three structures were homologous and that photosynthetic euglenoids arose from phagotrophic ancestors. MTR/pockets have since been reported in other photosynthetic euglenoids, including Euglena, Eutreptia, Eutreptiella, Cryptoglena, Tetreutreptia, and Phacus. We found MTR/pockets in three additional taxa, Lepocinclis, Trachelomonas, and Strombomonas, thereby demonstrating the presence of this complex in representatives of all the major photosynthetic genera. A comparison of the MTR/pocket complex across genera indicated a reduction in structural complexity that was consistent with recent phylogenetic schemes based on molecular characters. Three alternative hypotheses of the origin of MTR/pockets in phototrophic euglenoids are presented and discussed.
NEW PYRENOID FORMATION IN THE BROWN ALGA,SCYTOSIPHON LOMENTARIA(SCYTOSIPHONALES, PHAEOPHYCEAE)1
Authors: Nagasato Chikako , Motomura Taizo
Published: March 2003

TheScytosiphon lomentaria(Lyngbye) Link cell characteristically has only one chloroplast with a prominent protruding pyrenoid. We observed the appearance of a new pyrenoid in each chloroplast during first mitosis in zygotes ofS. lomentaria, using the freeze substitution technique. At first, a pyrenoid matrix appeared within the outermost stroma, in which thylakoid triplets and ribosomes were absent. At this time, the surface of this part remained smooth. The old pyrenoid was covered with a pyrenoid cap on the cytoplasmic side, whereas there was no pyrenoid cap on the new pyrenoid before protrusion. Irregularly shaped membranous sacs containing fine granular materials associated with the cytoplasmic side of the new pyrenoid. The sacs fused with each other and changed conformation and finally transformed into the pyrenoid cap. The new pyrenoid gradually protruded toward the cytoplasm, and the new pyrenoid cap became curved along the surface of pyrenoid. Cytokinesis occurred, and each chloroplast had two prominent protruding pyrenoids in two‐celled zygotes. We examined immunolocalization of β‐1,3‐glucans within the pyrenoid cap with a monoclonal antibody, using EM. Gold particles indicating localization of β‐1,3‐glucans were detected in vacuoles but never in the pyrenoid cap. This observation suggests that the pyrenoid cap in brown algae contains no photosynthetic products such as polysaccharide.
DIMETHYLSULFONIOPROPIONATE CLEAVAGE BY MARINE PHYTOPLANKTON IN RESPONSE TO MECHANICAL, CHEMICAL, OR DARK STRESS1
Authors: Wolfe Gordon V. , Strom Suzanne L. , Holmes Jan L. , Radzio T. , Olson M. Brady
Published: March 2003

Several bloom‐forming marine algae produce concentrated intracellular dimethylsulfoniopropionate (DMSP) and display high DMSP cleavage activity in vitro and during lysis after grazing or viral attack. Here we show evidence for cleavage of DMSP in response to environmental cues among different strains of the haptophyte Emiliania huxleyi (Lohmann) Hay et Mohler and the dinoflagellate Alexandrium spp. (Halim). Sparging or shaking live cells of either taxon increased dimethyl sulfide (DMS), especially in dinoflagellates, known to be very sensitive to shear stresses. Additions of polyamines, known triggers of exocytosis in some protists, also stimulated DMSP cleavage in a dose‐responsive manner. We observed DMS production by some algae after shifts in light regime. When most exponential‐phase E. huxleyi were transferred to continuous darkness, cells decreased in volume and DMSP content within 24 h; DMSP content per unit cell volume remained relatively steady. DMS accumulated as long as cells remained in the dark, but on returning to a light:dark cycle DMS accumulation ceased within 24 h. However, E. huxleyi strain CCMP 373, containing highly active in vitro DMSP lyase, produced only transient accumulations of DMS in the dark. This was apparently due to production and concomitant oxidation or uptake of DMS, because cells of this strain rapidly removed DMS added to cultures. Three strains of the dinoflagellate Alexandrium tamarense containing high in vitro DMSP lyase activity showed no DMS production in the dark, and all appeared to remove additions of DMS. Alexandrium tamarense strain CCMP 1771 also removed dimethyl disulfide, an inhibitor of bacterial DMS consumption. These data suggest that physical or chemical cues can trigger algal DMSP cleavage, but DMS production may be masked by subsequent oxidation and/or uptake.
EFFECT OF SUBSURFACE NUTRIENT SUPPLIES ON THE VERTICAL MIGRATION OF EUGLENA PROXIMA (EUGLENOPHYTA)1
Authors: Kingston Michael B.
Published: March 2003

