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PubMed1978

Light-mediated Activation of Nitrate Reductase in Synchronous Chlorella.

The mechanism underlying the sharp increase in activity of nitrate reductase (EC 1.6.6.1) in Chlorella vulgaris forma tertia (strain 211 8k) during the first hour of the 7 hours/5 hours light/dark cycle was investigated. Using the method of density labeling and isopycnic centrifugation, it could be demonstrated that this rapid increase in activity is based on light-mediated activation rather than de novo synthesis of the enzyme. The problematic nature of cycloheximide specificity and models of nitrate reductase activation are discussed.

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PubMed1979

Ozone alteration of membrane permeability in chlorella: I. Permeability of potassium ion as measured by rubidium tracer.

The addition of ozone to a suspension of Chlorella sorokiniana causes a rapid loss of K(+), as measured by efflux of (86)Rb from prelabeled cells. The efflux of the tracer is stimulated some 15 to 20 times over that of the control. For about 100 microliters per liter ozone, about 25 minutes (6 x 10(-8) moles O(3) delivered per minute) of exposure are required for a 50% depletion of the intracellular K(+). The stimulation of K(+) efflux is nearly linearly dependent upon the amount of ozone delivered into the solution. Following short pulses of ozone (lasting 1 to 5 minutes), efflux rates return to the control level but only after about 15 minutes.While influx of K(+) is ultimately inhibited by ozone, at low concentrations or for short exposure times the tracer influex is stimulated 100 to 200%. Ozone stimulation of an active pump mechanism is unlikely in view of a concomitant decrease in respiration. Thus, this influx may represent movement of K(+) along its electrochemical gradient. Assuming that influx and efflux are in steady-state according to the Goldman equation, it was calculated that the membrane potential for K(+) of -80 to -90 millivolts in control cells drops to -40 millivolts with ozone exposure and is accompanied by a calculated increased permeability to K(+) of 2- to 3-fold.

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PubMed1980

Dependence of Delayed Luminescence upon Adenosine Triphosphatase Activity in Chlorella.

Delayed luminescence and fluorescence yield after illumination by a short flash were measured in Chlorella pyrenoidosa in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Addition of tri-N-butyl-tin (TNBT), a specific inhibitor of ATPase, drastically increases the life-time of the reduced photosystem II primary acceptor Q(-) and decreases the intensity of delayed luminescence. This indicates a slowing of the charge recombination between the oxidized donor and reduced acceptor of photosystem II centers. No inhibition is observed in isolated chloroplasts when the membrane is permeable to ions, i.e. in the presence of Gramicidin D and KCl.It is suggested that there exists in dark-adapted algae a permanent proton gradient which stimulates the charge recombination process. This proton gradient results from the hydrolysis of a pool of ATP by membrane-bound ATPases and collapses after the addition of TNBT. The long lifetime of this proton gradient (several hours) indicates that the ATP probably comes from the mitochondria.The rate of the back reaction occurring from state S(3) (as defined by Kok, Forbush, and McGloin 1970 Photochem Photobiol 11: 457-475) is more dependent upon the pH gradient than for state S(2).

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PubMed1980

Utilization of Exogenous Inorganic Carbon Species in Photosynthesis by Chlorella pyrenoidosa.

The nature of the inorganic carbon utilized during photosynthesis by Chlorella pyrenoidosa was investigated using three experimental techniques (open gas analysis system with "artificial leaf" or "aqueous" chambers and O(2) electrode system) to measure carbon assimilation. Photosynthesis was studied as a function of pH and CO(2) concentration. The CO(2) concentration was inadequate to meet the requirements of photosynthesis only when HCO(3) (-) was added at high pH. Under all other conditions, the low and constant K(m) (CO(2)), in contrast to the highly variable K(m) (HCO(3) (-)), suggested that CO(2) was the major species utilized.Higher rates of photosynthesis were observed under limiting CO(2) conditions above pH 7.5 but rates of hydration of CO(2) were not consistent with the view that the stimulation in photosynthesis was supported by HCO(3) (-). In the same pH region lower rates of photosynthesis were observed under saturating CO(2) conditions. These conflicting changes seemed not to be related to pH but to some as yet undetermined effect of bicarbonate. No support was obtained for the view that the quantum efficiency was different under conditions where CO(2) was assimilated compared to conditions where CO(2) and HCO(3) (-) could be assimilated, although at saturating CO(2), lower maximal rates of photosynthesis were observed in the latter conditions.

