Measurement Of Oxygen Production Research Articles

Photocalorespirometry (Photo-CR): A Novel Method for Access to Photosynthetic Energy Conversion Efficiency

One key parameter for assessing the CO2 fixation in aquatic ecosystems but also for the productivity of photobioreactors is the energy conversion efficiency (PE) by the photosynthetic apparatus. PE strictly depends on a range of different fluctuating environmental conditions and is therefore highly variable. PE is the result of complex metabolic control. At the moment PE can only be determined indirectly. Furthermore, the currently available techniques either capture only short time processes, thus reflecting only parts of the photosynthetic engine, or quantify the total process but only with limited time resolution. To close this gap, we suggest for the first time the direct measurement of the fixed energy combined with respirometry, called photocalorespirometry (Photo-CR). The proof of the principle of Photo-CR was established with the microalga Chlamydomonas reinhardtii. The simultaneous measurement of oxygen production and energy fixation provides an calorespirometric ratio of −(437.9 ± 0.7) kJ mol−1 under low light conditions. The elevated calorespirometric ratio under high light conditions provides an indication of photo-protective mechanisms. The Photo-CR delivers the PE in real time, depending on the light intensity. Energetic differences less than 0.14% at radiation densities of up to 800 μE m−2 s−1 can be quantified. Other photosynthetic growth parameters (e.g. the specific growth rate of 0.071 h−1, the cell specific energy conservation of 30.9 ± 1.3 pW cell−1 at 150 µE m−2 s−1 and the number of photons (86.8) required to fix one molecule of CO2) can easily be derived from the Photo-CR data.

Mitigation methods for errors in oxygen measurement with redox cycling of materials for hydrogen and syngas production

In the search for new and improved materials for hydrogen and syngas production by solar thermochemical looping, test-reactors are employed which include a temperature controlled sample chamber and adjustable gas flows through or past the sample. The experiments performed in these devices enable researchers to find limiting factors like mass transfer, heat transfer, kinetics, and material durability in a time and cost efficient manner. The devices have proven their utility by their near universal employment by groups seeking and studying new materials. A review of past studies has revealed that the measurement of oxygen partial pressure during the reduction state is key to the evaluation of material productivity, yet the methods for this measurement are varied across different publications and are often given little focus. The majority of O2 sensing is achieved using a mass spectrometer or gas chromatograph, inferring behavior at the sample from measurements of gas that has traveled for some distance and time. In this paper, we investigate the potential errors which may be introduced by taking a single measurement of oxygen production at the system outlet to infer O2 production curves, and demonstrate some methods to correct this. We also investigate some of the issues related to including an oxygen sensor near the sample. Issues discussed include temporal delays between sensors, oxygen leakage, sensing an incompletely mixed flow, diffusion, and mixing downstream from the sample. Oxygen entering the system through inlet gas or leakage accounted for the largest source of error, but these errors can be corrected by straightforward methods. Numerical simulations are employed to investigate the mixing of the flow, while diffusion is estimated with an analytical model. During an example experiment, the applied correction methods reduced differences between two sensors' data from 20% to 7%, while the corrections led to a 36% change in calculated total oxygen production from raw to corrected data.

Bioinspired silicification of chloroplast for extended light-harvesting ability

We report a hybrid bioactive system inspired by the biosilicification of diatoms. Monodisperse chloroplast/silica hybrid microspheres with core–shell structure were designed and prepared. Natural fresh chloroplasts, the photosynthetic plant organelle, were surfacely covered with silica shell by mild sol–gel process. The charge of chloroplast surface attracts negatively charged silica particles in the sol generated from subsequent hydrolysis and condensation of the tetraethyl orthosilicate (TEOS), which benefits single-chloroplast encapsulation. SEM images confirm the closed topologies, sizes, and dispersions of hybrid microspheres comparable to those of parent chloroplasts. The elemental analysis using EDX, the particle size distribution analyses using DLS, the thermochemical analyses using TGA measurements and structural characterization using XRD provide evidence for the formation of silica coating. Monitoring declines in the visible light absorption production yields information regarding the declines in the light-harvesting ability of chlorophyll, which confirmed that the silica shell in the present work extends the photochemical vitality of chloroplasts. Results from oxygen production measurements also demonstrate the existence of silica shell confers real protection on the bioactivity of chloroplasts. We envisage that the stand-alone chloroplast encapsulation enables preparation of living-cell-templated microspheres exhibiting capacity for photosynthetic bioreactors, sensors, green coatings, catalysts, more generally opening a window for construction of stable, environment friendly, functional hybrid materials.

