Na-Stimulation of Photosynthesis in the Cyanobacterium Synechococcus UTEX 625 Grown on High Levels of Inorganic Carbon

Photosynthesis of washed cells of Synechococcus UTEX 625 grown on 5% CO₂ was markedly stimulated (647 ± 50%) at pH 8.0 by the addition of low concentrations of NaCl (concentration required for half-maximal response, K_½, = 18 micromolar). Studies with KCl and Na₂SO₄ showed that the stimulation was due to Na⁺. Photosynthesis at pH 6.1 was only slightly stimulated by Na⁺. The response of photosynthesis at pH 8.0 to [Na⁺] was strongly sigmoidal for dissolved inorganic carbon ([DIC] ≤ 500 micromolar). Cells grown with high total [DIC], but air-levels of CO₂, at pH 9.6 showed the same response to low [Na⁺]. The absence of Na⁺ could be partially, but not completely overcome, by higher [DIC]. Various methods for examining CO₂ or HCO₃⁻ use (K_½^CO₂ determination; isotopic disequilibrium; and consideration of HCO₃⁻ dehydration rate) were consistent with CO₂ use by the cells, but HCO₃⁻ use could not be ruled out. Isotopic disequilibrium studies showed that CO₂ use was stimulated by Na⁺. Cells grown on 5% CO₂ accumulated DIC against a concentration gradient by a process (or processes) dependent on Na⁺. No evidence for uptake of Na⁺ concomitant with DIC uptake could be found. The lack of O₂ evolution during the initial and most rapid period of DIC accumulation suggested that the required energy was obtained from cyclic photophosphorylation.     

CASEIN VISCOSITY STUDIES

1. Viscosity and pH curves of casein dissolved in NaOH, KOH, LiOH, and NH₄OH are shown and it is found that a maximum viscosity occurs at about the same pH point with each alkali; i.e., 9.1 to 9.25. The magnitude of the viscosity is largest in ammonia solutions. 2. The maximum viscosity occurs in 8 to 10 per cent solutions of casein in alkalies when about 98 x 10^–5 gram equivalents of base are combined with 1 gram of casein. 3. A maximum viscosity occurs in the same region (pH 9.1 to 9.25) when casein is dissolved in Na₂CO₃, Na₃AsO₄, Na₂SO₃, NaF, and Na₂PO₃. 4. The maximum viscosity obtained with borax solutions of casein occurs at 8.15 to 8.2 pH. It is suggested that casein acts like mannitol, glycerol, etc., in increasing the dissociation of boric acid. 5. The flattening of the viscosity curves of casein solutions, following the decline from maximum, is shown to be due to alkaline hydrolysis whence casein no longer exists as such but is cleaved into a major protein containing no phosphorus or sulfur and less nitrogen. This cleavage commences at pH 10.0 to 10.5. 6. When casein is prepared from solutions that have been subjected to high temperatures (60°C. and above) or has otherwise been heated during its preparation, it yields solutions in alkalies of high viscosity.     

Application of novel thermo-tolerant haloalkalophilic bacterium Halomonas stevensii for bio mitigation of gaseous phase CO2: Energy assessment and product evaluation studies

Present work deals with the bio-mitigation potential of gaseous phase CO₂ by chemolithotrophic bacterium Halomonas stevensii isolated from haloalkaliphilic habitat using thiosulfate ion (S₂O₃²⁻) as an energy source. H. stevensii was tested for various abiotic stress tolerances such as salt [2–12% (w/v)], temperature (10–60 °C) and pH (2–12). Batch studies were conducted for 6 days at 15 (±1) % (v/v) inlet CO₂ concentration to find the CO₂ fixing capability of H. stevensii under varying concentration of energy substrate i.e. 0, 50 and 100 mM Na₂S₂O₃. Approximately 98% CO₂ removal from gaseous phase was achieved at 50 and 100 mM Na₂S₂O₃. Evaluation of CO₂ fixation by H. stevensii and carbon allocation into different cellular organic pool (carbohydrate, proteins and primary metabolite) was carried out by growing H. stevensii at 5%, 10% and 15% (v/v) inlet CO₂ concentration for the duration of 6 days. The obtained leachate was quantified using chemical technique, FT-IR and GC. Utilization of gaseous phase CO₂ by H. stevensii was also proven by conducting the approximate materials balance and energy assessment for the present CO₂ fixation process. The mechanism of CO₂ metabolism by H. stevensii was evaluated using GC–MS and carbon partitioning into cellular organic pool analysis.     