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PubMed1980

Photorespiration and Oxygen Inhibition of Photosynthesis in Chlorella pyrenoidosa.

The inhibition of photosynthesis by O(2) in air-grown Chlorella pyrenoidosa was investigated using three experimental techniques (artificial leaf, aqueous method, and O(2) electrode) to measure carbon assimilation. CO(2) response curves were determined under different O(2), pH, and temperature conditions. Regardless of the experimental technique and condition, O(2) inhibition was not evident until a concentration of 50% was reached; V(max) values were reduced whereas K(m) (CO(2)) values were unaffected by the increasing O(2) concentration. The response of photosynthesis to O(2) was independent of CO(2) and HCO(3) (-) concentrations as well as temperature. Relative rates of photosynthesis showed a 4 to 5% stimulation in 2% O(2), a 12% inhibition in 50% O(2), and a 24% inhibition in 100% O(2). The inhibition by 50% O(2) was still reversible after 20 minutes exposure whereas 100% O(2) caused irreversible inhibition after only 4 minutes.The O(2) inhibition is discussed in terms of the oxygenase reaction and a Mehler reaction supporting pseudocyclic electron flow. The results are inconsistent with the proposals that photorespiration exists in these algae and that a CO(2)-concentrating mechanism suppresses the O(2) inhibition of photosynthesis.

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PubMed1980

Synthesis of Nitrate Reductase in Chlorella: I. EVIDENCE FOR AN INACTIVE PROTEIN PRECURSOR.

Synthesis of nitrate reductase (EC 1.6.6.1) in Chlorella vulgaris was studied under inducing conditions, i.e. with cells grown on ammonia and then transferred to nitrate medium. Cycloheximide (but not chloramphenicol) completely inhibited synthesis of the enzyme, but only if it was added at the start (i.e. at the time of nitrate addition) of the induction period. Cycloheximide inhibition became less effective as induction by nitrate proceeded. Enzyme from small quantities of culture (1 to 3 milliliters of packed cells) was purified to homogeneity with the aid of blue dextran-Sepharose chromatography. Incorporation of radioactivity from labeled arginine into nitrate reductase was measured in the presence and absence of cycloheximide. Conditions were found under which the inhibitor completely blocked the incorporation of labeled amino acid, but only slightly decreased the increase in nitrate reductase activity. The results indicate that synthesis of nitrate reductase from amino acids proceeds by way of a protein precursor which is inactive enzymically.

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PubMed1980

Synthesis of Nitrate Reductase in Chlorella: II. EVIDENCE FOR SYNTHESIS IN AMMONIA-GROWN CELLS.

Antiserum was prepared against nitrate reductase (EC 1.6.6.1) purified to homogeneity from Chlorella vulgaris Beijerinck. Both crude antiserum and anti-nitrate reductase antibodies prepared from it were used as re-agents to study the synthesis of nitrate reductase. Cell extracts from cultures which were grown with ammonia salts as the sole source of nitrogen contained almost no active enzyme. These extracts did contain material which binds to antibody and is thus immunologically related to purified nitrate reductase. The presence of this cross reacting material in cell extracts was detected by the ability of these extracts to (a) lower the titer of antisera; (b) form a biphasic precipitin curve with purified antibody; and (c) increase the peak height of a standard amount of purified nitrate reductase in rocket immunoelectrophoresis assay. These results suggest that ammonia-grown cells contain nitrate reductase precursor protein.

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PubMed1980

Regulation of Glutamine Synthetase by Light and during Nitrogen Deficiency in Synchronous Chlorella sorokiniana.