Laminaria hyperborea photosynthesis-irradiance relationship measured by oxygen production and pulse-amplitude-modulated chlorophyll fluorometry

Information about photosynthesis−irradiance (P−I) relationships is crucial in many primary production studies. This is frequently obtained using incubation experiments, which may not simulate in situ conditions where algae are adjusting their photosynthetic systems to perma- nent light variations. There has been increasing interest in pulse-amplitude-modulated (PAM) chlorophyll fluorometry—which measures instantaneous photosynthetic response—particularly in the use of rapid light curves (RLCs) to minimize the confounding effects of light acclimation encountered with traditional 'steady-state' light curves (SSLC). However, there is still a lack of information about how oxygen SSLC curves and estimations from fluorescence P−I curves are related. The present study addresses some of these topics, using Laminaria hyperborea. The objectives of this study were to (1) determine the effect of light sequence (increasing or decreas- ing) in the estimation of P−I parameters, (2) characterize the daily patterns of P−I curve parame- ters, (3) compare oxygen and fluorescence P−I parameters and (4) evaluate the possibility of con- verting fluorescence P−I parameters into oxygen production measurements. Results showed that light sequence had no significant effect on P−I parameters (fluorescence and oxygen) and that P−I curves exhibited considerable differences over the day (F-ratio analysis). Fluorescence SSLCs and RLCs were good oxygen production predictors only at sub-saturating irradiances, when signifi- cant linear relationships were obtained with results from oxygen incubations. Thus care should be taken when interpreting PAM fluorescence gross production estimations from higher light intensities.

Influence of the Quantity and Quality of Light on Photosynthetic Periodicity in Coral Endosymbiotic Algae

Symbiotic corals, which are benthic organisms intimately linked with their environment, have evolved many ways to deal with fluctuations in the local marine environment. One possible coping mechanism is the endogenous circadian clock, which is characterized as free running, maintaining a ∼24 h periodicity of circuits under constant stimuli or in the absence of external cues. The quantity and quality of light were found to be the most influential factors governing the endogenous clock for plants and algae. Unicellular dinoflagellate algae are among the best examples of organisms that exhibit circadian clocks using light as the dominant signal. This study is the first to examine the effects of light intensity and quality on the rhythmicity of photosynthesis in the symbiotic dinoflagellate Symbiodinium sp., both as a free-living organism and in symbiosis with the coral Stylophora pistillata. Oxygen production measurements in Symbiodinium cultures exhibited rhythmicity with a periodicity of approximately 24 h under constant high light (LL), whereas under medium and low light, the cycle time increased. Exposing Symbiodinium cultures and corals to spectral light revealed different effects of blue and red light on the photosynthetic rhythm, specifically shortening or increasing the cycle time respectively. These findings suggest that the photosynthetic rhythm is entrained by different light cues, which are wired to an endogenous circadian clock. Furthermore, we provide evidence that mRNA expression was higher under blue light for two potential cryptochrome genes and higher under red light for a phytochrome gene isolated from Symbiodinium. These results offer the first evidence of the impact of the intensity and quality of light on the photosynthetic rhythm in algal cells living freely or as part of a symbiotic association. Our results indicate the presence of a circadian oscillator in Symbiodinium governing the photosynthetic apparatus through a light-induced signaling pathway that has yet to be described.

