Phased cell division in natural and laboratory populations of marine planktonic diatoms

Phytoplankton samples were collected every 2 h and examined for percentage of dividing cells (doublets) during different times of the day. Thalassiothrix nitzschioids Grunow and Tropidoneis antarctica Grunow, var. polyplasta Gran, showed diurnal peaks in cell division at 1700. Thalassiosira rotula Meunier showed a nocturnal peak in cell division at 0300, while Chaetoceros vanheurckii Gran consistently exhibited low cell division rates with no apparent peaks. A culture of T. rotula kept under a similar L:D cycle to that present in the field (16:8 L:D) showed a diurnal peak in cell division at 1700. It appears from these data and recent literature that several factors are involved in the regulation of phased cell division in phytoplankton, including temperature, L:D cycle, nutrients, and size selective grazing by zooplankton.     

Acclimation of the diatom Stephanodiscus neoastraea and the cyanobacterium Planktothrix agardhii to simulated natural light fluctuations

Functional and structural characteristics of the photosynthetic apparatus were studied in the diatom Stephanodiscus neoastraea and the cyanobacterium Planktothrix agardhii which were grown semi-continuously under constant irradiance or under simulated natural light fluctuations. The light fluctuations consisted of 24 oscillations of exponentially increasing and decreasing irradiance over a 12-h light period. Maximum irradiance was 1100 μmol photons m⁻² s⁻¹ with the ratio of maximum to minimum intensities being 100, simulating Langmuir circulations with a ratio of euphotic to mixing depth of 1. S. neoastraea acclimated to the light fluctuations by doubling the number and halving the size of photosynthetic units (PS II) while the amount of chlorophylls and carotenoids remained unchanged. The chlorophyll-specific maximum photosynthetic rate was enhanced while the slope of the photosynthesis versus irradiance curves was not influenced by the light fluctuations. Acclimation of P. agardhii was mainly characterized by an increase in chlorophyll content. Both photosystems showed only little changes in number and size. Maximum photosynthetic rate, saturating irradiance and initial slope of the photosynthesis versus irradiance curves did not vary. Although both high and low light were contained in the fluctuating light, an analogy to low or high light acclimation was not found for the diatom nor for the cyanobacterium acclimated to light fluctuations. We suggest that the acclimation to fluctuating light is a response type outside the known scheme of low and high light acclimation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Growth light level and photon absorption by cells of Chlamydomonas rheinhardii,Dunaliella tertiolecta (Chlorophyceae,Volvocales), Scenedesmus obliquus (Chlorophyceae,Chlorococcales) and Euglena viridis (Euglenophyceae,Euglenales)

Reductions in the growth light level (40 to 6 μmol m^-2 s^-1) resulted in increases in chlorophyll and protein per cell for all of the species examined. Only Dunaliella tertiolecta exhibited a reduction in chlorophyll a:b ratio with decreases in the photon flux density. However, the specific absorption coefficient (ā? _i ) normalized to chlorphyll a (ā? _a remained invariant for all of the microalgae studied. Constant values for the specific absorption coefficient normalized to the total pigment content (ā? _a+b ) were also found for the species Chlamydomonas rheinhardii, Euglena viridis and Scenedesmus obliquus. In contrast ā? _a+b for D. tertiolecta decreased with a reduction in light level due to an increase in the proportion of chlorophyll b. Differences in ā? _i were related to cell size and pigment content and possible reasons for the constancy of ā? _a discussed. Increases in the absorption cross sections (¯sQ _a ) were also found at reduced light levels due to an increase in the absorptance per cell (α_cell). The lower α_cell for D. tertiolecta, compared with C. rheinhardii was exactly compensated for by a larger light-capturing area. Although the increase in α_cell does not compensate for the reduction in the incident light level, it does reduce this range by half on an absorbed light basis.     

