摘要:

ABSTRACTTemperature tolerances and relative growth rates were determined for different isolates of the tropical to warm temperate seaweed speciesCladophoropsis membranacea(C. Agardh) Boergesen (Siphonodadales, Chlorophyta) and some related taxa. Most isolates ofC membranaceasurvived undamaged at 18° C for at least 8 weeks. Lower temperatures (5°–15°C) were tolerated for shorter periods of time but caused damage to cells. All isolates survived temperatures up to 34° C, whereas isolates from the eastern Mediterranean and Red Sea survived higher temperatures up to 36°C. Growth occurred between 18° and 32° C, but an isolate from the Red Sea had an extended growth range, reaching its maximum at 35°C.Struvea anastomosans(Harvey) Piccone&Grunow,Cladophoropsis sundanensisReinbold, and an isolate ofC. membranaceafrom Hawaii were slightly less cold‐ tolerant, with damage occurring at 18°C. Upper survival temperatures were between 32° and 36° C in these taxa. Temperature response data were mapped onto a phylogenetic tree. Tolerance for low temperatures appears to be a derived character state that supports the hypothesis thatC. membranaceaoriginated from a strictly tropical ancestor. Isolates from the Canary Islands, which is near the northern limit of distribution, are ill adapted to local temperature regimes. Isolates from the eastern Mediterranean and Red Sea show some adaptation to local temperature stress. They are isolated from those in the eastern Atlantic by a thermal barrier at the entrance of the

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00777.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTWe examined the effect of ultraviolet‐B radiation (UV‐B, 290–320 nm) on the growth rate of the intertidal marine algaUlva expansa(Setch.) S.&G. (Chlorophyta). Segments of thallus collected from a natural population were grown in outdoor seawater tanks. Combinations of UV‐B‐opaque screens, UV‐B‐transparent screens, and UV‐B lamps were used to investigate the effects of solar UV‐B and solar plus supplemental UV‐B on the growth of these segments. Growth was measured by changes in segment surface area, damp weight, and dry weight. Growth rates of segments were inhibited under both solar UV‐B and solar plus supplemental UV‐B treatments. Growth rates were also inhibited by high levels of photosynthetically active radiation, independent of UV‐B fluence. These results indicate that increases in UV‐B resulting from further ozone depletion will have a negative impact

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00783.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTThe aggregate‐forming, nonheterocystous, filamentous blue‐green alga (cyanobacteria)Trichodesmiumspp. is a widespread and important planktonic N2fixer and primary producer in tropical and subtropical oceans. It is unique among nonheterocystous genera because it conducts N2and CO2fixation (O2evolution) simultaneously; a notable achievement, because O2is a potent inhibitor of N2fixation. Spatial and temporal CO2fixation patterns were examined in trichomes and aggregates from natural and cultured populations, utilizing microautoradiographic detection of14CO2incorporation. Parallel N2fixation (acetylene reduction) measurements were also made. Diel N2and CO2fixation patterns were similar, with co‐optimization of both processes near midday. Microautoradiographs revealed several trichome‐level14CO2incorporation patterns: 1)uniform, heavy labeling, 2)uniform, light labeling, 3) heavier labeling in distal as opposed, to proximal regions, and 4) virtually no labeling throughout. Similar patterns were observed in natural and cultured populations. Given previous immunochemical findings that N2fixation potential is widespread inTrichodesmiumspp. trichomes and aggregates, current results suggest a high degree of individuality, and possibly a “division of labor” in terms of CO2fixation, among trichomes comprising active N2‐fixing aggregates. Segregation of photosynthesis within and among trichomes facilitates simultaneous N2and CO2fixation inTrichodesmiumspp. trichomes a

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00790.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTA planktonic alga similar in general morphology and pigments toAureococcus anophagefferensHargraves and Sieburth has caused persistent and ecologically damaging blooms along the south Texas coast. Experiments using 100 μM NO3−, NO2−, and NH4+demonstrated that the alga could not use NO3−for growth but could use NO2−and NH4+. Doubling iron or trace metal concentrations did not permit growth on NO3−. Chemical composition data for cultures grown in excess NO3−or NH4+, respectively, were as follows: N·cell−1(0.88 vs. 1.3 pg), C:N ratio (25:1 vs. 6.4:1), C:chlorophylla(chla)(560:1 vs. 44:1), and chl a·cell−1(0.033 vs. 0.16 pg). These data imply that cells supplied with NO3−were N‐starved. Culture addition of 10 mM final concentration chlorate (a nitrate analog) did not affect the Texas isolate while NO3−utilizingA. anophagefferenswas lysed, suggesting that the NO3−reductase of the Texas isolate is nonfunctional. Rates of primary productivity determined during a dense bloom indicated that light‐saturated growth rates were ca. 0.45 d−1, which is similar to maximum rates determined in laboratory experiments (0.58 d−1± 0.16). However, chemical composition data were consistent with the growth rate of these cells being limited by N availability (C:N 28, C:chla176, chl a·cell−10.019). Calculations based on a mass balance for nitrogen suggest that the bloom was triggered by an input of ca. 69 μM NH4+that resulted from an

