n-3 PUFA productivity in chemostat cultures of microalgae

Eicosapentaenoic (EPA) and docosahexaenoic (DHA) acid productivities from chemostat cultures of an isolate of Isochrysis galbana have been studied. The productivities reached in the interval of dilution rates between 0.0295 h^–1 and 0.0355 h^–1 were 1.5mg·1^–1·h^–1 for lipids, 300 g·1^–1·h^–1 for EPA and 130g1·1^–1·h^–1 for DHA. Furthermore, light attenuation by mutual shading, and agitation speed influences on growth and fatty acid composition were analysed. A model relating steady-state dilution rates to internal average light intensity has been proposed, the parameter values of which obtained by non-linear regression were: maximum specific growth rate (_max)=0.0426 h^–1; the affinity of cells to light (I_k) = 10.92 W·m^–2; the exponent (n) = 5.13; regression coefficient (r ²)=0.9999. Correspondence to: E. Molina Grima     

Light response of D1 turnover and photosystem II efficiency in the seagrassZostera capricorni

Biochemical and biophysical parameters, including D1-protein turnover, chlorophyll fluorescence, oxygen evolution activity and zeaxanthin formation were measured in the marine seagrassZostera capricorni (Aschers) in response to limiting (100 mol·m^–2·^–1), saturating (350 mol·m^–2·s^–1) or photoinhibitory (1100 mol·m^–2·s^–1) irradiances. Synthesis of D1 was maximal at 350 mol·m^–2·s^–1 which was also the irradiance at which the rate of photosynthetic O₂ evolution was maximal. Degradation of D1 was saturated at 350 mol·m^–2·s^–1. The rate of D1 synthesis at 1100 mol·m^–2·s^–1 was very similar to that at 350 mol·m^–2·s^–1 for the first 90 min but then declined. At limiting or saturating irradiance little change was observed in the ratio of variable to maximal fluorescence (Fv/Fm) measured after dark adaptation of the leaves, while significant photoinhibition occurred at 1100 mol·m^–2·s^–1. The proportion of zeaxanthin in the total xanthophyll pool increased with increasing irradiance, indicative of the presence of a photoprotective xanthophyll cycle in this seagrass. These results are consistent with a high level of regulatory D1 turnover inZostera under non-photoinhibitory irradiance conditions, as has been found previously for terrestrial plants.We would like to thank Professor Peter Böger (Department of Plant Biochemistry, University of Konstanz, Germany) for the kind gift of D1 antibodies. This work was partly supported by a University of Queensland Enabling Grant to CC.     

Oxygen consumption and flight muscle activity during heating in workers and drones of Apis mellifera

Summary Instantaneous oxygen consumption, muscle potential frequency, thoracic and ambient temperature were simultaneously measured during heating in individual workers and drones of honey bees. Relationships between these parameters and effects of thoracic temperature on power input and temperature elevation were studied. Oxygen consumption increased above basal levels only when flight muscles became active. Increasing muscle potential frequencies correlated with elevated oxygen consumption and raised thoracic temperature. The difference between thoracic and ambient temperature and oxygen consumption were linearly related. Oxygen consumption per muscle potential (l O₂ · g _–1 ^thorax · MP^–1) was two-fold higher in drones than in workers. However, oxygen consumption for heating the thorax (l O₂ · g _–1 ^thorax · (T_th-T_a) · °C^–1) was nearly the same in workers and drones. Thoracic temperature affected the amount of oxygen consumed per muscle potential (R₁₀=1.5). Achieved temperature elevation per 100 MP was more temperature sensitive in drones (R₁₀=6–10) than in workers (R₁₀=3.6). Q₁₀ values for oxygen consumption were 3 in workers and 4.5–6 in drones. Muscle potential frequency decreased with a Q₁₀=1.8 in workers and 2.7 in drones. Heating behaviour of workers and drones was different. Drones generated heat less continuously than workers, and showed greater interindividual variability in predilection to heat. However, the maximal difference between ambient and thoracic temperature observed was 22 °C in drones and 14 °C in workers, indicating greater potential for drones.Abbreviations DL dorsal-longitudinal muscle - DV dorsoventral muscle - MP muscle potential - T _a ambient temperature - T _th thoracic temperature     

Glycolate photoproduction by free and alginate-entrapped cells of Chlamydomonas reinhardtii