Dissolved O2/Ar and other methods reveal rapid changes in productivity during a Lagrangian experiment in the Southern Ocean

We use continuous and discrete measurements of the dissolved O2/Ar ratio in the mixed layer to investigate the dynamics of biological productivity during the Southern Ocean Gas Exchange Experiment in March and April 2008. Injections of SF6 defined two water masses (patches) that were followed for up to 2 weeks. In the first patch, dissolved O2/Ar was supersaturated, indicating net biological production of organic carbon. In the second patch, rapidly decreasing O2/Ar could only be reasonably explained if the mixed layer was experiencing a period of net heterotrophy. The observations rule out dominant contributions from vertical mixing, lateral dilution, or respiration in the ship's underway seawater supply lines. We also compare nine different estimates of net community, new, primary, or gross production made during the experiment. Net community and new production estimates agreed well in the first patch but disagreed in the second patch, both during an initial net heterotrophic period but also during the apparently autotrophic period at the end of the observations. Rapidly changing productivity during the second patch complicated the comparison of methods that integrate over daily and several week timescales. Primary productivity values from on‐deck 24 h 14C incubations and gross carbon production values from photosynthesis‐irradiance experiments were nearly identical even during highly dynamic periods of net heterotrophy, while gross oxygen production measurements were 3.5–4.2 times higher but with uncertainties in that ratio near ±2. These comparisons show that the photosynthesis‐irradiance experiments based on 1–2 h 14C incubations underestimated gross carbon production.

Plankton metabolism in surface waters of the tropical and subtropical Pacific Ocean

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 62:1-12 (2011) - DOI: https://doi.org/10.3354/ame01451 FEATURE ARTICLE Plankton metabolism in surface waters of the tropical and subtropical Pacific Ocean Donn A. Viviani, Karin M. Björkman, David M. Karl, Matthew J. Church* Department of Oceanography, University of Hawaii, Honolulu, Hawaii 96822, USA *Corresponding author. Email: mjchurch@hawaii.edu ABSTRACT: We measured plankton metabolism and evaluated changes in plankton community structure within the central Pacific Ocean during a trans-equatorial cruise from the South Pacific Subtropical Gyre (SPSG) to the North Pacific Subtropical Gyre (NPSG). Rates of net community production (NCP) and respiration (R) were determined in near-surface ocean waters, based on light–dark bottle measurements of oxygen production and consumption. Gross primary production (GPP) was computed, where GPP = NCP + R. Rates of GPP and R in the oligotrophic SPSG and NPSG were tightly coupled, resulting in NCP that was either zero or slightly negative. These subtropical waters were characterized by very low concentrations of inorganic nutrients (e.g. nitrate+nitrite range: 0.004 to 0.033 µmol l–1). Within the relatively nutrient-enriched equatorial waters (e.g. nitrate+nitrite concentrations range: 0.67 to 5.7 µmol l–1), GPP exceeded R by up to 5-fold, resulting in positive NCP. GPP varied ~16-fold (0.25 to 4.05 µmol O2 produced l–1 d–1) while R varied ~5-fold (0.31 to 1.56 µmol O2 consumed l–1 d–1). Picoplankton cell abundances and diagnostic pigment biomarkers were used to determine regional differences in phytoplankton community structure. In the near-equatorial waters, abundances of Synechococcus and photosynthetic picoeukaryotes increased up to 100- and 10-fold, respectively, and diagnostic pigment biomarkers for eukaryotic phytoplankton (including diatoms, pelagophytes, and haptophytes) also increased. These results indicate that variability in nutrient availability constitutes an important regulator of net productivity and plankton community structure in large regions of the open ocean. KEY WORDS: Gross primary production · Respiration · Net community production · Equatorial Pacific · Subtropical gyres Full text in pdf format Information about this Feature Article NextCite this article as: Viviani DA, Björkman KM, Karl DM, Church MJ (2011) Plankton metabolism in surface waters of the tropical and subtropical Pacific Ocean. Aquat Microb Ecol 62:1-12. https://doi.org/10.3354/ame01451 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 62, No. 1. Online publication date: January 04, 2011 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2011 Inter-Research.