Euglena proxima Dangeard inhabits intertidal sand flats and displays a tidal rhythm in vertical migration. During daytime low tides when the sand flat is emersed, millions of cells are visible on the sediment surface, but the population remains below the surface at all other times. An earlier study demonstrated that the extent of downward migration of E. proxima is reinforced by the presence of a subsurface layer of black sediment. The present study was designed to test the hypothesis that the higher availability of inorganic nutrients or organic substrates in or above the black layer is responsible for the enhancement of downward migration in E. proxima. This hypothesis was tested experimentally by manipulating the bottom water in 24 mesocosm containers in a tidal tank. Six replicates of each of the following nutrient treatments were tested: seawater control; deep porewater collected from 70 cm below the sediment surface; seawater enriched with ammonium, nitrate, and phosphate; and seawater enriched with acetate, glucose, and the preceding inorganic nutrients. Multivariate analysis of variance revealed that the chl a biomass and chl a‐weighted mean depth of the population at high tide were significantly greater for replicates receiving inorganic nutrients. There was no difference between those receiving only inorganic nutrients and those enriched with inorganic nutrients, acetate, and glucose. These findings represent the first experimental evidence that subsurface nutrients are an important resource that reinforces the maintenance of vertical migration behavior in benthic microalgae.
PHYLOGENETIC POSITION OF CRUSTOMASTIX STIGMATICA SP. NOV. AND DOLICHOMASTIX TENUILEPIS IN RELATION TO THE MAMIELLALES (PRASINOPHYCEAE, CHLOROPHYTA)1
Authors: Zingone Adriana , Borra Marco , Brunet Christophe , Forlani Gandi , Kooistra Wiebe H. C. F. , Procaccini Gabriele
Published: March 2003

A new marine microalga from the Mediterranean Sea, Crustomastix stigmatica Zingone, is investigated by means of LM, SEM, TEM, and pigment and molecular analyses (nuclear‐encoded small subunit [SSU] rDNA and plastid‐encoded rbcL). Pigment and molecular information is also provided for the related species Dolichomastix tenuilepis Throndsen et Zingone. Crustomastix stigmatica has a bean‐shaped cell body 3–5 μm long and 1.5–2.8 μm wide, with two flagella four to five times the body length. The single chloroplast is pale yellow‐green, cup‐shaped, and lacks a pyrenoid. A small bright yellow stigma is located in the mid‐dorsal part of the cell under the chloroplast membrane. An additional accumulation of osmiophilic globules is at times seen in a chloroplast lobe. Cells lack flat scales, whereas three different types of hair‐like scales are present on the flagella. The main pigments of C. stigmatica are those typical of Mamiellales, though siphonein/siphonaxanthin replaces prasinoxanthin and uriolide is absent. The pigment pool of D. tenuilepis is more similar to that of Micromonas pusilla (Butcher) Manton et Parke and of other Mamiellales. The nuclear SSU rDNA phylogeny shows that the inclusion of C. stigmatica and D. tenuilepis in the Mamiellales retains monophyly for the order. The two species form a distinct clade, which is sister to a clade including all the other Mamiellales. Results of rbcL analyses failed to provide phylogenetic information at both the order and species level. No unique morphological or pigment characteristics circumscribe the mamiellalean clade as a whole nor its two daughter clades.
FIELD ASSAYS FOR MEASURING NITRATE REDUCTASE ACTIVITY IN ENTEROMORPHA SP. (CHLOROPHYCEAE), ULVA SP. (CHLOROPHYCEAE), AND GELIDIUM SP. (RHODOPHYCEAE)1
Authors: Lartigue Julien , Sherman Timothy D.
Published: March 2003

