PHOTOSYNTHESIS-IRRADIANCE RELATIONSHIPS IN SEA ICE MICROALGAE FROM McMURDO SOUND,ANTARCTICA1

Sea ice microalgae in McMurdo Sound, Antarctica were examined for photosynthesis-irradiance relationships and for the extent and time course of their photoadaptation to a reduction in in situ irradiance. Algae were collected from the bottom centimeter of coarse-grained congelation ice in an area free of natural snow cover. Photosynthetic rate was determined in short term (1 h) incubations at ?2° C over a range of irradiance from 0 to 286 μE·m^?2·s^?1. Assimilation numbers were consistently below 0.1 mg C·mg chl a^?1·h^?1. The I_k's³ averaged only 7 μE·m^?2·s^?1, and photosynthesis was inhibited at irradiances above 25 μE·m^?2·s^?1. Photosynthetic parameters of the ice algal community were examined over a nine day period following the addition of 4 cm of surface snow while a control area remained snow-free. A reduction of 40% in P_m^B relative to the control occurred after two days of snow cover; α, β, I_k, and I_m were not significantly altered. Low assimilation numbers and constant standing crop size, however, suggested that the algal bloom may have already reached stationary growth phase, possibly minimizing their photoadaptive response.     

PHYSIOLOGICAL RESPONSES OF ANABAENA VARIABILIS (CYANOPHYCEAE) TO INSTANTANEOUS EXPOSURE TO VARIOUS COMBINATIONS OF LIGHT INTENSITY AND TEMPERATURE1

Light intensity and temperature interactions have a complex effect on the physiological process rates of the filamentous bluegreen alga Anabaena variabilis Kütz. The optimum temperature for photosynthesis increased with increasing light intensity from 10°C at 42 μE·m^?2·s^?1 to 35°C at 562 μE·m^?2·s^?1. The light saturation parameter, I_K, increased with increasing temperatures. The maximum photosynthetic rate (2.0 g C·g dry wt.^?1·d^?1) occurred at 35°C and 564 μE·m^?2·s^?1. At 15°C, the maximum rate was 1.25 g C·g dry wt.^?1·d^?1 at 332 μE·m^?2·s^?1. The dark respiration rate increased exponentially with temperature. Under favorable conditions of light intensity and temperature the percent of extracellular release of dissolved organic carbon was less than 5% of the total C fixed. This release increased to nearly 40% under combinations of low light intensity and high temperature. A mathematical model was developed to simulate the interaction of light intensity and temperature on photosynthetic rate. The interactive effects were represented by making the light-saturation parameters a function of temperature.     

IMPORTANCE OF PHYSICAL VARIABLES ON THE SEASONAL DYNAMICS OF EPILITHIC ALGAE IN A HIGHLY SHADED CANYON STREAM1

The seasonal abundance of epilithic algae was correlated with major physico-chemical parameters in a first-order, heavily shaded stream in northern Arizona. Diatoms made up over 85%, by numerical abundance, of the epilithon community Light energy, water temperature, and stream discharge were most highly correlated with seasonal abundance of epilithic diatom taxa when analyzed with stepwise multiple regression. None of the chemical variables measured in the study (NO₃-N, O-PO₄, SiO₂, including PH) was found to be significantly correlated with the seasonal community structure of epilithic diatoms. Total diatom cell densities showed a significant negative correlation to stream bed light energy. Likewise, total diatom cell densities along a transect in the stream bed showed a negative correlation to current velocity during those months when base flow was low and stable, and current velocity was ≤25 cm·sec-¹. Most diatom taxa had highest cell densities at temperatures < 16°C and at daily mean stream bed light levels < 400 μE·m^?2·s^?1. Highest cell densities of green algae occurred at temperatures between 6–16°C and at daily mean stream bed light levels of > 400 μE·m^?2·s^?1. Blue-green algae (cyanobacteria) grew best at the highest recorded water temperatures and daily mean stream bed light energy (16–20°C and 900–1200 μE·m^?2·s^?1). Abrupt increases in NO₃-N coincided with a brief pulse of Nostoc pruniforme colonies during June, and leaf drop from Alnus oblongifolia during October.     