Effects of light fluctuations on the growth and productivity of Antarctic diatoms in culture

Summary This work shows that the low division rates observed in diatoms in Antarctic waters seem to be due to conditions of irradiance rather than to the low temperature: low light intensity and light fluctuations are two factors which depress the division rate of diatoms. However, with regard to the productivity, Antarctic diatoms seem well-adapted to their turbulent environment. Cells grown in alternating periods of light and dark, notably a 2:2 regime which simulates conditions of vertical mixing, reach a higher rate of productivity than algae grown in continuous light. This difference may be due to the better use of light energy observed in the former group. In the Antarctic Ocean, which is characterized by frequent mixing of water masses, this increased efficiency of light utilization could be a way of adaptation, allowing the algae to overcome the restraints imposed by low light and low temperature, and to reach a higher productivity than expected. The low values of I_k and I_max as well as the absence of detectable photoinhibition indicate that Antarctic diatoms are capable to sustain their maximum primary production rate over a wide range or irradiance levels. On the other hand, the highest productivity in 2:2 regime shows that these species are more efficient when grown under fluctuating light. These results lead us to assume that the Antarctic species are well-adapted to live in the extreme conditions of light encountered in Antarctic Ocean: low irradiance and alternance of low and high light intensities.     

Light absorption and scattering by cell suspensions of some cyanobacteria and microalgae

Absorption spectra of cyanobacteria (Anacystis nidulans, Anabaena variabilis, and Chlorogloeopsis fritschii), red (Cyanidium caldarum and Porphyridium cruentum), green (Dunaliella maritima and Dunaliella salina) and diatom (Thalassiosira weisflogii) alga cell suspensions are presented; the spectra were obtained by using an approach developed earlier to compensate for scattering [1, 2]. In all species, the shapes of the absorption spectra were independent of the cell concentration. For Th. weisflogii and D. maritima, the analysis of selective and nonselective scattering was carried out. The effect of mechanical cell disruption on optical properties (absorption, scattering, and “package” effect) on D. maritima was studied. The character and dynamics of optical changes in D. salina under the influence of sodium chloride were followed.     

Growth, gas vacuolation and buoyancy in a natural population of a planktonic blue-green alga

(1)The growth and development of a natural population of Anabaena circinalisis described in relation to physical and chemical conditions within a small, shallow eutrophic lake. (2)Germination of resting spores took place when the lake was destratified, in response to improving conditions of light and temperature. (3)The growth of the population was monitored for chlorophyll and nutrient content, and parallel determinations of heterocyst ratio, gas vacuole volume, turgor and buoyancy were made. (4)Growth of the population was probably limited by phosphorus deficiency. (5)Cessation of growth was marked by increases in gas vacuole volume and buoyancy. (6)Gas vacuole volume is determined primarily by the rate of increase of the alga. It is modified by turgor changes, associated with photosynthetic rates. (7)Surface blooms are the result of the redistribution of buoyant algae when turbulence currents are weak. (8)Buoyancy is increased in algae lodged at the surface.     

Weather-driven ecology of planktonic diatoms in Lake Tovel (Trentino,Italy)

The seasonal development of planktonic diatoms in Lake Tovel has been studied from 2002 to 2004 within the SALTO research project. The objective was to investigate the role of weather conditions and lake hydrology in regulating the development of Cyclotella and Fragilaria functional species groups. The different responses of the two species to the environmental variability and their reciprocal relationships were considered. Cyclotella showed a weak relationship with the selected environmental variables and its seasonal development was difficult to interpret, also in relation to its opportunistic behaviour. On the contrary, Fragilaria complex showed a prompt response to environmental variability and its seasonal development appeared to be mainly regulated by hydrological conditions, through nitrate nitrogen and, secondarily, by silica concentrations. Water temperature and thermal stability affected only Fragilaria species, while different nutrient requirements allowed Cyclotella species to grow under conditions of limited resources for Fragilaria. Since Lake Tovel has scarce internal nutrient reserves and its hydrology is strongly affected by precipitation both in winter and summer, diatom phenology seems to be indirectly regulated by weather conditions.     

