PHOTOINHIBITION OF PHOTOSYNTHESIS IN ASTERIONELLA FORMOSA (BACILLARIOPHYCEAE)1, 2

A laboratory study was made of the inhibition of photosynthesis, as measured by the radiocarbon method, of Asterionella Formosa Hass. by light from tungsten halogen lamps of irradiances up to that of full sunlight. The observed inhibitions were of total fixation of carbon and were not due to greatly increased release of extracellular products of photosynthesis. Inhibition increased width irradiance and with time of exposure. It was greater at high temperature, at high oxygen concentrations and when the cells were nutrient deficient. Recovery from exposure to high irradiances took place both in the dark and at low irradiances. The inhibition, which is similar to that observed under natural conditions, has the characteristics of photooxidative damage to both photochemical and dark reaction mechanisms.     

FUNGAL CONTROL OF POPULATION CHANGES OF THE PLANKTONIC DIATOM ASTERIONELLA FORMOSA IN A SHALLOW EUTROPHIC LAKE1

Parasitic fungi infected an Asterionella formosa Hass. population for 10 months of the year, during which time the population density of the alga was over 100 cells-L^?1. High injection rates of more than 20% of the cells were observed between February and July except on a few occasions such as late April and late June. Mortality of infected diatom cells was temperature dependent in dialysis tube culture experiments; the loss rate of field populations due to fungal injection also was affected by temperature. Loss rates of diatom cells were negligibly small m February even though infection percentages were more than 20%, but increased toward summer with an increase m temperature. High infection percentages and correspondingly high loss rates (e.g. 0.3 d^?1) occurred periodically during the summer. The results suggest that this type of host-parasite interaction is an important control of algal population size in natural waters.     

TEMPERATURE-DEPENDENT CHANGES IN COLONY SIZE OF THE FRESHWATER PENNATE DIATOM ASTERIONELLA FORMOSA (BACILLARIOPHYCEAE) AND THEIR POSSIBLE ECOLOGICAL IMPLICATIONS1

Changes in colony size (cell number per colony) of Asterionella Formosa Hass. were experimentally evaluated in relation to water temperature using two types of clones having colony sizes of four or eight cells. The clones were isolated from two different temperate freshwater lakes. Both clones showed the same general trend with changing temperature. Most of the colonies were normal in size at low temperatures, but colony size was twice as large at high temperatures. Variable colony sizes were present at low percentages. Colony separation occurred at the oldest connection within the colony after cell division. Culture experiments showed that the rates of specific growth and colony separation were balanced except for a rather short period of time when the temperature was changed. Optical and scanning electron micrography did not show any distinctive morphological structure at the point of connection except for porelli and mucilage pads. Seasonal changes in colony size of A. formosa observed in a freshwater lake are discussed based on these temperature results.     

DIATOM PRODUCTIVITY COMPARED TO OTHER ALGAE IN NATURAL MARINE PHYTOPLANKTON ASSEMBLAGES1,2

Total productivity rates and the component attributed to the diatom proportion in the crop were measured in natural water samples taken from the Scripts Pier (La Jolla, California) at ca, monthly intervals in 1975–76. Two other measurements were done in water samples taken from Saanich Intel, Vancouver Islands, British Columbia (Canada). The percent of photosynthesis by diatoms was compared with the proportion of diatom carbon in the crop. In all instances, percent diatom photosynthesis was higher than percent diatom carbon for dialoms were higher than those of other algae. It is hypothesized that, in the sea, diatoms can outcompete other algae. However, the assemblages consist of some tens of species coexisting, and no portion of the crop out competes the others to exclusion.     

