Distribution of Chlorophyll between the Two Photoreactions in Photosynthesis of the Blue-Green Alga Anacystis nidulans Grown at Two Different Light Intensities

Anacystis nidulans was grown in white light of two different intensities, 7 and 50 W ·m^?2. The in vivo pigmentations of the two cultures were compared. The ratio phycocyanin/chlorophyll a was 0.96 for cells grown at 7 W · m^?2 and 0.37 for cells grown at 50 W · m^?2. Phycocyanin-free photosynthetic lamellae (PSI-particles) were prepared, using French press treatment and fractionated centrifugation. Algae grown in the irradiance of 50 W · m^?2 showed a chlorophyll a/P700 ratio of 260, while algae grown at 7 W · m^?2 had a value of 140. Corresponding PSI-particles showed values of 122 and 109 respectively. Light-induced absorption difference spectra measured between 400–450nm indicated different ratios between cytochrome f and P700 in the two algal cultures. Enhancement studies of photosynthetic oxygen evolution were carried out. When a background beam of 691 nm was superimposed upon a signal beam of 625 nm, good enhancement was observed for both cultures. With the wavelengths 675 and 691 nm together a pronounced enhancement could be detected only in algae grown at the higher light level. Absorption spectra recorded on whole cells at 77°K revealed a small shift of the main red chlorophyll a absorption peak caused by light intensity. It is proposed that the reduction of the phycocyanin/chlorophyll a ratio in high light-grown cells is accompanied by an increased energy distribution by chlorophyll a into PSII.     

RESPONSE OF PROROCENTRUM MARIAE-LEBOURIAE (DINOPHYCEAE) TO LIGHT OF DIFFERENT SPECTRAL QUALITIES AND IRRADIANCES: GROWTH AND PIGMENTATION1

Growth and pigment concentrations of the, estuarine dinoflagellate, Prorocentrum mariae-lebouriae (Parke and Ballantine) comb. nov., were measured in cultures grown in white, blue, green and red radiation at three different irradiances. White irradiances (400–800 nm) were 13.4, 4.0 and 1.8 W · m^?2 with photon flux densities of 58.7 ± 3.5, 17.4 ± 0.6 and 7.8 ± 0.3 μM quanta · m^?2· s^?1, respectively. All other spectral qualities had the same photon flux densities. Concentrations of chlorophyll a and chlorophyll c were inversely related to irradiance. A decrease of 7- to 8-fold in photon flux density resulted in a 2-fold increase in chlorophyll a and c and a 1.6- to 2.4-fold increase in both peridinin and total carotenoid concentrations. Cells grown in green light contained 22 to 32% more peridinin per cell and exhibited 10 to 16% higher peridinin to chlorophyll a ratios than cells grown in white light. Growth decreased as a function of irradiance in white, green and red light grown cells but was the same at all blue light irradiances. Maximum growth rates occurred at 8 μM quanta · m^?2· s^?1 in blue light, while in red and white light maximum growth rates occurred at considerably higher photon flux densities (24 to 32 μM quanta · m^?2· s^?1). The fastest growth rates occurred in blue and red radiation. White radiation producing maximum growth was only as effective as red and blue light when the photon flux density in either the red or blue portion of the white light spectrum was equivalent to that of a red or of blue light treatment which produced maximum growth rates. These differences in growth and pigmentation indicate that P. mariae-lebouriae responds to the spectral quality under which it is grown.     

Positive effects of continuous low nitrate levels on growth and photosynthesis of Alexandrium tamarense (Gonyaulacales, Dinophyceae)

The growth and photosynthesis of Alexandrium tamarense (Lebour) Balech in different nutrient conditions were investigated. Low nitrate level (0.0882 mmol/L) resulted in the highest average growth rate from day 0 to day 10 (4.58 × 10² cells mL^?1 d^?1), but the lowest cell yield (5420 cells mL^?1) in three nitrate level cultures. High nitrate‐grown cells showed lower levels of chlorophyll a‐specific and cell‐specific light‐saturated photosynthetic rate (P_m^{chl a} and P_m^cell), dark respiration rate (R_d^chla and R_d^cell) and chlorophyll a‐specific apparent photosynthetic efficiency (α^chla) than was seen for low nitrate‐grown cells; whereas the cells became light saturated at higher irradiance at low nitrate condition. When cultures at low nitrate were supplemented with nitrate at 0.7938 mmol/L in late exponential growth phase, or with nitrate at 0.7938 mmol/L and phosphate at 0.072 mmol/L in stationary growth phase, the cell yield was drastically enhanced, a 7–9 times increase compared with non‐supplemented control culture, achieving 43 540 cells mL^?1 and 52 300 cells mL^?1, respectively; however, supplementation with nitrate in the stationary growth phase or with nitrate and phosphate in the late exponential growth phase increased the cell yield by no more than 2 times. The results suggested that continuous low level of nitrate with sufficient supply of phosphate may facilitate the growth of A. tamarense.     

