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PubMed1995

Leaf Phosphate Status, Photosynthesis, and Carbon Partitioning in Sugar Beet (IV. Changes with Time Following Increased Supply of Phosphate to Low-Phosphate Plants).

Changes in photosynthesis, carbon partitioning, and growth following resupply of orthophosphate (Pi) to moderately P-deficient plants (low-P) were determined for sugar beets (Beta vulgaris L. cv F58-554H1) cultured hydroponically in growth chambers. One set of plants was supplied with 1.0 mM Pi in half-strength Hoagland solution (control plants), and a second set (low-P plants) was supplied with 0.05 mM Pi. At the end of 2 weeks, the low-P plants were resupplied with 1.0 mM Pi. Low-P plants rapidly accumulated large amounts of Pi, and the photosynthesis rate increased to control values within 4 to 6 h. The rate of photosynthesis appeared to be controlled by ribulose-1,5-bisphosphate (RuBP); low P reduced photosynthesis and RuBP levels, and P resupply increased photosynthesis and RuBP in a manner parallel with time. Low-P treatment reduced adenylate levels substantially but not nicotinamide nucleotides; adenylate levels recovered to control values over 3 to 6 h. With low P, more photosynthate is allocated to non-P carbon compounds (e.g. starch, sucrose) than to sugar phosphates. When P is resupplied, sugar phosphates increase as starch and sucrose pools decrease; this increase in leaf (chloroplast) sugar phosphates was most likely responsible for the increases in RuBP and photosynthesis and may have increased adenylate levels (through enhanced levels of ribose-5-phosphate).

Journal Article↗
PubMed1998

Oxygen Requirement and Inhibition of C4 Photosynthesis. An analysis of c4 plants deficient in the c3 and c4 cycles An Analysis of C4 Plants Deficient in the C3 and C4 Cycles

The basis for O2 sensitivity of C4 photosynthesis was evaluated using a C4-cycle-limited mutant of Amaranthus edulis (a phosphoenolpyruvate carboxylase-deficient mutant), and a C3-cycle-limited transformant of Flaveria bidentis (an antisense ribulose-1,5-bisphosphate carboxylase/oxygenase [Rubisco] small subunit transformant). Data obtained with the C4-cycle-limited mutant showed that atmospheric levels of O2 (20 kPa) caused increased inhibition of photosynthesis as a result of higher levels of photorespiration. The optimal O2 partial pressure for photosynthesis was reduced from approximately 5 kPa O2 to 1 to 2 kPa O2, becoming similar to that of C3 plants. Therefore, the higher O2 requirement for optimal C4 photosynthesis is specifically associated with the C4 function. With the Rubisco-limited F. bidentis, there was less inhibition of photosynthesis by supraoptimal levels of O2 than in the wild type. When CO2 fixation by Rubisco is limited, an increase in the CO2 concentration in bundle-sheath cells via the C4 cycle may further reduce the oxygenase activity of Rubisco and decrease the inhibition of photosynthesis by high partial pressures of O2 while increasing CO2 leakage and overcycling of the C4 pathway. These results indicate that in C4 plants the investment in the C3 and C4 cycles must be balanced for maximum efficiency.

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PubMed1999

Decrease in phosphoribulokinase activity by antisense RNA in transgenic tobacco. Relationship between photosynthesis, growth, and allocation at different nitrogen levels

To study the direct effects of photosynthesis on allocation of biomass by altering photosynthesis without altering leaf N or nitrate content, phosphoribulokinase (PRK) activity was decreased in transgenic tobacco (Nicotiana tabacum L.) with an inverted tobacco PRK cDNA and plants were grown at different N levels (0.4 and 5 mM NH4NO3). The activation state of PRK increased as the amount of enzyme was decreased genetically at both levels of N. At high N a 94% decrease in PRK activity had only a small effect (20%) on photosynthesis and growth. At low N a 94% decrease in PRK activity had a greater effect on leaf photosynthesis (decreased by up to 50%) and whole-plant photosynthesis (decreased by up to 35%) than at high N. These plants were up to 35% smaller than plants with higher PRK activities because they had less structural dry matter and less starch, which was decreased by 3- to 4-fold, but still accumulated to 24% to 31% of dry weight; young leaves contained more starch than older leaves in older plants. Leaves had a higher ion and water content, and specific leaf area was higher, but allocation between shoot and root was unaltered. In conclusion, low N in addition to a 94% decrease in PRK by antisense reduces the activity of PRK sufficient to diminish photosynthesis, which limits biomass production under conditions normally considered sink limited.

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PubMed1977

Characterization of Photosynthetic Rhythms in Marine Dinoflagellates: II. Photosynthesis-Irradiance Curves and in Vivo Chlorophyll a Fluorescence.

Using data from light-dark cultures of Gonyaulax polyedra entrained to a 24-hour cycle, whole cell absorption curves and photosynthesis-irradiance curves were constructed for various circadian times. While whole cell absorbance and half-saturation constants of photosynthesis showed no statistical difference that could be directly related to the photosynthetic rhythm, the initial slope of the photosynthesis-irradiance curve was a time-dependent parameter which altered in direct proportion to the change in photosynthetic capacity. The results indicated a temporal change in the relative quantum yield of photosynthesis, and the circadian rhythmicity of light-limited photosynthesis was established under constant conditions. Circadian rhythmicity was detected in room temperature chlorophyll fluorescence yield. Low temperature fluorescence kinetics also showed fluctuations. The results suggest that regulation of photosynthesis by the biological clock of Gonyaulax may be mediated through the membrane-bound light reactions and a partial explanation of the underlying mechanism is proposed.

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PubMed1978

Photosynthesis by isolated protoplasts, protoplast extracts, and chloroplasts of wheat: influence of orthophosphate, pyrophosphate, and adenylates.

Protoplasts, protoplast extracts (intact chloroplasts plus extrachloroplastic material), and chloroplasts isolated from protoplasts of wheat (Triticum aestivum) have rates of photosynthesis as measured by light-dependent O(2) evolution of about 100 to 150 micromoles of O(2) per milligram of chlorophyll per hour at 20 C and saturating bicarbonate. The assay conditions sufficient for this activity were 0.4 molar sorbitol, 50 millimolar N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid KOH (pH 7.6), and 10 millimolar NaHCO(3) with protoplast, plus a requirement of 1 to 10 millimolar ethylenediaminetetraacetate (EDTA) and 0.2 to 0.5 millimolar inorganic orthophosphate (Pi) with protoplast extracts and chloroplasts. Protoplast extracts evolved approximately 6 micromoles of O(2) per milligram of chlorophyll before photosynthesis became largely dependent on exogenous Pi while photosynthesis by chloroplasts had a much stronger dependence on exogenous Pi from the outset.Photosynthesis by chloroplasts from 6-day-old wheat plants under optimum levels of Pi was similar to that with the addition of 5 millimolar inorganic pyrophosphate (PPi) plus 0.2 millimolar adenosine-5'-diphosphate (ADP). Either PPi or ADP added separately inhibited photosynthesis. When chloroplasts were incubated in the dark for 2 to 6 minutes, photosynthesis was strongly inhibited by 5 millimolar PPi and this inhibiting was relieved by including adenosine-5'-triphosphate (ATP) or ADP (0.2 to 0.6 millimolar). Chloroplasts from 9-day-old wheat leaves were slightly less sensitive to inhibition by PPi and showed little or no inhibition by ADP.Chloroplasts isolated from protoplasts and assayed with 0.3 millimolar Pi added before illumination have an induction time from less than 1 minute up to 16 minutes depending on the time of the assay after isolation and the components of the medium. In order to obtain maximum rates of photosynthesis and minimum induction time, NaHCO(3) and chelating agents, EDTA or PPi (+ATP), are required in the chloroplast isolation, resuspension and assay medium. With these inclusions in the isolation and resuspension medium the induction time decreased rapidly during the first 20 to 30 minutes storage of chloroplasts on ice. Requirements for isolating intact and photosynthetically functional chloroplasts from wheat protoplasts are discussed.