Summary Chlamydomonas reinhardtii cells provide an effective system for glycolate photoproduction, operative during 30 h when they are growing under low CO₂, in the presence of 1 mM aminooxyacetate and 50 M acetazolamide. Glycolate excretion by the cells can proceed for about 4 days if every other 12 h a high CO₂ level is restored in the culture in the absence of inhibitors. The immobilized system in alginate beads has about a twofold higher glycolate photoproduction rate (23 mol·mg chlorophyll (Chl)^–1·h^–1) than free-living cells (12 mol · mg Chl^–1 · h^–1). Offprint requests to: C. Vílchez     

Continuous chemotrophic growth and respiration of Chromatiaceae species at low oxygen concentrations

Endogenous and maximum respiration rates of nine purple sulfur bacterial strains were determined. Endogenous rates were below 10 nmol O₂ · (mg protein · min)^-1 for sulfur-free cells and 15–35 nmol O₂ · (mg protein · min)^-1 for cells containg intracellular sulfur globules. With sulfide as electron-donating substrate respiration rates were considerably higher than with thiosulfate. Maximum respiration rates of Thiocystis violacea 2711 and Thiorhodovibrio winogradskyi SSP1 (254.8 and 264.2 nmol O₂ · (mg protein · min)^-1, respectively) are similar to those of aerobic bacteria. Biphasic respiration curves were obtained for sulfur-free cells of Thiocystis violacea 2711 and Chromatium vinosum 2811. In Thiocystis violacea the rapid and incomplete oxidation of thiosulfate was five times faster than the oxidation of stored sulfur. A high affinity of the respiratoty system for oxygen (K _m =0.3–0.9 M O₂, V _max=260 nmol O₂ · (mg protein · min)^-1 with sulfide as substrate, K _m =0.6–2.4 M O₂, V _max=14–40 nmol O₂ · (mg protein · min)^-1 with thiosulfate as substrate), for sulfide (K _m =0.47 M, V _max=650 nmol H₂S · (mg protein × min)^-1, and for thiosulfate (K _m =5–6 M, V _max =24–72 nmol S₂O ₃ ^2- · (mg protein · min)^-1 was obtained for different strains. Respiration of Thiocystis violacea was inhibited by very low concentrations of NaCN (K _i =1.7 M) while CO concentrations of up to 300 M were not inhibitory. The capacity for chemotrophic growth of six species was studied in continuous culture at oxygen concentrations of 11 to 67 M. Thiocystis violacea 2711, Amoebobacter roseus 6611, Thiocapsa roseopersicina 6311 and Thiorhodovibrio winogradskyi SSP1 were able to grow chemotrophically with thiosulfate/acetate or sulfide/acetate. Chromatium vinosum 2811 and Amoebobacter purpureus ML1 failed to grow under these conditions. During shift from phototrophic to chemotrophic conditions intracellular sulfur and carbohydrate accumulated transiently inside the cells. During chemotrophic growth bacteriochlorophyll a was below the detection limit.     

Time course of vasopressin-induced formation of microvilli in granular cells of toad urinary bladder

Summary Vasopressin-induced transformation of ridges to microvilli on the surface of granular cells of toad urinary bladder occurs in conjunction with induced alterations in the water permeability of the luminal membrane. This study was designed to establish the relationship between the time course for induction of microvilli and the time course for induction of increased water permeability after vasopressin stimulation. Hemibladders were examined at 2.5, 5, 10, 20 and 30 min following exposure to 20 mU/ml of vasopressin and at 5, 10, 20, 30, 40, 50 and 60 min after washout of vasopressin. Within 2.5 min, vasopressin initiated complete transformation of ridges to microvilli on approximately 13% of the granular cells, while osmotic water flow (Jv) was 0.31±0.10 l·min^–1·cm^–2. Five minutes following vasopressin stimulation, microvilli were present on approximately 30% of granular cells andJv was 2.27±0.13 l·min^–1·cm^–2. At 10 minJv was maximum at 4.03±0.15 l·min^–1·cm^–2 and 50% of the granular cells were covered with microvilli. This percentage increased to 70% at 20 min and was maintained at 30 min, althoughJv decreased to 3.9±0.35 l·min^–1·cm^–2 at 30 min. Five minutes following vasopressin washout, ridges interspersed with microvilli reappeared asJv fell to 1.10±0.30 l·min^–1·cm^–2. At 10 min after vasopressin washout,Jv approached basal levels, but the reversal of microvilli to ridges remained incomplete. At 60 min after vasopressin washout, the granular cells had regained their original ridgelike surface structures. Thus, these studies establish a temporal relationship between the induction and reversibility of vasopressin-induced microvillous formation and alterations in the osmotic water permeability of the apical plasmalemma.     