Growth responses of planktonic desmid species in a temperature—light gradient

SUMMARY. 1. Isolates of twelve planktonic desmid species were tested for their growth response in batch culture, using an apparatus that generates crossed gradients of temperature and light intensity.
2. Up to 15°C, growth was mainly temperature-limited. At higher temperatures, there was an increasing effect of light limitation. Optimal growth temperatures were in the range 25–30°C.
3. Highest specific growth rates varied from 0.28 to 1.34 day⁻¹. Species with lowest growth rates originated from oligo-mesotrophic habitats, those with highest growth rates from eutrophic ones.
4. Ecophysiological aspects are discussed in some detail, as well as the significance of the experimental data for distributions in the field.     

Salinity effects on growth,photosynthetic parameters,and nitrogenase activity in estuarine planktonic cyanobacteria

Salinity has been suggested as being a controlling factor for blooms of N2-fixing cyanobacteria in estuaries. We tested the effect of salinity on the growth, N2 fixation, and photosynthetic activities of estuarine and freshwater isolates of heterocystous bloom-forming cyanobacteria. Anabaena aphanizomenoides and Anabaenopsis sp. were isolated from the Neuse River Estuary, North Carolina, and Cylindrospermopsis raciborskii from Lakes Dora and Griffin, central Florida. Salinity tolerance of these cyanobacteria was compared with that of two Nodularia strains from the Baltic Sea. We measured growth rates, N2 fixation (nitrogenase activity), and CO2 fixation at salinities between 0 and 20 g L(-1) NaCl. We also examined photosynthesis-irradiance relation-ships in response to salinity. Anabaenopsis maintained similar growth rates in the full range of salinities from 2 to 20 g L(-1) NaCl. Anabaena grew at up to 15 g L-', but the maximum salinity 20 g L(-1) NaCl was inhibitory. The upper limit for salinity tolerance of Cylindrospermopsis was 4 g L(-1) NaCl. Nodularia spp. maintained similar growth rates in the full range of salinities from 0 to 20 g L(-1) . Between 0 and 10 g L(-1), the growth rate of Nodularia spumigena was slower than that of the Neuse Estuary strains. In most strains, the sensitivity of nitrogenase activity and CO2 fixation to salinity appeared similar. Anabaenopsis, Anabaena, and the two Nodularia strains rapidly responded to NaCl by increasing their maximum photosynthetic rates (Pmn). Overall, both Neuse River Estuary and Baltic Sea strains showed an ability to acclimate to salt stress over short-(24 h) and long-term (several days to weeks) exposures. The study suggested that direct effect of salinity (as NaCl in these experiments) on cyanobacterial physiology does not alone explain the low frequency and magnitude of blooms of N2-fixing cyanobacteria in estuaries.     

Sulfate inhibition of molybdenum-dependent nitrogen fixation by planktonic cyanobacteria under seawater conditions: a non-reversible effect

The trace element molybdenum is a central component of several enzymes essential to bacterial nitrogen metabolism, including nitrogen fixation. Despite reasonably high dissolved concentrations (for a trace metal) of molybdenum in seawater, evidence suggests that its biological reactivity and availability are lower in seawater than in freshwater. We have previously argued that this difference is related to an inhibition in the uptake of molybdate (the thermodynamically stable form of molybdenum in oxic natural waters) by sulfate, a stereochemically similar ion. Low molybdenum availability may slow the growth rate of nitrogen-fixing cyanobacteria, and in combination with an ecological control such as grazing by zooplankton, keep fixation rates very low in even strongly nitrogen-limited coastal marine ecosystems. Here we present results from a seawater mesocosm experiment where the molybdenum concentration was increased 10-fold under highly nitrogen-limited conditions. The observed effects on nitrogen-fixing cyanobacterial abundance and nitrogen-fixation inputs were much smaller than expected. A follow-up experiment with sulfate and molybdenum additions to freshwater microcosms showed that sulfate (at seawater concentrations) greatly reduced nitrogen fixation by cyanobacteria and that additions of molybdenum to the levels present in the seawater mesocosm experiment only slightly reversed this effect. In light of these results, we re-evaluated our previous work on the uptake of radio-labeled molybdenum by lake plankton and by cultures of heterocystic cyanobacteria. Our new interpretation indicates that sulfate at saline estuarine levels (>8–10 mM) up to seawater (28 mM) concentrations does inhibit molybdenum assimilation. However, the maximum molybdenum uptake rate (V _max) was a function of the sulfate concentration, with lower V _max values at higher sulfate levels. This indicates that this inhibition is not fully reversed at some saturating level of molybdenum, as assumed in a simple competitive inhibition model. A multi-enzyme, mixed kinetics model with two or more uptake enzyme systems activated in response to the environmental sulfate and molybdate conditions may better explain the repressive effect of sulfate on Mo-mediated processes such as nitrogen fixation.     

