The Adaptation of Plankton Algae

The various aspects of the adaptation of plankton algae lo light and temperature are discussed. The shape of a light intensity-photosynthesis curve is shown to be an important means of describing the physiological adjustment of an algal population. If the algae are not exposed to adverse influences such as poisons, pronounced nutrient deficiency or light shocks, the rate of real photosynthesis per mg chlorophyll a at 1 Klux (incandescent light) should be about 0.4–0.6 mg C/hour. Hence this rate presents an excellent means of judging the quality of experiments. Experiments are presented where Chlorella pyrenoidosa was adapted to light intensities between 0.32 klux and 21 Klux. This alga adapts to different light intensities by varying the amount of pigments per cell. Algae grown at 1 Klux have about 10 times more chlorophyll per cell than those grown at 21 klux. Other species of algae—but by no means all—are shown to behave in the same way. The problem of algal resistance to photo-oxidation at high light intensities is discussed. Adaplation is shown to he one of the mechanisms which make the algae resistent. “Chlorophyll inactivation” is another. Experiments with the diatom Skeletonema costatum concerning adaptation to different temperatures have been performed. The fact that the alga has essentially the same rate of photosynthesis per cell at all light intensities at 20°C and 7°C, may be attributed to an increase of all the enzymes at the low temperature. The amount of protein per cell was twice as high at 7°C as at 20°C.     

INFLUENCE OF ULTRAVIOLET RADIATION ON GROWTH AND PHOTOSYNTHESIS OF TWO COLD OCEAN DIATOMS1

The influence of chronic exposure to UV-B and UV-A radiation on growth and photosynthesis of two polar marine diatoms (Pseudonitzschia seriata and Nitzschia sp.) was investigated in cultures exposed to moderate photon fluences for 3–7 days. Population growth rates were diminished 50% by UV-B. Fluorescence induction kinetics of photo-system II (PSII) revealed that UV-B caused lower F_v/F_m ratios and half-rise times, indicating damage to the reaction center of PSII and to related elements of the photosynthetic electron transport chain. Carbon assimilation rates per cell and per chlorophyll a were nonetheless highest for UV-B—exposed populations, which also had the highest chlorophyll a content per cell. The UV-B—exposed cells were, however, more vulnerable to visible light-induced photoinhibition. Exposure to UV-A in the absence of UV-B had little effect on growth, fluorescence induction of PSII, or chlorophyll a contents but did have some inhibitory effects on carbon assimilation per chlorophyll a and per cell. The increased photosynthetic capacity of UV-B-exposed cells suggested some ability to compensate for damage to the photosynthetic apparatus.     

Bioenergetic analysis of mixotrophic growth in Chlorella vulgaris and Scenedesmus acutus

The specific growth rate of Chlorella vulgaris in the presence of glucose (mixotroph) was always larger than that in autotroph when the light intensity was less than 10 klux. However, Scenedesmus acutus behaved differently, i.e., when the light intensity was more than 6 klux, the specific growth rate in mixotroph became smaller than that in autotroph. Cellular contents of chlorophyll a and b in Scenedesmus acutus that deteriorated more markedly in mixotroph than those of Chlorella vulgaris could account for these different growth behaviors. In other words, mechanisms relevant to the photosynthesis and the oxidative phosphorylation of glucose seem to function independently with respect to Chlorella Vulugaris.     

Photosynthetic Activity during the Life Cycle of Synchronous Skeletonema Cells

A culture of Skeletonema costatum grown at a light intensity of 3 klux and at 20°C was synchronized in diurnally intermittent illumination of 12 hour light and 12 hour dark. The culture was hardly fully synchronous as the cell division period lasted about 9 hours. The cell division started in the middle of the light period. The concentration of the pigments: chlorophyll a, chlorophyll 6 and fucoxanthin and the rate of light-saturated photosynthesis were followed every hour during the 24 hour period. Both the concentration of pigments and the photosynthetic activity showed a rhythmical variation. The concentration per cell of all three pigments examined increased during the development of the cells and decreased automatically during the period of cell division. An increase in the pigment concentration was found only in the light period. The rate of light-saturated photosynthesis calculated per unit of cell number increased during the cell development and decreased during the division period. The increase in the photosynthetic activity at light-saturation started about 4 hours after the end of cell division, which was 4 hours before the light was turned on while the increase in the concentration of chlorophyll a first started 1–2 hours after this moment. The variation in photosynthetic activity was compared with that found by other workers. The results found with Chlorella ellipsoidea by Japanese scientists (Nihci et al.) was explained as an inhibition phenomenon because the cells were not adapted to the experimental conditions.     

KINETICS OF CHLOROPHYLL a AND PLASTOQUINONE A: CHANGES IN RESPONSE TO LIGHT INTENSITY1

The thermophilic blue-green Synechococcus lividus Y52 was grown at several light intensities between 200 and 2400 ft-c. A 3.4-fold change of cellular chlorophyll (Chl) a content was found. The concentration of Plastoquinone A (PQA) per Chl a varied by a factor of 7, whereas PQA per cell varied by 1.4. Adaptation to light intensity appeared to occur through changes in size of the light-gathering antenna of chlorophyll and phycocyanin while the concentration of PQA remained nearly constant.     

EFFECTS OF IRON DEFICIENCY ON ISOCHRYSIS GALBANA (CHRYSOPHYCEAE) AND PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE)1

Cultures of Isochrysis galbana Parks and Phaeodactylum tricornutum Bohlin were grown in iron-limited chemostats. With increasing iron deficiency, photosynthetic rate per cell and assimilation number decreased. The pattern of photosynthesis was also altered; in Fe deficient cells the proportion of ¹⁴C fixed in glycine and serine decreased with an accompanying increase into alanine after 3 min assimilation. Although there was no significant effect of Fe deficiency on the proportion of ¹⁴C incorporated into total amino acids and amides, the percentage of total ¹⁴C fixed in protein increased with increasing Fe deficiency. Cellular levels of chlorophyll a, carotenoids, cytochromes and protein also decreased with increasing Fe deficiency. However, the reduction in chlorophyll a/cell was not as great as that of cytochrorne f₁ and Fe deficient cells therefore showed a marked increase in chlorophyll a:cytochrorne f₁ ratio.     

Photosynthetic and stomatal conductance responses to acid mist of red spruce seedlings

Abstract Two-year-old seedlings of Picea rubens, growing in open-top chambers in Scotland were treated twice weekly from July 1987 to December 1987, with mist containing ammonium sulphate and nitric acid at a pH of either 2.5 or 5.0. The response of photosynthesis and stomatal conductance to light flux density and carbon dioxide concentration were measured in March 1989. Leaf chlorophyll a and b contents were also measured. Acid mist (pH 2.5) resulted in several significant changes. First, both the rate of light saturated photosynthesis (A_max) and CO₂- saturated rate of photosynthesis (J) were substantially increased, when expressed per unit leaf area. Second, the apparent quantum yield and chlorophylls a and b content increased. Third, as a consequence of the greater chlorophyll content of the leaves treated with acid mist, the rate of A_max, and J, expressed per unit chlorophyll, was substantially reduced in pH 2.5 treated branches. Stomatal conductance was enhanced at all but the highest light flux densities, and was independent of the CO₂ concentration, remaining high for all values of CO₂ concentration used. These results show that acid mist caused a number of responses in the gas exchange and photosynthetic properties of red spruce.     

Effect of nitrate-nitrogen limitation on photosynthesis of the diatom Phaeodactylum tricornutum Bohlin (Bacillariophyceae)

Abstract Nitrate limited growth of the diatom Phaeodactylum tricornutum in chemostat cultures produced marked changes in biochemical composition and a six-fold reduction in the specific growth rate. This was associated with a reduction in the carbon and chlorophyll a specific light saturated rates, with little effect on light limited photosynthesis. Variations in specific growth rate were quantitatively related to carbon specific net photosynthesis and maximum chlorophyll a specific light saturated rates were positively correlated with cell nitrogen contents. The correlation between nitrogen content and photosynthesis for P. tricornutum and the differential effect of nitrogen supply on the light response curve of photosynthesis is qualitatively and quantitatively similar to published results for terrestrial vascular plants. There was little change in the photon (quantum) yield of photosynthesis which was not significantly different from 0.125mol O₂ mol photon^-1 the theoretical upper limit based on the Z scheme, even under severe nitrate deficiency. The capacity to maintain a high photon yield under nitrate limitation is discussed in relation to the nitrogen requirements of the stromal and membrane components of the photosynthetic apparatus.     

Abstracts of papers read at the winter meeting at the university of Newcastle Upon Tyne

Young plants of Laminaria hyperborea collected from the field were grown for 2·5–4 weeks in blue, green, red and white (simulated underwater) light fields at 5, 20 and 100 μmol m^-2s^-1. The absolute concentrations of all pigments showed little variation with irradiance in green and white light, but decreased in high irradiances of red and blue light. The ratio of fucoxanthin to chlorophyll a also increased in the latter treatments, as did the chlorophyll c:a ratio in bright red light. There was little difference in the action spectrum for photosynthesis between the different light qualities at any one irradiance, but the action spectra for plants grown at 100 μmol m^-2s^-1 showed deeper troughs and higher peaks than those for plants grown at lower irradiances. Gross photosynthesis per unit of thallus area at 10 μmol m^-2s^-1 decreased in plants with low total pigment concentrations, but the photosynthesis per unit of pigment concentration increased. This suggestion of self-shading of pigment molecules within the algal thalli was supported by a flattening of the action spectrum in plants with higher chlorophyll a contents. The variations observed between the action spectra for different plants could thus be attributed to the decrease in pigment content at high irradiances, and not to the light quality in which the plants were grown.     

Phytoplankton primary production in a eutrophic cooling water pond

The seasonal variation of phytoplankton photosynthesis was measured with ¹⁴C-method in a warmed ice-free pond in central Finland. Simultaneously with in situ measurements the photosynthesis was also measured in an incubator with different water temperatures and constant light (ca. 16 W m^–2). The total annual photosynthesis was 57.2 C m^–2 a^–1. The portion of the winter and spring production of the annual photosynthesis was 18.4%, that of the autumn production ws 17.4%. Thus 64.3% of the total annual phytoplankton photosynthesis occurred in the three summer months. The range of the daily integrated photosynthesis per unit area was 1.9—563 mg C m^–2d^–1. The photosynthetic rate per unit chlorophyll a varied in situ from 0.94 to 33.1 mg C (mg chl. a)^–1 d^–1. The highest value was measured in the beginning of July and the lowest in mid-January. The photosynthetic rate increased in situ exponentially with increasing water temperature. In the incubator the highest photosynthetic rate values were also found in July and August (at+20 °C) when the phytoplankton population was increasing and the minimum values occurred after every diatom maximum both in spring and autumn. Light was a limiting factor for photosynthesis from September to Mid-January, low water temperature was a limiting factor from late January through May. The efficiency of the photosynthesis varied between 0.1 and 0.7% of P.A.R. According to the incubator experiments the Q₁₀ values for the photosynthesis were 2.45 and 2.44 for the winter population between 1 and 10° C and for the summer population between 5 and 15° C, respectively, but the Q₁₀ values decrease at the higher temperatures. The main effect of the warm effluents on the yearly photosynthesis was the increase of production in spring months due to the lack of ice cover. However, the increase of total annual phytoplankton photosynthesis was only ca. 10–15%, because the water temperature was during the spring months below 10° C.     

Microscale Vertical Profiles of N2 Fixation, Photosynthesis, O2, Chlorophyll a, and Light in a Cyanobacterial Assemblage

Profiles of ¹⁵N₂ fixation, O₂ production (gross photosynthesis), O₂ concentration, chlorophyll a concentration, and photon fluence rates were measured with 50-μm resolution in colonies of the heterocyst-forming cyanobacterium Nostoc parmelioides. Microelectrode measurements were made after 20 h of incubation under ¹⁵N₂ gas. Colonies were frozen, and 50-μm sections were prepared by using a freezing microtome and analyzed for ¹⁵N enrichment and chlorophyll a concentration. Colonies exhibited steep spatial gradients in rates of gross photosynthesis, O₂ concentration, and irradiance, with the highest values generally occurring at the surface. O₂ concentration, photosynthesis, and irradiance all showed positive correlations, but chlorophyll a concentrations varied independently of photosynthesis and irradiance. Forty-four percent of the variation in ¹⁵N incorporation was explained by gross photosynthesis (a positive correlation) when incorporation of ¹⁵N was expressed per unit of biomass (chlorophyll a).     

The interaction of light intensity and DDT concentration upon the marine diatom,Nitzschia delicatissima cleve

Summary The effects of p, p-DDT were determined on photosynthesis and chlorophyll a content in the marine diatom Nitzschia delicatissima Cleve at four light intensities. A consistent reduction in carbon fixation and chlorophyll a per cell over controls in a 24-hour period was observed with increasing DDT concentration between 9.4 ppb and 1000 ppb. The maximum reductions of carbon uptake, chlorophyll a and carbon/chlorophyll a uptake per cell occurred at the highest light intensities. Carbon fixation per cell was reduced by as much as 94% in water containing an initial DDT concentration of 100 ppb, and chlorophyll a per cell by as much as 86% in 220 ppb DDT. Above 100 ppb, further decreases of carbon fixation and chlorophyll a per cell were not observed. Distortion of the chloroplasts in the cells exposed to DDT was also observed at the lowest concentration of DDT used. At 1000 ppb, chloroplasts were totally destroyed within 24 hours.

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Zusammenfassung Die Wirkung von p, p-DDT auf Photosynthese und Chlorophyll a Gehalt der Meeresdiatomee Nitschia delicatissima Cleve wurde untersucht unter vier Lichtintensitäten. Bei DDT Konzentrationen, steigend von 9,4 ppb bis 1000 ppb, wurde eine fortschreitende Reduktion der Kohlenstoff bindung und des Chlorophyll a Gehaltes pro Zelle gefunden, wobei die höchtse Lichtintensität die stärkste Reduktion, sowie auch die niedrigste Kohlenstoff/Chlorophyll a Aufnahme pro Zelle zeigte. In Wasser mit anfänglichem DDT Gehalt von 100 ppb, wurde die Kohlenstoff bindung pro Zelle 94% reduziert und beim DDT Gehalt von 220 ppb, wurde der Chlorophyll a Gehalt mit 86% reduziert. Bei Konzentrationen über 100 ppb, fielen Kohlenstoff bindung und Chlorophyll a Gehalt pro Zelle nicht weiter ab.Schädigungen der Chloroplasten in der Zelle wurden schon bei den niedrigsten DDT Gehalten festgestelt. Bei 100 ppb wurden die Chloroplasten innerhalb 24 Stunden völlig zerstört.

     

Photooxidative damage to the cyanobacterium Spirulina platensis mediated by singlet oxygen

Experiments on the specific growth rate, bleaching of pigments, O₂ evolution, lipid peroxidation, and loss of sulfhydryl (-SH) content in response to the varying light intensities (2–28 W/m²) suggested that photodamage to the Spirulina cells was maximum at or beyond the photosynthesis saturating light intensity (12 W/m²). However, photobleaching of the chlorophyll a was relatively higher than carotenoid. The results on the N,N-dimethyl-p-nitrosoaniline (RNO) bleaching in the presence of oxygen radical quenchers exhibited maximum effect of sodium azide and indicated about the generation of singlet oxygen. The chlorophyll a-sensitized production of singlet oxygen by a type II reaction cannot be ruled out because of maximum oxidative damage to the cells at or beyond the photosynthesis saturating light intensity, i.e., 12 W/m², when the availability of triplet chlorophyll is maximum.     

Cyclic variations of photosynthetic activity under nitrogen fixing conditions in Synchococcus RF-1

When nitrogen fixing cell cultures of Synechococcus RF-1 were subjected to an alternating lightdark regime (12 h:12 h), a cyclic decrease in the photosynthetic oxygen evolution potential was observed during the dark periods. This rhythm of net photosynthesis rate was maintained for at least two days after transition to continuous light. The decrease in net photosynthesis was accompanied by a stimulation of dark respiration. However, the magnitude of oxygen uptake was considerably smaller than the observed decrease in oxygen evolution. The photosynthetic activity of cells taken from the dark period was characterized by (i) a significantly lower quantum yield and (ii) a strong reduction in the light-saturated rate of photosynthesis. Growing the cultures on nitrate or under continuous light completely suppressed this rhythm. Protein synthesis was not necessary for the recovery of the light-saturated rate of photosynthesis during the light period. The cellular content of chlorophyll a and of phycobiliproteins did not vary between light and dark period, indicating that quantitative changes in the composition of the photosynthetic apparatus are not the basis for the observed oscillations. Regulatory modifications of the photosynthetic efficiency are proposed as an adaptation mechanism to adjust the intracellular oxygen concentration to the needs for nitrogenase activity.Abbreviation Chl chlorophyll     

Influence of low temperatures on the growth and photosynthetic activity of industrial chicory, <Emphasis Type="Italic">Cichorium intybus</Emphasis> L. partim

The cold stress effect on early vigour and photosynthesis efficiency was evaluated for five industrial chicory varieties with contrasting early vigour. The relationships between the growth and physiological parameters were assessed. The varieties were examined at three growth temperatures: 16 (reference), 8 (intermediate) and 4 °C (stress). The effect was measured using physiological processes (growth, photosynthesis, chlorophyll a fluorescence), and pigment content. The analysis of the measured growth parameters (dry leaf and root mass, and leaf area) indicated that temperature had a significant effect on the varieties, but the overall reaction of the varieties was similar with lowering temperatures. The photosynthesis and chlorophyll a fluorescence measurements revealed significant changes for the photosynthesis (maximum net photosynthesis, quantum efficiency, light compensation point and dark respiration) and chlorophyll a fluorescence parameters (photochemical and non-photochemical quenching) with lowering temperatures for Hera and Eva, two extremes in youth growth. No significant differences could be found between the extremes for the different temperatures. The pigment content analysis revealed significant differences at 4 °C in contrast to 16 and 8 °C, especially for the xanthophyll/carotenoid pool, suggesting a protective role. Subsequently, the relationship between the physiological processes was evaluated using principal component analysis. At 4 °C, 2 principal components were detected with high discriminating power for the varieties and similar classification of the varieties as determined in the growth analysis. This provides a preview on the possible relationships between photosynthesis and growth for industrial chicory at low temperatures.     

Growth and photosynthesis of pea plants under different iron supply

Soil conditions, leading to iron deficiency or toxicity, are widespread in nature. Our objective was to study the effect of Fe supply, ranging from complete deficiency to excess, on growth and on some photosynthetic indices of pea plants. Both iron deficiency and toxicity decreased shoot and root growth. Complete deficiency resulted in a lower shoot/root ratio and a higher content of dry biomass per unit of fresh biomass in roots, while iron excess led to higher content of dry biomass per unit of fresh biomass in shoot. Complete deficiency was also characterized by low chlorophyll and carotenoid content, elevated ratios of chlorophyll a/chlorophyll b and carotenoids/chlorophylls, a drop of photosynthetic rate per leaf area, and an increase of photosynthetic rate per chlorophyll. The stomatal resistance substantially increased, while the transpiration rate decreased. Smaller changes in stomatal resistance and transpiration rate, but not in photosynthetic rate per leaf area, were found under partial iron deficiency and under excess of iron. In the first case, the chlorophyll content decreased, while in the second it increased. The maximum efficiency of photosystem II was unaffected by iron supply. Even when no genetic or experimental differences existed, changes in growth, pigment content and photosynthesis due to variation of Fe supply depended on the type and severity of the imposed stress, as well as on the studied parameter. A combination of indices described better the effect of iron supply, especially when small differences were characterized.     

Relation between pigment content and photosynthetic characteristics in a blue-green algae

1. The blue-green alga Anacystis nidulans was cultured under steady state conditions at 25 and 39°C. and under several different light intensities to give five different types of cells. 2. Cells were submitted to pigment analysis based upon acetone extracts and aqueous extracts obtained by sonic disintegration. The different cell types show a threefold range of chlorophyll content and a fourfold range of phycocyanin content with only minor changes in the chlorophyll/phycocyanin ratio. Cells of highest pigment content were estimated to contain 2.8 per cent chlorophyll a and 24 per cent phycocyanin, the latter on a total chromoproteid basis. 3. Light intensity curves of photosynthesis were obtained for each of the cell types at 25 and at 39°C. The slopes of the light-limited regions of the curves are approximately linear functions of chlorophyll and phycocyanin contents. Maximum light-saturated rates of photosynthesis at 25 and 39° show no simple relation to pigment content.     

TEMPERATURE DEPENDENCE OF UV RADIATION EFFECTS ON ANTARCTIC CYANOBACTERIA

The mat-forming cyanobacterium Phormidium murrayi West and West isolated from a meltwater pond on the McMurdo Ice Shelf was grown in unialgal batch cultures to evaluate the temperature dependence of ultraviolet radiation (UVR) effects on pigment composition, growth rate, and photosynthetic characteristics. Chlorophyll a concentrations per unit biomass were generally reduced in cells grown under UVR (low UV-A plus UV-B). In vivo absorbance spectra showed that the carotenoid/chlorophyll a ratio increased as a function of photosynthetically available radiation (PAR) and UVR exposure and varied inversely with temperature. Ultraviolet inhibition of growth (percentage reduction of μ_max at each temperature) increased linearly with decreasing temperature, consistent with the hypothesis that net inhibition represents the balance between temperature-independent photochemical damage and temperature-dependent biosynthetic repair. There was no significant effect of UVR on photosynthesis over the first hour of exposure, but significant UV inhibition was observed after 5 days. Unlike growth, however, there was no apparent effect of temperature on the magnitude of UV inhibition of photosynthesis. These results imply that assays of UVR effects on photosynthesis are not an accurate guide to growth responses and that low ambient temperatures can have a major influence on the UV sensitivity of polar organisms. In a set of assays at 20° C (preacclimation under 300 μmol photons·m^?2·s^?1 and 20° C), growth was strongly depressed by UVR over the first day of exposure but then gradually increased over the subsequent 4 days, approaching the growth rates in the minus UVR control. This evidence of acquired tolerance indicates that the damaging effects of UVR will be most severe in environments where there is a mismatch between the timescale of change in exposure and the timescale of UV acclimation.     

The use of dialysis culture in a study of chlorophyll budget in a brackish lagoon,Japan

Growth rates of the entire phytoplankton community of a brackish lagoon in northeastern Japan were estimated by measuring increasing chlorophyll a content in dialysis bags during the summer and early autumn of 1986. The chlorophyll a contents of lagoon water fluctuated between 20 and 200 mg m^–3. At lower densities of phytoplankton (20–50 mg chl. a m^–3), growth rates (the rate of increase of chlorophyll a) exceeded 1 turnover per day, while at higher densities (more than 50 mg chl. a m^–3), the growth rate decreased rapidly. Tidal exchanges of chlorophyll a showed net exports of chlorophyll a from the lagoon to adjacent waters. The exchange rate of chlorophyll a was estimated to be 0.65 d^–1. At about 140 mg m^–3 of chlorophyll a concentration, the increase of chlorophyll in the lagoon water compensated for tidal export. Only a small proportion of primary production was consumed by zooplankton in the lagoon. There were also net exports of ammonium and phosphate from the lagoon. Nutrient flux from sediment exceeded the phytoplankton requirement and was the major source of the ammonium and phosphate exports from the lagoon. The low inorganic N/P atom supply ratio in the lagoon suggests that nitrogen is a major nutrient limiting phytoplankton growth.     

Effects of organic carbon sources on growth, photosynthesis, and respiration of Phaeodactylum tricornutum

The growth, photosynthesis, and respiration of the marine diatom Phaeodactylum tricornutum were examined under photoautotrophic and mixotrophic conditions. 100 mM glycerol, acetate, and glucose significantly increased specific growth rate, and mixotrophic growth achieved higher biomass concentrations. Under mixotrophic conditions, respiration rate (R _d) and light compensation irradiance (I _c) were significantly higher, but net maximum photosynthetic O₂ evolution rate (P _m) and saturation irradiance (I _k) were depressed. Organic carbon sources decreased the cell photosynthetic pigment content and chlorophyll a to c ratio, but with a higher carotenoid to chlorophyll a ratio. Ratios of variable to maximum chlorophyll fluorescence (F _v/F _m) and 77 K fluorescence spectra of mixotrophic cells indicated a reduced photochemical efficiency of photosystem II. The results were accompanied by lower electron transport rate. Therefore, organic carbon sources reduced the photosynthesis efficiency, and the enhancement of biomass of P. tricornutum implied that organic carbon sources had more pronounced effects on respiration than on photosynthesis.