ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1991.00661.x

出版商:Blackwell Science Inc    

年代:1991

数据来源: WILEY

摘要:

ABSTRACTA computerized oxygen electrode Astern was used to make rapid and accurate measurements of photosynthetic light and dissolved inorganic carbon (DIC) response cures with a macroalga.Ulva rotundataBlid. was grown in an outdoor, continuous flow system in seawater under sunlight or 9% of sunlight at Beaufort, North Carolina. The light compensation points in the shade‐ and sun‐grown plants, measured in seawater, were at photon flux densities (PFDs) of 16 and 27 μmol. Photons·m−2·s−1, respectively but the quantum yield of O2evolution was not significantly different. Rates of photosynthesis in seawater per unit area of thallus under saturating light and rates of dark respiration were about 1.5‐fold higher in sun‐ than in shade‐grown plants. The concentration of DIC in seawater (approximately 2 mM) limited photosynthesis at absorbed PFDs above 60–70 μmol photons·m−2·s−1Addition of 20 mM inorganic carbon had no effect on quantum yield but caused about a 1.5‐fold increase in the light‐saturated photosynthetic rate in both shade‐ and sun‐grownUlva.The effect of DIC supplementation was greatest in plants grown in October and least in plants grown in June. The light‐ and DIC‐saturated rate of photosynthesis in seawater was similar to the maximum rate obtained by exposingUlvato 10% CO2, in the gas phase. The carbon isotope values (δ13C, reflecting the13C/12C ratio compared to a standard) ofUlva grownin the same seawater supply were dependent on light and agitation. Samples from Beaufort Inlet were more negative (δ13C value, −20.03‰) than those grown in bright light with agitation (δ13C value, −17.78‰ outdoors; −17.23‰ indoors), whichmayi

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1991.00667.x

出版商:Blackwell Science Inc    

年代:1991

数据来源: WILEY

摘要:

ABSTRACTNitrogen uptake rates were measured as a function of time following saturating additions (15 μMg‐at N·−1) of15N‐labelid ammonium, urea, and nitrate to N‐starved cultures of the picoflagellateMicromonas pusillaButcher. Uptake rates were estimated from both the accumulation of15N into the cells and the disappearance of nitrogen from the medium. Transient elevated (surge) uptake rates of NH4+and urea were observed after enrichment. During the first 5 min the initial urea and NH4+uptake rates were 2‐ and 4‐fold greater than the maximum growth rate (μMmax)observed prior to No3−depletion in the cultures. The elevated urea uptake rates declined quickly to a relatively constant value, whereas the initial rates of NH4+uptake declined rapidly but were followed by a subsequent increase prior to remaining roughly constant. Nitrate was not taken up as readily by N‐starvedM. pusillaas the reduced N forms. Although NO3+uptake commenced immediately after enrichment (i.e. no lag period) the N‐Specific rate over the next 6 h averaged half the μMmaxobserved during N

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1991.00673.x

出版商:Blackwell Science Inc    

年代:1991

数据来源: WILEY

摘要:

ABSTRACTThe nitrogen‐fixing cyanobacteriumAnabaena flosaquaeLyngb.) De Breb. exhibited aggregation of heterocysts from different filaments in a eutrophic lake and when grown in unialgal culture. The resulting aggregated filaments formed unialgal flocculent masses having a thickness of several centimeters that apparently resulted from cohesive mucilage surrounding heterocysts. We tested the effects of heterocyst aggregation on nitrogenase activity (NA) and photosynthesis in relation to microscale environmental O2gradients. The redox indicator 2,3,5‐triphenyl tetrazolium chloride showed that aggregated heterocysts had lower intracellular redox potential than those that were dispersed. Microelectrode measurements showed that heterocyst aggregates in actively photosynthesizing flocculent masses were surrounded by a microzone of O230% higher than in the surrounding water: dispersed cells exhibited no such elevated O2microzone. Despite high levels of O2, NA was greater in aggregated than dispersed samples, Microscale irradiance measurements made with a fiber optic light probe showed that 40% of the incident light was absorbed within the first 3 mm of a 1‐cm‐thick flocculent mass. The microscale irradiance data, together with nitrogenase and photosynthesis versus irradiance data, imply that the ratio of N:C fixation is lowest in filaments on the outside of 1.5–2.0‐cm masses and increases toward

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1991.00680.x

出版商:Blackwell Science Inc    

年代:1991

数据来源: WILEY

摘要:

ABSTRACTThe benthic cyanobacteriumFischerella muscicola(Thur.) Gom. UTEX 1829 produces a secondary metabolite, fischerellin, that strongly inhibits other cyanobacteria and to a lesser extent members of the Chlorophyceae. Eubacteria are not affected. The major active compound is lipophilic and exhibits a molecular ion atm/z408. It is heat‐ and acid‐stable but decomposes in 1 M sodium hydroxide (80° C. 1 h). Fischerellin inhibits the photosynthetic but not the respiratory electron transport of cyanobacteria and chlorophytes. Its site of action is located in PS II. Two other species ofFischerellaalso produce fischerellin, indicating that the synthesis of such allelochemicals might be characteristic of the g

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1991.00686.x

出版商:Blackwell Science Inc    

年代:1991

数据来源: WILEY

摘要:

ABSTRACTBedrock erosional features in a small stream (Little Schultz Creek, Bibb County, Alabama) created a variety of habitats for epilithic growth. One suck habitat was illustrated by the occurrence of small falls (<0.3 m) in the main channel of the stream and blue‐green algal mats associated with them. The cohesive, laminar algal mats were found at 15 such sites along a 250‐m reach of the stream. The primary mat matrix consisted of the blue‐green algaOscillatoria submembranaceaArdissone and Strafforella. The uppermost portion of each mat consisted of a thin (<1 mm thick) green layer of biologically active filaments. The lower layers were thicker (up to 2 cm thick) and consisted of brown laminae ofOscillatoriafilaments, and associated sediments. In addition, numerous diatoms mere associated with the mat surface. Some were loosely attached (e.g.Achnanthes);others(Cymbella tumida(Bréb.) V. H.) were stalked. These mats were present throughout the year and showed a bimodal annual distribution with maxima hi February and July. In February, total mat coverage was higher than in July. This winter maximum may have been related to a mode of growth dependent upon sedimentation from storm events and subsequent upward growth of the alga. Mat primary productivity on an areal basis (432 mg C · m−2· d−1in March and 907 mg C · M−2· d−1in April) was 2–12 times the maxima measured on epizoic and cobbles surfaces and other bedrock surfaces in the same stream. The limited areal coverage of the mats, when compared to other surfaces available for algal colonization, made them less important than other epilithic and epizoic surfaces in terms of total primary production in this stream reach. However, we propose that the combination of their unique structure and high primary productivity may make these algal mats sites of high algal and bacterial metabolic activity, which may include anaerobic processes in midchannel, where such activity would not

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1991.00692.x

出版商:Blackwell Science Inc    

年代:1991

数据来源: WILEY

摘要:

ABSTRACTThe influence of spectral quality on growth and pigmentation was compared among five strains of marine and freshwater picocyanobacteria grown under the same photon flux density (28 μE · m−2·s−1). Growth and phycoerythrin (PE) concentration per unit carbon increased when marineSynechococcusWH7803 was grown under green light as compared to red light, but no change in phycocyanin concentration occurred. MarineSynechococcusstrain 48B66 also showed greater levels of PE when grown under green light than under red light, but no concomitant growth increase occurred. Both strains thus exhibited Group II chromatic adaptation. Additionally, strain 48B66 increased the relative level of phycourobilin compared to phycoerythrobilin when grown under red light. In contrast, both marine and freshwaterSynechococcusstrains containing no PE showed decreased growth under green light. Chlorophyllaconcentrations were greatest or among the greatest in all strains grown under green light. These results suggest that light quality, through its effects on growth rate, may be an important factor controlling the distribution and abundance of the various pigment types ofSynecho

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1991.00698.x

出版商:Blackwell Science Inc    

年代:1991

数据来源: WILEY

摘要:

ABSTRACTThe following nucleoside diphosphate monosaccharides (sugar nucleotides) were identified by HPLC fromPterocladia capillacea Bornand Thur.: ADP‐glucose, UDP‐glucose, UDP‐d‐galactose, and GDP‐glucose + mannose. GDP‐l‐galactose was not identified due to the lack of a standard. Several extraction methods were evaluated for their efficacy. A freeze/ thaw (liquid N2) step fallowed by formic acid (1 M) extraction, reduced pressure evaporation, and solubilization in water was the preferred method. Differences in media nitrate that resulted in different tissue‐N levels (1.8, 2.3, and 3.5% dry wt) and agar yields (34, 31, and 28% dry wt, respectively) also resulted in a marked difference in UDP‐d‐galactose and ADP‐glucose tissue levels (decrease with increasing tissue‐N) while the levels of the other sugar nucleotide agar precursors remained unchanged. Activities of UDP‐glucose, GDP‐glucose, and GDP‐mannose pyrophosphorylases, and UDP‐D‐glucose‐4‐epimerase were detected in cell‐free extracts using unlabeled and14C‐labeled substrates. This study‐strongly supports the proposition that thed‐galactose component of agar is synthesized via G‐1‐P→UDP‐glucose→ UDP‐d‐galactose and that, thel‐galactoae comp

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1991.00702.x

出版商:Blackwell Science Inc    

年代:1991

数据来源: WILEY

摘要:

ABSTRACTTotal extractable lipid (TEL) and lipid composition were studied throughout the growth cycle in three freshwater diatoms‐Cyclotella meneghinianaKütz.,Melosira variansC. A. Ag., andStephanodiscus binderanus(Kütz.) Krieg under three light regimes (16:8 h LD, 20:4 h LD, and 12:12 h LD) at 20°C. Two of the diatoms demonstrated strong daylength preferences for growth;C. meneghinianagrew best under long‐day (20: 4‐h LD) conditions, whereasS. binderanusgrew best under short‐day (12:12‐h LD) conditions. The lipid composition of the diatoms was similar throughout the growth cycle. Aged (2‐month‐old) cells were high in total lipid and triacylglycerols. Before the onset of active growth and during the early part of active growth, there was a reduction in total neutral lipids, primarily triacylglycerols, and an increase in all polar lipids, including chlorophylla, acetone‐mobile polar lipids, and phospholipids. While cell numbers were still increasing, triacylglycerols increased and polar lipids decreased to levels near those found in aged cultures, Results suggest that increased triacylglycerol content of freshwater diatoms is not necessarily indicative of sen

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1991.00710.x

出版商:Blackwell Science Inc    

年代:1991

数据来源: WILEY

摘要:

ABSTRACTActive gliding movement over long distances was observed and filmed in the marine pennate diatomArdissonea (Synedra) crystallina(Agardh) Kütz. Typical speeds measured ca. 1–2 μm‐s−1. Motion wax often smooth and steady; however, discontinuous jerky motions and rolling movements were common. Motion, was associated with secretion of twin or, less commonly, single straight trails of mucilage from one end of the cell. In a few instances, reversal in direction was related to cessation of mucilage secretion at one end and commencement at the other. Temporary cessation of movement due to an obstruction was accompanied by a build‐up of mucilage at one end of the cell. Mucilage was apparently secreted at two specific sites at each end of the cell and was stained by alcian blue.Persistent trails were visible under scanning electron microscopy (SEM). SEM confirmed that cells had no raphes or labiate processes. The apparent site of secretion was a deep groove formed at the junction of the valve and valvocopula (first girdle band) at each end of the cell. Transmission electron microscopy confirmed the presence of mucilage vesicles in the cytoplasm, but these were not in any manner obviously related to secretion nor was any morphological structure associated with secretion. Cells often become epiphytic through secretion of a terminal stipe. Both stipe secretion and movement may involve the same structural differentiation of the frustule.These results demonstrate a previously unrecorded type of diatom motility. The mechanism, involves mucilage secretion and appears similar to that seen, for example, in some other algae such as the desmids (gre

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1991.00718.x

出版商:Blackwell Science Inc    

年代:1991

数据来源: WILEY