Effects of gel processing on the properties of humic acid isolated from the alga Pilayella littoralis: A humic acid aerogel

Humic acid in the live alga Pilayellalittoralis was isolated as an aqueous gel by a standard sequential extraction method augmented with removal of alginic acid. Portions of the aqueous gel were (1) vacuum oven dried at 40 °C, (2) freeze freeze dried after cooling in liquid N₂, and (3) dried with supercritical fluid CO₂ after substitution of water in the gel with acetone. This paper compares the analytical and spectral properties of the products with compost derived HA and reports significant differences in their surface areas, packing densities, water retention, solute sorption and metal binding properties. The results are discussed in terms of different product morphologies determined by scanning electron microscopy. The aerogel obtained by supercritical fluid CO2 drying of an HA gel from Pilayella has the highest surface area (188 m² g^-1) reported for a humic acid. This revised version was published online in August 2006 with corrections to the Cover Date.     

Cell Wall Dissolution in Ripening Kiwifruit (Actinidia deliciosa) : Solubilization of the Pectic Polymers

Pectic polysaccharides solubilized in vivo during ripening, were isolated using phenol, acetic acid, and water (PAW) from the outer pericarp of kiwifruit (Actinidia deliciosa [A. Chev.] C.F. Liang and A.R. Ferguson var deliciosa `Hayward') before and after postharvest ethylene treatment. Insoluble polysaccharides of the cell wall materials (CWMs) were solubilized in vitro by chemical extraction with 0.05 molar cyclohexane-trans-1,2-diamine tetraacetate (CDTA), 0.05 molar Na₂CO₃, 6 molar guanidinium thiocyanate, and 4 molar KOH. The Na₂CO₃-soluble fraction decreased by 26%, and the CDTA-soluble fraction increased by 54% 1 day after ethylene treatment. Concomitantly, an increase in the pectic polymer content of the PAW-soluble fraction occurred without loss of galactose from the cell wall. The molecular weight of the PAW-soluble pectic fraction 1 day after ethylene treatment was similar to that of the Na₂CO₃-soluble fraction before ethylene treatment. Four days after ethylene treatment, 60% of cell wall polyuronide was solubilized, and 50% of the galactose was lost from the CWM, but the degree of galactosylation and molecular weight of pectic polymers remaining in the CWMs did not decrease. The exception was the CDTA-soluble fraction which showed an apparent decrease in molecular weight during ripening. Concurrently, the PAW-soluble pectic fraction showed a 20-fold reduction in molecular weight. The results suggest that considerable solubilization of the pectic polymers occurred during ripening without changes to their primary structure or degree of polymerization. Following solubilization, the polymers then became susceptible to depolymerization and degalactosidation. Pectolytic enzymes such as endopolygalacturonase and β-galactosidase were therefore implicated in the degradation of solubilized cell wall pectic polymers but not the initial solubilization of the bulk of the pectic polymers in vivo.     