Journal Article↗
PubMed1979

Effects of Variations in Daylength and Temperature on Net Rates of Photosynthesis, Dark Respiration, and Excretion by Isochrysis galbana Parke.

The effects of variable daylength and temperature on net rates of photosynthesis, dark respiration, and excretion of a unicellular marine haptophyte, Isochrysis galbana Parke, were examined and related to division rates. Six combinations of daylength (18:6, 12:12, 6:18 light:dark, LD) and temperature (20, 25 C) were used. Daily rates of net photosynthesis were closely correlated to division rates, suggesting a direct relationship, and were maximal when cells were grown at 12:12 LD at both temperatures and 18:6 LD at 20 C. A daylength of 6 hours decreased daily rates by decreasing the time for carbon uptake. Further, cells grown with this daylength had maximal chlorophyll a contents, suggesting a physiological adaptation by photosynthetic units to short light periods. A photoperiod of 18:6 LD at 25 C decreased daily rates of net photosynthesis by reducing the hourly rate of net photosynthesis via an unidentified mechanism. The importance of rates of net dark respiration in controlling daily net photosynthesis was small, with carbon lost during dark periods varying between 4 and 14% of that gained during light periods. Also, the influence of net excretion was small, varying between 1.0 and 5.5% of daily net photosynthesis.

Journal Article↗
PubMed1982

Photocontrol of the Functional Coupling between Photosynthesis and Stomatal Conductance in the Intact Leaf : Blue Light and Par-Dependent Photosystems in Guard Cells.

The photocontrol of the functional coupling between photosynthesis and stomatal conductance in the leaf was investigated in gas exchange experiments using monochromatic light provided by lasers. Net photosynthesis and stomatal conductance were measured in attached leaves of Malva parviflora L. as a function of photon irradiance at 457.9 and 640.0 nanometers.Photosynthetic rates and quantum yields of photosynthesis were higher under red light than under blue, on an absorbed or incident basis.Stomatal conductance was higher under blue than under red light at all intensities. Based on a calculated apparent photon efficiency of conductance, blue and red light had similar effects on conductance at intensities higher than 0.02 millimoles per square meter per second, but blue light was several-fold more efficient at very low photon irradiances. Red light had no effect on conductance at photon irradiances below 0.02 millimoles per square meter per second. These observations support the hypothesis that stomatal conductance is modulated by two photosystems: a blue light-dependent one, driving stomatal opening at low light intensities and a photosynthetically active radiation (PAR)-dependent one operating at higher irradiances.When low intensity blue light was used to illuminate a leaf already irradiated with high intensity, 640 nanometers light, the leaf exhibited substantial increases in stomatal conductance. Net photosynthesis changed only slightly. Additional far-red light increased net photosynthesis without affecting stomatal conductance. These observations indicate that under conditions where the PAR-dependent system is driven by high intensity red light, the blue light-dependent system has an additive effect on stomatal conductance.The wavelength dependence of photosynthesis and stomatal conductance demonstrates that these processes are not obligatorily coupled and can be controlled by light, independent of prevailing levels of intercellular CO(2). The blue light-dependent system in the guard cells may function as a specific light sensor while the PAR-dependent system supplies a CO(2)-modulated energy source providing functional coupling between the guard cells and the photosynthesizing mesophyll.

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PubMed1982

Inhibition of photosynthesis by ethylene-a stomatal effect.

Ethylene at hormonally significant levels inhibited net photosynthesis of the cultivated peanut (Arachis hypogaea L.) as measured by gas analysis. Upon the removal of ethylene, the inhibition was naturally overcome at the concentration-exposure duration combinations tested. Increased length of exposure of 1 microliter of ethylene per liter of air up to 6 hours increased the degree of net photosynthesis inhibition (68% reduction after 6-hour exposure). Significantly greater inhibition of photosynthesis by ethylene was detected on peanut genotypes having higher photosynthetic efficiency. In contrast to peanut, hormonal concentrations of ethylene only moderately inhibited sweet potato, Jerusalem artichoke, and sunflower photosynthesis and was without effect on beans, peas, Irish potato, Mimosa pudica, and white clover. No inhibition could be found by ethylene on ribulose 1,5-biphosphate carboxylase activity in vitro. Photosynthesis was lowered at all CO(2) concentrations below ambient at an O(2) concentration of 1.5%, indicating that the action of ethylene was not affected by low O(2); concomitantly, an increase in the CO(2) compensation point occurred. Diffusion resistance measurements of leaf water vapor loss made on ethylene-treated peanut leaves showed a measurable decrease in leaf conductance which correlated with net photosynthesis decrease. Ethylene influenced the conductance of abaxial stomata more so than adaxial.

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PubMed1984

Kok effect and the quantum yield of photosynthesis : light partially inhibits dark respiration.

The linear response of photosynthesis to light at low photon flux densities is known to change abruptly in the vicinity of the light compensation point so that the quantum yield seems to decrease as radiation increases. We studied this ;Kok effect' in attached sunflower (Helianthus annuus L. cv IS894) leaves using gas exchange techniques. The effect was present even though respiration was constant in the dark. It was observed at a similar photon flux density (7 to 11 micromole photons per square meter per second absorbed photosynthetically active radiation) despite a wide range of light compensation points as well as rates of photosynthesis. The effect was not apparent when photorespiration was inhibited at low pO(2) (1 kilopascal), but this result was complicated because dark respiration was quite O(2)-sensitive and was partially suppressed under these conditions. The Kok effect was observed at saturating pCO(2) and, therefore, could not be explained by a change in photorespiration. Instead, the magnitude of the effect varied as dark respiration varied in a single leaf, and was minimized when dark respiration was minimized, indicating that a partial suppression of dark respiration by light is responsible. Quantum yields measured at photon flux densities between 0 and 7 to 11 micromole photons per square meter per second, therefore, represent the combined yields of photosynthesis and of the suppression of a component of dark respiration by light. This leads to an overestimate of the quantum yield of photosynthesis. In view of these results, quantum yields of photosynthesis must be measured (a) when respiration is constant in the dark, and (b) when dark respiration has been inhibited either at low pO(2) to eliminate most of the light-induced suppression of dark respiration or at photon flux densities above that required to saturate the light-induced suppression of dark respiration. Significant errors in quantum yields of photosynthesis can result in leaves exhibiting this respiratory behavior if these principles are not followed.

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PubMed1985

Photosynthate supply and utilization in alfalfa : a developmental shift from a source to a sink limitation of photosynthesis.

Long-term carbon dioxide enrichment, (14)CO(2) feeding, and partial defoliation were employed as probes to investigate source/sink limitations of photosynthesis during the development of symbiotically grown alfalfa. In the mature crop, long-term CO(2) enrichment does not affect the rates of net photosynthesis, relative growth, (14)C export to nonphotosynthetic organs, or the rates of (14)C label incorporation into leaf sucrose, starch, or malate. The rate of glycolate labeling is, however, substantially reduced under these conditions. When the mature crop was partially defoliated, a considerable increase in net photosynthesis occurred in the remaining leaves. In the seedling crop, long-term CO(2) enrichment increased dry matter accumulation, primarily as a result of increases in leaf starch content. Although the higher rates of starch synthesis are not maintained, the growth enhancement of the enriched plants persisted throughout the experimental period. These results imply a source limitation of seedling photosynthesis and a sink limitation of photosynthesis in more mature plants. Consequently, both the supply and the utilization of photosynthate may limit seasonal photosynthesis in alfalfa.

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PubMed1985

O(2)-insensitive photosynthesis in c(3) plants : its occurrence and a possible explanation.

Leaves of C(3) plants which exhibit a normal O(2) inhibition of CO(2) fixation at less than saturating light intensity were found to exhibit O(2)-insensitive photosynthesis at high light. This behavior was observed in Phaseolus vulgaris L., Xanthium strumarium L., and Scrophularia desertorum (Shaw.) Munz. O(2)-insensitive photosynthesis has been reported in nine other C(3) species and usually occurred when the intercellular CO(2) pressure was about double the normal pressure. A lack of O(2) inhibition of photosynthesis was always accompanied by a failure of increased CO(2) pressure to stimulate photosynthesis to the expected degree. O(2)-insensitive photosynthesis also occurred after plants had been water stressed. Under such conditions, however, photosynthesis became O(2) and CO(2) insensitive at physiological CO(2) pressures. Postillumination CO(2) exchange kinetics showed that O(2) and CO(2) insensitivity was not the result of elimination of photorespiration.It is proposed that O(2) and CO(2) insensitivity occurs when the concentration of phosphate in the chloroplast stroma cannot be both high enough to allow photophosphorylation and low enough to allow starch and sucrose synthesis at the rates required by the rest of the photosynthetic component processes. Under these conditions, the energy diverted to photorespiration does not adversely affect the potential for CO(2) assimilation.

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PubMed1989

Maintenance of photosynthesis at low leaf water potential in wheat : role of potassium status and irrigation history.

The interaction of low water potential effects on photosynthesis, and leaf K(+) levels in wheat (Triticum aestivum L.) plants was studied. Plants were grown at three K(+) fertilization levels; 0.2, 2, and 6 millimolar. With well watered plants, 2 millimolar K(+) supported maximal photosynthetic rates; 0.2 millimolar K(+) was inhibitory, and 6 millimolar K(+) was superoptimal (i.e. rates were no greater than at 2 millimolar K(+)). Photosynthesis was monitored at high (930 parts per million) and low (330 parts per million) external CO(2) throughout a series of water stress cycles. Plants subjected to one stress cycle were considered nonacclimated; plants subjected to two successive cycles were considered acclimated during the second cycle. Sensitivity of photosynthesis to declining leaf water potential was affected by K(+) status; 6 millimolar K(+) plants were less sensitive, and 0.2 millimolar K(+) plants were more sensitive than 2 millimolar K(+) plants to declining water potential. This occurred with nonacclimated and acclimated plants at both high and low assay CO(2). It was concluded that the K(+) effect on photosynthesis under stress was not mediated by treatment effects on stomatal resistance. Differences between the K(+) treatments were much less pronounced, however, when photosynthesis of nonacclimated and acclimated plants was plotted at a function of declining relative water content during the stress cycles. These results suggest that K(+) effects on the relationship between relative water content and water potential in stressed plants was primarily responsible for the bulk of the K(+)-protective effect on photosynthesis in stressed plants. In vitro experiments with chloroplasts and protoplasts isolated from 2 millimolar K(+) and 6 millimolar K(+) plants indicated that upon dehydration, K(+) efflux from the chloroplast stroma into the cytoplasm is less pronounced in 6 millimolar K(+) protoplasts.

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PubMed1989

Selection and characterization of tobacco plants with novel o(2)-resistant photosynthesis.