In situ and in vitro nitrate reductase (NR) activity assays designed for use in the field on Enteromorpha sp., Ulva sp., and Gelidium sp. are described. In optimizing each assay, a variety of compounds and assay conditions were tested for their ability to extract NR and preserve its activity. Enteromorpha sp. had similar levels of in vitro NR activity after exposure to the in situ assay buffer, demonstrating that neither NR induction nor activation likely occurs during the in situ assay. Storing freshly collected Enteromorpha sp. led to a reduction in NR activity over time. However, the use of liquid nitrogen to freeze algal tissue on site and subsequent storage at −80° C preserved NR activity and allowed for later laboratory use of the optimized in vitro assay. Application of the in situ and in vitro assays to stands of Enteromorpha sp., Ulva sp., and Gelidium sp. in the field consistently found NR activity. In situ NR activity over 9 consecutive days in January demonstrated that Enteromorpha sp. responds to increases in nitrate availability. The influence of light on diel patterns of in vitro NR activity in the field was demonstrated for the first time as well. For the three species tested, these two assays provide a reliable tool for field investigation of the interaction between environmental signals (e.g. nutrient levels) and physiological signals (e.g. tissue metabolite levels) on nitrate reduction.
MITOCHONDRIAL GENOME CONFORMATION AMONG CW‐GROUP CHLOROPHYCEAN ALGAE1
Authors: Laflamme Mark , Lee Robert W.
Published: March 2003

Most green algal taxa have circular‐mapping mitochondrial genomes, whereas some have linear genome‐ or subgenomic‐sized mitochondrial DNAs (mtDNA). It is not clear, however, if the circular‐mapping genomes represent genome‐sized circular molecules, if such circular molecules and the linear forms are the predominant in vivo mtDNA structures, or if the linear forms arose only once or multiple times among extant green algal lineages. We therefore examined the DNA components detected with homologous mtDNA probes after pulsed‐field gel electrophoresis of total cellular DNA from the chlorophycean basal bodies displaced clockwise(CW)‐group taxa Chlamydomonas reinhardtii and Chlamydomonas moewusii. For C. reinhardtii, the 15.8‐kb linear mtDNA was the only DNA component detected, and there was no evidence of circular or large linear precursors of this DNA. In the case of C. moewusii, which is known to have a circular‐mapping 22.9‐kb mitochondrial genome, three DNA components were detected; these appeared to be circular (relaxed and supercoiled) and genome‐sized linear DNA molecules, the latter of which likely resulted from random double‐strand breaks in the circular forms during DNA isolation. In further studies, DNA from additional CW‐group taxa was examined using conventional gel electrophoresis and DNA‐filter blot analysis with C. reinhardtii and C. moewusii mtDNA probes. We conclude that all taxa from the “Volvox clade” (sensuNakayama et al. 1996 of the CW‐group have genome‐ or subgenomic‐sized linear mtDNAs as their predominant mtDNA form and that these arose from a genome‐sized circular form in an ancestor that existed near the base of this clade.
PHYLOGENETIC POSITION OF TOXARIUM, A PENNATE‐LIKE LINEAGE WITHIN CENTRIC DIATOMS (BACILLARIOPHYCEAE)1
Authors: Kooistra Wiebe H. C. F. , De Stefano Mario , Mann David G. , Salma Nancy , Medlin Linda K.
Published: March 2003

The diatom genus Toxarium Bailey has been treated as a pennate because of its elongate shape and benthic lifestyle (it grows attached to solid substrata in the marine sublittoral). Yet its valve face lacks all structures that would ally it with the pennates, such as apical labiate processes, a midrib (sternum) subtending secondary ribs and rows of pores extending perpendicularly out from the midrib, or a raphe system. Instead, pores are scattered irregularly over the valve face and only form two distinct rows along the perimeter of the valve face. In our nuclear small subunit rDNA phylogenies, Toxarium groups with bi‐ and multipolar centrics, as sister to Lampriscus A. Schmidt. Thus, the genus acquired a pennate‐like shape and lifestyle independently from that of the true pennates. The two species known, T. hennedyanum Grunow and T. undulatum Bailey, differ only in a single feature: the valve perimeter of the former shows only a central expansion, whereas that of the latter possesses in addition a regular undulation. Yet both forms were observed in our monoclonal cultures, indicating that the two taxa represent extremes in a plasticity range. Toxarium resembles another elongate and supposedly araphid diatom, Ardissonea De Notaris, in being motile. Cells can move at speeds of up to 4 μm·s−1 through secretion of mucilage from the cell poles or they remain stationary for longer periods, when they form short polysaccharide stalks. Division during longer periods of quiescence leads to the formation of small colonies of linked or radiating cells.