Long-term survival of marine planktonic diatoms and dinoflagellates in stored sediment samples

Sediment samples from Scottish coastal sites, taken over the last 9 years, were stored in closed containers at 5C. Slurry cultures were used to determine the survival of phytoplankton in these sediments. A range of diatom and dinoflagellate species survived for at least 27 months in these stored samples. A number of species grew for which no resting stage has yet been described: Thalassiosira angulata, T.pacifica, T.punctigera, T.eccentrica, T.minima and T.anguste-lineata. Notable results were survival times of 73 months for Skeletonema costatum, 96 months for Chaetoceros socialis, C.didymus and C.diadema, 109 months for Scrippsiella sp. and 112 months for Lingulodinium polyedrum. A single sample was stored and repeatedly cultured for diatoms over a period of 16 months. The number of species cultured from the sediment declined over this time. Lingulodinium polyedrum cysts isolated from sediments collected at least 18 months previously gave a hatching success of 97%, and cysts isolated from a 9-year-old sample gave a hatching success of 3%. The study indicated the potential importance of coastal sediments as a source of phytoplankton to their overlying waters. The validity of using marine planktonic diatoms and dinoflagellates for modelling geological events is discussed.      

The influence of irradiance,photoperiod and temperature on the growth kinetics of three planktonic diatoms

The influence of irradiance, photoperiod and temperature was determined for the growth kinetics of the diatoms Aulacoseira subarctica, Stephanodiscus astraea and Stephanodiscus hantzschii and the results compared with those of cyanobacteria. Irradiance and photoperiod relationships were qualitatively similar to those for cyanobacteria in that: (1) growth rate (K) was proportionally greater under short photoperiods, with ratios of K under continuous light to K under 3:21 light:dark (LD) cycles of 1·50, 1·80 and 2·96 for A. subarctica, S. astraea and S. hantzschii respectively; (2) at subsaturating irradiances, K was proportional to irradiance and independent of temperature with a negligible predicted maintenance growth rate requirement. Apparent growth efficiencies (GE) at subsaturating irradiances were 0·26±0·03, 0·42±0·03 and 0·50±0·03 divisions mol^-1m² for A. subarctica, S. astraea and S. hantzschii with the values for Stephanodiscus species comparable to values for Oscillatoria species. Under a 3:21 LD cycle at 4 °C, light-saturated growth rates were 0·066±0·004, 0·197±0·033 and 0·285±0·018 divisions day^-1 for A. subarctica, S. astraea and S. hantzschii. S. hantzschii growth rate at 4 °C exceeded maximum Oscillatoria growth rates at 23 °C and the S. astraea growth rate at 4 °C was equivalent to O. agardhii growth rate at 20 °C. Temperature increases above 4 °C gave Q₁₀ values between 4 °C and 12 °C of 3·68, 2·39 and 1·92 for A. subarctica, S. astraea and S. hantzschii, but higher temperatures resulted in minor increases in K. S. astraea growth rate peaked at 16 °C, declining sharply at higher temperatures. February to March in situ growth rates in Lough Neagh, mean temperature 4·3 °C, showed that the A. subarctica in situ K of 0·058 divisions day^-1 was close to the laboratory K at 4 °C, but that S. astraea in situ K of 0·101 divisions day^-1 was lower than the laboratory K at 4 °C.     