A method is described to achieve density labeling of proteins in unicellular algae by using (13)CO(2). This is a satisfactory procedure especially for work on nitrogen metabolism. The increase in activity of glutamine synthetase (EC 6.3.1.2.) and glutamate synthase (EC 1.4.7.1.) in Chlorella sorokiniana mediated by a dark/light shift and by nitrogen starvation were investigated. Using the method of density labeling and isopycnic centrifugation, we demonstrated that the increase in enzyme activity after a dark/light shift is based on activation rather than de novo synthesis. The increase in enzyme activity after transfer to nitrogen-deficient medium is based both on activation and de novo synthesis.

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PubMed1981

Photosynthetic Apparatus Formation during the Cell Cycle of Chlorella.

Synchronous cell division in cultures of Chlorella vulgaris Beijerinck was induced by intermittent illumination: 9 hours light, 6 hours darkness. The rate of photosynthetic O(2) evolution per cell increases 4-fold in a one-step manner at the beginning of the light period, to the same extent as the increase in cell number. Over the division cycle, the following accumulation times during the light period were found: chlorophyll a, between 2 and 8 hours, chlorophyll b, between 5 and 8 hours, reaction centers of photosystems I and II, between 2 and 6 hours; and cytochrome f, between 2.5 and 5 hours. Cytochrome f accumulation is closely followed by an increase in amplitude of the rapid phase in light-induced absorption increase at 520 nanometers and in intensity of the delayed light emission. Enhancement of the delayed fluorescence yield per flash under continuous illumination (caused by the establishment of the pH difference across the thylakoid membrane) is maximal by the first hour of the light period.These findings, and others described in the text, suggested that the 4-fold growth of photosynthetic apparatus in the course of the cell cycle cannot be the result of gradual rise of electron-transport chain number. Rather, it is the result of a series of successive syntheses of its individual components. The rate-limiting step of electron transport is probably located between plastoquinone and cytochrome f.

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PubMed1981

Light requirement for induction and continuous accumulation of an ammonium-inducible NADP-specific glutamate dehydrogenase in chlorella.

The ammonium-inducible NADP-specific glutamate dehydrogenase of Chlorella sorokiniana was shown to require light for both its induction by ammonia in uninduced cells, and its continuous accumulation in fully induced cells. Addition of ammonia to uninduced cells in the light resulted in a 35-minute induction lag followed by linear and coincident increases in enzyme activity and antigen. Enzyme activity was not induced in the dark; however, transfer of these cells to the light resulted in an immediate increase in enzyme activity and antigen. The absence of an induction lag suggested that mRNA sequences and/or an enzyme precursor with different antigenic properties than the active holoenzyme accumulated in cells in the dark in ammonium medium. When fully induced cells were transferred to the dark, the activity of the enzyme quickly ceased to accumulate. In contrast to the NADP-specific isozyme, the cells also contain a constitutive NAD-specific isozyme which was shown to accumulate in cells in the dark in either ammonium or nitrate medium.

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PubMed1981

Effects of Environmental pH on the Internal pH of Chlorella pyrenoidosa, Scenedesmus quadricauda, and Euglena mutabilis.

The effect of external pH on two laboratory-cultured acid-intolerant species (Chlorella pyrenoidosa Chick and Scenedesmus quadricauda Turp. Bréb.) and one acid-tolerant species from a natural population (Euglena mutabilis Schmitz) was examined by measuring internal pH. These measurements were made with the weak acid (14)C-dimethyloxazolidine-2,4-dione after cells had been incubated for 2 and 6 hours at external pH levels from 3.0 to 8.0. Photosynthetic and respiration rates of the three species were also measured over the range of external pH levels.All three species regulated their internal pH levels over the 6-hour incubation time. C. pyrenoidosa and S. quadricauda had internal pH levels around 7.0, regardless of external pH. E. mutabilis had a wider internal pH range, from 5.0 at low external pH to 8.0 at high external pH. External pH had no effect on either photosynthetic or respiration rates. Statistical comparisons showed that there was a significant difference between the acid-intolerant and acid-tolerant species with regard to the level of internal pH maintained and the response of internal pH to external pH.