LIGHT ACCLIMATION IN PORPHYRIDIUM PURPUREUM (RHODOPHYTA): GROWTH,PHOTOSYNTHESIS, AND PHYCOBILISOMES1

Acclimation to three photon flux densities (10, 35, 180 μE.m^?2.s^?1) was determined in laboratory cultures of Porphyridium purpureum Bory, Drew and Ross. Cultures grown at low, medium, and high PPFDs had compensation points of <3, 6, and 20 μE-m^?2.s^?1, respectively, and saturating irradiances in the initial log phase of 90, 115, 175 μE.m^?2.s^?1 and up to 240 μE.m^?2.s^?1 in late log phase. High light cells had the smallest photosynthetic unit size (phycobiliproteins plus chlorophyll), the highest photosynthetic capacity, and the highest growth rates. Photosystem I reaction centers (P700) per cell remained proportional to chlorophyll at ca. 110 chl / P700. However, phycobiliprotein content decreased as did the phycobilisome number (ca. 50%) in high light cells, where as the phycobilisome size remained the same as in medium and low light cells. We concluded that acclimation of this red alga to varied PPFDs was manifested by the plasticity of the photosystem II antennae with little, if any, effect noted on photosystem I.     

THE WAVELENGTH DEPENDENCE OF MASSIVE CAROTENE SYNTHESIS IN DUNALIELLA BARDAWIL (CHLOROPHYCEAE)1

Dunaliella bardawil Ben-Amotz & Avron accumulates high concentrations of β-carotene when grown under high light intensity. The β-carotene is composed mainly of 9-cis and all-trans β-carotene. Accumulation of β-carotene and an increase in the ratio of the 9-cis to the all-trans isomer are strongly dependent on the light intensity under which the algae are cultivated but are independent of light quality within the photosynthetically active radiation range. Cells grown under continuous red (>645 nm) or white light of 500 W·m^?2 reach a value of about 32 pg β-carotene·cell^?1 and a ratio of 9-cis to all-trans β-carotene of around 2, whereas cells grown under low red or white light intensity of 25 W·m^?2 contain about 3 pg·cell^?1 and a ratio of isomers of around 0.3.     

Effects of growth irradiance on the photosynthetic action spectra of the marine dinoflagellate,Glenodinium sp.

Summary Whole cell absorption curves of the marine dinoflagellate Glenodinium sp., cultured at irradiances of 250W/cm² (low light) and 2500W/cm² (high light), were measured and their difference spectrum determined. Absorption by low light grown cells exceeded that of high light grown cells throughout the visible spectrum by a factor which ranged from 2 to 4. The difference spectrum supported the view that increased pigmentation, resulting from low light conditions, was largely due to an increase in cell content of a peridinin-chlorophyll a-protein (PCP) and an unidentified chlorophyll a component of the chloroplast membrane. Photosynthetic action spectrum measurements indicated that chlorophyll a, peridinin, and very likely chlorophyll c, were effective light-harvesting pigments for photosynthesis in both high and low light grown cultures of Glenodinium sp. Comparison of action spectra and absorption spectra suggested that low light grown cells selectively increased cellular absorption in the 480 nm to 560 nm region, and effectively utilized this spectral region for the promotion of oxygen evolution.Abbreviations PCP peridinin-chlorophyll a-protein - SIO (F.T. Haxo) Scripps Institution of Oceanography collection     

INORGANIC CARBON REPLETION DISRUPTS PHOTOSYNTHETIC ACCLIMATION TO LOW TEMPERATURE IN THE CYANOBACTERIUM SYNECHOCOCCUS ELONGATUS1