Supercritical fluid CO2 extraction accelerates isolation of humic acid from livePilayella littoralis (Phaeophyta)

Supercritical fluid CO₂ extraction of the live, dried algaPilayella littoralis efficiently removes non-humic substances in hours instead of the days required for sequential extraction with ether, acetone, ethanol and dioxane. Completion of extraction (including aqueous removal of alginic acids) with either preliminary in a standard procedure gives humic acid samples with closely comparable properties.Authors for correspondence     

Engineering of photosynthetic mannitol biosynthesis from CO2 in a cyanobacterium

d-Mannitol (hereafter denoted mannitol) is used in the medical and food industry and is currently produced commercially by chemical hydrogenation of fructose or by extraction from seaweed. Here, the marine cyanobacterium Synechococcus sp. PCC 7002 was genetically modified to photosynthetically produce mannitol from CO₂ as the sole carbon source. Two codon-optimized genes, mannitol-1-phosphate dehydrogenase (mtlD) from Escherichia coli and mannitol-1-phosphatase (mlp) from the protozoan chicken parasite Eimeria tenella, in combination encoding a biosynthetic pathway from fructose-6-phosphate to mannitol, were expressed in the cyanobacterium resulting in accumulation of mannitol in the cells and in the culture medium. The mannitol biosynthetic genes were expressed from a single synthetic operon inserted into the cyanobacterial chromosome by homologous recombination. The mannitol biosynthesis operon was constructed using a novel uracil-specific excision reagent (USER)-based polycistronic expression system characterized by ligase-independent, directional cloning of the protein-encoding genes such that the insertion site was regenerated after each cloning step. Genetic inactivation of glycogen biosynthesis increased the yield of mannitol presumably by redirecting the metabolic flux to mannitol under conditions where glycogen normally accumulates. A total mannitol yield equivalent to 10% of cell dry weight was obtained in cell cultures synthesizing glycogen while the yield increased to 32% of cell dry weight in cell cultures deficient in glycogen synthesis; in both cases about 75% of the mannitol was released from the cells into the culture medium by an unknown mechanism. The highest productivity was obtained in a glycogen synthase deficient culture that after 12 days showed a mannitol concentration of 1.1 g mannitol L⁻¹ and a production rate of 0.15 g mannitol L⁻¹ day⁻¹. This system may be useful for biosynthesis of valuable sugars and sugar derivatives from CO₂ in cyanobacteria.     

Na2CO3-responsive Photosynthetic and ROS Scavenging Mechanisms in Chloroplasts of Alkaligrass Revealed by Phosphoproteomics

Alkali-salinity exerts severe osmotic, ionic, and high-pH stresses to plants. To understand the alkali-salinity responsive mechanisms underlying photosynthetic modulation and reactive oxygen species (ROS) homeostasis, physiological and diverse quantitative proteomics analyses of alkaligrass (Puccinellia tenuiflora) under Na₂CO₃ stress were conducted. In addition, Western blot, real-time PCR, and transgenic techniques were applied to validate the proteomic results and test the functions of the Na₂CO₃-responsive proteins. A total of 104 and 102 Na₂CO₃-responsive proteins were identified in leaves and chloroplasts, respectively. In addition, 84 Na₂CO₃-responsive phosphoproteins were identified, including 56 new phosphorylation sites in 56 phosphoproteins from chloroplasts, which are crucial for the regulation of photosynthesis, ion transport, signal transduction, and energy homeostasis. A full-length PtFBA encoding an alkaligrass chloroplastic fructose-bisphosphate aldolase (FBA) was overexpressed in wild-type cells of cyanobacterium Synechocystis sp. Strain PCC 6803, leading to enhanced Na₂CO₃ tolerance. All these results indicate that thermal dissipation, state transition, cyclic electron transport, photorespiration, repair of photosystem (PS) II, PSI activity, and ROS homeostasis were altered in response to Na₂CO₃ stress, which help to improve our understanding of the Na₂CO₃-responsive mechanisms in halophytes.     

Variations in short term products of inorganic carbon fixation in exponential and stationary phase cultures of Aphanocapsa 6308

Aphanocapsa 6308 metabolizes both NaHCO₃ and Na₂CO₃. The short term incorporation (5-s) metabolic pattern and the patterns of incorporation of bicarbonate for exponential versus stationary phase cultures differ, however. Cells were equilibrated for 10 min in air and distilled water prior to injection of either NaH¹⁴CO₃ at pH 8.0, or Na₂ ¹⁴CO₃ at pH 11.0. Hot ethanol extracts were analyzed via paper chromatography and autoradiography for products of CO₂ fixation. At 5 s, malate (51.5%) predominates slightly as a primary bicarbonate fixation product over 3-phosphoglycerate (40.3%); 3-phosphoglycerate is the primary product of carbonate fixation. At 60 s, the carbonate and bicarbonate labelling patterns are similar. Cells in stationary phase fix in 5 s a greater proportion of bicarbonate into malate (36% vs. 14% for 3-phosphoglycerate) than do cells in exponential growth. Likewise, 60 s incorporations show a large amount of bicarbonate fixed into aspartate (30.9%) in stationary phase cells over that of exponential phase (11.6%). These data suggest an operative C₄ pathway for purposes not related to carbohydrate synthesis but rather as compensation for the incomplete tricarboxylic acid cycle in cyanobacteria. The enhancement of both aspartate fixation and CO₂ fixation into citrulline in stationary phase correlates with an increase in cyanophycin granule production which requires both aspartate and arginine.Nonstandard Abbreviations 3-PGA 3-phosphoglyceric acid - TCA tricarboxylic acid     

Economic valuation of kelp forests in northern Chile: values of goods and services of the ecosystem

Kelp beds, besides being one of the most important benthic resources in northern Chile, provide a variety of environmental goods and services. In order to evaluate economically the wild kelp populations in northern Chile (26° to 32° S) more than simply their commercial value as a source of raw materials for alginate extraction, we used several economic indicators to holistically assess the value of a group of brown seaweeds of economic importance, Lessonia spp. and Macrocystis pyrifera: (1) market value of biomass as a source of raw material for extraction of alginic acid, (2) market value of associated species of economic importance, (3) value as a source of scientific information, (4) value as a climate buffer (CO₂ capture and release of O₂), (5) value of associated biodiversity (non-commercial species), (6) value as cultural heritage and (7) value as a reservoir of biodiversity. Existence values of kelp beds which estimate the willingness of citizens to pay and work without payment to preserve the ecosystem were calculated using the contingent valuation technique. The results indicate that kelp beds in northern Chile have a total value of US $540 million. Of this total, kelp fishery accounts for 75 % and associated-species fisheries account for 15 %. In this context, the economic value of Chilean kelp beds is mainly associated with the industry of alginate extraction. By contrast, existence value as a source of scientific information or environmental buffer for CO₂ capture or O₂ production represents only 9 % of the total value, representing a very low relative importance to society. The economic valuation of coastal resources and marine ecosystems is a complementary tool for decision making and implementation of public policies related to the conservation and sustainable exploitation of renewable resources and their ecosystems.     

Cofactor and CO2 donor regulation involved in reductive routes for polymalic acid production by Aureobasidium pullulans CCTCC M2012223

Polymalic acid (PMA) is a water-soluble polyester with many attractive properties for biomedical application. Its monomer l-malic acid is widely used in the food industry and also a potential C4 platform chemical. Cofactor and CO₂ donor involved in the reductive routes were investigated for PMA production by Aureobasidium pullulans. Biotin as the key cofactor of pyruvate carboxylase was favor for the PMA biosynthesis. Na₂CO₃ as CO₂ donor can obviously improved PMA titer when compared with no CO₂ supplier NaOH, and also exhibit more advantages than the other donor CaCO₃ because of its water-soluble characteristic. A combinational process with addition of biotin 70 mg/L and Na₂CO₃ as the CO₂ donor was scaled-up in 50 L fermentor, achieving the high product 34.3 g/L of PMA and productivity of 0.41 g/L h. This process provides an efficient and economical way for PMA and malic acid production, and is promising for industrial application.     

Carbohydrates of the brown seaweeds : Part III. Desmarestia aculeata

Mannitol, sucrose, and laminitol have been isolated from ethanolic extracts of the brown seaweed Desmarestia aculeata and characterised, and rhamnose, sedoheptulose, glucose, fructose, and 2-O-methyl- and 3-O-methyl-fucose have been identified by their chromatographic mobilities and g.l.c. retention times. Laminarin, alginic acid, and “fucans” were isolated also and characterised. The laminarin contained 1.7% of mannitol end-groups, and the fucans a relatively high proportion of galactose which was present as end-group and (1→3)-linked units.     

