ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00001.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTWe examined the effect of the presence or absence of coccoliths on the growth and sinking rates of an oceanic isolate of the coccolithophoreEmiliania huxleyi(Lohmann) Hay et Mohler isolated from the northeastern subarctic Pacific. Coccolith‐forming and non‐coccolith‐forming (i.e. naked, nonmotile) strains were obtained from the same isolate and grown under both saturating and limiting irradiance levels with either nitrate or ammonium as the primary nitrogen source. Sinking rate, growth rate, and cell volume (excluding coccoliths) were measured for each culture. Under saturating irradiance, coccolith‐forming cells grew significantly slower than naked cells, had significantly higher sinking rates, and had larger cell volumes than naked cells. Under limiting irradiance levels, growth rates of the two strains were identical, sinking rates were higher for coccolith‐forming cells in stationary‐phase cultures only, and cell volumes remained greater for coccolith‐forming cells.The sinking rates achieved for this ubiquitous coccolithophore ranged from<0.1 to 0.5 m · d−1. Sinking rates were not statistically different between coccolith‐forming and naked strains ofE. huxleyiunder limiting irradiance conditions for log‐phase cultures, but sinking rates were greater for coccolith‐forming cells under some of the other conditions tested. However, the average sinking rate was never more than twice as great as for coccolith‐forming cells, with the exception of nitrate‐grown, senescent cells under limiting irradiance (3.4 times greater). Cell volumes (excluding coccoliths) were consistently ca. 1.5 times greater for coccolith‐forming cells than for naked cells.Nitrogen source had an effect on growth rate and cell volume, with ammonium‐grown cultures growing faster and having larger cell volumes than nitrate‐grown cultures of both strains. However, despite the difference in growth rate and cell volume, nitrogen source had litt

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00017.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTThis study tests the hypotheses that substrate stability and rugose microtopography are the main factors that determine the tissue‐specific epiphytism in the chlorophyteSporocladopsis novae‐zelandiaeChapman. Bothin vitroand field experiments showed that the epiphyte did not develop on stable algal surfaces nor on artificial (smooth or rugose) substrata. In field experiments, however, other macroalgae settled more abundantly on rugose substrata. Similarly, our field experiments did not support the hypothesis that the physical environment provided by the spatial location of the host in the intertidal or subtidal was a relevant factor associated with specificity. In contrast, our laboratory experiments suggested that some component of the host cell wall might trigger the formation of penetrating rhizoids. These did not develop in isolated cultures of the epiphyte but were detected when the epiphyte contacted its natural host. Also, preliminary results showed that rhizoid‐like structures developed, although at very low frequency, only in plants grown in culture medium containing a crude extract of sorus cortical t

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00022.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTThe association of the limpetTectura testudinalis(Müller 1776) and the crustose coralline red algaClathromorphum circumscriptum(Strömfelt) Foslie (Melobesioideae) is considered a species‐specific mutualism between grazer and prey. Anatomical features ofC. circumscriptum, especially those associated with epithallial cells, have been viewed as being unusual and directly related to the mutualism. Transmission and scanning electron microscopic methods were used to investigate the structure and development of epithallial cells inC. circumscriptum.Contrary to prior reports, terminal cells of the epithallial filaments ofC. circumscriptumundergo senescence and shedding much like epithallial cells in other members of the Corallinales; hence, multicellular epithallial filaments did not evolve in this alga simply because epithallial cells were unable to slough. Although epithallial cells in many coralline algae are lightly calcified, those inC. circumscriptumare heavily mineralized, more so than the underlying initial cells and cells comprising the cortex. As in other coralline algae, starch is absent from the epithallial cells ofC. circumscriptum.The feature of having abundant chloroplasts in the epithallial cells of C. circumscriptum is shared by other species with multi‐cellular epithallial filaments and transiently by species with single epithallial cells. Except for having a thick epithallus, a feature found in other genera and in other species ofClathromorphum, the anatomy ofC. circumscriptumis unexcept