Validation and identification of molecular markers linked to the leaf rust resistance gene <Emphasis Type="Italic">Lr</Emphasis>28 in wheat

Leaf rust resistance gene Lr28 controls one of the important resistances in the Indian subcontinent against the most prevalent Puccinia triticina pathotype 77-5. Pyramiding Lr28 with other resistance genes would therefore, provide durable resistance against rust, a process that can be facilitated by DNA markers. A microsatellite marker wmc313 linked to Lr28 at a distance of 5.0 cM was identified in the population HD2329 × HW2037. The marker was validated in another population developed from WL711× CS + Lr28: 2D/2M 3/8 (acc. 2956) as well as in a few near- isogenic lines (NILs) carrying gene Lr28. Compared to the previously reported marker TPSCAR SCS421₅₇₀, wmc313 is more closely linked to Lr28. Both these markers flanking the gene should be useful in the deployment of Lr28 into the breeding program using marker-assisted selection allowing pyramiding with other effective genes to confer durable resistance.     

LIGHT AND TEMPERATURE AS FACTORS REGULATING SEASONAL GROWTH AND DISTRIBUTION OF ULOTHRIX ZONATA (ULVOPHYCEAE)1

Ulothrix zonata (Weber and Mohr) Kütz. is an unbranched filamentous green alga found in rocky littoral areas of many northern lakes. Field observations of its seasonal and spatial distribution indicated that it should have a low temperature and a high irradiance optimum for net photosynthesis, and at temperatures above 10°C it should show an increasingly unfavorable energy balance. Measurements of net photosynthesis and respiration were made at 56 combinations of light and temperature. Optimum conditions were 5°C and 1100 μE·m^?2·s^?1 at which net photosynthesis was 16.8 mg O₂·g^?1·h^?1. As temperature increased above 5° C optimum irradiance decreased to 125 μE·m^?2·s^?1 at 30°C. Respiration rates increased with both temperature and prior irradiance. Light-enhanced respiration rates were significantly greater than dark respiration rates following irradiance exposures of 125 μE·m^?2·s^?1 or greater. Polynomials were fitted to the data to generate response surfaces. Polynomial equations represent statistical models which can accurately predict photosynthesis and respiration for inclusion in ecosystem models.     

EFFECT OF TEMPERATURE,LIGHT AND pH ON GROWTH,PHOTOSYNTHESIS AND RESPIRATION OF THE DINOFLAGELLATE PERIDINIUM CINCTUM FA. WESTII IN LABORATORY CULTURES1

Optimum light, temperature, and pH conditions for growth, photosynthetic, and respiratory activities of Peridinium cinctum fa. westii (Lemm.) Lef were investigated by using axenic clones in batch cultures. The results are discussed and compared with data from Lake Kinneret (Israel) where it produces heavy blooms in spring. Highest biomass development and growth rates occurred at ca. 23° C and ≥50 μE· m^?2·s¹ of fluorescent light with energy peaks at 440–575 and 665 nm. Photosynthetic oxygen release was more efficient in filtered light of blue (BG 12) and red (RG 2) than in green (VG 9) qualities. Photosynthetic oxygen production occurred at temperatures ranging from 5° to 32° C in white fluorescent light from 10 to 105 μE·m^?2·s^?1 with a gross maximum value of 1500 × 10^?12 g·cell^?1·h^?1 at the highest irradiance. The average respiration amounted to ca. 12% of the gross production and reached a maximum value of ca. 270·10^?12 g·cell^?1·h^?1 at 31° C. A comparison of photosynthetic and respiratory Q₁₀-values showed that in the upper temperature range the increase in gross production was only a third of the corresponding increase in respiration, although the gross production was at maximum. Short intermittent periods of dark (>7 min) before high light exposures from a halogen lamp greatly increased oxygen production. Depending on the physiological status of the alga, light saturation values were reached at 500–1000 μE·m^?2·s^?1 of halogen light with compensation points at 20–40 μE·m^?2·s^?1 and I_k-values at 100–200 μE·m^?2·s^?1. The corresponding values in fluorescent light in which it was cultured and adapted, were 25 to 75% lower indicating the ability of the alga to efficiently utilize varying light conditions, if the adaptation time is sufficient. Carbon fixation was most efficient at ca. pH 7, but the growth rates and biomass development were highest at pH 8.3.     