Compartmentation and flux characteristics of ammonium in spruce

Using ¹³NH ₄ ⁺ as a tracer, compartmental analyses for NH ₄ ⁺ were performed in non-mycorrhizal roots of intact Picea glauca (Moench) Voss. seedlings at four different concentration regimes of external NH ₄ ⁺ ([NH ₄ ⁺ ]_o), i.e. 0, 10, 100, and 1500 M. Three kinetically distinct compartments were identified, with half-lives of exchange of approximately 2 s, 30 s, and 14 min, assumed to represent surface adsorption, Donnan free space, and cytoplasm, respectively. No significant differences were found in half-lives of exchange with changes in [NH ₄ ⁺ ]_o. Influx was calculated to be 0.96 mol·g^–1·h^–1 in N-deprived plants (measured at 10 M [NH ₄ ⁺ ]_o), while under steady-state conditions it was 0.21 mol·g^–1h^–1 at 10 M [NH ₄ ⁺ ]_o, 1.96 mol·g^–1h·^–1 at 100 M [NH ₄ ⁺ ]_o, and 6.45 mol·g^–1·h^–1 at 1.5 mM [NH ₄ ⁺ ]_o. Efflux measured over the same range constituted approximately 9% of influx in N-deprived plants, 10% at 10 M, 28% at 100 M, and 35% at 1.5 mM [NH ₄ ⁺ ]_o. Cytoplasmic [NH ₄ ⁺ ] was estimated at 6 m M in N-deprived plants, 2 mM at 10 M [NH ₄ ⁺ ]_o, 14 mM at 100 M, and 33 mM at 1.5 mM. Free-space [NH ₄ ⁺ ] was 84 M, 50 M, 700 M, and 8 mM, respectively. In comparison with previously published data on fluxes and compartmentation of NO ₃ ^– in white-spruce seedlings, results of this study identify a pronounced physiological preference of this species for NH ₄ ⁺ over NO ₃ ^– as an inorganic N source in terms of uptake and intracellular accumulation. The significant ecological importance of this N-source preference is discussed.The research was supported by a Natural Sciences and Engineering Research Council, Canada, grant to Dr. A.D.M. Glass and a University of British Columbia Graduate Fellowship to Herbert J. Kronzucker. Our thanks go to Dr. M. Adam and Mr. P. Culbert at the particle accelerator facility TRIUMF on the University of British Columbia campus for providing ¹³N, to Drs. R.D. Guy and S. Silim for providing plant material, and to Dr. M.Y. Wang, Mr. J. Bailey, Mr. J. Mehroke and Mr. P. Poon for essential assistance in experiments.     

Determination of specific monoclonal antibody secretion rate during very slow hybridoma growth

A total cell recycling suspension perfusion reactor has been constructed for investigation of specific monoclonal antibody secretion rate of the 9.2.27 murine hybridoma under conditions of a very low growth rate. By rapidly recycling hybridoma cells using a thermostated tangential flow filter, 3.6 mg cell dry weight/cm³ could be maintained at growth rate of <0.05 _max for over 250 h. Under these conditions, secretion of lactate, ammonia and l-alanine were directly related to the rate of l-glutamine supply. Monoclonal antibody accumulated in the reactor to levels in excess of 1400 g/ cm³. Surprisingly, as specific growth rate decreased, the specific immunoglobulin secretion rate remained constant, implying that monoclonal antibody synthesis could be uncoupled from growth.List of Symbols CMF cm³/(min · cm²) cross membrane flow rate - D h^–1 dilution rate - DOT % air saturation dissolved oxygen tension - F _R cm³/min perfusion rate - GlcPR mg/min glucose provision rate - GlnPR mg/min l-glutamine provision rate - N _A mmoles O₂/(dm³ · h) oxygen transfer rate - q _ala mmoles/h l-alanine secretion rate - q _MAB mg MAB · 10^–8 viable cells ^–1 · day^–1 specific MAB secretion rate by viable cells - ¯q _MAB (dimensionless) ¯q _MAB/¯q _{MAB MAX} - ¯q _{NH 3} mmoles/h ammonia secretion rate - S _R mg/cm³ limiting substrate concentration - h^–1 specific growth rate - _app h^–1 apparent growth rate - ¯ (dimensionless) / _MAX - VC cells/cm³ viable cell number     