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00028.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTGrazing of fluorescent latex beads, bacteria, and various species of phytoplankton byPoterioochromonas malhamensis(Pringsheim) Peterfi (about 8.0 μm in diameter) was surveyed. The alga ingested fluorescent beads and various live or killed and nomnotile or motile organisms including bacteria, blue‐green algae, green algae, diatoms, and chrysomonads. The size range of grazed prey was from 0.1 to 6.0 μm for latex beads and from 1.0 μm (bacteria) to about 21 μm(Carteria inverse)for organisms. As many as 17 latex beads (2.0 μm) or more than 10Microcystiscells (5–6 μm) were ingested by a singleP. malhamensiscell. Following such grazing, the cell increased in volume by up to about 30‐fold. The range of cell volume of ingested prey was from 0.52 μm3(bacteria) to about 3178 μm3(Carteria inversa).This study demonstrates for the first time thatP. malhamensisis capable of grazing algae 2–3 times larger in diameter than its own cell and of grazing intact motile algae.Poterioochromonas malhamensisis an omnivorous grazer. Food vacuole formation and digestion processes were examined. The membrane that was derived from the plasma membrane and surrounded the prey disappeared sometime after ingestion. The food vacuole was then formed by successive fusion of numerous homogeneous vesicles accumulated around the prey. The prey was enclosed in a single membrane‐bound food vacuole

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00037.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTIn stratified lakes, dominance of the phytoplankton by cyanobacteria is largely the result of their buoyancy and depth regulation. Bloom‐forming cyanobacteria regulate the gas vesicle and storage polymer contents of their cells in response to interactive environmental factors, especially light and nutrients. While research on the roles of nitrogen and phosphorus in cyanobacterial buoyancy regulation has reached a consensus, evaluations of the roles of carbon have remained open to dispute. We investigated the various effects of changes in carbon availability on cyanobacterial buoyancy with continuous cultures ofMicrocystis aeruginosaKuetz. emend. Elenkin (1924), a notorious bloom‐former. Although CO2limitation of photosynthesis can promote buoyancy in the short term by preventing the collapse of turgor‐sensitive gas vesicles and/or by limiting polysaccharide accumulation, we found that sustained carbon limitation restricts buoyancy regulation by limiting gas vesicle as well as polysaccharide synthesis. These results provide an explanation for the positive effects of bicarbonate enrichment on cyanobacterial nitrogen uptake and bloom formation in lake experiments and may help to explain the pattern of cyanobacterial dominance in phosphorus‐enriched, low‐car

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00047.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTThe heterotrichous algaStigeoclonium tenueKüetzing is dominant in many streams with high densities of herbivores. Previousin situstudies in Walker Branch (WB), a woodland stream in eastern Tennessee, indicated that dominance byStigeocloniumbasal cells was “grazer‐dependent”; however,Stigeocloniumalso appeared to have a lower biomass–specific productivity rate than other species that dominated when snails were experimentally removed. Here, an explicit test of the grazing dependence ofStigeocloniumwas made with unialgal cultures established in the laboratory. Five different “assemblage types” were tested: 1 and 2) unialgal cultures ofStigeocloniumat low and high biomass, 3 and 4) a mixed assemblage of diatoms at low and high biomass, and 5) a natural stream community. Reduction in chlorophyllaafter exposure to snail grazing was dependent on assemblage type (one‐way ANOVA,P<0.0001); low biomassStigeocloniumtiles and tiles from the stream (on which basal cells ofStigeocloniumwere dominant) were most grazer‐resistant. In addition,Stigeocloniumhad a lower biomass‐specific productivity rate (measured as H14CO3−uptake) than a mixed assemblage of diatoms, regardless of biomass level, suggesting an underlying tradeoff between resistance to herbivory and competitive ability. Additional laboratory experiments were conducted to determine the response ofStigeocloniumto high (approx. 150 μmol quanta ·m−2· s−1)and low (approx. 25 μmol quanta · m−2· s−1) irradiance when nutrients were at 1) ambient WB concentrations and 2) increased 1000× ambient concentrations. There was a positive response of growth to increased irradiance only under high nutrient conditions. This suggests that observed reductions in the abundance ofStigeocloniumunder high irradiance/low nutrient conditions that occur on a seasonal basis in WB can be explained in part by autecological resource requirements of this alga. We use these results to model the response of algal communities dominated by basal‐regenerating species (e.g.Stigeoclonium)to gradients in herbivory and productivity. The results of our culture studies, combined with an overview of factors affecting communities dominated by grazer‐resistant species, illustrate how both broad‐scale (e.g. functional form) and species‐specific studies can be combined to ach

