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PubMed1967

Enhanced Dark CO(2) Fixation by Preilluminated Chlorella pyrenoidosa and Anacystis nidulans.

The products of short time photosynthesis and of enhanced dark (14)CO(2) fixation (illumination in helium prior to addition of (14)CO(2) in dark) by Chlorella pyrenoidosa and Anacystis nidulans were compared. Glycerate 3-phosphate, phosphoenolpyruvate, alanine, and aspartate accounted for the bulk of the (14)C assimilated during enhanced dark fixation while hexose and pentose phosphates accounted for the largest fraction of isotope assimilated during photosynthesis. During the enhanced dark fixation period, glycerate 3-phosphate is carboxyl labeled and glucose 6-phosphate is predominantly labeled in carbon atom 4 with lesser amounts in the upper half of the C(6) chain and traces in carbon atoms 5 and 6. Tracer spread throughout all the carbon atoms of photosynthetically synthesized glycerate 3-phosphate and glucose 6-phosphate. During the enhanced dark fixation period, there was a slow formation of sugar phosphates which subsequently continued at 5 times the initial rate long after the cessation of (14)CO(2) uptake. To explain the kinetics of changes in the labelling patterns and in the limited formation of the sugar phosphates during enhanced dark CO(2) fixation, the suggestion is made that most of the reductant mediating these effects did not have its origin in the preillumination phase.It is concluded that a complete photosynthetic carbon reduction cycle operates to a limited extent, if at all, in the dark period subsequent to preillumination.

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PubMed1968

Studies of sulfate utilization by algae. 4. Properties of a cell-free sulfate-reducing system from chlorella.

A cell-free system from Chlorella pyrenoidosa Chick (Emerson strain 3) which produces acid-volatile radioactivity from (35)SO(4) (2-) is described. A high speed supernatant from cells broken in the French Press at pH 7.0 shows maximal activity when fortified with ATP, an ATP-generating system (creatine phosphate and creatine phosphokinase), TPN, a TPN-reducing system (glucose-6-phosphate and glucose-6-phosphate dehydrogenase) and MgCl(2). This system is quite labile and is not stable to dialysis. Addition of low concentrations of 2,3,-dimercaptopropan-1-ol (BAL) to the buffers used for enzyme preparation stabilize the extracts and permit them to be dialyzed for 4 hours without loss of activity. If additional BAL is also added to the incubation mixtures it can replace TPNH as a reductant. DPNH also shows appreciable acticity.The system prepared with BAL-containing buffers shows maximal activity at pH 9.0. At this pH, the system requires only ATP, Mg(2+) and additional BAL and has high activity and stability compared with the other conditions tried. The optimum concentrations of these reactants has been determined and the kinetics of production of acid-volatile radioactivity are described. Nucleoside triphosphates other than ATP are not appreciably active in this system. In all cases, anaerobic conditions are required for maximal activity, the enzyme extracts are labile to heat, and no unequivocal requirement for thioctic acid can be demonstrated.

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PubMed1968

Studies of sulfate utilization by algae. 5. Identification of thiosulfate as a major Acid-volatile product formed by a cell-free sulfate-reducing system from chlorella.

Separation of the products formed from sulfate-(35)S by cell-free extracts of Chlorella pyrenoidosa (Emerson Strain 3) has permitted the identification of thiosulfate as a major product which yields acid-volatile radioactivity. The products formed, as separated by Dowex-1-nitrate chromatography, are qualitatively the same whether extracts at pH 7.0 (using TPNH as the reductant) or extracts at pH 9 [using 2,3-dimercaptopropan-1-ol, (BAL) as reductant] are employed. While thiosulfate can be separated without the addition of carrier, the inclusion of carrier improves the recovery. High concentrations of ATP which have been shown previously to inhibit the formation of acid-volatile radioactivity from radioactive sulfate, inhibit the formation of thiosulfate almost completely. Degradation of the thiosulfate formed at normal ATP concentrations reveals that most of the radioactivity is in the SO(3)-sulfur of the molecule suggesting that the SH-sulfur is derived from the enzyme extracts. If carrier sulfite is present during thiosulfate formation from sulfate-(35)S, radioactive sulfite is recovered at the expense of radioactive thiosulfate. Reconstruction experiments utilizing specifically-labeled thiosulfates indicate that radioactive sulfite formation is probably not the result of trapping a normal intermediate, but can be attributed to non-enzymatic exchange between labeled thiosulfate formed from sulfate and the non-radioactive sulfite added, suggesting that free sulfite is not an intermediate in thiosulfate formation from sulfate.