Nitrate induction in spruce: an approach using compartmental analysis

Using ¹³NO ₃ ^– -efflux analysis, the induction of nitrate uptake by externally supplied nitrate was monitored in roots of intact Picea glauca (Moench) Voss. seedlings over a 5-d period. In agreement with our earlier studies, efflux analysis revealed three compartments, which have been identified as surface adsorption, apparent free space, and cytoplasm. While induction of nitrate uptake was pronounced, NO ₃ ^– fluxes in induced plants were decidedly lower and the induction response was slower than in other species. Influx rose from 0.1 mol·g^–1·h^–1 (measured at 100 M [NO ₃ ^– _o) in uninduced plants to a maximum of 0.5 mol·g^–1h^–1 after 3 d of exposure to 100 M [NO ₃ ^– _o and declined to 0.3–0.4 mol·g^–1h^–1 at the end of the 5-d period. Efflux remained relatively constant around 0.02-0.04 mol·g^–1h^–1, but its percentage with respect to influx declined from initially high values (around 30%) to steady-state values of 4–7%. Cytoplasmic [NO ₃ ^– ] ranged from the low micromolar in uninduced plants to a maximum of 2 mM in plants fully induced at 100 M [NO ₃ ^– ]_o. In-vivo root nitrate reductase activity (NRA) was measured over the same time period, and was found to follow a similar pattern of induction as influx. The maximum response in NRA slightly preceded that of influx. It increased from 25 nmol·g^–1·h^–1 without prior exposure to NO ₃ ^– to peak values around 150 nmol· g^–1h^–1 after 2 d of exposure to 100 M [NO ₃ ^– ]_o. Subsequently, NRA declined by about 50%. The dynamics of flux partitioning to reduction, to the vacuole, the xylem, and to efflux during the induction process are discussed.The research was supported by an Natural Sciences and Engineering Research Council, Canada, grant to Dr. A.D.M. Glass and by a University of British Columbia Graduate Fellowship to Herbert J. Kronzucker. Our thanks go to Dr. M. Adam and Mr. P. Culbert at the particle accelerator facility TRIUMF on the University of British Columbia campus for providing ¹³N, to Drs. R.D. Guy and S. Silim for providing plant material, and to Dr. M.Y. Wang, Mr. J. Bailey, Mr. J. Mehroke and Mr. J. Vidmar for essential assistance in experiments.     

Photosynthetic production of hydrogen peroxide by Ulva rigida C. Ag. (Chlorophyta)

Production of hydrogen peroxide has been found in Ulva rigida (Chlorophyta). The formation of H₂O₂ was light dependent with a production of 1.2 mol·g FW^–1·h^–1 in sea water (pH 8.2) at an irradiance of 700 mol photons m^–2·s^–1. The excretion was also pH dependent: in pH 6.5 the production was not detectable (< 5 nmol·g FW^–1·h^–1) but at pH 9.0 the production was 5.0 mol·g FW^–1·h^–1. The production of H₂O₂ was totally inhibited by 3-(3,4-dichlorophenyl)-1,1 dimethylurea (DCMU). The ability of U. rigida growing in tanks (7501) under a natural light regime to excrete H₂O₂ was checked and found to be seven times higher at 08.00 hours than other times of the day. The H₂O₂ concentration in the cultivation tank (density: 2 g FW·l^–1) reached the highest value (3 M) at 11.00 hours. Photosynthesis was not influenced by H₂O₂ formation. The H₂O₂ is suggested to come from the Mehler reaction (pseudocyclic photophosphorylation). With an oxygen evolution of 120 mmol·g FW^–1·h^–1 at pH 8.2 and 90 mmol·g FW^–1·h^–1 at pH 9.0, 0.5% and 2.7% of the electrons were used for extracellular H₂O₂ production. The H₂O₂ production is sufficiently high to be of physiological and ecological significance, and is suggested to be a part of the defence against epi and endophytes.Abbreviations ACL artificial, continuous light - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - GNL greenhouse - LDC Luminol-dependent chemiluminescence - SOD Superoxide dismutase This investigation was supported by SAREC (Swedish Agency for Research Cooperation with Developing Countries), Hierta-Retzius Foundation, Marianne and Marcus Wallenberg Foundation, the Swedish Environmental Protection Board, and CICYT Spain.     