Pseudo-continuous culture of marine recombinant cyanobacteria under a light dark cycle

Summary Pseudo-continuous culture of recombinant marine cyanobacteria was carried out under a light dark cycle. As a model foreign gene, the structural gene of chloramphenicol acetyl transferase (CAT) was used. Under a light dark alternate conditions, a steady state cell concentration was observed. However, the level of CAT expression did not show a stationary phase, but oscillated with the light dark cycle. This may be due to the lack of energy for foreign peptide synthesis during dark incubation. This result also indicates the possibility of regulation of foreign gene expression by controlling light illumination.     

Occurrence of planktonic blooms under environmental fluctuations and its possible control mechanism--mathematical models and experimental observations

Planktonic blooms and its control is an intriguing problem in ecology. To investigate the oscillatory successions of blooms, three simple phytoplankton-zooplankton systems are proposed. It is observed that if the uptake function is linear and the process of toxin liberation is instantaneous, the oscillatory nature of blooms is not observed. On the other hand, periodic planktonic blooms are observed when toxin liberation process follows discrete time variation. The bloom phenomena described by this mechanism can be controlled through toxin producing phytoplankton (TPP). Introducing environmental fluctuation in the system, a critical value of time delay in terms of correlation time of the fluctuation is worked out. We observed from our mathematical analysis, numerical simulation and field observation that TPP and control of the rapidity of environmental fluctuation are key factors for the termination of planktonic blooms.     

Changes in the photosynthetic apparatus of maize in response to simulated natural temperature fluctuations

The response of the photosynthetic apparatus to low temperature periods differed among three hybrids of maize (Zea mays L.) grown in a phytotron. Light-saturated photosynthetic rates, leaf chlorophyll content, and mesophyll cell photosynthetic unit density all declined with increasing duration of low temperature. No single metabolic or physiological parameter appeared to control the response of the three hybrids to low temperature stress. Among all temperature treatments, net photosynthetic rate on a leaf area basis was more closely correlated with leaf chlorophyll content than with any other measured parameter. Final shoot dry weight was most highly correlated with stomatal conductance to CO₂.     

Growth,yield and reproduction of dwarf tomato grown under simulated microgravity conditions

Abstract

A closed hydroponic system combined with a horizontal uniaxial clinostat has been used to grow tomato plants (Solanum lycopersicum L.) under simulated microgravity conditions. The study was carried out to evaluate the quanti-qualitative traits (growth, yield and quality) of the dwarf tomato variety ‘Micro-Tom’ grown under simulated microgravity conditions and to determine if tomato plants would complete their life cycle (‘seed-to-seed’). Morphological and growth characteristics of ‘Micro-Tom’ were modified during clinorotation treatment. The ‘Micro-Tom’ plants grown under simulated microgravity exhibited a spreading growth and an increasing of the internode length. Total fruit yield, small fruit yield, leaf area, leaf dry weight, fruit dry weight, total dry weight and shoot – root ratio were lower in the clinorotated tomato plants than those grown in the control treatment. Foliar amount of carotenoids, and chlorophyll a and b were also substantially reduced under simulated microgravity conditions. Quality parameters (total soluble solids and fruit dry matter) of tomato plants were also negatively affected by clinorotation. The number of flowers per plant was increased by 32% in clinorotated plants versus controls. Fruit setting was reduced by 46% under clinorotation, while no significant difference was recorded for the pollen fertility and the seed number in small and large fruits. Clinorotation-exposed and control seeds were used in a germination trial in order to evaluate whether the seeds so formed were viable and if subsequent generations might be obtained in microgravity. Seeds formed under simulated microgravity proved to be biologically and functionally complete (germination = 78.6%) showing that ‘Micro-Tom’ plants could realize complete ontogenesis, from seed to seed in microgravity.     