Plants were obtained with novel O(2)-resistant photosynthetic characteristics. At low CO(2) (250-350 muL CO(2) L(-1)) and 30 degrees C when O(2) was increased from 1% to 21% to 42%, the ratio of net CO(2) uptake in O(2)-resistant whole plants or leaf discs compared to wild type increased progressively, and this was not related to stomatal opening. Dihaploid plantlets regenerated from anther culture were initially screened and selected for O(2)-resistant growth in 42% O(2)/160 muL CO(2) L(-1) and 0.18% of the plantlets showed O(2)-resistant photosynthesis. About 30% of the progeny (6 of 19 plants) of the first selfing of a fertile plant derived from a resistant dihaploid plant had O(2)-resistant photosynthesis, and after a second selfing this increased to 50% (6 of 12 plants). In 21% O(2) and low CO(2), net photosynthesis of the resistant plants was about 15% greater on a leaf area basis than wild type. Net photosynthesis was compared in leaf discs at 30 and 38 degrees C in 21% O(2), and at the higher temperature O(2)-resistant plants showed still greater photosynthesis than wild type. The results suggest that the O(2)-resistant photosynthesis described here is associated with a decreased stoichiometry of CO(2) release under conditions of rapid photorespiration. This view was supported by the finding that leaves of O(2)-resistant plants averaged 40% greater catalase activity than wild type.

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PubMed1989

Light adaptation/acclimation of photosynthesis and the regulation of ribulose-1,5-bisphosphate carboxylase activity in sun and shade plants.

The consequences of light adaptation and acclimation of photosynthesis on photosynthetic nitrogen use efficiency (NUE), particularly as it relates to the efficiency of ribulose-1,5-bisphosphate carboxylase (Rubisco) use in photosynthetic CO(2) assimilation, was studied in the sun species Glycine max and the shade species Alocasia macrorrhiza. Both G. max and A. macrorrhiza were found to possess the capacity for light acclimation of CO(2) assimilation, but over distinctly different ranges of photon flux density (PFD). For each species, light acclimation of photosynthesis had little effect on the rate of photosynthesis per unit Rubisco protein or the light response of Rubisco carbamylation and CA 1P metabolism. In contrast, photosynthesis per unit Rubisco protein was significantly higher in G. max than in A. macrorrhiza, due in part to a lower total (fully carbamylated) molar activity (activity per unit enzyme) of A. macrorrhiza Rubisco than that of G. max. Comparison of the light response of Rubisco regulatory mechanisms between G. max and A. macrorrhiza indicated some degree of adaptation, such that carbamylation was higher and CA 1P levels lower at lower PFDs in the shade species than the sun species. However, this adjustment was not sufficient for Rubisco in low light grown A. macrorrhiza to be fully active at the growth PFD. Photosynthesis in A. macrorrhiza appeared to become RuBP regeneration-limited at lower PFDs than G. max, and this was probably the determinant of the light saturated rate of photosynthesis in the shade species. The low efficiency of Rubisco use in A. macrorrhiza was a major contributing factor to its five- to sixfold lower photosynthetic NUE than G. max. Shade species such as A. macrorrhiza appear to make far from maximal use of Rubisco protein N.

Journal Article↗
PubMed1986

Adaptation to Hydrogen Sulfide of Oxygenic and Anoxygenic Photosynthesis among Cyanobacteria.

Four different types of adaptation to sulfide among cyanobacteria are described based on the differential toxicity to sulfide of photosystems I and II and the capacity for the induction of anoxygenic photosynthesis. Most cyanobacteria are highly sensitive to sulfide toxicity, and brief exposures to low concentrations cause complete and irreversible cessation of CO(2) photoassimilation. Resistance of photosystem II to sulfide toxicity, allowing for oxygenic photosynthesis under sulfide, is found in cyanobacteria exposed to low H(2)S concentrations in various hot springs. When H(2)S levels exceed 200 muM another type of adaptation involving partial induction of anoxygenic photosynthesis, operating in concert with partially inhibited oxygenic photosynthesis, is found in cyanobacterial strains isolated from both hot springs and hypersaline cyanobacterial mats. The fourth type of adaptation to sulfide is found at H(2)S concentrations higher than 1 mM and involves a complete replacement of oxygenic photosynthesis by an effective sulfide-dependent, photosystem II-independent anoxygenic photosynthesis. The ecophysiology of the various sulfide-adapted cyanobacteria may point to their uniqueness within the division of cyanobacteria.

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PubMed1986

Transition from Anoxygenic to Oxygenic Photosynthesis in a Microcoleus chthonoplastes Cyanobacterial Mat.

Benthic cyanobacterial mats with the filamentous Microcoleus chthonoplastes as the dominant phototroph grow in oxic hypersaline environments such as Solar Lake, Sinai. The cyanobacteria are in situ exposed to chemical variations between 200 mumol of sulfide liter at night and 1 atm pO(2) during the day. During experimental H(2)S to O(2) transitions the microbial community was shown to shift from anoxygenic photosynthesis, with H(2)S as the electron donor, to oxygenic photosynthesis. Microcoleus filaments could carry out both types of photosynthesis concurrently. Anoxygenic photosynthesis dominated at high sulfide levels, 500 mumol liter, while the oxygenic reaction became dominant when the sulfide level was reduced below 100 to 300 mumol liter (25 to 75 mumol of H(2)S liter). An increasing inhibition of the oxygenic photosynthesis was observed upon transition to oxic conditions from increasing sulfide concentrations. Oxygen built up within the Microcoleus layer of the mat even under 5 mmol of sulfide liter (500 mumol of H(2)S liter) in the overlying water. The implications of such a localized O(2) production in a highly reducing environment are discussed in relation to the evolution of oxygenic photosynthesis during the Proterozoic era.

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PubMed1958

Photosynthesis.

With the establishment of conditions for optimum culturing and measurement, there is now final proof that in photosynthesis at high as well as low light intensities the light energy can be almost completely converted into chemical energy. There is thus drawn to a close an investigation that was initiated many years ago in Berlin in the Imperial Institute of Physics (9). The second result is the establishment of a general physical mechanism of photosynthesis, involving an interplay between light energy and respiratory energy, and therewith the solution of the quantum problem in photosynthesis. The third result is the establishment of the function of chlorophyll as a stoichiometric, chemically reacting component in photosynthesis. There remains the special chemistry of photosynthesis. In this still-unfinished field of investigation, the latest discovery is the labile carbon dioxide of Chlorella, connected with the decomposition and resynthesis of glutamic acid in living Chlorella, and connected with the possible function of the amino acids, aspartic and glutamic, in the binding and reduction of carbonic acid. The dissociating CO(2) is bound by Chlorella only in the presence of O(2) and of cellular glutamic acid. This CO(2) is released if the oxygen pressure is lowered below 2 mm of water or if-in the presence of oxygen-the glutamic acid is split in the living Chlorella, for example, by N/10,000 benzoquinone. This is the CO(2) that is used in light and taken up in the dark (8).

Berlin↗
PubMed1991

Hydrogen peroxide and the evolution of oxygenic photosynthesis.

The early atmosphere of the Earth is considered to have been reducing (H2 rich) or neutral (CO2-N2). The present atmosphere by contrast is highly oxidizing (20% O2). The source of this oxygen is generally agreed to have been oxygenic photosynthesis, whereby organisms use water as the electron donor in the production of organic matter, liberating oxygen into the atmosphere. A major question in the evolution of life is how oxygenic photosynthesis could have evolved under anoxic conditions--and also when this capability evolved. It seems unlikely that water would be employed as the electron donor in anoxic environments that were rich in reducing agents such as ferrous or sulfide ions which could play that role. The abiotic production of atmospheric oxidants could have provided a mechanism by which locally oxidizing conditions were sustained within spatially confined habitats thus removing the available reductants and forcing photosynthetic organisms to utilize water as the electron donor. We suggest that atmospheric H2O2 played the key role in inducing oxygenic photosynthesis because as peroxide increased in a local environment, organisms would not only be faced with a loss of reductant, but they would also be pressed to develop the biochemical apparatus (e.g., catalase) that would ultimately be needed to protect against the products of oxygenic photosynthesis. This scenario allows for the early evolution of oxygenic photosynthesis while global conditions were still anaerobic.

Atmosphere↗