CO2 gas exchange of the understory plantAsarum europaeum L. in November

The CO₂ gas exchange rates of the Central European perennial understory plantAsarum europaeum L. were measured in late autumn (October 30 to November 30) in its natural habitat day and night.During these measurements the temperature ranged from 0 to 15°C and the absolute air humidity from 3 to 10 mg H₂O·1^–1. Temperature and absolute air humidity over these ranges did not affect CO₂ net assimilation which was determined almost entirely by quantum flux density.CO₂ net assimilation was light saturated at about 100 M·m^–2·s^–1 quantum flux density. The uptake rate at this point was 4.3 mg·dm^–2·h^–1. The compensation point occurred at approximately 1 M·m^–2·s^–1.     

Two components of onset and recovery during photoinhibition of Ulva rotundata

Short-term (up to 5 h) transfers of shade-adapted (100 mol · m^–2 · s^–1) clonal tissue of the marine macroalga Ulva rotundata Blid. (Chlorophyta) to higher irradiances (1700, 850, and 350 mol · m^–2 · s^–1) led to photoinhibition of room-temperature chlorophyll fluorescence and O₂ evolution. The ratio of variable to maximum (F_v/F_m) and variable (F_v) fluorescence, and quantum yield () declined with increasing irradiance and duration of exposure. This decline could be resolved into two components, consistent with the separation of photoinhibition into energy-dissipative processes (photoprotection) and damage to photosystem II (PSII) by excess excitation. The first component, a rapid decrease in F_v/F_m and in F_v, corresponds to an increase in initial (F_o) fluorescence and is highly sensitive to 1 mM chloramphenicol. This component is rapidly reversible under dim (40 mol · m^–2 · s^–1) light, but is less reversible with increasing duration of exposure, and may reflect damage to PSII. The second (after 1 h exposure) component, a slower decline in F_v/F_m and F_v with declining F_o, appears to be associated with the photoprotective interconversion of violaxanthin to zeaxanthin and is sensitive to dithiothreitol. The accumulation of zeaxanthin in U. rotundata is very slow, and may account for the predominance of increases in F_o at high irradiances.Abbreviations and Symbols CAP chloramphenicol - DTT dithiothreitol - F_o, F_m, F_v initial, maximum, and variable fluorescence - quantum yield - PFD photon flux density - PSII photosystem II To whom correspondence should be addressedWe are grateful to O. Björkman and S. Thayer, Carnegie Institution of Washington, Stanford, Cal., USA, for analysis of xanthophyll pigments reported here. This research was supported by National Science Foundation grant OCE-8812157 to C.B.O. and J.R. Support for G.L. was provided by a NSF-CNRS (Centre National de la Recherche Scientifique) exchange fellowship.     

Calcium influx at the plasmalemma of Chara corallina

Influx of ⁴⁵Ca into internodal cells of Chara corallina has been measured, using short uptake times, and a wash in ice-cold La³⁺-containing pondwater after the labelling period to overcome the difficulty of distinguishing extracellular tracer from that in the cell. Over 5–15 min the uptake was linear with time, through the origin. The basal influx from 0.1 mM Ca²⁺ externally was 0.25–0.5 pmol·cm^-2·s^-1, but some batches of cells showed higher fluxes. The influx was markedly stimulated by depolarisation in pondwater containing 20 mM K⁺. In cells in which the control flux was less than about 0.5 pmol·cm^-2·s^-1 there was no effect of 50 M nifedipine. In cells in which the control flux was greater than about 0.5 pmol·cm^-2·s^-1 (whether by natural variability, pretreatment, or by depolarisation in 20 mM K⁺), the flux was reduced by 50 M nifedipine to a value in the range 0.25–0.59 pmol·cm^-2·s^-1. It is suggested that two types of Ca-channel are probably involved, both opening on depolarisation, but only one sensitive to nifedipine. The flux was inhibited by 10 M BAY K 8644, which in animal cells more commonly opens Ca-channels. The apparent influx measured over long uptake times was much reduced, and the kinetics indicated filling a pool of apparent size about 1.45 nmol·cm^-2 with a halftime of about 38 min, probably representing cytoplasmic stores. It is argued that in spite of the very small pool of (free+bound) cytoplasmic Ca²⁺ the measured influx is a reasonable estimate of the influx at the plasmalemma.Abbreviations 0.4K-APW6 artificial pondwater, pH 6, containing 0.4 mM KCl - 20 K-APW6 artificial pondwater, pH 6, containing 20 mM KCl - Ca_o external Ca²⁺     

Excretion of photosynthetically fixed organic carbon by metalimnetic phytoplankton