Characterization of the na-requirement in cyanobacterial photosynthesis

The Na⁺ requirement for photosynthesis and its relationship to dissolved inorganic carbon (DIC) concentration and Li⁺ concentration was examined in air-grown cells of the cyanobacterium Synechococcus leopoliensis UTEX 625 at pH 8. Analysis of the rate of photosynthesis (O₂ evolution) as a function of Na⁺ concentration, at fixed DIC concentration, revealed two distinct regions to the response curve, for which half-saturation values for Na⁺ (K_½[Na⁺]) were calculated. The value of both the low and the high K_½(Na⁺) was dependent upon extracellular DIC concentration. The low K_½(Na⁺) decreased from 1000 micromolar at 5 micromolar DIC to 200 micromolar at 140 micromolar DIC whereas over the same DIC concentration range the high K_½(Na⁺) decreased from 10 millimolar to 1 millimolar. The most significant increases in photosynthesis occurred in the 1 to 20 millimolar range. A fraction of total photosynthesis, however, was independent of added Na⁺ and this fraction increased with increased DIC concentration. A number of factors were identified as contributing to the complexity of interaction between Na⁺ and DIC concentration in the photosynthesis of Synechococcus. First, as revealed by transport studies and mass spectrometry, both CO₂ and HCO₃⁻ transport contributed to the intracellular supply of DIC and hence to photosynthesis. Second, both the CO₂ and HCO₃⁻ transport systems required Na⁺, directly or indirectly, for full activity. However, micromolar levels of Na⁺ were required for CO₂ transport while millimolar levels were required for HCO₃⁻ transport. These levels corresponded to those found for the low and high K_½(Na⁺) for photosynthesis. Third, the contribution of each transport system to intracellular DIC was dependent on extracellular DIC concentration, where the contribution from CO₂ transport increased with increased DIC concentration relative to HCO₃⁻ transport. This change was reflected in a decrease in the Na⁺ concentration required for maximum photosynthesis, in accord with the lower Na⁺-requirement for CO₂ transport. Lithium competitively inhibited Na⁺-stimulated photosynthesis by blocking the cells' ability to form an intracellular DIC pool through Na⁺-dependent HCO₃⁻ transport. Lithium had little effect on CO₂ transport and only a small effect on the size of the pool it generated. Thus, CO₂ transport did not require a functional HCO₃⁻ transport system for full activity. Based on these observations and the differential requirement for Na⁺ in the CO₂ and HCO₃⁻ transport system, it was proposed that CO₂ and HCO₃⁻ were transported across the membrane by different transport systems.     

Extraction of Structural Extracellular Polymeric Substances from Aerobic Granular Sludge

To evaluate and develop methodologies for the extraction of gel-forming extracellular polymeric substances (EPS), EPS from aerobic granular sludge (AGS) was extracted using six different methods (centrifugation, sonication, ethylenediaminetetraacetic acid (EDTA), formamide with sodium hydroxide (NaOH), formaldehyde with NaOH and sodium carbonate (Na₂CO₃) with heat and constant mixing). AGS was collected from a pilot wastewater treatment reactor. The ionic gel-forming property of the extracted EPS of the six different extraction methods was tested with calcium ions (Ca²⁺). From the six extraction methods used, only the Na₂CO₃ extraction could solubilize the hydrogel matrix of AGS. The alginate-like extracellular polymers (ALE) recovered with this method formed ionic gel beads with Ca²⁺. The Ca²⁺-ALE beads were stable in EDTA, formamide with NaOH and formaldehyde with NaOH, indicating that ALE are one part of the structural polymers in EPS. It is recommended to use an extraction method that combines physical and chemical treatment to solubilize AGS and extract structural EPS.     