Acclimation of cyanobacteria to ambient fluctuations in inorganic carbon (Ci) and temperature requires reorganization of the major protein complexes involved in photosynthesis. We grew cultures of the picoplanktonic cyanobacterium Synechococcus elongatus Naegeli across most of its range of tolerable temperatures from 23 to 35°C at both low (<0.1 mM) and high Ci (approximately 4 mM). Over that range of temperatures, the chl‐based doubling time did not differ between low and high Ci grown cells but did increase with decreasing temperature. Cells grown at 23°C high Ci showed an elongated morphology, which was not present in 23°C low Ci cells nor at 35°C high and low Ci. Furthermore, 23°C high Ci cells showed premature senescence and death compared with all other treatments. Phycocyanin per cell was greater in high Ci grown cells at all temperatures but showed a characteristic decrease with decreasing temperature. Functional PSII determination showed that 23°C high Ci cells had 1.5 × 10⁵ PSII·cell^–1 compared with only 6.9 × 10⁴ PSII·cell^–1 for 23°C low Ci. The 35°C high and low Ci cells had 7.7 × 10⁴ and 6.4 × 10⁴ PSII·cell^–1, respectively. These data were supported by immunoblot determinations of PsbA content·cell^–1. As a result of their high PSII·cell^–1, 23°C high Ci cells generated more reductant from PSII than could be accommodated by downstream assimilative metabolism, resulting in early senescence and death of 23°C high Ci cells, probably as a result of the generation of reactive byproducts of electron transport.     

Characterization of the Carotenoidless Strain of Scenedesmus obliquus,Mutant C-6E,a Living Photosystem I Model*

When grown heterotrophically in the dark on enriched culture medium, the pigment-deficient strain of Scenedesmus obliquus, mutant C-6E, is uniquely characterized by a complete deficiency in carotenoids and chlorophyll b while retaining a low level of chlorophyll a which is exclusively utilized in photosystem I-type reactions. The strain lacks photosystem II activity but exhibits all PS-I reactions tested, including P700 redox reactions, photoreduction of CO₂ with hydrogen as electron donor, and O₂ uptake following methyl viologen reduction. The mutant contains 10 times more P700 per chlorophyll than the wild type and develops the pigment-protein complex of PS-I, CP-I. The action spectrum for methyl viologen reduction compares favorable to the low temperature absorption spectrum of whole cells. Both the chlorophyll fluorescence excitation and emission spectra of pigment-protein complexes derived from cells of C-6E show patterns typical of PS-I. The strain lacks the LHCs and CP-II as well as their respective apoproteins. The absence of carotenoids appears to prevent the development of the normal variety of pigment-protein complexes and the accumulation of Chl b. This inability is also expressed by the presence of only single stranded thylakoid membranes in the chloroplast of C-6E. When heterotrophically grown cells of this mutant are exposed to white light of 8 or 22 W m^?2, 50% of its chlorophyll is lost by photooxidation within 4 or 1.5 hours, respectively.     

Photosynthetic characteristics of Dunaliella salina (Chlorophyceae,Dunaliellales) in relation to β-carotene content

Photosynthetic characteristics of Dunaliella salina with high (red form) and low β-carotene (green form) concentrations were studied. D. salina growing in brine saltworks exhibited a high level of β-carotene (15 pg cell⁻¹). The rate of oxygen evolution as a function of irradiance was higher in the red than in the green form (on chlorophyll basis). Photosynthetic inhibition of the green form was observed above 500 μmol m⁻² s⁻¹. The red form appeared more resistant to high irradiance and no inhibition in O₂ evolution was observed up 2000 μmol m⁻² s⁻¹. However, when these results are expressed on a cell number basis the rate of oxygen evolution was significantly higher in the green form. Carbonic anhydrase (CA) activity (total, soluble, membrane bound) was found in red and green forms. CA was higher in the red form on a chlorophyll basis, but lower if expressed on a protein basis. The light dependent rate of oxygen evolution and photoinhibition depends on the concentration of β-carotene in D. salina cells.     

Effects of prey abundance and light intensity on the mixotrophic chrysophyte Poterioochromonas malhamensis from a mesotrophic lake

1. Previous studies of mixotrophy in the flagellate Poterioochromonas malhamensis (Chrysophyceae) were performed on strains that had been in culture for > 30 years. This study aims to compare mixotrophy in a cultured strain with one recently isolated from a mesotrophic lake (Lacawac) in Pennsylvania, U.S.A. 2. P. malhamensis from the lake exhibited a nutritional flexibility similar to that of the culture strain, growing phototrophically but inefficiently in comparison to other nutritional modes (growth rate (μ) = 0.015 h^?1). Supplementing an inorganic salts medium with 1 mM glucose resulted in a doubling of μ to 0.035 h^?1 and 0.033 h^?1 in the light and the dark, respectively. Addition of an algal prey, Nannochloris, to the inorganic salts medium increased growth to rates similar to those observed with glucose. Maximum growth of the lake strain, 0.095 h^?1, was achieved when bacteria was supplied as food. During growth on bacteria, cellular chlorophyll a (Chl a) decreased from 140 fg cell^?1 to 10 fg cell^?1 over 22 h when cultured either in the light or dark. In illuminated cultures, cell-specific Chl a concentration recovered to 185 fg cell^?1 after bacteria became limiting. 3. In contrast to the cultured strain, however, the lake isolate exhibited an inverse relationship between light intensity and ingestion rate. Calculated grazing rates, based upon the ingestion of fluorescently labeled bacteria, were 3.2, 5.2 and 9.4 bacteria flagellate^?1 h^?1, for P. malhamensis incubated in high light, low light and darkness, respectively. Phagotrophy is thus influenced by a light regime in this predominately heterotrophic mixotroph.     

Coupled effects of irradiance and iron on the growth of a harmful algal bloom-causing microalga Scrippsiella trochoidea

Effects of irradiance and iron on the growth of a typical harmful algal blooms (HABs) causative dinoflagellate, Scrippsiella trochoidea, were investigated under various irradiances (high light: 70 μmol m^?2 s^?1 and low light: 4 μmol m^?2 s^?1) and iron concentrations (low iron: 0.063 mg L^?1, medium iron: 0.63 mg L^?1 and high iron: 6.3 mg L^?1), and evaluated by the parameters of algal cell density, specific growth rate, optical density and chlorophyll a content. The results indicated that there was significant difference in the cell density of dinoflagellate S. trochoidea between high light and low light intensity treatments across the entire experiments, 7-fold higher at high irradiance as compared with low irradiance, which was further enhanced by the iron concentration. It was found that the maximum cell density of 25 × 10⁴ cell mL^?1 occurred under the combination of high light intensity and high iron concentration, followed by 23 × 10⁴ cell mL^?1 in the combination of high light and medium iron, and 20 × 10⁴ cell mL^?1 in the combination of high light and low iron. There was no significant effect of iron concentration on the cell density under low light intensity. The cell density maintained about 3 × 10⁴ cell mL^?1 across all combinations of iron concentrations and low light in the end of experiments. Such interactive effects of light intensity and iron level dependent were also observed for the specific growth rate, OD₆₈₀ and chlorophyll a content of S. trochoidea. The maximum values of specific growth rate, OD₆₈₀ and chlorophyll a content peaked at the condition of high irradiance and high iron, which were 0.22 d^?1, 0.282 and 0.673 mg L^?1, respectively. In general, their values increased significantly with the increasing of iron concentration at high irradiance, whereas no significant difference was observed among three iron concentrations at low irradiance, all remaining approximately 0.06 d^?1, 0.03 and 0.050 mg L^?1, respectively. Those results suggest that there may be a strong interactive effect between irradiance and iron on microalgal growth and their physiological characteristics. The combination of high light and high iron concentration may accelerate algal cell growth and pigment biosynthesis, thus leading to massive occurrence of HABs.     

The Molecular Analysis of the Light Adaptation Reactions in the Yellow-green Alga Pleurochloris meiringensis (Xanthophyceae)

The xanthophycean alga Pleurochloris meiringensis was homocontinuously cultured under high light (16 W/m²) and low light (2 W/m²) conditions. In low light cells, the chlorophyll a content and the dry weight on per cell basis is increased, the maximal photosynthetic capacity per chlorophyll is decreased. The content of chlorophyll c, vaucheriaxanthin-ester and heteroxanthin is similar in both cultures, whereas the content of diadinoxanthin and ß-carotene is twice as high in high light cultures. High light cells contain more photosystem I and cytochrome f per chlorophyll than low light cells, whereas the Q_B content is found to be unchanged. Therefore, the ratio reaction center II/reaction center I is twofold higher in low light cells than in high light ones. The regulation of energy distribution between the photosystems is examined by fluorescence emission spectra at 77 K scanned after different preillumination of the cells. No wavelength dependent state I/state II transition can be detected. However, P. meiringensis regulates the energy distribution in response to light intensity: The higher the irradiance of preillumination, the higher the energy transfer to photosystem I. The sensitivity of the regulation to light intensity is increased in low light cells.     