THF INFLUENCE OF IRRADIANCE ON THF BIOCHEMICAL COMPOSITION OF THE PRYMNESIOPHYTE ISOCHRYSIS SP. (CLONE T-ISO)1

The effects of irradiance on the biochemical composition of the prymnesiophyte microalga, Isochrysis sp. (Parke; clone T-ISO), a popular species for mariculture, were examined. Cultures were grown under a 12:12 h light: dark (L:D) regime at five irradiances ranging from 50 to 1000 μE·m ²·s^?1 and harvested at late-logarithmic phase for analysis of biochemical composition. Gross composition varied aver the range of irradiances. The highest levels of protein were present in cells from cultures grown at 100 and 250 μE·m ³·s¹, and minimum levels of carbohydrate and lipid occurred at 50 μE·m^?2·s^?1. Because the cell dry weight was reduced at lower irradiances, different trends were evident when results were expressed as percentage of dry weights. Protein percentages were highest at Wand 100 μE·m^?2·s^?1 and carbohydrate at 100 μE·m^?2·s^?1. The composition of amino acids did not differ over the range of irradiances. Glutamate and aspartate were always present in high proportions (9.0–13.5%); histidine. methionine, tryptophan, cystine, and hydroxy-proline were minor constituents (0.0–2.6%). Glucose was the predominant sugar in all cultures, ranging from 23.0% (50 μE·m^?2·s^?1) to 45.0% (100 μE·m^?2·s^?1) of total polysaccharide. No correlation was found between the proportion of any of the sugars and irradiance. The proportions of the lipid class components and fatty acids showed little change with irradiance. The main fatty acids were 14:0, 16:0, 16:1(n-7), 18:1(n-9), 18:3(n-3). 18:4(n-3), 18:5(n-3), and 22:6(n-3). Proportions of 22: 6(n-3) increased, whereas l8:3(n-3). 18:3(n-6). and 18:4(n-3) decreased, with increasing irradiance. Pigment concentrations were highest in cultures grown at 50 μE·m^?2·s^?1, except for fucoxanthin and diadinoxanthin (100 μE·m^?2·s^?1). The concentrations of accessory pigments correlated with chlorophyll a, which decreased in concentration with increasing irradiance. On the basts of biochemical composition, an irradiance of 100 μE·m^?1·s^?1 (12:12 h L:D cycle)for the culture of Isochrysis sp. (clone T-ISO) may provide optimal nutritional value for maricultured animals, although feeding trials are now necessary to substantiate this.     

Tagging of an Aegilops speltoides Derived Leaf Rust Resistance Gene Lr 28 with a Microsatellite Marker in Wheat

Leaf rust resistance gene Lr28 has been transferred form Aegilops speltoides into bread wheat on chromosome 4AL. To identify the molecular markers linked to Lr28 the available microsatellite markers for wheat chromosome arm 4AL were surveyed on near isogenic lines (NILs) of Triticum aestivum cultivars having Lr28 gene, other Lrgenes and susceptible cultivars. A null allele of Xgwm 160 marker was found to be associated with Lr28. Linkage between the marker and the Lr28 resistance gene was confirmed using F₂ mapping population of cross PBW343 and HD2329 + Lr28.     

Synthesis of a series of first-row tris-imidazolylphosphine sandwich complexes and their potential for formation of polymetallic species

A series of tris-[2-(1-methylimidazolyl)phosphine] sandwich complexes with Co²⁺ (1), Ni²⁺ (2), Cu²⁺ (3) and Zn²⁺ (4) have been synthesized and characterized with the intent of using these complexes as templates for building polymetallic species. X-ray analysis reveals that each metal is six-coordinate with octahedral geometry. Compound 3 exhibits a tetragonal distortion resulting from a Jahn-Teller distortion of a Cu²⁺ (d⁹) complex. Electrochemistry of 1-4 displayed peaks assigned to both ligand-based oxidation at 1.45-1.56 V and a perchlorate-based reduction at −2.36 to −2.78 V versus FcH⁺/FcH. Metal-based reduction was also observed for 2, with a reversible Ni^2+/3+ oxidation at 0.89 V, consistent with the relatively poor donor ability of the imidazolyl nitrogen bases; and 3, with a irreversible Cu^2+/1+ reduction at −1.29 V versus FcH⁺/FcH, consistent with the decomposition of the complex upon reduction. X-ray structures indicate large steric crowding around the phosphorus atom resulting from the orientation of the methyl substituent on the imidazoles. This crowding may prohibit the formation of polymetallic species through phosphorus-metal bonding.     