PHOSPHATE AND SILICATE GROWTH AND UPTAKE KINETICS OF THE DIATOMS ASTERIONELLA FORMOSA AND CYCLOTELLA MENEGHINIANA IN BATCH AND SEMICONTINUOUS CULTURE1

Information on the nutrient kinetics of Asterionella formosa Hass. and Cyclotella meneghiniana Kutz. under either phosphate or silicate limitation was obtained for use in a Monod model and in a variable internal stores model of growth. Short-term batch culture growth experiments were fit to the Monod model and long-term semicontinuous culture experiments and short-term uptake experiments were fit to the variable internal stores model. Mathematical analysis indicates that the parameters of the 2 models may be expressed in terms of each other at steady state. The qualitative results of both batch and steady state culture methods agree. For limiting phosphate experiments. A. formosa is better able to grow at low PO₄-P concentrations than C. meneghiniana, as shown by its lower K for PO₄-P limited growth. The k_Q of A. formosa compared to C. meneghiniana found in long-term semicontinuous culture indicates that A. formosa is almost an order of magnitude more efficient at using internal phosphate for growth. The qualitative results under silicate-limited growth of C. meneghiniana is less than that of A. formosa. The k_Q from semicontinuous culture experiments indicates that C. meneghiniana is the more efficient at using internal silicate for growth. Nutrient uptake experiments showed more variability from a Michaelis-Menten relationship than short-term growth experiments. There were no significant differences between the 2 species in half saturation constants for either phosphate or silicate uptake. We observed a marked dependence of the coefficient of luxury consumption (R) of phosphate on the steady state growth rate. A. formosa has a higher R than C. meneghiniana.     

PARASITISM OF ASTERIONELLA FORMOSA HASS. BY A CHYTRID IN TWO LAKES OF THE RAWAH WILD AREA OF COLORADO1

The populations of Asterionella formosa Hass. in two subalpine lakes in the Rawah Wild Area, Colorado, were composed of colonies of five distinct size classes Based on frustule length. The spring bloom in these two lakes was dominated by cells of the Beta or Gamma population, whereas the fall pulse was dominated by cells of the Alpha and Beta, or Alpha populations. The Beta population was physiologically unique in that it was parasitized by the chytrid Rhizophidium planktonicum Canter. The development of the parasite population could not be correlated with the concentration or the growth phase of the host population. The occurrence of parasitism did not noticeably affect the population growth patterns of the Asterionella populations.     

THE RELATIONSHIP BETWEEN PHOTOSYNTHESIS AND LIGHT FOR NATURAL ASSEMBLAGES OF COASTAL MARINE PHYTOPLANKTON1

In a series of 188 experiments on the, light-saturation curve for natural assemblages of phytoplankton at 3 stations in Nova Scotia coastal waters, it was found that both the initial slope (α) of the curve and the assimilation number (P_m^B) varied about 5-fold throughout the year. No differences could be detected between stations, but both α and P_m^B decreased with depth. The mean value of α for all the experiments was 0.21 mg C[mg Chl a]^?1· h^?1· W^?1· m² with a range from 0.03 to 0.63. An explanation is offered for the nonconstancy of a in terms of the effect of cell-size and shape on self-shading. An estimate is made from first principles of the physiological maximum-attainable value of α. This estimate corresponds, within the limits of experimental error, to the highest values of α observed in the study. It is deduced that on the average the phytoplankton were photosynthesizing at only 44% maximum capacity. The mean value of P_m^B for all experiments was 4.9 mg C[mg Chl a]^?1· h^?1, with a range from 0.73 to 24.8. In the matrix of partial correlation coefficients, α and P_m^B were positively correlated with each other; α was correlated with mean solar radiation averaged over the 3 days prior to the experiment, but uncorrelated with temperature; P_m^B was correlated strongly with temperature but uncorrelated with recent solar radiation. The results show that P_m^B could be estimated from α and temperature using an empirical multiple regression equation, independent of depth. It is suggested that α and P_m^B are both correlated with some other factor not measured in the study, perhaps the mean cell-size of the populations, or the nutrient status of the cells. The predictability of primary production is discussed in the light of this evidence.     