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00800.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTThe impact of storm‐flow on river biofilm architecture was investigated using transmission (TEM) and scanning (SEM) electron microscopy. TEM resin substrata were colonized under light‐grown (LG) or dark‐grown (DG) conditions for 33 weeks in the Clywedog River, North Wales, prior to exposure to ambient‐flow (approx. 60 cm·s−1) or storm‐flow (approx. 235 cm·s−1+ river sediment) in a laboratory flume. Line transect methodology was used to quantify information from TEM ultrathin sections of LG material. In the LG ambient‐flow biofilm, bacteria were more abundant directly adjacent to the substratum and were noticeably denser directly under the adnate diatomCocconeis.Higher in the biofilm, the bacteria were loosely dispersed in the matrix between other cells. Cyanobacteria occurred most frequently as single cells but were also found in large “palisade” formations adjacent to the substratum. Significant horizontal and vertical nearest‐neighbor associations were noted for both bacteria and cyanobacteria. Cells ofCocconeiswere common adjacent to the substratum, providing shelter to, and often elevated upon, an “organic pad” of bacteria, cyanobacteria, and densely staining exopolysaccharide. Cyanobacteria andCocconeiswere resistant to removal by storm‐flow, butCocconeisfrustules were sometimes damaged. Bacteria in the LG storm‐flow samples were less common adjacent to the substratum and were sometimes more dispersed higher in the biofilm than in ambient‐flow samples. We suggest that storm‐flow hydrodynamic forces may redistribute bacteria adjacent to the substratum into higher areas of the biofilm. In addition, bacteria and the exopolysaccharide matrix were sometimes removed down to the substratum by storm‐flow, unless beneathCocconeis.The DG biofilm consisted almost entirely of bacteria. Storm‐flow only removed surface growth from DG biofilms, and SEM revealed peritrich stalk abrasion and “blow‐down.” Pre‐disturbance biofilm architecture appears to influence the form of destruction. We suggest that the “microcosms” ofCocconeisand their underlying cells not only serve as an inoculum to recolonize the surface when conditions permit but enhance immigrati

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00807.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTThis article describes the effect of various environmental conditions on the speed of freshwater diatoms. The diatoms display a wide distribution of cell speeds, from 0 to>20 μm·s−l, as indicated by both the distribution of speeds within a cell population as well as the distribution of 1‐s interval speeds of individual cells. Cell length has little or no effect on cell speed, as the speed of large postconjugal populations ofCraticulaand smaller preconjugal cell populations were not significantly different. The diatoms showed a broad pH tolerance, withCraticula spp.andNitzschia spp.displaying active motility between pH 3 and 12 and pH 4 and 10, respectively, with velocity maxima for both species at approximately pH 7. In contrast to previous reports on marine diatoms, these freshwater diatoms do not require millimolar levels of external calcium for motility, as bothCraticula spp.andNitzschia spp.showed significant motility in distilled water (<0.5 μM calcium) for up to 5 h. Although addition of ≥500 μM of EGTA inhibited motility, this inhibition did not appear to be due to calcium chelation, as EGTA solutions preincubated with up to 20‐fold excess calcium, magnesium, or both still inhibited motility with the same dose‐dependent response as EGTA alone. Moreover, significant motility was restored by rinsing EGTA‐treated cells in distilled water, Ca‐free medium, or regular diatom medium. The calcium channel inhibitors lanthanum and ruthenium red also inhibited motility in a dose‐dependent manner, suggesting that regulation of internal calcium stores may be important in motility.Craticulamotility also declines rapidly in medium ≥50 mOsM while the isotonic concentration appears to be 100–120 mOsM, suggesting that movement may require the plasma membrane to be exerting a force ≥50–70 mOsM osmotic pressure (1–1