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PubMed1969

Environmentally-induced changes in the Fatty acids of chlorella.

Qualitative and quantitative analyses were made of the major fatty acids of Chlorella fusca, Shihira and Krauss, in both autotrophic and heterotrophic culture. Cells grown heterotrophically were subjected to CO(2) concentrations as great as 40%-in-air.The major fatty acids of autotrophic cells grown under a 1% environmental concentration of CO(2), in order of concentration were 16:0, 18:3, 16:4, 18:2, 18:1, and 16:3. The analysis of heterotrophic cells at 1% CO(2), by comparison, indicated a complete absence of 16:4, reduced amounts of 18:3, and increased amounts of the other major acids.An increase in the environmental concentration of CO(2) (from 1%-30%) over the heterotrophic cultures produced a 40% increase in total lipids and nearly a 50% increase in fatty acids. Palmitic acid (16:0) and 18:1 largely account for the fatty acid change by increasing from 12 mg to 33 mg/g dry wt and 8 mg to 17 mg/g dry wt respectively. Possible explanations for this enhanced synthesis of fatty acids are suggested.

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PubMed1969

Photosynthetic Light Reactions in Chemically Fixed Anacystis nidulans, Chlorella pyrenoidosa, and Porphyridium cruentum.

The photochemical activities of various species of unicellular algae (Anacystis nidulans, Chlorella pyrenoidosa, and Porphyridium cruentum) were studied following chemical fixation. Fixation with formaldehyde and glutaraldehyde yielded cells which retained their ability to perform photosystem I and photosystem II reactions. The photochemical efficiencies of some fixed algae are as great as those of unfixed spinach chloroplasts. Fixed algae containing accessory pigments appear to be useful models for further studies of the light reactions of photosynthesis.

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PubMed1970

Some observations on the carbon dioxide burst in chlorella and chlamydomonas.

In the course of mass spectrometer studies with the algae Chlorella and Chlamydomonas, data were obtained which indicate that the CO(2) burst and gulp are sensitive to oxygen. Furthermore, the CO(2) burst was found to be strongly suppressed when wave lengths shorter than 460 nanometers were blocked at intensities adequate to saturate photosynthesis. Under appropriate conditions at 30 degrees , the CO(2) burst was interrupted by a brief CO(2) gulp and the post illumination gulp by a brief burst of CO(2). The post illumination gulp of CO(2) could be induced during illumination by interposition of a filter blocking wave lengths shorter than 460 nanometers. These data are discussed in relation to earlier reports of the phenomenon and briefly as they affect the detection of photorespiration.

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PubMed1970

Effect of Oxygen on the Light-enhanced Dark Carbon Dioxide Fixation in Chlorella Cells.

With Chlorella ellipsoidea cells, the effect of oxygen was investigated on the products of enhanced dark (14)CO(2) fixation immediately following preillumination in the absence of CO(2). When the reaction mixture was made aerobic by bubbling air (CO(2)-free) throughout preillumination and the following dark (14)CO(2) fixation periods, the initial fixation product was mainly 3-phosphoglyceric acid. When nitrogen gas had been used instead of air, only about one-half of the total radioactivity in the initial fixation products was in 3-phosphoglyceric acid and the rest in aspartic, phosphoenolpyruvic, and malic acids. The percentage distribution of radioactivity incorporated in these initial products rapidly decreased during the rest of the dark period. Concurrent with the decrease in the initial (14)CO(2) fixation products, some increase was observed in the radioactivities of the sugar phosphates. The maximal radioactivity incorporated in sugar mono- and diphosphates accounted for only 10% of total (14)C, under either the aerobic or anaerobic conditions. Under anaerobic conditions most of the (14)C incorporated was eventually transferred to alanine, whereas the main end products under aerobic conditions were aspartate and glutamate. The pattern of (14)CO(2) fixation products was unaffected by the atmospheric condition during the period of preillumination. The preferential flow of the fixed carbon atom to alanine or aspartate depended on the presence or absence of oxygen during the period of dark CO(2) fixation.

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PubMed1970

Observations on the mechanism of copper damage in chlorella.

Addition of excess copper to nongrowing cells of a normal, green Chlorella caused a reduction in total pigments and a blue shift of chlorophyll absorption, concurrent with the inhibition of photosynthesis. Chlorophylless yellow and white mutant strains of the same alga showed a rise in nonspecific absorption (i.e., change in light scatter) within 5 to 10 minutes after the addition of CuSO(4); concomitantly a lowering of packed cell volume and a rise in respiration occurred. Glutathione prevented all copper-induced changes, whereas MnCl(2) protected only partially. Selective inhibition of some responses to copper was observed when O(2) was absent or an antioxidant present.