The effects of light intensity, oxygen concentration, and pH on the rates of photosynthesis and net excretion by metalimnetic phytoplankton populations of Little Crooked Lake, Indiana, were studied. Photosynthetic rates increased from 1.42 to 3.14 mg C·mg^–1 chlorophylla·hour^–1 within a range of light intensities from 65 to 150E·m^–2·sec^–1, whereas net excretion remained constant at 0.05 mg C·mg^–1 chlorophylla·hour^–1. Bacteria assimilated approximately 50% of the carbon released by the phytoplankton under these conditions. Excreted carbon (organic compounds either assimilated by bacteria or dissolved in the lake water) was produced by phytoplankton at rates of 0.02–0.15 mg C·mg^–1 chlorophylla·hour^–1. These rates were 6%–13% of the photosynthetic rates of the phytoplankton. Both total excretion of carbon and bacterial assimilation of excreted carbon increased at high light intensities whereas net excretion remained fairly constant. Elevated oxygen concentrations in samples incubated at 150E· m^–2·sec^–1 decreased rates of both photosynthesis and net excretion. The photosynthetic rate increased from 3.0 to 5.0 mg C·mg^–1 chlorophylla· hour^–1 as the pH was raised from 7.5 to 8.8. Net excretion within this range decreased slightly. Calculation of total primary production using a numerical model showed that whereas 225.8 g C·m^–2 was photosynthetically fixed between 12 May and 24 August 1982, a maximum of about 9.3 g C·m^–2 was released extracellularly.     

Ozone detoxification in the apoplasm and symplasm of spinach,broad bean and beech leaves at ambient and elevated concentrations of ozone in air

Spinach (Spinacia oleracea L.), broad bean (Vicia faba L.) and beech (Fagus sylvatica L.) plants were exposed to ozone at concentrations often measured in air during the summer months (120–300 g·m^–3) and antioxidants were determined in the leaf tissue and in the aqueous phase of the cell wall, the apoplasm. Concentrations of both reduced ascorbate (AA) and its oxidized form, dehydroascorbate (DHA), showed the tendency to increase transiently in the apoplasm of spinach leaves 6–24 h after starting fumigation with ozone. In beech leaves, apoplasmic AA and DHA increased 3–7 d after beginning of treatment. At the very high concentration of 1600 g O₃·m^–3, an increase of apoplasmic AA was already measured after 1 d in beech leaves. Apparently, spinach and beech leaves respond to oxidative stress by increasing AA transport into the apoplasm and by accelerating DHA export. In contrast to these observations, DHA accumulated during 3 d of fumigation with only 120 g O₃·m^–3 in the apoplasm of broad bean leaves, while AA contents did not increase. After termination of fumigation, the extracellular redox state of ascorbate normalized within 1 d. Glutathione could not be detected in the apoplasm of any of the three leaf species. Intracellular AA changed its redox state in response to exposure to elevated concentrations of ozone. After 4–6 weeks of fumigation with 200–300 g O₃·m^–3 an increase of intracellular DHA was measured in beech leaves. At the same time, chlorophyll contents decreased and characteristic symptoms of ozone damage could be observed. However, no significant change in the redox state of apoplasmic ascorbate could be detected in beech leaves. Evidently, detoxification of ozone by apoplasmic AA was insufficient to protect the leaf tissue. Fumigation with a high ozone concentration (1600 g·m^–3) caused an appreciable increase in the cellular contents of the oxidized forms of ascorbate and glutathione in beech leaves. Whereas in spinach leaves intracellular antioxidant contents and redox states were not altered during fumigation with 120–240 g O₃·m^–3, in broad bean leaves the intracellular DHA concentration increased and intracellular ascorbate became more oxidized after fumigation of the plants with 120 g O₃·m^–3. Apparently, broad bean leaves are more sensitive to ozone than beech and spinach leaves.Abbreviations AA ascorbate, reduced form - DHA ascorbate, oxidized form (dehydroascorbate) - FW fresh weight - GSH glutathione, reduced form - GSSG glutathione, oxidized form - IWF intercellular washing fluid - V_air intercellular air space volume of leaves - V_apo apoplasmic water volume of leaves This work was supported within the Sonderforschungsbereich 251 of the University of Würzburg.     