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00054.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTThe marine diatomThalassiosira pseudonana(Hustedt, clone 3H) Hasle and Heimdal was cultured under three different light regimes: 100 μmol photon · m−2· s−1on 12:12 h light : dark (L:D) cycles; 50 μmol photon · m−2· s−2on 24:0 h L:D; and 100 μmol photon · m−2· s−1on 24:0 h L:D. It was harvested during logarithmic and stationary phases for analysis of biochemical composition. Across the different light regimes, protein (as % of organic weight) was highest in cells during logarithmic phase, whereas carbohydrate and lipid were highest during stationary phase. Carbohydrate concentrations were most affected by the different light regimes; cells grown under 12:12 h L:D contained 37–44% of the carbohydrate of cells grown under 24:0 h L:D. Cells in logarithmic phase had high proportions of polar lipids (79 to 89% of total lipid) and low triacylglycerol (≤10% of total lipid). Cells in stationary phase contained less polar lipid (48 to 57% of total lipid) and more triacylglycerol (22 to 45% of total lipid). The fatty acid composition of logarithmic phase cells grown under 24:0 h L:D were similar, but the 100 μmol photon · m−2· s−1(12:12 h L:D) cells at the same stage contained a higher proportion of polyunsaturated fatty acids (PUFAs) and a lower proportion of saturated and monounsaturated fatty acids due to different levels of 16:0, 16:1(n‐7), 16:4(n‐1), 18:4(n‐3), and 20:5(n‐3). With the onset of stationary phase, cells grown at 100 μmol photon · m−2· s−1(both 12:12 and 24:0 h L:D) increased in proportions of saturated and monounsaturated fatty adds and decreased in PUFAs. Concentrations (% organic or dry weight) of 14:0, 16:0, 16:1(n‐7), 20:5(n‐3), and 22:6(n‐3) increased in cells of all cultures during stationary phase. The amino acid compositions of cells were similar irrespective of harvest stage and light regime. For mariculture, the recommended light regime for culturingT. pseudonanawill depend on the nutritional requirements of the animal to which the alga is fed. For rapidly growing bivalve mollusc larvae, stationary‐phase cultures grown under a 24:0 h L:D regime may provide more energy by virtue of their higher percentage of carbohydrate and high proportions a

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00064.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTMarine planktonic algae are frequently exposed to metallic contaminants. Because heavy metals can be assimilated and accumulated by algal cells, they can then be transferred to higher trophic levels of food chains. We studied the effects of cadmium on protein production and the growth of the marine prasinophyteTetraselmis gracilis(Kylin) Butcher. By means of toxicological assays, we estimated the LC50of cadmium as 3.2 ppm and 1.8 ppm after 48 h and 96 h of exposure to this heavy metal, respectively. The growth curves and survival percentages of cell cultures in the presence of cadmium were determined, and a proportional reduction of both parameters with increasing metal concentrations was found. When chronically exposed to sublethal concentrations of cadmium,T. graciliscontained high levels of superoxide dismutase (SOD) activity, one of the main enzymes of the cell's antioxidant defense mechanism. Under these growth conditions, total SOD activity in crude extracts was increased by 41% (at 1.5 ppm) and 107% (at 3.0 ppm). Assays of SOD activity in nondenaturing polyacrylamide gels also showed a similar induction by cadmium. These results show that cadmium has potentially toxic properties since it significantly inhibited the growth ofT. gracilisat low concentrations and promoted the induction of SOD activity, suggestive of an oxidative stress state. Besides being the first report of SOD inT. gracilis, this work describes experimental evidence of SOD induction by cadmium in this species.

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00074.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTDinoflagellates have substantially lower growth rates than other taxa of similar size. These low growth rates have been suggested to reflect the lower chlorophyllato carbon ratio (Chla:C) in dinoflagellates, but that speculation has never been widely tested. This study tests if the variations in growth rates among taxa are related to differences in Chla:C using published data. I collected 92 data entries from the literature representing 31 species, mostly from two divisions (Chrysophyta and Pyrrophyta), and found a significant relation(r2=0.39) between growth and Chla:C. Since Chla:C is almost independent of C content, I also developed a growth model using both C and Chla:C. Together, the two variables explain 68% of variation in algal growth. However, a further 6.4% of the variance in growth can still be attributed to phyletic differences. Low Chla:C is only a partial explanation for the low growth rates of the dinoflagellates.

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1996.00080.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY