Dependent Oxygen Evolution Research Articles

Unveiling the facet-dependent electrocatalytic activity of a 3D-CoSn(OH)6 perovskite material for overall water splitting: Interfacial engineering with Mn3+ and CH3COO- ions

In this study, we report morphologically dependent electrocatalytic oxygen and hydrogen evolution reactions in an alkaline medium. The bifunctional electrocatalyst such as cobalt tin hydroxide (CoSn(OH)6) was prepared by hydrothermal method. Importantly, tuning the morphological variation of CoSn(OH)6 into cubes, octa- and dodecahedra and their corresponding growth mechanisms are analyzed and explored the electrochemical studies. Among the different morphologies, the CoSn(OH)6 dodecahedron (CTH-DH) displays a substantially enhanced overall electrocatalytic water splitting reaction. It is firmly due to the [Mn3+] and [CH3COO-] ions do enable the morphological progression of the CTH cubic crystals with more facets. The highly active catalytic sites on the facets of CTH-DH permit the adsorption of abundant OH groups during the hydrogen and oxygen evolution reactions. Moreover, in a two-electrode system, the CTH-DH ǁ CTH-DH electrolyzer exhibits a cell potential of 1.60 V at 10 mA cm–2 with a remarkable reliable long-term stability. In addition, the structural transformations of the as-prepared CoSn(OH)6 crystals are monitored before and after electrocatalysis using TEM study. As a result, the study highlights the potential of Mn-containing CTH-DH facets as viable electrocatalysts in efficient H2 production.

Surface facets dependent oxygen evolution reaction of single Cu2O nanoparticles

Understanding and establishing the structure-activity relation of nanoparticles is a prerequisite for rational design of high-performance electrocatalysts. Cu 2 O nanoparticles enclosed with different crystal facets, namely, o-Cu 2 O NPs with {111} facets, c-Cu 2 O NPs with {100} facets are prepared and their electrocatalytic properties for oxygen evolution reaction (OER) in alkaline condition are evaluated at single nanoparticle level with a combination of scanning electrochemical cell microscopy and scanning electron microscopy. It is found that the o-Cu 2 O NPs have significantly superior OER electrocatalytic activity compared to c-Cu 2 O, which is almost inert. The estimated turnover frequency (TOF) at 1.97 V vs. RHE on {111} facet increases from 4 s −1 to 115 s −1 with the octahedron edge length decreasing from 1.3 µm to 100 nm. Deposition of carbon on c-Cu 2 O surface barely promotes the activity, suggesting the inherent poor electric conductivity within the nanocrystal is most likely the reason for low activity. This work provides direct probing to single transition metal oxide crystals with dramatically different activity. We endeavor to directly establish the correlation between nanoparticle surface facets with the intrinsic electrocatalytic OER activity from electrochemical measurement at single Cu 2 O nanoparticles using a combination of SECCM and SEM.

Exploring the thickness dependent photocatalytic oxygen evolution performance for Bi4TaO8Cl two-dimensional semiconductor

The utilization of solar energy for water splitting has great potential to alleviate the worsening environmental issues. Two-dimensional (2D) materials, possessing tunable band gap, large surface area with more active sites, and short photogenerated carriers migrating distance, have attracted massive research interests as promising photocatalysts. In the water splitting reaction, compared with the hydrogen evolution reaction, the four elementary steps of oxygen evolution reaction (OER) is a complex and difficult reaction. Among 2D materials, Bi4TaO8Cl exhibits great potential for the OER. It is worth noting that the thicknesses of 2D materials is a significant factor for modifying physicochemical properties. However, the thickness dependence of OER performance remains unclear in Bi4TaO8Cl. Here, we systematically studied the effects of thicknesses on photocatalytic performance. Interestingly, we found that the few-layer Bi4TaO8Cl possesses more remarkable photocatalytic properties than monolayer Bi4TaO8Cl deriving from interlayer coupling effect. Compared with monolayer Bi4TaO8Cl, the few-layer exhibits broader range of light absorption accompanied with larger transition dipole moment, stronger reduction potential to drive the OER, and lower recombination probability of photogenerated electron and hole. The interlayer coupling interaction improves the photocatalytic properties, which promotes the progress of 2D material at photocatalytic water splitting reaction.

Crystal phase determined Fe active sites on Fe2O3 (γ- and α-Fe2O3) yolk-shell microspheres and their phase dependent electrocatalytic oxygen evolution reaction

Transition metal oxide nanomaterials have been extensively applied to the field of oxygen evolution reaction (OER), but few works have been studied to demonstrate the relationship between their crystal phases and OER performance. Herein, we compare the OER performance of the two different crystal phase iron oxide (α-Fe2O3 and γ-Fe2O3). The iron oxide yolk-shell microspheres were facile realized via one-step solvothermal method and the subsequent annealing treatment. An interesting phenomenon is present that α-Fe2O3 yolk-shell microspheres with a smaller specific surface area have better OER performance than that of γ-Fe2O3 yolk-shell microspheres. The crystal structure and X-ray photoelectron spectroscopy (XPS) results show that α-Fe2O3 yolk-shell microspheres have better electrocatalytic activity, which is due to the presence of more Fe active sites (Fe3+) exposured on the surface. These Fe active sites are beneficial to enhance the adsorption of hydroxyl groups in water molecules, leading to a higher OER performance. As an application example, the Fe2O3 yolk-shell microspheres are employed as an efficient OER electrocatalyst, showing the interdependence between phase and OER behavior.

O2 supports 3-phosphoglycerate-dependent O2 evolution in chloroplasts from spinach leaves

We tested the hypothesis that the Mehler-ascorbate peroxidase (MAP) pathway supports 3-phosphoglycerate (PGA)-dependent oxygen (O2) evolution using intact chloroplasts. Lowering O2 concentration (<1 µM) suppressed PGA-dependent O2 evolution rate. High O2 concentration (about 250 µM) enhanced the electron fluxes in Photosystem II (PSII). Also, high O2 concentration oxidized both QA in PSII and Cyt f in thylakoid membranes. These results indicated that the MAP pathway stimulated photosynthetic electron transport. Furthermore, electrochromic shift signal was also increased at high O2 concentration, compared to low O2 concentration. Non-photochemical quenching of chlorophyll fluorescence was also enhanced at high O2 concentration. These data support our hypothesis that the MAP pathway functioned in intact chloroplasts and accelerated PGA-dependent O2 evolution by inducing ΔpH formation to produce and supply adenosine triphosphate (ATP) to the conversion reaction of PGA to glyceraldehyde 3-phosphate through 1,3-diphosphoglycerate in chloroplasts.

Transcriptional regulation of the CO2-concentrating mechanism in a euryhaline, coastal marine cyanobacterium, Synechococcus sp. Strain PCC 7002: role of NdhR/CcmR.

Cyanobacterial photosynthesis occurs in radically diverse habitats and utilizes various forms of a CO(2)-concentrating mechanism (CCM) featuring multiple inorganic carbon (C(i)) transporters. Cyanobacteria from dynamic environments can transform CCM activity depending on C(i) availability, and yet the molecular basis for this regulation is unclear, especially in coastal strains. LysR family transcription factors resembling the Calvin cycle regulator CbbR from proteobacteria have been implicated in the expression of C(i) transporter genes in freshwater cyanobacteria. Our survey of related factors revealed a group of divergent CbbR-like sequences confined to freshwater and coastal or offshore cyanobacteria. Inactivation of the single gene (termed ccmR) from this variable cluster in the euryhaline (coastal) strain Synechococcus sp. strain PCC 7002 led to constitutive expression of a high-affinity CCM. Derepression of HCO(3)(-) transporter gene transcription, including that of BicA, a recently discovered HCO(3)(-) transporter (G. D. Price et al., Proc. Natl. Acad. Sci. USA 101:18228-18233, 2004), was observed. A unique CcmR-regulated operon containing bicA plus 9 open reading frames encoding likely Na(+)/H(+) antiporters from the CPA1 and Mnh families was defined that is essential for maximal HCO(3)(-)-dependent oxygen evolution. The promoter region required for C(i)-regulated transcription of this operon was defined. We propose that CcmR (and its associated regulon) represents a specialization for species inhabiting environments subject to fluctuating C(i) concentrations.

Effects of UV -B radiation on inorganic carbon acquisition by the marine microalga Dunaliella tertiolecta (Chlorophyceae)

The chlorophyte alga Dunaliella tertiolecta was exposed to UV-B radiation (UVBR) and the characteristics of dissolved inorganic carbon (DIC)-dependent oxygen evolution, carbon fixation and CO2-concentrating mechanism (CCM) activity were examined. Exposure response measurements were carried out under 2.8 W m−2 UVBR (unweighted), and the maximum quantum yield of photosystem II (PSII), ΦPSII-max, was monitored until cell suspensions were ~ 50% inhibited. Under these conditions, although photosystem II (PSII) activity was severely inhibited, photosystem I capacity decreased by only < l5%. UVBR-treated cells exposed to H14CO3− took up the same amount of label as did untreated cells, though the proportion fixed into organic matter decreased under UVBR and the internal DIC pool increased. The increase in internal DIC pools was paralleled by an increase in conductance for DIC, measured as the increase in the initial slope of oxygen evolution vs [DIC] plots. Thus, although carbon assimilation rates are inhibited by UVBR, CCM activity is unaffected. The ecological significance of these findings is discussed.

Ca 2+ Function in Photosynthetic Oxygen Evolution Studied by Alkali Metal Cations Substitution

Effects of adding monovalent alkali metal cations to Ca 2+-depleted photosystem (PS)II membranes on the biochemical and spectroscopic properties of the oxygen-evolving complex were studied. The Ca 2+-dependent oxygen evolution was competitively inhibited by K +, Rb +, and Cs +, the ionic radii of which are larger than the radius of Ca 2+ but not inhibited significantly by Li + and Na +, the ionic radii of which are smaller than that of Ca 2+. Ca 2+-depleted membranes without metal cation supplementation showed normal S 2 multiline electron paramagnetic resonance (EPR) signal and an S 2Q A − thermoluminescence (TL) band with a normal peak temperature after illumination under conditions for single turnover of PSII. Membranes supplemented with Li + or Na + showed properties similar to those of the Ca 2+-depleted membranes, except for a small difference in the TL peak temperatures. The peak temperature of the TL band of membranes supplemented with K +, Rb +, or Cs + was elevated to ∼38°C which coincided with that of Y D +Q A − TL band, and no S 2 EPR signals were detected. The K +-induced high-temperature TL band and the S 2Q A − TL band were interconvertible by the addition of K + or Ca 2+ in the dark. Both the Ca 2+-depleted and the K +-substituted membranes showed the narrow EPR signal corresponding to the S 2Y Z + state at g = 2 by illuminating the membranes under multiple turnover conditions. These results indicate that the ionic radii of the cations occupying Ca 2+-binding site crucially affect the properties of the manganese cluster.

Microscopic green algae and cyanobacteria in high-frequency intermittent light

The effects of fluctuations in the irradiance onScenedesmus quadricauda, Chlorella vulgaris andSynechococcus elongatus were studied in dilute cultures using arrays of red light emitting diodes. The growth rate and the rate of photoinhibition were compared using intermittent and equivalent continuous light regimes in small-size (30 ml) bioreactors. The CO2 dependent photosynthetic oxygen evolution rates in the intermittent and continuous light regimes were compared for different light/dark ratios and different mean irradiances. The kinetics of the electron transfer reactions were investigated using a double-modulation fluorometer. The rates of photosynthetic oxygen evolution normalized to equal mean irradiance were lower or equal in the intermittent light compared to the maximum rate found in the equivalent optimal continuous light regime. In contrast, the growth rates in the intermittent light can be higher than the growth rate in the equivalent continuous light. Photoinhibition is presented as an example of a physiological process affecting the growth rate that occurs at different rates in the intermittent and equivalent continuous lights. The difference in the dynamics of the redox state of the plastoquinone pool is proposed to be responsible for the low photoinhibition rates observed in the intermittent light.

Photosystem II Independent Carbon Dioxide Fixation in Plectonema boryanum During Photoautotrophic Growth Under Nitrogen Fixation Conditions

The non-heterocystous filamentous cyanobacterium Plectonema boryanum UTEX 594 grew rapidly microaerobically under nitrogen-starvation conditions in continuous high light intensity by conducting oxygenic photosynthesis and oxygen sensitive nitrogen-fixation in alternating cycles. During diazotrophic phase, the light harvesting pigment phycocyanin declined with a concomitant depression in light dependent oxygen evolution by the cyanobacterium. A substantial component of light dependent carbon dioxide fixation during diazotrophic phase was not inhibited by DCMU in spite of complete cessation of photosynthetic oxygen evolution. Endogenous-reductant dependent electron transfer to photosystem I during diazotrophic phase is postulated even during photoautotrophic growth.

Calcification and utilization of inorganic carbon by the coccolithophorid Emiliania huxleyi Lohmann

summaryThe relationship between inorganic‐carbon dependent photosynthetic oxygen evolution and calcification was investigated in high‐ and low‐calcifying strains of Emiliania huxleyi showing a ten‐fold difference in calcification rate. Unlike the low‐calcifying strain calcifying cultures showed a four‐fold increase in inorganic carbon (1 mM) dependent photosynthetic oxygen over the pH range 5‐8.3 resulting in a 20 fold difference in photosynthetic rate between the two strains at pH 8.3. Calcifying cells have a high affinity for HCO3−, the concentration of dissolved inorganic carbon [DIC] required for half‐maximal rate of photosynthetic O2 evolution (K0.5[DIC]) being 200 μM at pH 8‐3. In mid‐exponential phase cultures the stoichiometry between 14CO2 fixation and calcification was 1 : 1 so it is likely that the high photosynthetic rate at pH 8.3 is sustained by 14CO2, released from H 14CO2 during calcification.Measurement of bicarbonate transport by the silicone‐oil‐layer centrifugal filtering technique demonstrated a rapid uptake and achievement of equilibrium (less than 3 s) between the intracellular and external inorganic carbon concentrations in low and high‐calcifying cells. Subsequent metabolism of the 14C intracellular inorganic carbon pool did not occur in low‐calcifying cells suggesting the block in calcification occurs either in transport into or within the coccolith vesicle.

Bicarbonate utilization by the marine diatomPhaeodactylum tricornutumBohlin

summaryThe measurement of inorganic carbon dependent photosynthetic oxygen evolution in air‐grown cells ofPhaeodactylum tricornulumBohlin has shown that sodium ions increased the affinity of the cells for bicarbonate. Lithium ions (50 mmol 1−1) inhibited bicarbonate‐dependent photosynthetic oxygen evolution but this inhibition was overcome at saturating bicarbonate concentrations. Bicarbonate‐dependent photosynthetic oxygen evolution was also inhibited by lithium ions in cells ofPhaeodactylumgrown in high CO2, (5 % v/v). Acetazolamide and ethoxyzolamide were potent inhibitors of carbonic anhydrase in cell extracts. At pH 8.0 the K0.5(the concentration of inorganic carbon required for 50% or the maximal rate of photosynthetic oxygen evolution) was increased from 53 to 542 μmol I−1in the presence of ethoxyzolamide whereas in the presence of acetazolamide the K0.5.(CO2) increased to 130 μmol 1−1. In the presence of ethoxyzolamide the internal dissolved inorganic carbon (DIC) concentration was increased but this increase was prevented in the presence of lithium ions when bicarbonate transport into the cell is inhibited. These results are in agreement with bicarbonate transport across the plasmalemma and intracellular carbonic anhydrase increasing the steady‐state flux of CO2from inside the plasmalemma to ribulose‐1,5‐bisphosphate carboxylase‐oxygenase by facilitating the interconversion of HCO−3and CO2.