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PubMed1970

The photosynthetic response to a shift in the chlorophyll a to chlorophyll B ratio of chlorella.

The chlorophyll a:b ratio was shifted in Chlorella vannielii by varying the illuminance under which the cells were cultured-the ratio increased from 2.9, 3.0, 4.0, and 4.8 to 6.2, respectively, at 100, 300, 900, 2,700 and 6,000 foot candles. The 6,000-foot candle cells retained an optimal growth rate at the chlorophyll a:b ratio of 6.2 which was the upper limit of normal growth. Comparisons were made between the 300-and 6,000-foot candle cultures to determine the significance to the photosynthetic mechanism of a shift in the chlorophyll a:b ratio.The high light cells (6,000 foot candles) contained only one-tenth the total amount of chlorophyll of the low light cells (300 foot candles) based on dry weight. The total chlorophyll per cell of the high light cells was one-fifth of that in the low light cells. Electron micrographs indicated differences in chloroplast structure. An average of five or six thylakoids composed a granum-like region of the low light chloroplasts, whereas only a pair of thylakoids at most was found in the high light chloroplasts. The high light chloroplasts had more starch. On a dry weight basis, the high light cells had a respiration rate 3 times that of the low light cells. Based on chlorophyll, the respiration rate of the high light cells was 26 times greater. Based on dry weight, the oxygen evolution for both cultures was essentially the same at 6,000 foot candles; however, at 300 foot candles the rate for the low light cells was about 5 times faster than that of the high light cells. With chlorophyll as the index, the rates of the high light cells were higher than those of the low light cells-7 times faster at 6,000 and 2 times faster at 300 foot candles. At 10,000 foot candles, the low light-grown cells underwent photooxidation, whereas the high light grown cells photosynthesized at a rate slightly higher than at 6,000 foot candles.Action spectra of system II (oxygen evolution) from a modulated polarograph indicated photochemical participation of chlorophyll b in the high light deficient cells, although the participation was much less than in the low light cells. Enhancement was 1.11 for the low light cells, and 1.05 for the high light cells.In order to account for the energy balance in the two cultures it was concluded that perhaps oxidative phosphorylation supplemented a reduced photophosphorylation in the high light cells. Experiments with peroxyacetyl nitrate support the view that cyclic photophosphorylation is less in the chlorophyll b-deficient cells. Chlorophyll b served also to broaden absorption for the photosynthetic unit-a detrimental role when cells are illuminated above saturation.

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PubMed1971

Effects of Flashes of Red or Blue Light on the Composition of Starved Chlorella pyrenoidosa.

Autotrophically grown cells of Chlorella pyrenoidosa (211-8b) were starved 3 to 4 days in darkness, flashes of blue light, or flashes of red light. The blue flashes were sufficient to maintain the maximal rate of light-stimulated oxygen uptake during short term experiments. However, after 24 hours, the respiration rate in red flashes was equal to, or greater than, the rate in blue flashes. Starvation in darkness reduced the chlorophyll content by 11%, altered the blue absorbance of the nonsaponifiable material only 1 to 2%, and reduced the dry weight by 13%. Starvation in the presence of blue or red flashes reduced the dry weight by an additional 11 or 12% respectively. Protein per unit cell volume was not changed significantly during 3 to 4 days starvation in darkness or in blue flashes, even though dry weight per unit cell volume decreased 13% in darkness and 23% in blue flashes. In contrast, cells starved under red flashes showed a 20% decrease in protein per unit cell volume and a 24% decrease in dry weight per unit cell volume.

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PubMed1971

Chlorophyll synthesis in chlorella: regulation by degree of light limitation of growth.

The degree of light limitation of growth is the primary controlling factor of chlorophyll synthesis during photoautotrophic growth of Chlorella. The chlorophyll content of the cells increases when light is limiting for growth as occurs in dense cultures, or in cultures under low incident light, or when the light is used less efficiently through partial inhibition of photosynthesis by 3-(p-chlorophenyl)-1, 1-dimethylurea. The chlorophyll content decreases when light is not limiting for growth, as occurs in cells in high light intensity and in dilute suspensions. The initial lag in rate of chlorophyll synthesis in a freshly inoculated culture can be attributed to light at first not being growth limiting, and then becoming growth limiting as the cell suspension becomes denser. Continuous culture experiments support the above conclusions by showing that under steady state conditions the chlorophyll content is inversely related to the relative available light.

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PubMed1971

Studies of Sulfate Utilization by Algae: 9. Fractionation of a Cell-free System from Chlorella into Two Activities Necessary for the Reduction of Adenosine 3'-Phosphate 5'-Phosphosulfate to Acid-Volatile Radioactivity.

Further properties of the enzymatic system obtained from Chlorella pyrenoidosa (Emerson strain 3) which reduces adenosine 3'-phosphate 5'-phosphosulfate-(35)S to acid-volatile radioactivity, when fortified with Mg(2+) and 2, 3-dimercaptopropan-1-ol as reductant, are described. Optimal concentrations of adenosine 3'-phosphate 5'-phosphosulfate-(35)S and Mg(2+) and the pH optimum have been determined. 2,3-Dimercaptopropan-1-ol can be replaced by dithiothreitol, mercaptoethanol, reduced glutathione, cysteine, and cysteamine. Treatment of the crude extracts with ammonium sulfate and alumina C-gamma gel yields two fractions, designated "S" and "A," which must be recombined to obtain acid-volatile radioactivity. Further fractionation of fraction S by ammonium sulfate gradient elution and diethylaminoethyl cellulose chromatography yields approximately a 50-fold increase in specific activity compared to that found in the crude extract. This material appears to contain an active component with a molecular weight estimated by agarose gel chromatography of about 330,000.

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PubMed1971

The photosynthetic unit in chlorella measured by repetitive short flashes.

Apparent size of the photosynthetic unit in Chlorella pyrenoidosa was estimated by the method of Emerson and Arnold: rate of oxygen evolution was measured under repetitive saturating flashes of about 10-microsecond duration separated by dark periods of 0.033 to 0.100 second. Cells used were taken from six steady state cultures maintained at different light intensities. Cell characteristics included a variation in chlorophyll content from 1 to 5%. Apparent size of the photosynthetic unit varied systematically with chlorophyll content in the range of 1560 to 2350 chlorophylls per O(2) per flash. Values for unit size showed no unusual statistical distribution and were not changed significantly by addition of low level background light at 645 or 705 nanometers. Maximal rate of unit turnover, calculated from light-saturated rate and unit size, varied inversely with chlorophyll content in the range of 70 to 180 per second.

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PubMed1972

Studies on Effects of Certain Quinones: II. Photosynthetic Incorporation of CO(2) by Chlorella.

The effects of various quinone herbicides and fungicides on the photosynthetic (14)CO(2) fixation and the incorporation of (14)C among the products of photosynthesis in Chlorella pyrenoidosa was investigated. Addition of 30 mum 2,3-dichloro-1,4-naphthoquinone (dichlone), 2-amino-3-chloro-1,4-naphthoquinone (06K-quinone), or 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil) inhibited CO(2) fixation, whereas 1,4-benzoquinone had no effect. Treatment with 3 mum or higher concentrations of dichlone, 06K-quinone or 1,4-benzoquinone also produced marked changes in the pattern of (14)C distribution. A noticeable effect was an increase in the proportion of (14)C in sucrose and glycine accompanied by a reduction in (14)C lipids and glutamic acid. These changes appear to occur as a result of shifts in the flow of carbon along various biosynthetic pathways of photosynthetic CO(2) fixation. It is suggested that inactivation of coenzyme A and shortage of reduced triphosphopyridine nucleotide in the quinone-treated cells inhibited the synthesis of lipids and glutamic acid, thereby diverting more carbon into sucrose and glycine.

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PubMed1972

The development of photosynthesis in a greening mutant of chlorella and an analysis of the light saturation curve.

Photosynthetic oxygen evolution considerably precedes the rise in chlorophyll during the greening of a yellow mutant of Chlorella vulgaris. Dark-grown cells required 20 times more light to saturate photosynthesis than light-grown or normal cells. The chlorophyll appears to add first to active reaction centers, then to fill in a more general antenna. The carotenoid pigments seem to add more randomly to the reaction centers. The shape of the light saturation curves can be explained with the assumption that an excitation in the antenna can reach several reaction centers. The efficiency of the total unit is constant during the greening process.

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PubMed1972

Nitrate Reductase and Chlorate Toxicity in Chlorella vulgaris Beijerinck.