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PubMed1981

Modulation of PSI and PSII Organization During Loss and Repair of Photosynthetic Activity in a Temperature Sensitive Mutant of Chlorella pyrenoidosa.

Photosynthetic activity and organization of chlorophyll(Chl)-protein complexes in a temperature sensitive mutant of Chlorella pyrenoidosa have been investigated. The mutant is practically indistinguishable from wild type cells when grown at 25 C. However, mutant cells grown at 33 C do not synthesize Chl and lose their ability to evolve O(2). O(2) evolution and Chl synthesis are restored upon incubation of the 33 C grown cells at 25 C in absence of cell division (repair).Based on polarographic measurements of photosynthetic activities, variable fluorescence, 77 K fluorescence emission, excitation spectra, analysis of Chl-protein complexes, membrane polypeptide pattern and radioactive labeling using sodium dodecyl sulfate-polyacrylamide gel electrophoresis techniques during growth at 33 C and/or under repair conditions, it is concluded that: a, polypeptides of chloroplastic translation required for H(2)O-splitting activity are absent from membranes of 33 C grown cells. Their synthesis and/or assembly during the repair process is light-dependent. b, Polypeptides required for the formation of photosystem II and photosytem I reaction centers continue to be formed during growth at 33 C in absence of Chl synthesis. These can be assembled into functional units following Chl synthesis and energization of the membranes during the repair process. c, The Chl-protein complex serving as an antenna of photosystem I is disorganized, and the Chl is used for the formation of functional reaction centers of photosystem I during growth at 33 C.These results show that Chl-protein complexes can be dissociated in vivo and reassembled in a different way; and formation of Chl-protein complexes can occur stepwise from previously synthesized and newly formed components including both polypeptides and Chl.

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PubMed1981

Photorespiration in Air and High CO(2)-Grown Chlorella pyrenoidosa.

Oxygen inhibition of photosynthesis and CO(2) evolution during photorespiration were compared in high CO(2)-grown and air-grown Chlorella pyrenoidosa, using the artificial leaf technique at pH 5.0. High CO(2) cells, in contrast to air-grown cells, exhibited a marked inhibition of photosynthesis by O(2), which appeared to be competitive and similar in magnitude to that in higher C(3) plants. With increasing time after transfer to air, the photosynthetic rate in high CO(2) cells increased while the O(2) effect declined. Photorespiration, measured as the difference between (14)CO(2) and (12)CO(2) uptake, was much greater and sensitive to O(2) in high CO(2) cells. Some CO(2) evolution was also present in air-grown algae; however, it did not appear to be sensitive to O(2). True photosynthesis was not affected by O(2) in either case. The data indicate that the difference between high CO(2) and air-grown algae could be attributed to the magnitude of CO(2) evolution. This conclusion is discussed with reference to the oxygenase reaction and the control of photorespiration in algae.

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PubMed1982

Ozone Inhibition of Photosynthesis in Chlorella sorokiniana.

Exposure of Chlorella sorokiniana (07-11-05) to ozone inhibits photosynthesis. In this study, the effects of ozone on O(2) evolution and fluorescence yields are used to characterize this inhibition. At an ozone dose of about 3 micromoles delivered to 2 x 10(9) cells, the photosynthetic rate of the cells is inhibited 50%, as indicated by a decrease in bicarbonate-stimulated O(2) evolution (control rate, 1.4 +/- 0.3 x 10(-15) moles per cell per minute).Normal patterns of chlorophyll fluorescence are also altered. Upon continuous exposure to ozone (3.5 x 10(-7) moles O(3) per minute), three stages of change in relative fluorescence yields are observed: (a) a rise in variable yield with no corresponding change in nonvariable yield (after 1-2 minutes), which was interpreted to be a shift in the energy flow pathway; (b) a decline in variable yield with a slight rise in nonvariable yield (requiring 3-5 minutes), interpreted to be a blockage in the CO(2) fixation pathways; and (c) complete blockage of variable yield with a concurrent decline in nonvariable yield (8-10 minutes), interpreted to be a destruction of the pigment system. The timing of each stage depended upon the ozone concentration and its delivery rate to the cell suspension. These results are compared with ozone-induced decline in photosynthesis and leaf water potential changes reported for other plant systems.Evidence is also presented to suggest that ozone effects on the photosynthetic processes are attributable to ionic imbalances brought about by ozone interaction with the plasmalemma rather than a direct effect on the chloroplast.