Highly purified intact chloroplasts from mesophyll protoplasts of the C4 plant Digitaria sanguinalis. Inhibition of phosphoglycerate reduction by orthophosphate and by phosphoenolpyruvate

Purified mesophyll protoplasts from the C4 plant Digitaria sanguinalis were used to prepare intact mesophyll chloroplasts with low cytoplasmic contamination. The procedure involved breakage of protoplasts, differential centrifugation, partition in a dextran‐polyethylene glycol two‐phase system, and Percoll density gradient centrifugation. The final chloroplast preparation contained about 80% intact chloroplasts with a phosphoenolpyruvate carboxylase contamination of 0.2–1% of the original protoplast activity, corresponding to 1–6 μmol 14CO2 fixed/mg Chl h. The purified chloroplasts showed substrate‐dependent oxygen evolution in the range of 40–150 μmol substrate reduced/mg Chl h, with phosphoglycerate or oxaloacetate as substrate. Both reactions were stimulated 1.5 fold by pyruvate and further by addition of the other substrate. These measurements indicated that phosphoglycerate reduction was limited by substrate transport across the chloroplast envelope. Without added substrate, the chloroplasts consumed oxygen via pseudo‐cyclic electron transport in the light. Also this reaction was stimulated by pyruvate.Phosphoglycerate‐dependent oxygen evolution was inhibited by Pi and by phosphoenolpyruvate to about the same extent with purified chloroplasts, but only by Pi with protoplast extracts. This suggests that phosphoglycerate, Pi and phosphoenolpyruvate share a common carrier, similar to the Pi‐translocator in C3 chloroplasts, and that the lack of inhibition obtained with phosphoenolpyruvate and unpurified chloroplasts is artefactual, possibly due to oxaloacetate formation from added phosphoenolpyruvate and concomitant stimulation of oxygen evolution by oxaloacetate reduction. Furthermore, the results suggest that phosphoenolpyruvate is transported with a Km similar to that of Pi in C4 mesophyll chloroplasts.

The role of photophosphorylation in SO2 and SO 3 2- inhibition of photosynthesis in isolated chloroplasts

Sulphur dioxide inhibits noncyclic photophosphorylation in isolated envelope-free chloroplasts. This inhibition was shown to be reversible and competitive with phosphate, with an inhibitor constant of Ki=0.8mM. The same inhibition characteristics were observed when phosphoglycerate (PGA)- or ribulose-1,5-bisphosphate (RuBP)-dependent oxygen evolution was examined in a reconstituted chloroplast system in the presence of SO 3 (2-) . Using an ATP-regenerating system (phosphocreatine-creatine kinase), it was demonstrated that the inhibition of PGA-dependent oxygen evolution is solely the result of inhibited photophosphorylation. It is concluded that at low SO2 and SO 3 (2-) concentrations the inhibition of photophosphorylation is responsible for the inhibition of photosynthetic oxygen evolution.

Herbicides which Inhibit Electron Transport or Produce Chlorosis and Their Effect on Chloroplast Development in Radish Seedlings I. Chlorophyll a Fluorescence Transients and Photosystem II Activity

Abstract Diuron and bentazon are very strong inhibitors of the photosynthetic electron transport in isolated radish chloroplasts. The chlorosis producing herbicide SAN 6706 also inhibited the photosystem II dependent oxygen evolution. Aminotriazole had no effect. The inhibitor concentration for 50% inhibition of photosystem II activity was 10-7 m for diuron and 10-4 m for bentazon and SAN 6706 respectively. Diuron and bentazon quenched the chlorophyll a fluorescence transients in isolated radish chloroplasts drastically, while aminotriazole was not effective. It was of particular interest that the bleaching herbicide SAN 6706 inhibited photosystem II dependent oxygen evolution in a similar concentration as bentazon but had no effect on the chlorophyll a-fluorescence transients suggesting that SAN 6706 is not binding to the same site of the electron transport chain as diuron and bentazon. Apart from their direct influence on electron transport in isolated photosynthetically active chloroplasts the photosystem II and bleaching herbicides assayed also strongly affected photosynthesis in radish seedlings that were grown in the presence of the herbicides for a long time. As already obtained using isolated chloroplasts, photosystem II dependent oxygen evolution like the chlorophyll a fluorescence transients were strongly inhibited by the photosystem II herbicides diuron and bentazon. A reduction but no inhibition of photosystem II activity was observed in plants that were grown in the presence of aminotriazole. The pyridazinone SAN 6706 was behaving contradictory. In partly green plants photosystem II activity was still maintained and even higher than in untreated plants while in albinistic plants no photosynthetic activity was detected.

Stabilization by glutaraldehyde fixation of chloroplast membrane structure and function against heavy metal ion induced damage

Stabilization by glutaraldehyde fixation of chloroplast membrane structure and function against the damage by heavy metal ions has been investigated. Zn 2+, Co 2+ and Pb 2+ ions inhibit dichlorophenol indophenol supported oxygen evolution in isolated chloroplasts, as well as enhance the magnitude of 90°-light scattering by chloroplasts. Fixation of chloroplasts with glutaraldehyde protects the thylakoid membranes against the damage caused by Cd 2+ and Co 2+ ions to photosystem II (PS II) dependent oxygen evolution. On the other hand, Zn 2+ and Pb 2+ inactivate chloroplasts oxygen evolving system even in fixed chloroplasts. Fixation of chloroplasts with glutaraldehyde reduces the extent of enhancement of 90°-light scattering of chloroplasts caused by the addition of salts. Thus the fixation of chloroplast membranes with glutaraldehyde does not completely arrest the increase in light scattering induced by metal ions which suggests that some microconformational changes still persist even after glutaraldehyde fixation. Our results indicate that Zn 2+ and Pb 2+ cause damage to the electron transport system of chloroplasts and that glutaraldehyde fixation does not provide protection against Zn 2+ -and Pb 2+ -induced damage of chloroplast function. Co 2+ and Cd 2+ appear to bring about a loss in chloroplast function probably by alteration of its structure and glutaraldehyde fixation arrests such ion induced damage of PS II mediated oxygen evolution.

Aspartate Decarboxylation in Bundle Sheath Cells of Zea mays and Its Possible Contribution to C3 Photosynthesis

Strands of bundle sheath cells isolated from the NADP malic enzyme type C4 species, Zea mays, rapidly decarboxylate malate via NADP malic enzyme. The present studies show that these cells also decarboxylate aspartate, but at much lower rates. Aspartate decarboxylation is dependent upon added 2-oxoglutarate, is partially light dependent, and apparently proceeds via the following reaction sequence: aspartate ͛4 oxaloacetate ͛4 malate ͛4 pyruvate + CO2. Studies of the activity, properties, and location of enzymes indicated that these reactions are catalysed by a mitochondrial aspartate aminotransferase, mitochondrial or cytoplasmic NAD malate dehydrogenase, and chloroplast-located NADP malic enzyme, respectively. A mitochondria preparation isolated from Z. mays bundle sheath cells converted aspartate to oxaloacetate (with 2-oxoglutarate) and also pyruvate to alanine (with glutamate); the preparation did not reduce oxaloacetate to malate or decarboxylate malate at significant rates. Bundle sheath strands of Z. mays have a relatively limited capacity for HCO3- plus ribose 5-phosphate dependent oxygen evolution and rates were almost as high with aspartate plus 2-oxoglutarate. We suggest that amongst NADP malic enzyme type C4 species there may be a direct relationsip between the capacity of bundle sheath cells to decarboxylate aspartate and their potential for the photosystem II-mediated oxygen evolution.

On the control of long-chain-fatty acid synthesis in isolated intact spinach (Spinacia oleracea) chloroplasts.

1. Chloroplasts isolated from spinach leaves by using the low-ionic-strength buffers of Nakatani & Barber [(1977) Biochim. Biophys. Acta.461, 510-512] had higher rates of HCO(3) (-)-dependent oxygen evolution (up to 369mumol/h per mg of chlorophyll) and higher rates of [1-(14)C]acetate incorporation into long-chain fatty acids (up to 1500nmol/h per mg of chlorophyll) than chloroplasts isolated by using alternative procedures. 2. Acetate appeared to be the preferred substrate for fatty acid synthesis by isolated chloroplasts, although high rates of synthesis were also measured from H(14)CO(3) (-) in assays permitting high rats of photosynthesis. Incorporation of H(14)CO(3) (-) into fatty acids was decreased by relatively low concentrations of unlabelled acetate. Acetyl-CoA synthetase activity was present 3-4 times in excess of that required to account for rates of [1-(14)C]acetate incorporation into fatty acids, but pyruvate dehydrogenase was either absent or present in very low activity in spinach chloroplasts. 3. Rates of long-chain-fatty acid synthesis from [1-(14)C]acetate in the highly active chloroplast preparations, compared with those used previously, were less dependent on added cofactors, but showed a greater response to light. The effects of added CoA plus ATP, Triton X-100 and sn-glycerol 3-phosphate on the products of [1-(14)C]acetate incorporation were similar to those reported for less active chloroplast preparations. 4. Endogenous [(14)C]acetyl-CoA plus [(14)C]malonyl-CoA was maintained at a constant low level even when fatty acid synthesis was limited by low HCO(3) (-) concentrations. Endogenous [(14)C]acyl-(acyl-carrier protein) concentrations increased with increasing HCO(3) (-) concentration and higher rates of fatty acid synthesis, but were slightly lower in the presence of Triton X-100. It is proposed that rates of long-chain-fatty acid synthesis in isolated chloroplasts at saturating [1-(14)C]acetate concentrations and optimal HCO(3) (-) concentrations may be primarily controlled by rates of removal of the products of the fatty acid synthetase.

The Effect of a Quaternary Amine (Aliquat 336) on Growth and Photosynthesis of the Green Alga Chlorella emersonii, and the Effect on Photosynthesis in Isolated Spinach Chloroplasts

AbstractA quaternary amine, Aliquat 336, inhibits the growth of the green alga Chlorella emersonii, 14C‐fixation of the alga is also inhibited. The effect and the site of action of the compound was studied by using isolated spinach chloroplasts. The carbon dioxide dependent oxygen evolution of the chloroplasts is inhibited directly upon the addition of the amine and the oxygen evolution is replaced by an oxygen uptake. By investigating some electron transport reactions in the chloroplasts we were able to show that Aliquat 336 affects the electron transport on the level of photophosphorylation. The results from the in vivo and the in vitro experiments thus show that the quaternary amine affects the photosynthetic process.Aliquat 336 is a solvent extractant used in several industrial processes for extraction of metals from aqueous solutions. Aliquat 336 could be considered a presumptive water pollutant as the compound could enter a recipient water body and thus affect photosynthesis.

A reconstituted chloroplast system from Helianthus Annuus

Intact chloroplasts of sunflower ( Helianthus annuus) show only very low rates of 14CO 2 fixation or CO 2 dependent oxygen evolution, compared with intact chloroplasts of spinach. However, envelope-free sunflower chloroplasts will show good rates in a reconstituted chloroplast system using chloroplast extract. Sunflower chloroplasts can also be used in a reconstituted chloroplast system with spinach chloroplast extract, or vice versa, giving rates comparable to the spinach system. Preliminary assays of the enzymes of the reductive pentose phosphate pathway in sunflower indicate that the levels are not significantly different from those in spinach.