EFFECTS OF Si:P CONCENTRATION RATIOS AND NUTRIENT LIMITATION ON THE CELLULAR COMPOSITION AND MORPHOLOGY OF ASTERIONELLA FORMOSA (BACILLARIOPHYCEAE)1

The freshwater diatom Asterionella formosa Haas. was grown in semicontinuous culture at 20°C under continuous cool-white fluorescent light of ca. 20 μEin · m^?2· s ·^?1 in a medium containing Si: P in various concentration ratios. The cell quotas of P and Si changed in relation to the available concentrations of P and Si at constant μ= 0.11 and 0.16 d^?1. Under Si-limitation, the P cell quota increased by over an order of magnitude as the influent [Si:P] decreased. The Si cell quota increased with increase in [Si] in the influent medium, and it increased as [P] increased at a specific [Si]. Under P-limitation, the P cell quotas were fairly constant and low; the Si cell quotas were relatively high and decreased slightly as influent [P] and [Si] increased. Asterionella stored up to 28 times more P and 2 times more Si than needed. The number of Asterionella cells per colony varied as a function of the influent [Si:P] and nutrient limitation being usually less than or equal to 6 when P-limited, and greater than 10 when Si-limited.     

PHOTOSYNTHETIC PIGMENT ORGANIZATION IN DIATOMS (BACILLARIOPHYCEAE)1

The isolation and characterization of six pigment-protein complexes from five diatom species (Phaeodactylum tricornutum Bohlin, Chaetoceros gracilis Schutt, Nitzschia sp. Mono Lake, Nitzschia laevis Hust. and Thalassiosira pseudonana (Hust.) Hasle and Heimdal) was accomplished by membrane dissociation with digitonin followed by gel electrophoresis. Six analogous complexes obtained from all species were correlated in spectral characteristics and relative mass with complexes from higher plants obtained by the same procedure. The largest of these complexes, comprising about 15% of the total Chl a, contained reaction centers of Photosystem I (PSI) and antenna pigments (LHC₁).Some PSI complexes also separated from LHC₁ in the gel. For the first time in diatoms, a Photosystem II complex was isolated and identified from its position in the gels, absorption and fluorescence spectra, lack of P700, and enrichment carotene. Three antenna pigment-protein complexes in addition to LHC₁ occurred in varying proportion under different experimental conditions but in sum, they accounted for 70% of the total Chl a. All three bands were highly enriched in Chl c and fucoxanthin, although the ratio of Chl c/ xanthophyll decreased between the slowest migrating LHC₂ and fastest moving LHC₄ LHC₃ contained the highest proportio of pigment-protein and was composed primarily of polypeptides of about 18,000 D. Essentially all α- and β-carotene was bound to the reaction center complexes. The Nitzschia from Mono Lake differed from the other species in that PSI complexes could not be readily dissociated from its membrane by digitonin treatment, a characteristic which may reflect a different chloroplast membrane structure in this alga.     

DISTRIBUTION OF DIATOMS IN THE PLANKTON OF YAQUINA ESTUARY,OREGON1

The distributional patterns of diatoms in the plankton of the Yaqnina Estuary, Oregon, were, investigated and related to selected climatic and hydrographic factors. Distribution was strongly influenced by seasonal patterns of rainfall resulting in the introduction of a large volume of fresh water into the estuary during fall and winter. Plankton assemblages in spring, summer and fall had fewer diatom species and exhibited a more rapid rate of change in species composition than in winter. Winter assemblages were further characterized by many pennate diatoms, apparently dislodged from the benthos during periods of high freshwater discharge and silt loads. A statistical measure of community difference indicated an increase in taxonomic homogeneity among assemblages throughout the estuary with the onset of the rainy season in late fall and a gradual transition to a more heterogeneous system again during late spring. Canonical correlation ordered 20 prominent diatom taxa along the salinity gradient and identified possible relationships among certain taxa and selected environmental variables, namely visible light energy and temperature. Redundancy in the species data given the environmental data was only 40%, emphasizing the difficulty in demonstrating a quantitive relationship between plankton dynamics in the field and concurrent measurements of chemical and physical variables.     