Water chemistry changes in the gill micro-environment of rainbow trout: experimental observations and theory

Summary Soft water of low buffer capacity was drawn from near the branchial surface of rainbow trout (Salmo gairdneri) at 15°C, using opercular catheters, to determine pH changes in water passing over the gills. Latex masks allowed measurement of ventilation volume, and concentrations of carbon dioxide, oxygen, ammonia, and titratable base in expired water were compared to concentrations in inspired water. Water passing over the gills was more basic than inspired water if the inspired water was pH 4–6 (maximum increase: +0.7 pH units near pH 5). Expired water was more acidic than inspired water if the inspired water was pH 6–10 (maximum decrease: –1.7 pH units near pH 9). Ventilation volume (0.37 l·kg^–1·min^–1) and oxygen consumption (1.7 mmol·kg^–1·h^–1) were constant in the pH range 4.6–10.1, but both increased by 1.6–2.4× near pH 4. Carbon dioxide transfer near the gills was about 100 M, ammonia transfer about 15 M, and titratable base added at the gills was about 30 M. A theoretical model using CO₂, titratable base, and ammonia added at the gills, the titration characteristics of the defined soft water medium, and aquatic equilibria for CO₂ and ammonia, adequately explained the experimentally observed changes in pH near trout gills. Our observations and predictive model indicate that any gill contaminant whose toxicity varies with pH may be more or less toxic at the gills than predicted from bulk water chemistry alone.Abbreviations pH _ex expired pH - pH _in inspired pH     

Compartmentation and flux characteristics of nitrate in spruce

The radiotracer¹³N was used to undertake compartmental analyses for NO ₃ ^– in intact non-mycorrhizal roots ofPicea glauca (Moench) Voss. seedlings. Three compartments were defined, with half-lives of exchange of 2.5 s, 20 s, and 7 min. These were identified as representing surface adsorption, apparent free space, and cytoplasm, respectively. Influx, efflux, and net flux as well as cytoplasmic and apparent-free-space nitrate concentrations were estimated for three different concentration regimes of external nitrate. After exposure to external NO ₃ ^– for 3 d, influx was calculated to be 0.09 mol·g^–1·h^–1 (at 10 M [NO ₃ ^– ]_o), 0.5mol·g^–1·h^–1 (at 100 M [NO _inf3 ^sup– ]_o), and 1.2 mol · g^–1· h^–1 (at 1.5 mM [NO ₃ ^– ]_o). Efflux increased with increasing [NO ₃ ^– ]_o, constituting 4% of influx at 10 M, 6% at 100 M, and 21% at 1.5 mM. Cytoplasmic [NO ₃ ^– ] was estimated to be 0.3 mM at 10 uM [NO ₃ ^– ]_o, 2mM at 100 M [NO ₃ ^– ]_o, and 4mM at 1.5 mM [NO ₃ ^– ]_o, while free-space [NO ₃ ^– ] was 16 M, 173 M, and 2.2 mM, respectively. A series of experiments was carried out to confirm the identity of the compartments resolved by efflux analysis. Pretreatment at high temperature or application of 2-chloro-ethanol, sodium dodecyl sulphate or hydrogen peroxide made it possible to distinguish the metabolic (cytoplasmic) phase from the remaining two (physical) phases. Likewise, varying [Pi] of the medium altered efflux and thereby [NO ₃ ^– ]_cyt, but did not affect [NO ₃ ^– ]_{free space}.Abbreviations and Symbols [NO ₃ ^– ]_cyt cytoplasmic NO ₃ ^– concentration - [NO ₃ ^– ]_{free space} apparent-free-space NO ₃ ^– concentration - [NO ₃ ^– ]_o concentration of NO ₃ ^– in the external solution - NO ₃ ^– flux - _co efflux from the cytoplasm - _oc influx to the cytoplasm - _net net flux - _xylem flux to the xylem - _red/vac combined flux to reduction and the vacuole The research was supported by a Natural Sciences and Engineering Research Council, Canada, grant to Dr. A.D.M. Glass and by a University of British Columbia Graduate Fellowship to Herbert J. Kronzucker. Our thanks go to Dr. M. Adam and Mr. P. Culbert at the particle accelerator facility TRIUMF on the University of British Columbia Campus for providing¹³NO ₃ ^– , Drs. R.D. Guy and S. Silim for providing plant material, and Dr. M.Y. Wang, Mr. J. Mehroke and Mr. P. Poon for assistance in experiments and for helpful discussions.     