A study of the growth-inhibiting effect of chlorate on the Berlin strain of Chlorella vulgaris Beijerinck provided complete confirmation of the theory of chlorate toxicity first proposed by Aberg in 1947. Chlorate was toxic to the cells growing on nitrate, and relatively nontoxic to the cells growing on ammonium. The latter cells contained only 0.01 as much NADH-nitrate reductase as the nitrate-grown cells. Chlorate could substitute for nitrate as a substrate of the purified nitrate reductase with Km = 1.2 mm, and V(max) = 0.9V(max) for nitrate. Bromate, and to a much smaller extent, iodate, also served as alternate substrates. Nitrate is a reversible competitive inhibitor of chlorate reduction, which accounts for the partial reversal, by high nitrate concentrations, of the observed inhibition of cell growth by chlorate. During the reduction of chlorate by NADH in the presence of purified nitrate reductase, there was a progressive, irreversible inhibition of the enzyme activity, presumably brought about by the reduction product, chlorite. Both the NADH-nitrate reductase activity and the associated NADH-cytochrome c reductase activity were inactivated to the same extent by added chlorite. The spectral properties of the cytochrome b(557) associated with the purified enzyme were not affected by chlorite. The inactivation of the nitrate reductase by chlorite could account for the toxicity of chlorate to cells grown on nitrate, though the destruction of other cell components by chlorite or its decomposition products cannot be excluded.

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PubMed1973

Light and calcium interactions in chlorella inhibited by sodium chloride.

Analysis of NaCl toxicity in Chlorella sorokiniana showed decreased growth rates, increased dry weight per cell, increased intracellular Na(+) and Cl(-), more total chlorophyll per cell, a decreased chlorophyll a to chlorophyll b ratio, increased rates of O(2) evolution, and decreased rates of CO(2) fixation when the extracellular concentration of NaCl was increased from zero to 0.3 m. Cultures did not grow at concentrations greater than 0.3 m NaCl unless 10 mm calcium salts were present. Inclusion of that concentration of Ca(2+) extended the tolerance to 0.5 m NaCl before growth stopped. Increasing the light intensity from 1.2 to 9.4 mw/cm(2) increased growth rates for cultures in 0.10 to 0.45 m NaCl. At 14 mw/cm(2) added Ca(2+) reduced growth rates of cultures in 0.3 m NaCl compared to controls without added Ca(2+). Maximal growth rates for cultures in NaCl media were achieved by addition of 10 mm CaSO(4) and maintenance of the light intensity at 9.4 mw/cm(2). The maximal growth rate of the organism was 9.6 doublings/day achieved at 2.7 mw/cm(2) for control cultures. In 0.3 m NaCl the growth rate was 4.3 doublings/day at 2.7 mw/cm(2) and 8.2 doublings/day at 9.4 mw/cm(2) with 10 mm CaSO(4) added.Increasing light intensities from 2.7 to 9.4 to 14 mw/cm(2) decreased intracellular Na(+) in cells cultured in 0.3 m NaCl medium without added Ca(2+) and increased Cl(-) uptake in cells cultured in 0.3 m NaCl medium with and without added Ca(2+). For cells cultured in 0.3 m NaCl medium at 14 mw/cm(2) intracellular Na(+) was 0.68 meq/g dry weight with Ca(2+) added and 0.81 meq/g dry weight without Ca(2+) added. Addition of Ca(2+) at 2.7 mw/cm(2) reduced intracellular Na(+) to similar values. It is postulated that energy requirements for active Na(+) exclusion were reduced by addition of Ca(2+) allowing more energy to be used for cell growth resulting in increased growth rates.O(2) evolution and CO(2) fixation studies indicated that increased photosynthetic energy, probably actuated by a high proton gradient accompanying Cl(-) influx and uncoupled from CO(2) fixation, was available for maintenance of cellular integrity and active control of intracellular ionic ratios. The O(2) evolving capacity was destroyed at 12 and 29 mw/cm(2) for cells cultured in 0.3 m NaCl medium respectively with and without the addition of Ca(2+). Control cultures continued producing O(2) at light intensities up to 115 mw/cm(2).

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PubMed1973

Physiology and Ultrastructure of an Oxygen-resistant Chlorella Mutant under Heterotrophic Conditions.

The oxygen-resistant strain of Chlorella sorokiniana (Shihira and Krauss), distinguished by its ability to grow autotrophically under high partial pressures of oxygen, was studied and partially characterized in heterotrophic culture. Ultrastructural analysis of glucose-grown oxygen-resistant strain and wild type cells reveals that osmiophilic deposits (possibly polyphosphate) are present only in wild type, while oxygen-resistant strain apparently contains increased amounts of starch and endoplasmic reticulum. Of major physiological significance are the observations that: (a) oxygen-resistant strain requires 6 to 8 days to completely adapt to dark, heterotrophic conditions, whereas wild type acclimates in 1 day; (b) oxygen-resistant strain is resistant to high oxygen tension only when grown on glucose, but not on acetate; and (c) the respiratory rate, but not the photosynthetic rate, of heterotrophic oxygen-resistant strain is abnormal compared to wild type.

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