Photosynthetic performance of outdoor Nannochloropsis mass cultures under a wide range of environmental conditions

The unicellular alga Nannochloropsis sp. (Eustigmatophyta) is a rich source of lipids, polyunsaturated fatty acids (such as eicosapentaenoic acid) and carotenoids (violaxanthin), which makes it valuable for human consumption, aquaculture and biofuel production. Mass production of Nannochloropsis sp. can be easily achieved in high-rate algal ponds (HRAP), in flat panel photobio- reactors (FPP) or in tubular photobioreactors. While easy to operate, these systems are prone to un- favorable growth conditions, which affect productivity. In the present study, we cultivated Nan- nochloropsis sp. in 2 outdoor production systems and monitored photosynthetic activity. Unfavorable conditions (stressors), such as high temperature and high pH in combination with high irradiance, were induced in FPP, causing a substantial reduction in the photosynthetic rate. The measurements of Nannochloropsis sp. photosynthetic activity using several chlorophyll fluorescence techniques as well as oxygen production measurements showed that this species is able to withstand high irradi- ance levels. Although some photodamage due to high irradiance was found, the cultures rapidly recovered. Nannochloropsis sp. coped well with high pH conditions under physiological tempera- tures. However, a temperature rise above 32°C was detrimental, with repair processes being unable to keep up with the rate of damage. The cultures in the FPP were more prone to damage by extreme temperatures than those in the HRAP due to the high surface:volume ratio, which complicated tem- perature regulation within the physiological range.

IMPACT OF BLEACHING STRESS ON THE FUNCTION OF THE OXYGEN EVOLVING COMPLEX OF ZOOXANTHELLAE FROM SCLERACTINIAN CORALS(1).

Global climate change is leading to the rise of ocean temperatures and is triggering mass coral bleaching events on reefs around the world. The expulsion of the symbiotic dinoflagellate algae is believed to occur as a result of damage to the photosynthetic apparatus of these symbionts, although the specific site of initial impact is yet to be conclusively resolved. Here, the sensitivity of the oxygen evolving complex (OEC) to bleaching stress was studied as well as its natural variation between seasons. The artificial electron donor, diphenyl carbazide (DPC), was added to cultured, freshly isolated and expelled (bleaching treatments only) zooxanthellae suspensions. Chl a fluorescence and oxygen production measurements showed that upon addition of DPC, no restoration of diminished photochemical efficiency occurred under control or bleaching conditions. This result was consistent between 12 h and 5 d bleaching treatments on Pocilloporadamicornis, indicating that the OEC is not the primary site of damage, and that zooxanthellae expulsion from the host is a nonselective process with respect to the functioning of the OEC. Further experiments measuring fast induction curves (FICs) revealed that in both summer and winter, the temperature when OEC function was lost occurred between 7°C and 14°C above the sea surface temperature. FIC and oxygen production measurements of P. damicornis during exposure to bleaching stress demonstrated that the thermotolerance of the OEC increased above the temperature of the bleaching treatment over a 4 h period. This finding indicates that the OEC has the capacity to acclimate between seasons and remains functional at temperatures well above bleaching thresholds.

Initial Measurements of Benthic Photosynthesis and Respiration in Lake Erie

The first reported in situ measurements of benthic primary production in Lake Erie were made on rocky substrata using oxygen and dissolved inorganic carbon change in 1997 and 1998. The productivity quotient for net benthic algal growth was determined to be 1.1 based on contemporaneous measurement of oxygen production and carbon uptake. Highest rates of gross photosynthesis were > 300 mg O 2/m 2/h on rocky substrata with mixed stands of Cladophora and dreissenid mussels. These stands also exhibited the greatest rates of oxygen consumption in the dark. Bare rock substrata had lower rates of gross photosynthesis than rock occupied by mussels or Cladophora, but even these habitats had rates that would place them among the highest rates measured in fresh water. Areal benthic photosynthetic rates would greatly exceed areal pelagic photosynthesis in depths shallower than 5 m depth in the eastern basin; and, at greater depths, the importance of declining benthic areal photosynthesis relative to generally increasing integral pelagic production with depth would depend on substratum type and water clarity. Dreissenid mussels had a positive effect on benthic photosynthesis that was especially evident in stimulating Cladophora growth over the course of the 1998 season.

Seasonal and short-time-scale dynamics of microplankton community production and respiration in an inshore upwelling system

An intensive study of pelagic primary production and microplankton community respiration was carried out during an entire upwelling season in the Ria de Vigo (NW Spain). From April to November measurements of oxygen production and respiration using the light-dark bottle technique were made twice a week at the surface, 1% light depth (1 % LD, 12 ± 4 m) and 40 m (8 m above sea floor) alongside routine physical, chemical and biological measurements. During the major part of the survey period intermittent intrusions of cold, nutrient-rich upwelled water were observed in the ria with a periodicity of about 2 wk. Rates of gross primary production (GPP) were high but variable averaging 37.3 ± 30.7 μM O 2 d -1 and 3.6 ± 4.8 μM O 2 d -1 at the surface and 1% LD respectively over the period of survey (n = 50). Rates of dark community respiration (DCR) were also high and variable with maximum values being observed in the surface layer where the seasonal average was 12.2 ± 9.8 μM O 2 d -1 . At the 1% LD and 40 m, DCR averaged 5.3 ± 4.4 and 2.8 ± 3.0 μM O 2 d -1 respectively. Although seasonal average and maximal DCR (up to 46.5 μM O 2 d -1 ) were among the highest reported for coastal areas, microplankton production over the period of survey was dominated by autotrophic processes. Respiration losses by the microplankton community in the euphotic zone represented on average 43% of estimated mean seasonal water column GPP (2.1 to 2.7 g C m -2 d -1 ). Net heterotrophy in the aphotic layer consumed the equivalent of a further 25 % of estimated water column GPP. The degree of coupling between primary production and respiration was primarily controlled by upwelling. During upwelling events respiration was generally low in the water column but it increased as a linear function of chlorophyll a concentration (R 2 = 0.55, n = 13) and GPP (R 2 = 0.47, n = 13) in the surface layer. Under such condition phytoplankton appears as the dominant component of community respiration consuming 14% of GPP. During periods of upwelling relaxation respiration was high relative to GPP. High water column respiration rates extending occasionally down to 40 m took place at the expense of organic matter trapped inside the bay. The seasonal breakdown of thermal stratification in autumn presented a relationship between surface respiration and chlorophyll a or GPP similar to that observed during upwelling events. The large excess primary production during this period was not remineralised inside the ria, suggesting that a large fraction may be exported towards the shelf.

Whole-cell biosensor for determination of volatile organic compounds in the form of aerosols

A biosensor using Chlorella microalgae immobilized on the membrane of an oxygen electrode has been designed to operate in the gas phase for determination of volatile organic compounds in the form of aerosols. Perchloroethylene (tetrachloroethylene) is used as an example to produce aerosols and vapours since it is toxic to the people working in dry-cleaning atmospheres and municipal treatment plants. A home-made controlled atmosphere chamber is constructed for perchloroethylene detection. Monitoring of perchloroethylene is achieved by the measurement of oxygen production during the algae photosynthetic process. The use of whole cells as bioreceptors allows the detection of a toxic aerosol in the gas phase without preliminary trapping of the analyte in a solution.

Light dependence of quantum yields for PSII charge separation and oxygen evolution in eucaryotic algae

Quantum yields of photosystcm II (PSII) charge separation (ΦP and oxygen production () were determined by simultaneous measurements of oxygen production and variable fluorescence in four different aquatic microalgae representing three different taxonomic groups: the freshwater alga Scenedesmus protuberans (Chlorophyceae) and the marine algae Phaeocystis globosa (Prymnesiophyceae), Emiliania huxleyi (Prymnesiophyceae), and Phaeodactylum tricornutum (Bacillariophyceae). In S. protuberans, P. tricornutum, and E. huxleyi, light‐dependent variability was observed in the ratio of to ΦP i.e. in the number of oxygen molecules produced per electron generated by PSII. The ratio :ΦP was highly variable at low light intensities (E < 0.5 Ek), and at higher light intensities (E > 0.5 EK) :ΦP showed a nonlinear decrease with increasing light intensity. In contrast, in P. globosa a trend in :ΦP could not be distinguished, and this species showed a decrease in :ΦP during the day, indicating a dependency of :ΦP on light history. Additionally, considerable interspecific quantitative differences in :ΦP were observed. Two possible interpretations to explain the variability in :ΦP are discussed. Assuming that ΦP is a reliable measure of the quantum yield for charge separation at PSII, one interpretation is that net oxygen production is influenced by processes that consume oxygen or affect linear electron transport (e.g. cyclic electron transport around PSII, pseudocyclic electron transport in the Mehler reaction, Rubisco oxygenase activity, and lightdependent mitochondrial respiration). A second interpretation, however, suggests that at saturating light, changes in photosynthesis turnover time occur, such that ΦP does not predict the steady‐state O2 yield.

Measurement of oxygen production by in vitro human and animal lenses with an oxygen electrode

PURPOSE. This paper describes an advantageous method of measuring the activity of the enzyme catalase, which has an important antioxidative role in the lens. This method allows the measurement of catalase in whole lenses. METHODS. Exposure to UVA (99% UV-A) radiation was used to stress animal and human (Eye Bank) lenses in vitro. The ability of lens catalase to convert H 2 O 2 into O 2 was measured directly, using an oxygen electrode and meter. This method is very specific, as catalase is the only enzyme that converts H 2 O 2 to O 2. RESULTS. Catalase in the lenses of humans, rabbits, and squirrels catalyzed the production of O 2 from H 2 O 2 very efficiently. The anterior equatorial regions of these lenses were the most active O 2 producing areas. More than 95% of lens catalase activity was found in the capsule-epithelium layer. Exposure to UVA radiation, up to ~100 J/cm 2 in 18 h, strongly inhibited O 2 production from 0.77 mM H 2 O 2 by the lenses. Catalase activity decreased with increasing age. Mixed cataractous human lenses produced O2 from H 2 O 2 at only 60% of the rate of normal lenses of similar ages. Nuclear cataracts produced O 2 at only 75% of the rate of normal lenses. Alpha-tocopherol (10 -5 M) protected lens catalase activity strongly. Alpha-tocopherol is known to accumulate in and protect against cell membrane peroxidation, and against singlet oxygen formation. These oxidative mechanisms appear to contribute to catalase photoinactivation. CONCLUSIONS. The method described indicated that catalase is a crucial antioxidative enzyme in the normal lens. Its inactivation could upset the oxidation-reduction balance in the lens and stimulate lens opacification.

In situ measurements of oxygen production and consumption using paramagnetic fusinite particles injected into a bean leaf

Photosynthetic oxygen production and respiratory oxygen consumption in the interior of a bean leaf ( Vicia faba) were monitored by following the amplitude of the electron paramagnetic resonance spectra of coal derivative particles (fusinite) injected into a leaf. We observed the explicit decrease in oxygen concentration due to respiration in the dark, and the light-induced oxygen production (about 2-fold increase in the oxygen partial pressure) only in the case of a closed water-filled chamber which prevented oxygen exchange with the surrounding atmosphere. However, under normal physiological conditions, when the sample was exposed to air (a leaf in the open holder) we did not observe any significant changes in the level of the oxygen partial pressure inside the leaf, neither in the dark nor during illumination. This observation, together with our earlier measurements of oxygen concentration in the aqueous phase of the leaf interior with the microscopic spin-label probes (Ligeza, A., Wisniewska, A. Subczynski, W.K., and Tikhonov, A.N. (1994) Biochim. Biophys. Acta 1186, 201–208), has led us to the conclusion that the ventilation of the leaf interior appears to be sufficient for maintaining the oxygen partial pressure practically on the same level, both in the dark and in the course of intensive light-induced production of oxygen by chloroplasts. Such ventilation should protect leaf tissues against the dangerous increase in the level of oxygen evolved by chloroplasts.

Measurement of oxygen production and demand in lake waters

Abstract By use of a modern BOD bottle probe, a digital read‐out meter, and quadruplicate sampling, oxygen concentrations were routinely measured with a precision of ± 0.02 g DO m−3. This level of accuracy permitted measurement of Water Oxygen Demand (WOD), Net Production (NP), and Gross Production (GP) at all depths in the water column of lakes. Sediment Oxygen Demand (SOD) was also measured and found to be small when compared to the total water column oxygen demand in unstratified water but was a significant part of the hypolimnetic oxygen uptake. Measurements of GP were found to correlate closely with primary production values determined independently by means of the 14C technique. Significant GP was also found in the hypolimnion of a mesotrophic lake, indicating that WOD does not always provide a measure of hypolimnetic oxygen uptake; net production does so in this situation. Further, WOD was found to decrease by about 20% per day in incubated samples, revealing that WOD incubations should never excee...

Entrapment of chloroplasts and thylakoids in polyvinylalcohol-SbQ. Optimization of membrane preparation and storage conditions

Chloroplasts and thylakoids isolated from spinach were entrapped in six different polyvinylalcohol bearing styrylpyridinium groups (PVA-SbQ). Measurements of oxygen production were carried out in 0.01 M phosphate buffer (pH 6) at 25 °C. Immobilized preparations were compared for their electron transport activity measured as the initial rate of oxygen evolution with p-benzoquinone as artificial electron acceptor. The entrapped chloroplasts in PVA-SbQ 1700 and 3500 betaine retained 20% of their initial activity after 90-day storage in the dark at + 4 °C. A membrane made with PVA-SbQ 2300 kept 20% activity after 427-day storage at −18 °C in the dark whereas the same membrane retained only 10% activity after 90-day storage at + 4 °C in the dark. A 1% BSA concentration increased the stability of the membrane. The limits of detection (corresponding to a 10% inhibition) of atrazine were 10 μg/l and 12 μg/l for native and entrapped chloroplasts, respectively. The good stability of entrapped chloroplasts suggests that this system could be useful for the detection of pollutants in water.

Coulometric measurement of oxygen consumption during development of marine invertebrate embryos and larvae

Determining the metabolic rate of larval invertebrates from aquatic habitats is complicated by the problems of small size and the scarcity of suitable measurement techniques. In this study, coulometric respirometry (a new technique for the study of marine embryos and larvae) was used to explore several issues associated with the rate of energy use during embryonic and larval development of marine invertebrates from three phyla. Coulometric respirometry measures rates of oxygen consumption under normoxic conditions by electrochemically replacing the oxygen consumed by organisms during an experiment. This technique is based on the assumption that all electrons consumed by the anodic reactions result in the production of oxygen. We verify this assumption using direct measurements of oxygen production and show that the technique is sensitive enough (1 nmol O2 h-1) to quantify the oxygen consumption of a single individual swimming freely in a relatively large volume (2 ml). Continuous measurements can span days, and embryos in the coulometric respiration chambers develop to the larval stage at normal rates of differentiation. Measurements of metabolic rates were made with the coulometric respirometer during the complete life-span of larvae of three species (asteroid, Asterina miniata; bivalve, Crassostrea gigas; echinoid, Dendraster excentricus). For these species, metabolic power equations had mass exponents near unity (0.9­1.1), showing that metabolic rate scales isometrically with mass during larval growth. Metabolic rates were independent of the concentration of larvae used in the respirometer chambers for a range of larval concentrations from 4 to 400 larvae ml-1 (coulometric respirometer) and from 241 to 809 larvae ml-1 (polarographic oxygen sensor). Metabolic rates were measured using coulometric respirometry and two other commonly used techniques, polarographic oxygen sensors and Winkler's titration. Polarographic oxygen sensors in small, sealed chambers (100 µl) consistently gave the lowest values (by as much as 80 %) for the asteroid, echinoid and molluscan larvae. By comparison, rates of oxygen consumption measured using coulometric respirometry and Winkler's titration (to measure the change in oxygen concentration over time) were similar and consistently higher. Although the polarographic oxygen sensor is the most widely used method for measuring the metabolism of small animals in sealed 100­1000 µl chambers, it appears that the metabolism of some larvae is adversely affected by the conditions within these respirometers.

Micro-autoradiographic determination of the viability of algae inhabiting deep sediment layers

Examination of sediment cores taken from shallow coastal regions of the Baltic showed that some algae were still alive at depths beyond the depth of light penetration. Their cells contained chlorophyll and photosynthesis resumed when they were exposed to light. Photosynthesis was detected by simultaneous measurement of oxygen production and 14C uptake. Autoradiography was used to detect incorporated 14C. The autoradiographic method was improved by a few modifications.

Live Algae in Deep Sediment Layers

AbstractExamination of sediment cores taken from shallow coastal regions of the Baltic showed that some algae were still alive at depths beyond the depth of light penetration. Their cells contained chlorophyll and photosynthesis resumed when they were exposed to light. Photosynthesis was detected by simultaneous measurement of oxygen production and 14C uptake. Autoradiography was used to detect incorporated 14C. The autoradiographic method was improved by a few modifications.