DISTRIBUTION OF CARBON AMONG PHOTOSYNTHETIC END-PRODUCTS IN PHYTOPLANKTON OF THE EASTERN CANADIAN ARCTIC1

The distribution of ¹⁴C among photosynthetic end-products was examined in eastern Canadian arctic phytoplankton, with particular emphasis on the synthesis of lipids. The pattern of ¹⁴C distribution for phytoplankton at each of three depths was generally similar among populations from 12 stations. About 18% of the total ¹⁴C fixed was incorporated into lipids. At one station, phytoplankton were experimentally subjected to temperature and light conditions different from those in situ: lipid-¹⁴C did not exceed 30% of total ¹⁴C fixed within the temperature range -1.0 to 6.0° C and irradiance range 1 to 700 W · m^?2. It is suggested that low temperatures and low light intensities, even when, maintained for prolonged periods, are not fully sufficient conditions for eliciting high relative rates of ¹⁴C incorporation into lipids. It is possible that differences in species composition may be a factor accounting for different patterns of ¹⁴C distribution between north and south polar phytoplankton under apparently similar environmental conditions.     

PHOTOSYNTHETIC LIGHT-HARVESTING FUNCTION OF VIOLAXANTHIN IN NANNOCHLOROPSIS SPP. (EUSTIGMATOPHYCEAE)1

Whole cell absorption spectra of the Eustigmatophycean algae Nannochloropsis salina Bourrelly and Nannochloropsis sp. reveal the presence of a distinct absorption peak at 490 nm. The lack of chlorophylls b and c in these species indicates that this peak must be attributed to carotenoid absorption. In vivo fluorescence excitation spectra for chlorophyll a emission show a corresponding maximum at 490 nm. This peak is more clearly resolved than carotenoid maxima in other algal classes due to the absence of accessory chlorophylls. The carotenoid composition of the two Nannochloropsis species shows that violaxanthin and vaucheriaxanthin are the main contributors to 490 nm absorption. Violaxanthin accounts for approximately 60% of the total carotenoid in both clones. We conclude that light absorption by violaxanthin, and possibly by vaucheriaxanthin, is coupled in energy transfer to chlorophyll a and that violaxanthin is the major light-harvesting pigment in the Eustigmatophyceae. This is the first report of the photosynthetic light-harvesting function of this carotenoid.     

PHOTOSYNTHETIC LIGHT-HARVESTING FUNCTION OF VIOLAXANTHIN IN NANNOCHLOROPSIS SPP. (EUSTIGMATOPHYCEAE)1

Whole cell absorption spectra of the Eustigmatophycean algae Nannochloropsis salina Bourrelly and Nannochloropsis sp. reveal the presence of a distinct absorption peak at 490 nm. The lack of chlorophylls b and c in these species indicates that this peak must be attributed to carotenoid absorption. In vivo fluorescence excitation spectra for chlorophyll a emission show a corresponding maximum at 490 nm. This peak is more clearly resolved than carotenoid maxima in other algal classes due to the absence of accessory chlorophylls. The carotenoid composition of the two Nannochloropsis species shows that violaxanthin and vaucheriaxanthin are the main contributors to 490 nm absorption. Violaxanthin accounts for approximately 60% of the total carotenoid in both clones. We conclude that light absorption by violaxanthin, and possibly by vaucheriaxanthin, is coupled in energy transfer to chlorophyll a and that violaxanthin is the major light-harvesting pigment in the Eustigmatophyceae. This is the first report of the photosynthetic light-harvesting function of this carotenoid.     