CELL‐SPECIFIC EXTRACELLULAR PHOSPHATASE ACTIVITY OF DINOFLAGELLATE POPULATIONS IN ACIDIFIED MOUNTAIN LAKES1

High bulk extracellular phosphatase activity (PA) suggested severe phosphorus (P) deficiency in plankton of three acidified mountain lakes in the Bohemian Forest. Bioavailability of P substantially differed among the lakes due to differences in their P loading, as well as in concentrations of aluminum (Al) and its species, and was accompanied by species‐specific responses of phytoplankton. We combined the fluorescently labeled enzyme activity (FLEA) assay with image cytometry to measure cell‐specific PA in natural populations of three dinophyte species, occurring in all the lakes throughout May–September 2007. The mean cell‐specific PA varied among the lakes within one order of magnitude: 188–1,831 fmol · cell^?1 · h^?1 for Gymnodinium uberrimum (G. F. Allman) Kof. et Swezy, 21–150 fmol · cell^?1 · h^?1 for Gymnodinium sp., and 22–365 fmol · cell^?1 · h^?1 for Peridinium umbonatum F. Stein. To better compare cell‐specific PA among the species of different size, the values were normalized per unit of cell biovolume (amol · μm^?3 · h^?1) for further statistical analysis. A step‐forward selection identified concentrations of total and ionic Al together with pH as significant factors (P < 0.05, Monte Carlo permutation test), explaining cumulatively 57% of the total variability in cell‐specific PA. However, this cell‐specific PA showed an unexpected reverse trend compared to an overall gradient in P deficiency of the lake plankton. The autecological insight into dinophyte cell‐specific PA therefore suggested other factors, such as light availability, mixotrophy, and/or zooplankton grazing, causing further PA variations among the acidified lakes.     

EFFECTS OF ULTRAVIOLET‐A RADIATION AND NUTRIENT AVAILABILITY ON THE CELLULAR COMPOSITION OF PHOTOPROTECTIVE COMPOUNDS IN GLENODINIUM FOLIACEUM (DINOPHYCEAE)1

The photoprotective response in the dinoflagellate Glenodinium foliaceum F. Stein exposed to ultraviolet‐A (UVA) radiation (320–400 nm; 1.7 W · m²) and the effect of nitrate and phosphate availability on that response have been studied. Parameters measured over a 14 d growth period in control (PAR) and experimental (PAR + UVA) cultures included cellular mycosporine‐like amino acids (MAAs), chls, carotenoids, and culture growth rates. Although there were no significant effects of UVA on growth rate, there was significant induction of MAA compounds (28 ± 2 pg · cell^?1) and a reduction in chl a (9.6 ± 0.1 pg · cell^?1) and fucoxanthin (4.4 ± 0.1 pg · cell^?1) compared to the control cultures (3 ± 1 pg · cell^?1, 13.3 ± 3.2 pg · cell^?1, and 7.4 ± 0.3 pg · cell^?1, respectively). In a second investigation, MAA concentrations in UVA‐exposed cultures were lower when nitrate was limited (P < 0.05) but were higher when phosphate was limiting. Nitrate limitation led to significant decreases (P < 0.05) in cellular concentration of chls (chl c₁, chl c₂, and chl a), but other pigments were not affected. Phosphate availability had no effect on final pigment concentrations. Results suggest that nutrient availability significantly affects cellular accumulation of photoprotective compounds in G. foliaceum exposed to UVA.     