An Electrochemical Study of the Factors Responsible for Modulating the Reduction Potential of Putidaredoxin

 The gene coding for putidaredoxin has been synthesized using a combination of chemical and enzymatic methods and subsequently expressed in Escherichia coli. The recombinant protein characterized by electronic spectroscopy, mass spectrometry, and electrochemistry was found to be identical to putidaredoxin obtained from Pseudomonas putida. Polylysine was found to promote the fast and reversible electrochemistry of putidaredoxin at negatively charged electrodes such as indium-doped tin oxide or gold surfaces modified with mercaptoalkanoate groups. The value of the heterogeneous electron transfer rate constant obtained from solutions containing a mixture of putidaredoxin and polylysine (k _s =1.3×10^–3 cm/s) is one order of magnitude larger than the values reported previously at gold electrodes modified with mercaptoethylamine or at antimony-doped tin oxide semiconductor electrodes. It was observed that when the reduction potential of putidaredoxin is measured by cyclic voltammetry, the resultant value is consistently more positive (64 mV) than the reduction potential measured with potentiometric titrations. A comparison between the electrochemical responses of putidaredoxin and spinach ferredoxin, combined with the examination of their corresponding three-dimensional structures, indicates that the positive shift in the reduction potential of putidaredoxin originates from the formation of a transient complex between putidaredoxin and polylysine at the electrode surface. The formation of this transient complex modulates the reduction potential of putidaredoxin by lowering the value of the dielectric constant around its iron-sulfur cluster microenvironment, specifically by neutralizing negative charges surrounding the active site and by excluding water from the solvent exposed iron sulfur cluster. The observed positive shift in E°′, which is induced by complexation with polylysine at the electrode-surface, suggests that similar factors are likely to contribute to the anodic shift in the E°′ of cytochrome P450_cam-bound putidaredoxin (+44 mV) with respect to the E°′ measured for free putidaredoxin. Received: 14 June 1999 / Accepted: 6 August 1999     

RFLP analysis of an Aegilops ventricosa chromosome that carries a gene conferring resistance to leaf rust (Puccinia recondita) when transferred to hexaploid wheat

RFLP analysis has been used to characterise XM^v, a chromosome of Aegilops ventricosa present in a disomic addition line of wheat. This chromosome is known to carry a major gene conferring resistance to leaf rust (Lr). The analysis demonstrated that XM^v is translocated with respect to the standard wheat genome, and consists of a segment of the short arm of homoeologous group 2 attached to a group 6 chromosome lacking a distal part of the short arm. Lr was located to the region of XM^v with homoeology to 2S by analysis of a leaf rust-susceptible deletion line that was found to lack the entire 2S segment. Confirmation and refinement of the location of Lr was obtained by analysis of a spontaneous resistant translocation in which a small part of XM^v had been transferred to wheat chromosome 2A.     

CRITICAL IRRADIANCE LEVELS AND THE INTERACTIVE EFFECTS OF QUANTUM IRRADIANCE AND DOSE ON GAMETOGENESIS IN THE GIANT KELP,MACROCYSTIS PYRIFERA1

Gametophytes of Macrocystis pyrifera (L.) C. Ag. were cultured under a series of quantum irradiances in three photoperiod regimes. The quantum irradiances in each photoperiod were adjusted to provide equal daily irradiation dosages between photoperiods which allowed a critical examination of the interactions between quantum irradiance and quantum dose in determining gametophyte fertility. The lowest quantum irradiance which stimulated gametogenesis in more than 50% of the female gametophytes was 5 μE·m^?2·s^?1. The saturating irradiance was ca. 10 μE·m^?2·s^?1 at photoperiods of 12 h or greater. In terms of daily quantum dose, the lowest dose at which greater than 50% gametogenesis occurred was 0.2 E·m^?2·d^?1. However, this critical quantum dose was higher (0.4 E·m^?2·d^?1) when instantaneous irradiances were less than 5 μE·m^?2·s^?1. The saturation quantum dose was also affected by the rate at which the quantum dose was received and varied from 0.4 to 0.8 E·m^?2·d^?1. Gametophytes in all three photoperiods reached 100% fertility at quantum irradiances above 5 μE·m^?2·s^?1. Photoperiod effects were small and could be accounted for by quantum dosage effects.     

Activation-deactivation reactions in the ATPase enzyme in Rhodospirillum rubrum chromatophores

(1) The ATPase enzyme in untreated chromatophores from Rhodospirillum rubrum is in a low-activity state (designated as E°). It can be activated by application of a transmembrane generated by light-induced electron transport, or by application of acid-base jumps. (2) After rapid dissipation of the light-induced , the active state of the ATPase enzyme decays (in the absence of added substrates or products) to a low-activity state (designated as E′), with a half-time of the order of 2–4 min. This state differs from E° in that E′ (but not E°) can be rapidly reactivated by addition of substrate, but only when the Mg²⁺ concentration is kept below 20–30 μM. Since this is characteristic of an activated enzyme containing tightly bound ADP (Slooten, L. and Nuyten, A. (1981) Biochim. Biophys. Acta 638, 313–326), it is suggested that release of endogenous, tightly bound ADP is one of the factors involved in activation of the ATPase enzyme.     

Analysis of the binding of phenylalanine to phenylalanyl-tRNA synthetase

Using the complete rate equation for the PP_i-ATP exchange reaction at equilibrium, the dissociation constants of phenylalanine (10^?5m), phenylalanine butyl ester (8 × 10^?5m), benzyl alcohol (6 × 10^?4m), phenylalaninol (2 × 10^?4m), hydrocinnamic acid (3 × 10^?3m) and glycine (>1 m) with the phenylalanyl-tRNA synthetase (Escherichia coli K12) were determined. Taking the model of Koshland (1962) for the estimation of the configurational free energy change due to proximity and orientation, and decomposing the process of binding into several thermodynamic steps, the contribution to binding of the benzyl group, glycine unit, protonated amino group, carboxylate group and joint interactions were estimated. The results are: (1) the standard free energy contributions for binding phenylalanine are benzyl group (?8.2 kcal/mol), glycine unit (?2.5 kcal/mol), protonated amino group (?0.8 kcal/mol) and carboxylate group (1 kcal/mol). (2) The standard free energy change due to the change in the interaction between the protonated amino group and carboxylate group when they are transferred from the aqueous environment to the enzyme environment is ?2.7 kcal/mol. (3) A dissociation constant for glycine of 7.5 m is calculated without the hypothesis that a conformational change occurs in the enzyme when the benzyl unit of phenylalanine binds, permitting an interaction of the enzyme with the protonated amino and/or carboxylate groups.The detection of E·AA² and E·ATP shows that a sequential addition of substrates is not necessary for binding. A comparison of the dissociation constants of E·AA (10^?5m), E·ATP (1.5 × 10^?3m), E·PP (5.5 × 10^?4m), E·I (8 × 10^?5m) and the mixed complexes E·I·ATP (6 × 10^?8m²), E·I·PP (5 × 10^?8m²) and E·AA·PP (7 × 10^?9m²), with phenylalanine butyl ester as the inhibitor, indicates no strong interaction between the binding of ATP or PP_i with the binding of phenylalanine.     

Nitrogen cycling in an Antarctic ecosystem 2. Estimation of the amount of nitrogen fixation in a moss community on East Ongul Island

Nitrogen fixation by cyanobacteria in a moss community on East Ongul Island (69°00'S 39°35'E), Antarctica was investigated using the acetylene reduction method. The mean acetylene reduction rate at 10°C and 200 μE·m⁻²·s⁻¹ photosynthetically active radiation was 7.12 nmol C₂H₄ per square centimeter of moss community per hour. The effects of temperature, radiation, desiccation and rehydration on the acetylene reduction rates were examined. A simple predictive model was constructed in order to estimate the amount of nitrogen fixed in the field. Using this model, the daily amount of nitrogen fixation was calculated from microclimatic data (temperature and radiation) measured in the experimental field at Syowa Station on East Ongul Island between 1983 and 1984. The cumulative amount of nitrogen fixation in the growing season during this period was estimated to be 329 mg N per square meter of moss community. It is suggested that nitrogen fixation by cyanobacteria in the moss community is important as a nitrogen source for the community growth on East Ongul Island.     

Functions of calcium in the interaction of progesterone-receptor complex with nuclear components

Chick oviduct cytosol [³H]progesterone-receptor complex treated with 30 mm Ca²⁺ at 0 °C demonstrated a twofold greater binding to isolated chick oviduct nuclei or DNA-cellulose than such complexes activated thermally (25 °C). Divalent ions such as Mg²⁺ and Mn²⁺ were unable to mimic the effect of Ca²⁺ under identical conditions. The capacity of the Ca²⁺-treated progesterone-receptor complex to bind to nuclei or DNA-cellulose reached a peak within 45 min of Ca²⁺ treatment of the complex at 0 °C. This binding gradually declined as a function of incubation time and after 24 h at 0 °C no significant binding was observed. The Ca²⁺- and heat-treated chick oviduct [³H]progesterone-receptor complex was also characterized by DEAE-cellulose and agarose gel nitration chromatography. While heat-activated receptor could be resolved into A and B subunits on DEAE-cellulose, the receptor exposed to Ca²⁺ for 45 min at low temperature yielded the “A” subunit and a broad peak with poor affinity for the anion exchanger. The peak corresponding to “B” subunit was not discernible. The broad peak which eluted before the A peak was subsequently resolved by agarose gel filtration into receptor forms IV and V as described previously by Sherman et al. (M. Sherman, S. Atienza, J. Shansky, and L. Hoffman, 1974, J. Biol. Chem., 249, 5351–5363; M. Sherman, L. Pickering, F. Rollwagen and L. Miller, 1978, Fed. Proc., 37, 167–173). Again DEAE-cellulose chromatography of the progesterone-receptor complex treated as long as 24 h at 0 °C with Ca²⁺ revealed a poorly bound peak which on agarose gel filtration corresponded exclusively to form V. A correlation was apparent between an increase in form V and a gradual decrease in the binding capacity of the Ca²⁺-treated steroid-receptor complex to nuclei, DNA-cellulose, or DEAE-cellulose filters.Based on these findings, I postulate that Ca²⁺ has a functional role in the mechanism of progesterone action in chick oviduct. Firstly, it enhances a low temperature, time dependent binding of the progesterone-receptor complex to chick oviduct nuclear components, and subsequently promotes, by possible activation of endogenous protease(s) the cleavage of the receptor subunits.     

Integrated thermodynamic analysis of electron bifurcating [FeFe]-hydrogenase to inform anaerobic metabolism and H2 production

Electron bifurcating, [FeFe]-hydrogenases are recently described members of the hydrogenase family and catalyze a combination of exergonic and endergonic electron exchanges between three carriers (2 ferredoxin_red⁻ + NAD(P)H + 3 H⁺ = 2 ferredoxin_ox + NAD(P)⁺ + 2 H₂). A thermodynamic analysis of the bifurcating, [FeFe]-hydrogenase reaction, using electron path-independent variables, quantified potential biological roles of the reaction without requiring enzyme details. The bifurcating [FeFe]-hydrogenase reaction, like all bifurcating reactions, can be written as a sum of two non-bifurcating reactions. Therefore, the thermodynamic properties of the bifurcating reaction can never exceed the properties of the individual, non-bifurcating, reactions. The bifurcating [FeFe]-hydrogenase reaction has three competitive properties: 1) enabling NAD(P)H-driven proton reduction at pH₂ higher than the concurrent operation of the two, non-bifurcating reactions, 2) oxidation of NAD(P)H and ferredoxin simultaneously in a 1:1 ratio, both are produced during typical glucose fermentations, and 3) enhanced energy conservation (~10 kJ mol⁻¹ H₂) relative to concurrent operation of the two, non-bifurcating reactions. Our analysis demonstrated ferredoxin E°′ largely determines the sensitivity of the bifurcating reaction to pH₂, modulation of the reduced/oxidized electron carrier ratios contributed less to equilibria shifts. Hydrogenase thermodynamics data were integrated with typical and non-typical glycolysis pathways to evaluate achieving the ‘Thauer limit’ (4 H₂ per glucose) as a function of temperature and pH₂. For instance, the bifurcating [FeFe]-hydrogenase reaction permits the Thauer limit at 60 °C if pH ₂ ≤ ~10 mbar. The results also predict Archaea, expressing a non-typical glycolysis pathway, would not benefit from a bifurcating [FeFe]-hydrogenase reaction; interestingly, no Archaea have been observed experimentally with a [FeFe]-hydrogenase enzyme.     

Bacterial Pu(V) reduction in the absence and presence of Fe(III)–NTA: modeling and experimental approach

Plutonium (Pu), a key contaminant at sites associated with the manufacture of nuclear weapons and with nuclear-energy wastes, can be precipitated to “immobilized” plutonium phases in systems that promote bioreduction. Ferric iron (Fe³⁺) is often present in contaminated sites, and its bioreduction to ferrous iron (Fe²⁺) may be involved in the reduction of Pu to forms that precipitate. Alternately, Pu can be reduced directly by the bacteria. Besides Fe, contaminated sites often contain strong complexing ligands, such as nitrilotriacetic acid (NTA). We used biogeochemical modeling to interpret the experimental fate of Pu in the absence and presence of ferric iron (Fe³⁺) and NTA under anaerobic conditions. In all cases, Shewanella alga BrY (S. alga) reduced Pu(V)(PuO₂ ⁺) to Pu(III), and experimental evidence indicates that Pu(III) precipitated as PuPO_4(am). In the absence of Fe³⁺ and NTA, reduction of PuO₂ ⁺ was directly biotic, but modeling simulations support that PuO₂ ⁺ reduction in the presence of Fe³⁺ and NTA was due to an abiotic stepwise reduction of PuO₂ ⁺ to Pu⁴⁺, followed by reduction of Pu⁴⁺ to Pu³⁺, both through biogenically produced Fe²⁺. This means that PuO₂ ⁺ reduction was slowed by first having Fe³⁺ reduced to Fe²⁺. Modeling results also show that the degree of PuPO_4(am) precipitation depends on the NTA concentration. While precipitation out-competes complexation when NTA is present at the same or lower concentration than Pu, excess NTA can prevent precipitation of PuPO_4(am).     

Carotenoid composition in Zea mays developed at sub-optimal temperature and different light intensities

The content and composition of pigments were examined in the third leaf of Zea mays L. plants grown under controlled environment at near-optimal temperature (24°C) or sub-optimal temperature (14°C) at a light intensity of either 200 or 600 μmol m^?2 s^?1. Compared to leaves grown at 24°C, leaves grown at 14°C showed a large reduction in the chlorophyll (Chl) content, a marked decrease in the Chl a/b ratio, and a large increase in the ratio of total carotenoids/Chl a+b. Leaves grown at 14°C showed a much lower content of β-carotene than leaves grown at 24°C, while the content of the carotenoids of the xanthophyll cycle (violaxanthin [V] + antheraxanthin [A] + zeaxanthin [Z]) was markedly higher in the former leaves as compared to the latter leaves; neoxanthin and lutein were affected by the growth temperature to a much lesser extent. The xanthophylls/β-carotene ratio was about three times higher in leaves grown at 14°C as compared to leaves grown at 24°C. On a chlorophyll basis, the two types of leaves hardly differed in their level of β-carotene, while the levels of the xanthophylls (including lutein and neoxanthin) were higher in 14°C-grown leaves as compared to 24°C-grown leaves. In leaves grown at 14°C, 40 and 56% of the V+A+Z pool was in the form of zeaxanthin at low light intensity and high light intensity, respectively. Only trace amounts of zeaxanthin, if any, were present in leaves grown at 24°C. The changes in the pigment composition induced by growth at sub-optimal temperature were more pronounced at a light intensity of 600 as compared to 200 μmol m^?2 s^?1. In the given range, the light intensity slightly affected the composition of pigments in leaves grown at 24°C. The physiological significance of the modifications to the pigment composition induced by growth at sub-optimal temperature is discussed.     

A New Fe/V Redox Flow Battery Using a Sulfuric/Chloric Mixed‐Acid Supporting Electrolyte

A redox flow battery using Fe²⁺/Fe³⁺ and V²⁺/V³⁺ redox couples in chloric/sulfuric mixed‐acid supporting electrolyte is investigated for potential stationary energy storage applications. The Fe/V redox flow cell using mixed reactant solutions operates within a voltage window of 0.5–1.35 V with a nearly 100% utilization ratio and demonstrates stable cycling over 100 cycles with energy efficiency >80% and no capacity fading at room temperature. A 25% improvement in the discharge energy density of the Fe/V cell is achieved compared with a previously reported Fe/V cell using a pure chloride acid supporting electrolyte. Stable performance is achieved in the temperature range between 0 and 50 °C as well as when using a microporous separator as the membrane. The improved electrochemical performance makes the Fe/V redox flow battery a promising option as a stationary energy storage device to enable renewable integration and stabilization of the electric grid.