COMPARATIVE EFFECTS OF pH AND ALUMINUM ON SILICA-LIMITED GROWTH AND NUTRIENT UPTAKE IN ASTERIONELLA RALFSII VAR. AMERICANA (BACILLARIOPHYCEAE)1

The acidophilic diatom Asterionella ralfsii cf. var. americana Körn. was grown in continuous culture to examine the influences of both pH and Al on Si-limited growth and uptake kinetics. In contrast to nutrient-replete cultures of A. ralfsii, lowering pH from approximately 6 to 5 reduced algal cell density, chlorophyll a concentration, and intensity of in vivo fluorescence (IVF) at steady state. The lower pH treatments were also characterized by lower Si cell quotas and higher residual dissolved Si concentrations in chemostats with similar nutrient supply rates. Physiological responses to Al stress differed from those to pH reduction when cultures were Si-limited. Nominal Al additions of 20 μmol·L^?1 reduced chlorophyll a concentration and IVF values at higher pH, but all other biomass and chemical parameters remained constant at steady state. The combined efects of Al and reduced pH were more severe than either stress alone, inducing culture washout at pH 4.8. Short-term Si uptake experiments performed at pH 6 showed that Al influenced Michaelis-Menten parameter estimates. Half-saturation (K_s and maximum uptake rate (V_m) constants increased approximately 8- and 2-fold in the presence of Al, respectively, but this difference was only significant for V_m. Similar to previously observed effects of Al on cell morphology in A. ralfsii, Si uptake kinetics were more sensitive to Al additions than to Silimited growth per se.     

PHOTOSYNTHETIC CARBON METABOLISM IN ENTEROMORPHA COMPRESSA (CHLOROPHYTA)1

The intertidal macroalga Enteromorpha compressa showed the ability to use HCO₃^? as an exogenous inorganic carbon (Ci) source for photosynthesis. However, although the natural seawater concentration of this carbon form was saturating, additional CO₂ above ambient Ci levels doubled net photosynthetic rates. Therefore, the productivity of this alga, when submerged, is likely to be limited by Ci. When plants were exposed to air, photosynthetic rates saturated at air-levels of CO₂ during mild desiccation. Based on carbon fixing enzyme activities and Ci pulsechase incorporation patterns, it was found that Enteromorpha is a C₃ plant. However, this alga did not show O₂ inhibited photosynthetic rates at natural seawater Ci conditions. It is suggested that such a C₄- like gas exchange response is due to the HCO₃^? utilization system concentrating CO₂ intracellularly, thus alleviating apparent photorespiration.     

A MORPHOMETRIC STUDY OF LEAD AND COPPER EFFECTS ON DIATOMA TENUE VAR. ELONGATUM (BACILLARIOPHYTA)1

Polyphosphate bodies containing lead were induced in laboratory cultures of Diatoma tenue var. elongatum Lyngb. by the addition of phosphorus and 0.05 μg-atoms/l Pb to P deficient medium. Morphometric analysis of cells exposed to Pb showed a significant decrease in number of mitochondria with a concomitant increase in their volume and an increase in membranous organelles in the vacuole compared to phosphorus starved and phosphorus sufficient controls. Exposure of cultures to 0.08 μg-atoms/l copper resulted in reduction of the number of polyphosphate bodies formed during luxury uptake but no other significant morphological changes in cellular organelles. Ecological implications of the interactions between nutrients and low level trace metal contamination are discussed.     

DETERMINATION OF RNA AND DNA CONCENTRATIONS IN NATURAL PLANKTON SAMPLES USING THIAZOLE ORANGE IN COMBINATION WITH DNASE AND RNASE DIGESTIONS1

A fluorometric technique, based on the combination of RNase and DNase incubation with the use of thiazole orange (RNase/DNase method), was investigated to determine DNA and RNA concentrations in marine plankton. Tests were performed to optimize both RNase and DNase assay conditions. The RNase assay should be conducted at 37° C for 20 min with 0.5 μg·mL^?1 of DNase-free RNase. An incubation at 25° C for 20 min with 10 units ·mL^-1 of RNase-free DNase were the optimal conditions required for DNA digestion by DNase. The detection limits in terms of minimum biomass for reliable measurements of DNA and RNA were 7.5 and 10 μg of protein · (mL assay)^?1, respectively. RNA and DNA concentration were estimated in oligotrophic water samples using the RNase/DNase and other available methods (e.g. a double fluorochrome method). The different techniques provided similar DNA estimations. However, the RNase/DNase method provided the highest sensitivity and a low variability for the estimation of RNA.