Nutrient uptake and alkaline phosphatase (ec 3:1:3:1) activity of emiliania huxleyi (PRYMNESIOPHYCEAE) during growth under n and p limitation in continuous cultures

Emiliania huxleyi (strain L) expressed an exceptional P assimilation capability. Under P limitation, the minimum cell P content was 2.6 fmol P·cell^?1, and cell N remained constant at all growth rates at 100 fmol N·cell^?1. Both, calcification of cells and the induction of the phosphate uptake system were inversely correlated with growth rate. The highest (cellular P based) maximum phosphate uptake rate (V_max^P) was 1400 times (i.e. 8.9 h^?1) higher than the actual uptake rate. The affinity of the P‐uptake system (dV/dS) was 19.8 L·μmol^?1·h^?1 at μ = 0.14 d^?1. This is the highest value ever reported for a phytoplankton species. V_max and dV/dS for phosphate uptake were 48% and 15% lower in the dark than in the light at the lowest growth rates. The half‐saturation constant for growth was 1.1 nM. The coefficient for luxury phosphate uptake (Q_maxt/Q_min) was 31. Under P limitation, E. huxleyi expressed two different types of alkaline phosphatase (APase) enzyme kinetics. One type was synthesized constitutively and possessed a V_max and half‐saturation constant of 43 fmol MFP·cell^?1·h^?1 and 1.9 μM, respectively. The other, inducible type of APase expressed its highest activity at the lowest growth rates, with a V_max and half‐saturation constant of 190 fmol MFP·cell^?1·h^?1 and 12.2 μM, respectively. Both APase systems were located in a lipid membrane close to the cell wall. Under N‐limiting growth conditions, the minimum N quotum was 43 fmol N·cell^?1. The highest value for the cell N‐specific maximum nitrate uptake rate (V_max^N) was 0.075 h^?1; for the affinity of nitrate uptake, 0.37 L·μmol^?1·h^?1. The uptake rate of nitrate in the dark was 70% lower than in the light. N‐limited cells were smaller than P‐limited cells and contained 50% less organic and inorganic carbon. In comparison with other algae, E. huxleyi is a poor competitor for nitrate under N limitation. As a consequence of its high affinity for inorganic phosphate, and the presence of two different types of APase in terms of kinetics, E. huxleyi is expected to perform well in P‐controlled ecosystems.     

Photoinhibition and P700 in the Marine Diatom Amphora sp

The marine diatom Amphora sp. was grown at a light intensity of 7.0 × 10¹⁵ quanta centimeter⁻² second⁻¹. Light saturation of photosynthesis for these cells was between 6.0 and 7.0 × 10¹⁶ quanta centimeter⁻² second⁻¹. At light intensities greater than saturation, photosynthetic ¹⁴CO₂ fixation was depressed, while P700 unit size (chlorophyll a concentration/P700 activity) increased and number of P700 units per cell decreased. After a 1-hour exposure of Amphora sp. to a photoinhibitory light intensity of 2.45 × 10¹⁷ quanta centimeter⁻² second⁻¹, there was a 45 to 50% decrease in the rate of ¹⁴CO₂ fixation relative to the rate at the culture light intensity. There also was a 25% increase in P700 unit size and a 30% reduction in the number of P700 units per cell but no change in total chlorophyll a concentration. Following this period of photoinhibition, the cells were returned to a light regime similar to that in the original culture conditions. Within 1 hour, both number of P700 units per cell and P700 unit size returned to levels similar to those of cells which were kept at the culture light intensity. The rates of photosynthesis did not recover as rapidly, requiring 2 to 3 hours to return to the rate for the nonphotoinhibited cells. Our results indicate that a decrease in P700 activity (with a resultant increase in P700 unit size) may be partially responsible for the photoinhibition of algal photosynthetic carbon dioxide fixation.     

Photosystem 1 preparations from dark-and light-grown cells of the cyanobacterium,Chlorogloea fritschii

Photosystem 1 (PS1) enriched preparations have been extracted from the cyanobacterium Chlorogloea fritschii grown either in darkness or in the light. Absorption spectra show that the main chlorophyll peak has shifted from 678 nm in PS1 from light grown cells to 675 nm in PS1 from dark grown cells. Fluorescence spectra show a similar blue shift in wavelength maximum from 690 nm to 678 nm and the fluorescence intensity is higher in PS1 from dark grown cells. Allophycocyanin is present in PS1 from light grown cells, but absent from preparations from C. fritschii grown in the dark. P700: chlorophyll a ratios of the preparations from light and dark grown cells are 1:35 and 1:80 respectively, all P700 being photoactive. The results are interpreted to suggest that allophycocyanin is not attached to PS1 in dark grown C. fritschii, neither is all chlorophyll arranged in such a way as to ensure efficient energy transfer to P700.     