Growth characteristics of selected thermophilic strains of cyanobacteria using crossed gradients of temperature and light

Growth requirements of 10 possibly thermophilic strains of cyanobacteria were compared under a wide spectrum of light and temperature conditions (7–80Wm^?2, 12–40°C). The strains were isolated from different localities: six of thermal springs in Slovakia (4 from Pie??any, 2 from Sklené Teplice), one from thermal waters in Rupite, Bulgaria, 2 strains from a hypersaline lake Chott-el-Djerid, Tunisia, and one strain from the tropical island of Cebu, Philippines. Although the crossed gradient unit allowed only sub-optimal temperature range with respect to thermophile definition, i.e. optimum temperature above 45°C, there were difference among the strains. The most thermophilic and high-light tolerant strain was Synechococcus bigranulatus strain Lukavsky 2005/66, with a peak above 45°C; the second was Chroococcidiopsis thermalis strain Hindák 2008/9, and Isocystis sp. strain Hindák 2006/1. The temperature requirements of other strains were similar; the least thermophilic were both Slovakian strains of the genus Hapalosiphon. Growth was not limited below 80 W m^?2, except for H. fontinalis strain Hindák 2008/3, which prefers lower irradiance. Hapalosiphon delicatulus strain Hindák 2007/20, isolated from a bark tree on the tropical island of Cebu was rather mesophilic than thermophilic and shade-preferring. The CCA revealed that the ecologically similar strains originated from the same or nearby localities. There were no significant correlations between temperature optima in culture and in nature. Bulgarian and Tunisian strains preferred higher irradiances.     

Behaviour of catalase in some members of Chlorophyceae and Cyanophyceae

Summary The activation energy of catalase revealed statistically significant variations in Chlorophyceae and Cyanophyceae. The differences in two classes of algae may suggest a close catalase-chlorophyll relationship.     

A revised checklist of planktonic diatoms and dinoflagellates from Helgoland (North Sea,German Bight)

A checklist based on net samples taken twice weekly from 2001 until May 2003 is presented. Identification is based on observations under direct light microscopy and after taking some organisms in culture. The checklist includes 227 taxa observed at the Helgoland Reede sampling station. One hundred and thirty-two species of diatoms from 53 genera and 95 species of dinoflagellates from 35 genera have been recorded from net samples and cultures. Thirty-five diatom and 28 dinoflagellate taxa were documented in the Helgoland phytoplankton for the first time. The list does not claim to be complete, but provides an updated list of the taxa found at Helgoland and, for convenience, also includes data published for different adjacent areas.Communicated by K. Wiltshire     

Sulfonylurea-resistant mutants and natural tolerance of cyanobacteria

The herbicide sulfometuron methyl (SM) inhibited the growth of the cyanobacterium Synechococcus sp. PCC7942, but not of Synechocystis sp. PCC6714. The inhibitory effect was alleviated by the simultaneous addition of valine, leucine and isoleucine. SM resistant mutants were isolated from Synechococcus 7942, two types of which were further analysed. In these mutants, SM3/20 and SM2/32, the activity of acetolactate synthase (ALS) — a key enzyme in the biosynthesis of branched-chain amino acids —appeared 2600- and 300-fold, respectively, more resistant to SM than that of their wild type. Strain SM2/32 also exhibited a low level of ALS activity. Although the growth of the latter mutant was extremely inhibited by valine, the sensitivity of its ALS activity to feed-back inhibition by the amino acid was unaltered. At high concentrations valine inhibited growth of the wild type strains and of the mutant SM3/20. Isoleucine alleviated the valine-induced growth inhibition. Unlike that of Synechococcus 7942, the ALS activity of Synechocystis was found to tolerate high concentrations (100-fold) of the herbicide. The study confirms that the SM mutations are correlated with a cyanobacterial ilv gene.Abbreviations ALS acetolactate synthase; ile, isoleucine - leu leucine - NTG N-methyl-N-nitro-N-nitrosoguanidine - SM sulfometuron methyl - SM^r sulfometuron methyl resistant - val valine