Carbohydrates of the seaweeds,Desmarestia ligulata and D. firma

Crystalline mannitol and some oligosaccharides were separated from ethanolic extracts of Desmarestia ligulata and D. firma. Laminaran, ‘fucans’ and alginic acid were also isolated from both species. The laminaran from D. ligulata comprised both M- and G-chains but no M-chains were found in the laminaran from D. firma. In both species the amount of ‘fucan’ was small, particularly in D. firma. Both ‘fucans’ contained glucuronic acid, galactose, xylose and fucose and that from D. ligulata also contained mannose. After sequential extraction of D. ligulata with water, acid and alkali evidence was obtained for the presence of cellulose, a uronan, and protein in the residual material.     

Effect of endophyte infection on chlorophyll a fluorescence in salinity stressed rice

We have earlier reported that the endophyte infection can enhance photosynthetic capacity and antioxidant enzyme activities in rice exposed to salinity stress. Now, the changes in primary photochemistry of photosystem (PS) II induced by Na₂CO₃ stress in endophyte-infected (E+) and endophyte-uninfected (E-) rice seedlings were studied using chlorophyll a fluorescence (OJIP-test). Performance indices (PI_ABS and PI_Total) of E- and E+ rice seedlings revealed the inhibitory effects of Na₂CO₃ on PS II connectivity (occurrence of an L-band), oxygen evolving complex (occurrence of a K-band), and on the J step of the induction curves, associated with an inhibition of electron transport from plastoquinone A (Q_A) to plastoquinone B (Q_B). In E+ seedlings, Na₂CO₃ effects on L and K bands were much smaller, or even negligible, and also there was no pronounced effect on the J step. Furthermore, the OJIP parameters indicated that 20 mM Na₂CO₃ had a greater influence on the photosystem (PS) II electron transport chain than did the 10 mM Na₂CO₃, and that changes were greater in E- than in E+. Endophyte infection was therefore deemed to enhance the photosynthetic mechanism of Oryza sativa exposed to salinity stress.     

Na2CO3 Influence on DNA Double Helix Stability: Strong Anion Destabilizing Effect

Abstract

Addition of Na₂CO₃ to almost salt-free DNA solution (5·10^?5M EDTA, pH=5.7, Tm=26.5 °C) elevates both pH and the DNA melting temperature (Tm) if Na₂CO₃ concentration is less than 0.004M. For 0.004M Na₂CO₃, Tm=58 °C is maximal and pH=10.56. Further increase in concentration gives rise to a monotonous decrease in Tm to 37 °C for 1M N₂CO₃ (pH=10.57). Increase in pH is also not monotonous. The highest pH=10.87 is reached at 0.04M Na₂CO₃ (Tm=48.3 °C). To reveal the cause of this DNA destabilization, which happens in a narrow pH interval (10.56÷10.87) and a wide Na₂CO₃ concentration interval (0.004÷1M), a procedure has been developed for determining the separate influences on Tm of Na⁺, pH, and anions formed by Na₂CO₃ (HCO₃ ^? and CO₃ ^2-). Comparison of influence of anions formed by Na₂CO₃ on DNA stability with Cl^? (anion inert to DNA stability), ClO₄ ^? (strong DNA destabilizing “chaotropic” anion) and OH^? has been carried out. It has been shown that only Na⁺ and pH influence Tm in Na₂CO₃ solution at concentrations lower than 0.001M. However, the Tm decrease with concentration for [Na₂CO₃]≥0.004M is only partly caused by high pH≈10.7. Na₂CO₃ anions also exert a strong destabilizing influence at these concentrations. For 0.1M Na₂CO₃ (pH=10.84, [Na⁺]=0.2M, Tm=42.7 °C), the anion destabilizing effect is higher 20 °C. For NaClO₄ (ClO₄ ^? is a strong “chaotropic” anion), an equal anion effect occurs at much higher concentrations ～3M. This means that Na₂CO₃ gives rise to a much stronger anion effect than other salts. The effect is pH dependent. It decreases fivefold at neutral pH after addition of HCl to 0.1M Na₂CO₃ as well as after addition of NaOH for pH>11.2.     

Stromal acidification mediates in vivo water stress inhibition of nonstomatal-controlled photosynthesis

Stromal acidification has been reported to mediate reduced osmotic potential (ψ_π) effects on photosynthesis in the isolated spinach chloroplast (Berkowitz, Gibbs 1983 Plant Physiol 72: 1100-1109). To determine if stromal acidification mediates osmotic dehydration inhibition of photosynthesis in vivo, the effects of a weak base (NH₄Cl), which raises stromal pH, on CO₂ fixation of vacuum-infiltrated spinach leaf slices, Chlamydomonas reinhardii cells and Aphanocapsa 6308 cells under isotonic and dehydrating conditions were investigated. Five millimolar NH₄Cl stimulated spinach leaf slice CO₂ fixation by 43% under stress (0.67 molar sorbitol) conditions, and had little effect on fixation under isotonic (0.33 molar sorbitol) conditions. Chlamydomonas cells were found to be more sensitive to reduced ψ_π than spinach leaf slices. CO₂ fixation in the cells of the green alga Chlamydomonas reinhardii was 99 and 17 micromoles per milligram chlorophyll per hour, respectively, at 0.1 molar mannitol and 0.28 molar mannitol. Five millimolar NH₄Cl stimulated CO₂ fixation of Chlamydomonas cells by 147% under stress (0.28 molar mannitol) conditions. Aphanocapsa 6308 cells (blue-green alga) were also found to be sensitive to reduced ψ_π, and inhibitions in photosynthesis were partially reversed by NH₄Cl. These data indicate that in vivo water stress inhibition of photosynthesis is facilitated by stromal acidification, and that this inhibition can be at least partially reversed in situ.     

The pyruvate: Ferredoxin oxidoreductase in heterocysts of the cyanobacteriuim Anabaena cylindrica

Heterocyst preparations have been obtained which actively perform nitrogen fixation (C₂H₂ reduction) and contain the enzymes of glycolysis and some of the tricarboxylic acid cycle. Pyruvate: ferredoxin oxidereductase has been unambiguously demonstrated in extracts from heterocysts by the formation of acetylcoenzyme A, CO₂ and reduced methyl viologen (ferredoxi) from pyruvate, coenzyme A and oxidized methyl viologen (ferredoxin) as well as by the synthesis of pyruvate from CO₂, acetylcoenzyme A and reduced methyl viologen. Pyruvate supports C₂H₂ reduction by isolated heterocysts, however, with lower activity than Na₂S₂O₄ and H₂. α-Ketoglutarate: ferredoxin oxidoreductase is absent in Anabaena cylindrica, confirming that the organism has an incomplete tricarboxylic acid cycle.     

Effects of NaCl and Na2CO3 stresses on photosynthetic ability of Chlamydomonas reinhardtii

Chloride and carbonate salts are the main salts causing salinization and widely exist in aquatic environment, so algae may suffer from salinization stress for high water evaporation. In this study, in order to investigate and compare the toxic effects of the two salts on algal photosynthesis, we used NaCl and Na₂CO₃ to stress Chlamydomonas reinhardtii. Under the two salt stresses, the content of O ₂ ^?· and H₂O₂ in the cells was increased significantly, and it was much higher in Na₂CO₃ treatment than in NaCl treatment at the same Na⁺ concentration. The absorbance spectra and 4^th derivative spectra of photosynthetic pigments were declined under 300 mM NaCl and 25 mM Na₂CO₃ stresses, and remarkably changed under 50 mM and 100 mM Na₂CO₃ stresses. When the cells stressed by the two salts, the maximum quantum yield (Fv/Fm), electron transport rate (ETR) and photochemical quenching (qP) were reduced markedly, but the nonphotochemical dissipation (NPQ) was increased markedly. At the same Na⁺ concentration, Na₂CO₃ stress had stronger toxic effects on photosynthetic ability than NaCl stress.