The ecology of Lake Nakuru (Kenya)

Summary Abiotic factors, standing crop and photosynthetic production were studied in the equatorial alkaline-saline closed-basin Lake Nakuru (cond. 10,000–160,000 S). Meteorological conditions and abiotic factors offer suppositions for a high primary productivity: mean solar radiation is 450–550 kerg·cm^-2·s^-1, with little seasonal variation, regular winds circulate the lake every day and nutrient concentrations are usually high (>100 g P–PO₄·l^-1). Oxygen concentrations near sediments were <1 gO₂·m^-3 for at least 6 h·d^-1 in 1972/73, resulting in a release of 45 mg P–PO₄·m^-2·d^-1. Attenuation coefficients vary from 3.6–16.5 according to algal densities and mean depth from 0–400 cm. Algal biomass was 200 g·m^-3 (d.w.) in 1972/73, due to a lasting Spirulina platensis bloom (98.5% of algal biomass). In 1974 algal biomass suddenly dropped to 50 g·m^-3 (d.w.). Spirulina and several consumer organisms almost vanished, but coccoid cyanobacteria, Anabaenopsis and diatoms increased. Several causes for this change in ecosystem structure are discussed. The use of the light/dark bottle method to measure photosynthetic production in eutrophic alkaline lakes is discussed and relevant experiments were done. Oxygen tensions of 2–35 gO₂·m^-3 do not influence primary production rates. Net photosynthetic rates (mgO₂·m^-3·h^-1; photosynthetic quotient=1.18) reached 12–17.7 in 1972/73 and 2–3 in 1974, but vertically integrated rates were only 1–1.4 in 1972/73 and 0.8 in 1974, and daily net photosynthetic rates (gO₂·m^-3·24 h^-1) 3.5 in 1972/73 and 1 in 1974. 50% of areal rates were produced within the 10 most productive cm of the depth profile. The disproportion between high algal standing crops and relatively low production rates is due to self-shading of the algae, reducing the euphotic zone to 35 cm in 1972/73 and 77 cm in 1974. Efficiency of light utilization is 0.4–2%, varying with time of day and phytoplankton density. In situ efficiencies show an inverse relationship to light intensities. Photosynthetic rates of L. Nakuru remain within the range of other African lakes (0.1–3 gO₂·m^-2·h^-1). The relation of O₂ produced/Chl a of the euphotic zone is 50% lower then in tropical African freshwater lakes and conforms to lakes of temperate regions.     

Analysis of oxygen evolution during photosynthetic induction and in multiple-turnover flashes in sunflower leaves

Exchange of CO₂ and O₂ and chlorophyll fluorescence were measured in the presence of 360 1 · 1^–1 CO₂ in nitrogen in Helianthus annuss L. leaves which had been preconditioned in the dark or at a photon flux density (PFD) of 24 mol · m^–2 · s^–1 either in 21 or 0% O₂. An initial light-dependent O₂ outburst of 6 mol · m^–2 was measured after aerobic dark incubation. It was attributed to the reduction of electron carriers, predominantly plastoquinone. The maximum initial rate of O₂ evolution at PFD 8000 mol · m^–2 · s^–1 was 170 mol · m^–2 · s^–2 or about four times the steady CO₂-and light-saturated rate of photosynthesis. Fluorescence measurements showed that the rate was still acceptor-limited. Fast O₂ evolution ceased after electron carriers were reduced in the dark-adapted leaf, but continued for a short time at the lower rate of 62 mol · m^–2 · s^–1 in the light-adapted leaf. The data are interpreted to show that enzymes involved in 3-phosphoglycerate reduction are dark-inhibited, but were fully active in low light. In a dark-adapted leaf, respiratory CO₂ evolution continued under nitrogen; it was partially inhibited by illumination. Prolonged exposure of a leaf to anaerobic conditions caused reducing equivalents to accumulate. This was shown by a slowly increasing chlorophyll fluorescence yield which indicated the reduction of the PSII acceptor Q_A in the dark. When the leaf was illuminated, no O₂ evolution was detected from short light pulses, although transient O₂ production was appreciable during longer light pulses. This indicates that an electron donor (pool size about 2–3 e/PSII reaction center) became reduced in the dark and the first photons were used to oxidise this donor instead of water.Abbreviations Chl chlorophyll - CRC carbon reduction cycle - GAPDH NADP-glyceraldehyde-phosphate dehydrogenase - PFD photon flux density - PGA 3-phosphoglycerate - RuBP ribulose bisphosphate - TCA tricarboxylic acid cycle To whom correspondence should be addressedThis work received support by the Estonian Academy of Sciences, the Gottfried-Wilhelm-Leibniz Program of the Deutsche For-schungsgemeinschaft and the Sonderforschungsbereich 251 of the University of Würzburg.