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PubMed1982

A Thioredoxin-Mediated Activation of Glutamine Synthetase and Glutamate Synthase in Synchronous Chlorella sorokiniana.

The effects of thioredoxin, dithioerythrol, and mixtures of both on enzymes involved in N metabolism of Chlorella sorokiniana have been studied. Glutamine synthetase, inactivated in vivo, was activated 8-fold by thioredoxin and dithioerythrol. By the same treatment, the activity of glutamate synthase was stimulated nearly 4-fold. Thus, two key enzymes of N metabolism were shown to be regulated via thioredoxin. The enzymes of the nitrate reducing system, i.e. nitrate reductase and nitrite reductase, were not affected by thiols. From these results, a model of NO(3) (-) metabolism is put forward which considers the regulating effect of light.

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PubMed1982

Accumulation of Free Fatty Acids during Hardening of Chlorella ellipsoidea.

Chlorella ellipsoidea Gerneck (IAM C-27) was synchronously grown, and cells at an intermediate stage in the ripening phase of the cell cycle were hardened at 3 degrees C for 48 hours. A nonpolar lipid which increased greatly during hardening was analyzed by gas-liquid chromatography. Palmitic, oleic, linoleic, and linolenic acids were the main components of the lipid. Electron micrographs revealed the appearance of lipid bodies in hardened cells. When formation of free fatty acids and lipid bodies was inhibited with cycloheximide, oligomycin, and 3-(3,4-dichlorophenyl)-1,1-dimethylurea, the development of a high level of hardiness was always inhibited. However, the converse results were not always realized. Cells hardened in the dark in the absence of glucose developed a measurable hardiness in spite of their failure to form free fatty acids. The appearance of lipid bodies was invariably accompanied by the formation of the fatty acids. In pulse-labeling with [(14)C]NaHCO(3) for 4 minutes at zero time and at the 12th hour of hardening, initial incorporation rates of (14)C into total lipids of whole cells and the cellular membrane fraction were significantly higher than that into free fatty acids. These results suggest that, although fatty acids are inserted into membrane lipids during hardening, the accumulation of free fatty acids and the appearance of lipid bodies per se are not involved in the development of frost hardiness.

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PubMed1983

On the Ratio of Photosynthetic Reaction Centers RC2/RC1 in Chlorella.

Chlorella pyrenoidosa (Emerson strain) was grown under high and under low irradiance. Measurements of the O(2) flash yield and the P700 absorption change gave estimates for the ratio of photoreaction centers RC2/RC1 at 1.2 to 1.5. A background light 1 did not increase flash yield.

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PubMed1983

Glycolate Formation and Excretion by Chlorella pyrenoidosa and Netrium digitus.

Conditions are described whereby suspensions of Chlorella pyrenoidosa and Netrium digitus photosynthetically biosynthesize and excrete glycolate continuously in high yields. Aminooxyacetic acid, an inhibitor of pyridoxal phosphate-linked enzymes, increased the excretion of glycolate approximately 4-fold in 1 hour (8 millimolar) and 20-fold in 4 hours (40 millimolar) in the presence of 0.2% CO(2) in air. The amount of glycolate excreted in the presence of aminooxyacetate and an atmosphere of 0.2% CO(2) in air equaled or exceeded the amount excreted in 0.2% CO(2) in O(2) minus aminooxyacetate. CO(2) and light were required for glycolate excretion. Aminooxyacetate also stimulated photosynthetic glycolate excretion in an atmosphere of 0.2% CO(2) in nitrogen or helium, although the stimulation was not as great as when air or O(2) was present.The excreted glycolate was converted to H(2) and CO(2) by the combined action of glycolic oxidase and the formic hydrogenlyase complex found in Escherichia coli in total conversion yields of 80%.

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