Photosynthetic acclimation of plants to growth irradiance: the relative importance of specific leaf area and nitrogen partitioning in maximizing carbon gain

Changes in specific leaf area (SLA, projected leaf area per unit leaf dry mass) and nitrogen partitioning between proteins within leaves occur during the acclimation of plants to their growth irradiance. In this paper, the relative importance of both of these changes in maximizing carbon gain is quantified. Photosynthesis, SLA and nitrogen partitioning within leaves was determined from 10 dicotyledonous C₃ species grown in photon irradiances of 200 and 1000 µmol m^?2 s^?1. Photosynthetic rate per unit leaf area measured under the growth irradiance was, on average, three times higher for high‐light‐grown plants than for those grown under low light, and two times higher when measured near light saturation. However, light‐saturated photosynthetic rate per unit leaf dry mass was unaltered by growth irradiance because low‐light plants had double the SLA. Nitrogen concentrations per unit leaf mass were constant between the two light treatments, but plants grown in low light partitioned a larger fraction of leaf nitrogen into light harvesting. Leaf absorptance was curvilinearly related to chlorophyll content and independent of SLA. Daily photosynthesis per unit leaf dry mass under low‐light conditions was much more responsive to changes in SLA than to nitrogen partitioning. Under high light, sensitivity to nitrogen partitioning increased, but changes in SLA were still more important.     

Quantification of Tetradesmus obliquus (Chlorophyceae) cell size and lipid content heterogeneity at single‐cell level

Much of our current knowledge of microbial growth is obtained from studies at a population level. Driven by the realization that processes that operate within a population might influence a population's behavior, we sought to better understand Tetradesmus obliquus (formerly Scenedesmus obliquus ) physiology at the cellular level. In this work, an accurate pretreatment method to quantitatively obtain single cells of T. obliquus , a coenobia‐forming alga, is described. These single cells were examined by flow cytometry for triacylglycerol (TAG ), chlorophyll, and protein content, and their cell sizes were recorded by coulter counter. We quantified heterogeneity of size and TAG content at single‐cell level for a population of T. obliquus during a controlled standard batch cultivation. Unexpectedly, variability of TAG content per cell within the population increased throughout the batch run, up to 400 times in the final stage of the batch run, with values ranging from 0.25 to 99 pg · cell^?1. Two subpopulations, classified as having low or high TAG content per cell, were identified. Cell size also increased during batch growth with average values from 36 to 70 μm³ · cell^?1; yet cell size variability increased only up to 16 times. Cell size and cellular TAG content were not correlated at the single‐cell level. Our data show clearly that TAG production is affected by cell‐to‐cell variation, which suggests that its control and better understanding of the underlying processes may improve the productivity of T. obliquus for industrial processes such as biodiesel production.     

COCCOLITH PRODUCTION AND DETACHMENT BY EMILIANIA HUXLEYI (PRYMNESIOPHYCEAE)1

Laboratory experiments were performed with the prymnesiophyte Emiliania huxleyi (Lohm.) Hay and Mohler, strain 88E, to quantify calcification per cell, coccolith detachment, and effects of coccolith production on optical scattering of individual cells. ¹⁴C incorporation into attached and detached coccoliths was measured using a bulk filtration technique. ¹⁴C-labeled cells also were sorted using a flow cytometer and analyzed for carbon incorporation into attached coccoliths. The difference between the bulk and flow cytometer analyses provided a ¹⁴C-based estimate of the rate of production of detached coccoliths. Coccolith production and detachment were separated in time in batch cultures, with most detachment happening well after calcification had stopped. Accumulation of coccoliths was maximum at the end of logarithmic growth with 50–80 coccoliths per cell (three to five complete layers of coccoliths around the cells). Net accretion rates of coccoliths were on the order of 7 coccoliths· cell^?1·d^?1 while net detachment rates were as high as 15 coccoliths· cell^?1·d^?1 for stationary phase cells. Equal numbers of coccoliths were attached and detached early in logarithmic growth, and as cells aged, the numbers of detached coccoliths exceeded the attached ones by a factor of 6. Our results demonstrate pronounced charges of forward angle light scatter and 90° light scatter of cells as they grow logarithmically and enter stationary phase. Counts of loose coccoliths in batch cultures are consistent with the detachment of coccoliths in layers rather than individual coccoliths.