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00818.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTThe growth characteristics ofHaematococcus pluvialisFlotow were determined in batch culture. Optimal temperature for growth of the alga was between 25° and 28°C, at which the specific growth rate was 0.054 h−1. At higher temperatures, no cell division was observed, and cell diameter increased from 5 to 25 μm. The saturated irradiance for growth of the alga was 90 μmol quanta · m−2·s−1; under higher irradiances (e.g. 400 μmol quanta·m−2·s−1) astaxanthin accumulation was induced. Growth rate, cell cycle, and astaxanthin accumulation were significantly affected by growth conditions. Careful attention should be given to the use of optimal growth conditions when studyi

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00829.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTThe effects of growth temperature on the marine chlorophyteDunaliella tertiolectaButcher were studied to provide a more mechanistic understanding of the role of environmental factors in regulating bio‐optical properties of phytoplankton. Specific attention was focused on quantities that are relevant for modeling of growth and photosynthesis. Characteristics including chlorophylla(chl z)‐specific light absorption (a*ph(λ)), C:chlaratio, and quantum yield for growth (φμ) varied as functions of temperature under conditions of excess light and nutrients. As temperature increased over the range examined (12°‐28°C), intracellular concentrations of chlaincreased by a factor of 2 and a*ph(λ) values decreased by more than 50% at blue to green wavelengths. The lower values of a*ph(λ) were due to both a decrease in the abundance of accessory pigments relative to chlaand an increase in pigment package effects arising from higher intracellular pigment concentrations. Intracellular pigment concentration increased as a consequence of higher cellular pigment quotas combined with lower cell volume. At high growth temperatures, slightly more light was absorbed on a per‐cell‐C basis, but the dramatic increases in growth rate from μ= 0.5 d−1at 12° C to μ= 2.2 d−1at 28°C were primarily due to an increase inφμ(0.015–0.041 mol C (mol quanta)−1).By comparison with previous work on this species, we conclude the effects of temperature on a*ph(λ) and φμare comparable to those observed for light and nutrient limitation. Patterns of variability in a*ph(λ)and φμas a function of growth rate at different temperatures are similar to those previously documented for this species grown at the same irradiance but under a range of nitrogen‐limited conditions. These results are discussed in the context of implications for bio‐optical modeling of aqu

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00833.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTThe regulation of photosystem II (PSII)‐related parameters was characterized forChlorella pyrenoidosaChick grown in continuous nutrient‐replete culture and acclimated to a light field simulating fluctuations of a natural environment. The maximum quantum yield for charge separation at PSII showed a light‐driven decrease during the first half of the photoperiod when incident irradiance (integrated hourly) was increasing to a midday maximum, This change was accompanied by a decrease in the effective cross‐section for all PSIIs and the connectivity between PSIIs, while the cross‐section for inactive centers increased. Furthermore, a decrease in the number of active PSII centers and the amount of QBbound to D1 became evident. During the second half of the day, as irradiance declined toward the end of the photoperiod, all the observed changes in PSII photochemistry were reversed. The low quantum yield values at the middle of the photoperiod returned to 85% of the value at the end of the photoperiod by the addition of far‐red light, suggesting that a State I–II–I transition took place during the day. Measured rates of oxygen production correlated well with fluorescence‐derived estimates of photosynthesis. The overall results suggest that PSII photochemistry is optimized to minimize the susceptibility to photoinhibition and to allow balanced growth under fluctuating irradiation and that the impact of these alterations on primary production can be adequately monitored through bio‐optical

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00841.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTDuring fertilization of the red algaPalmariasp. (Palmariales), the prophase‐arrested nucleus of the uninucleate spermatium resumes its division after direct attachment of the spermatium to the trichogyne of a carpogonium. Treatments that reduce Ca2+influx inhibit the progression of spermatial nuclear division. The ratio of the number of spermatia released from prophase arrest (those in meta‐phase to binucleate stages) to the total spermatia attached to trichogynes was significantly reduced by incubating the spermatia in the culture solution having low Ca2+concentration. Similar inhibition was observed by addition of either inorganic (La3+and Co2+) or organic (nifedipine and tetramethrin) Ca2+channel inhibitors to the culture solution containing 10 mM Ca2+. These results indicate that the prophase/metaphase transition of spermatial nuclear division requires an influx of Ca2+and suggest that Ca2+acts as a second messenger to the mechanical or chemical stimulus that initiates mitotic progression of spermatia in this a

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00853.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY