摘要:

ABSTRACTAlthough the spectral quality of light in the ocean varies considerably with depth, the effect of light quality on different physiological processes in marine phytoplankton remains largely unknown. In cases where experiments are performed under full spectral irradiance, the meaning of these experimentsin situis thus unclear. In this study, we determined whether variations in spectral quality affected the sinking rates of marine diatoms. Semicontinuous batch cultures ofThalassiosira weissflogii(Gru.) Fryxell et Hasle andDitylum brightwellii(t. West) Grunow in Van Huerk were grown under continuous red, white, or blue light. ForT. weissflogii, sinking rates (SETCOL method) were twice as high (∼0.2 m·d−1)for cells grown under red light as for cells grown under white or blue light (∼0.08 m·d−1), but there were no significant differences in carbohydrate content (∼105 fg·μm−3) or silica content (∼ 17 fg·μ−3) to account for the difference in sinking rates.Thalassiosira weissflogii grownunder blue light was significantly smaller (495 μm3) than cells grown under red light (661 μm3), which could contribute to its reduced sinking rate. However, cells grown under white light were similar in size to those grown under red light but had sinking rates not different from those of cells grown under blue light, indicating the involvement of factors other than size. There were no significant differences in sinking rate (∼0.054 m·d−1) or silica content (∼20 fg·μm−3) inD. brightwelliigrown under red, white, or blue light, but cells grown under red light were significantly (20%) larger and contained significantly (20%) more carbohydrate per μm3than cells grown under white or blue light. Spectral quality had no consistent effect on sinking rate, biochemical composition (carbohydrate or silica content), or cell volume in the two diatoms studied. The similarity in sinking rate of cells grown under white light compared to those grown under blue light supports the ecological validity of sinking

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00353.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTWe tested the hypothesis that positive relationships between sinking rate and irradiance were due to increases in cell density caused by accumulations of carbohydrate. In semicontinuous batch cultures ofThalassiosira weissflogii(Gru.) Fryxell el Hasle andDitylum brightwellii(t. West) Grunow in Van Huerk, carbohydrate content was varied by growing cells under diel cycles of high or low light. Sinking rate was measured at the end of the light period and the end of the dark period, on live and heat‐killed cells. No positive correlations were found between sinking rate (which varied from – 0.060 to 0.13 m·d−1) and carbohydrate content (which varied from 10 to 950 pg · cell−1), indicating that accumulations of carbohydrate did not significantly affect sinking rate. There were no large diel variations in the sinking rate ofT. weissflogii, but sinking rates ofD. brightwelliigrown under high light ranged from being negative (i.e. cells were floating) at the end of the light period to positive at the end of the dark period. This is the first report of positive buoyancy in vegetativeD. brightwellii, a phenomenon that may only occur inD. brightwelliigrown under di

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00360.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTA temperate cyanophage was found to lysogenize the marine cyanophytePhormidium persicinum(Reinke) Com. (Provasoli strain). The lytic cycle was induced by the addition of mitomycin C or by brief illumination with ultraviolet light. The lytic process observed under the electron microscope showed that phage particles appeared in a nucleoplasm region 15 to 24 h after the addition of mitomycin C. The induction of the lytic process occurred simultaneously in almost all cells of every trichome. Matured phage particles were released to the medium 30 to 50 h after the addition of mitomycin C. Phage particles isolated from algal lysates had a polyhedral head (about 40 nm in diameter) with a long (about 300 nm) and noncontractile tail. The most abundant protein, presumably a structural protein, had an apparent molecular mass of about 38 kDa. The genome size estimated from restriction analysis was about 50 kbp. Phage DNA was digested with several restriction endonucleases includingSau3AI andDpnI. However,MboI failed to digest the phage DNA, suggesting that the phage DNA is highly methylated. Southern blot analysis suggested that some part of the phage was in the lytic cycle in algal cells growing under normal conditions. A possible role of temperate cyanophages in the regulation of cyanophyte populations in the marine environment is discussed.

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00365.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTProduction of domoic acid (DA), a neurotoxin, by the diatomPseudo‐nitzschia multiseries(previouslyNitzschia pungensf.multiseries) Hasle and its cellular chemical composition were studied in phosphate‐limited chemostat continuous cultures and in subsequent batch cultures. Under steady‐state chemostat conditions, DA production increased from 0.01 to 0.26 pg DA · cell−1· d−1as the growth rate decreased. When the nutrient supply was discontinued (to produce a batch culture), DA production was enhanced by a factor of ca. 3. DA production was temporarily suspended upon addition of phosphate to the batch cultures but resumed 1 d later at a higher rate coincident with the decline of phosphate uptake. In both steady‐state continuous culture and batch culture, more DA was produced when alkaline phosphatase activity (APA) was high. The association of high DA production with high levels of APA and high cellular N:P ratios strongly suggests that phosphate limitation enhances DA production. Also, DA production was high when other primary metabolism (e.g. uptake of carbon, nitrogen, phosphorus and silicon, and cell division) was low, but chlorophyllaand adenosine triphosphate were generally high. This suggests that the synthesis of DA requires a substantial amount of bi

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00371.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTA non‐colony‐forming axenic strain ofPhaeocystis globosa(Harlot) Lagerheim was shown to produce a water‐soluble β‐d‐glucan. This glucan consisted of about 20 glucose units, mainly (l→3)‐linked, with branching at position 6. Therefore, it can be classified as a chrysolaminaran. Glucan production occurred mainly during the stationary growth phase and resulted in concentrations as high as 76 pg glucose per cell. When cultures were deprived of light the glucans were consumed, which supports their possible role as compounds used for temporary sto

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00382.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTThe effects of nitrogen starvation in the presence or absence of sodium in the culture medium were monitored in batch cultures of the marine diatomPhaeodactylum tricornutumBohlin. During nitrogen starvation in the presence of sodium, cell nitrogen and chlorophylladecreased, mainly as a consequence of continued cell division. These decreases were accompanied by decreases in the rates of photosynthesis and respiration. There was no change in either cell volume or carbohydrate, but both carbon and lipid increased. During nitrogen starvation in the absence of sodium, cell division ceased. Cell nitrogen and chlorophyllaremained constant, and respiration did not decrease, but the changes in the photosynthetic rate and the lipid content per cell were similar to cultures that were nitrogen‐starved in the presence of sodium. The carbon‐to‐nitrogen ratio increased in both cultures. Nitrogen, in the form of nitrate, and sodium were resupplied to cultures that had been preconditioned in nitrogen‐ and sodium‐deficient medium for 5 d. Control cultures to which neither nitrate or sodium were added remained in a static state with respect to cell number, volume, and carbohydrate but showed slight increases in lipid. Cells in cultures to which 10 mM nitrate alone was added showed a similar response to cultures where no additions were made. Cells in cultures to which 50 mM sodium alone was added divided for 2 d, with concomitant small decreases in all measured constituents. Cell division resumed in cultures to which both sodium and nitrate were added. The lipid content fell dramatically in these cells and was correlated to metabolic oxidation via measured increases in the activity of the glyoxylate cycle enzyme, isocitrate lyase. We conclude that lipids are stored as a function of decreased growth rate and are metabolized to a small extent when cell division resumes. However, much higher rates of metabolism occur if cell division resumes in the presence of a nitrog

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00388.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTChanges in the size of intracellular nitrogen pools and the potential feedback by these pools on maximum N uptake (NH4+and NO3−) rates were determined forChaetomorpha linum(Müller) Kützing grown sequentially under nutrient‐saturating and nutrient‐limiting conditions. The size of individual pools in N‐sufficient algae could be ranked as residual organic N (RON) comprised mainly of amino acids and amino compounds>protein N>NO3−>NH4+>chlorophyll N. When the external N supply was removed, growth rates remained high and individual N pools were depleted at exponential rates that reflected both dilution of existing pools by the addition of new biomass from growth and movement between the pools. Calculated fluxes between the tissue N pools showed that the protein pool increased throughout the N depletion period and thus did not serve a storage function. RON was the largest storage reserve; nitrate was the second largest, but more temporary, storage pool that was depleted within 10 days. Upon N resupply, the RON pool increased 3 × faster than either the inorganic or protein pools, suggesting that protein synthesis was the rate‐limiting step in N assimilation and caused a buildup of intermediate storage compounds. Maximum uptake rates for both NH4+and NO3−varied inversely with macroalgal N status and appeared to be controlled by changes in small intracellular N pools. Uptake of NO3−showed an initial lag phase, but the initial uptake of NH4+was enhanced and was present only when the intracellular NH4+pool was depleted in the absence of an external N supply. A strong negative correlation between the RON pool size and maximum assimilation uptake rates for both NH4+and NO3−suggested a feedback control on assimilation uptake by the buildup and depletion of organic compounds. Enhanced uptake and the accumulation of N as simple organic compounds or nitrate both provide a temporary mechanism to buffer against the asynchrony of N supply a

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00393.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTWhenChlamydomonas eugametosMoewus cells are starved of phosphate, they accumulate32Pimuch faster than before starvation. Phosphate accumulation is stimulated by calcium. Less than 5% of the32Pitaken up by the cell is present in soluble molecules, suggesting that most is in a metabolically inactive, storage form. Nuclear magnetic resonance and X‐ray microanalysis data are presented to show that it is stored as polyphosphate in electron‐dense bodies hi the cytoplasm. The same bodies accumulate divalent cations, in particular calcium. The P/Ca ratio in the bodies was maintained between 5.4 (1‐week‐old cells) and 3.3 (5‐week‐old cells) during cultivation, suggesting that the calcium and phosphorus relations of the bodies are coupled. The possibility that these electron‐dense bodies represent calcium stores that can be released to activate calcium signaling

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00402.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTImmunoblotting experiments performed with an anti‐ubiquitin antibody revealed thatSkeletonema costatum(Grev.) Cleve cells contained free ubiquitin as well as ubiquitin conjugated to various endogenous proteins. A temperature shift from 18° to 30°C greatly increased the total amount of ubiquitin and particularly the ubiquitin fraction in high molecular mass conjugates. A solid‐phase immunoassay indicated values of 0.031 ± 0.004 pmol·10−6cells for free ubiquitin and 0.046 ± 0.004 pmol·10−6cells for conjugated ubiquitin for cells grown at 18°C, and 0.056 ± 0.008pmol·10−6cells and 0.21 ± 0.03 pmol·10−6cells, respectively, after a temperature increase from 18° to 30°C. Cell‐free extracts ofS. costatumwere equally able to form thiol ester linkages with125I‐ubiquitin in an adenosine triphosphate–dependent manner at 18° C and at 30°C. Cell‐free extracts were also able to conjugate125I‐ubiquitin to endogenous proteins, but the ubiquitin conjugation rate at 30°C was lower than at 18°C. Incubation ofS. costatumfor 3 h at 30°C and then for 3 h at 18°C resulted in the formation of high amounts of ubiquitin conjugates, suggesting that partially inactive or denaturated proteins accumulate during heat stress. These denaturated proteins are then conjugated to ubiquitin very efficiently when the physiological temperature is restored. Thus,S. costatumcells contain ubiquitin and an active ubiquitin conjugation system responding to stress conditions (temperature stress). The intracellular concentration of ubiquitin conjugates is most likely limited by the availability of protein substrates to be conjugated rathe

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00409.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTWe investigated howProrocentrum micansEhrenberg, a planktonic dinoflagellate common in Portuguese coastal waters, is able to tolerate and recover from sublethal concentrations of copper(II). The experimental design simulated events in inshore waters, whereP. micansis subjected to high levels of pollutants, including copper. Decrease in growth rate, induction of a growth lag phase, temporary loss of motility, and potassium leakage were the effects induced inP. micanscultures by 90 nM labile copper. A 10–20‐fold increase in cellular copper concentration was observed in toxicity experiments. Copper efflux (representing a 50% decrease in cellular metal content) was a short‐term tolerance mechanism. A 25‐kDa protein was detected after only 3 h of exposure to copper, but there was no evidence of phytochelatin synthesis. Ultracytochemical labeling of metals with the sulfide‐silver procedure showed that copper was associated with the thecal plates, starch grains, and, to a lesser extent, lipid droplets. High values affixation capacities and average conditional stability constants for copper binding by starch, amylopectin, and cellulose support the location of copper in thecal plates and starch grains. We conclude thatP. micansresponds rapidly to copper toxicity and has two tolerance mechanisms for copper: copper efflux and sequestration in polymeric s

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00416.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY