Respiratory gas exchange in the airbreathing fish,Synbranchus marmoratus

Synopsis The partitioning of O₂ uptake between aquatic and aerial gas exchange and its dependence on ambient water PO₂ was studied in the facultative air breathing teleost Synbranchus marmoratus, after acclimation to well aerated water and after acute and chronic exposure to hypoxic water. O₂ uptake was also studied following acute air exposure and after prolonged entrapment in soil. Breathing rates during water and air breathing in response to reduced water PO₂ and tidal volume during air breathing were also studied. S. marmoratus satisfies its O₂ requirement by water breathing alone until water PO₂ falls below 30–50 mm Hg (switching PO₂) depending on the acclimation history. Below the switching PO₂, air breathing is adopted while active water breathing stops. The O₂ uptake varied little for all groups when the principal mode of gas exchange changed at the switching PO₂. The highest O₂ uptake prevailed when the fish employed the mode of gas exchange in operation during the acclimation period (i.e. water breathing for normoxia-acclimated, air breathing for hypoxic-acclimated).Acclimation to chronic hypoxia gave a much higher switching PO₂ 55 mm Hg) than for the other groups (about 30 mm Hg). S. marmoratus maintained its O₂ uptake when acutely exposed to air. When entrapped in soil in an aestivating state, the O₂ uptake was reduced to 25% of that in water or during acute air exposure. The overall gas exchange ratio for air breathing was very low (R_E 0.1).Branchial water pumping increased with lowering of water PO₂. The rate of air breathing was independent of water PO₂.The findings are discussed in the light of the ecophysiological conditions confronting S. marmoratus.     

The malonyl gramicidin channel: NMR-derived rate constants and comparison of calculated and experimental single-channel currents

Summary Malonyl gramicidin is incorporated into lysolecithin micelles in a manner which satisfies a number of previously demonstrated criteria for the formation of the transmembrane channel structure. By means of sodium-23 nuclear magnetic resonance, two binding sites are observed: a tight site and a weak site with binding constants of approximately 100m ^–1 and 1m ^–1, respectively. In addition, off-rate constants from the two sites were estimated from NMR analyses to bek _off ^t 3×10⁵/sec andk _off ^w 2×10⁷/sec giving, with the binding constants, the on-rate constants,k _on ^t 3×10⁷/msec andk _on ^w 2×10⁷/m sec.Five different multiple occupancy models with NMR-restricted energy profiles were considered for the purpose of calculating single-channel currents as a function of voltage and concentration utilizing the four NMR-derived rate constants (and an NMR-limit placed on a fifth rate constant for intrachannel ion translocation) in combination with Eyring rate theory for the introduction of voltage dependence.Using the X-ray diffraction results of Koeppe et al. (1979) for limiting the positions of the tight sites, the two-site model and a three-site model in which the weak sites occur after the tight site is filled were found to satisfactorily calculate the experimental currents (also reported here) and to fit the experimental currents extraordinarily well when the experimentally derived values were allowed to vary to a least squares best fit. Surprisingly the best fit values differed by only about a factor of two from the NMR-derived values, a variation that is well within the estimated experimental error of the rate constants.These results demonstrate the utility of ion nuclear magnetic resonance to determine rate constants relevant to transport through the gramicidin channel and of the Eyring rate theory to introduce voltage dependence.     

The fixation probability of a beneficial allele in a population dividing by binary fission

We derive formulae for the fixation probability, P, of a rare benefical allele segregating in a population of fixed size which reproduces by binary fission, in terms of the selection coefficient for the beneficial allele, s. We find that an earlier result P 4s does not depend on the assumption of binary fission, but depends on an assumption about the ordering of events in the life cycle. We find that P 2s for mutations occurring during chromosome replication and P 2.8s for mutations occurring at random times between replication events.     

Mapping of brain activity in mesencephalic and diencephalic structures of toads during presentation of visual key stimuli: a computer assisted analysis of (14C)2DG autoradiographs

Summary The (¹⁴C)2DG autoradiographic technique has been employed to quantitatively map glucose utilization in the mesencephalon, the diencephalon and the cerebellum, of toads in response to configurational moving visual stimuli: (i) a 0.4 cm × 2.8 cm worm-like stripe (W) which elicited prey catching responses, (ii) a 8.4 cm × 8.4 cm square (S) that released predator avoidance responses, and (iii) a 2.8 cm × 0.4 cm antiworm-like stripe (A) which elicited no motor activity.For various brain nuclei different relationships were obtained: The optic tectum showed statistical significant higher 2DG uptake during worm-stimulation (¯X _W) than during antiworm stimulation (¯X _A), i.e.¯X _W>¯X _A. The latter visual pattern led to a 2DG utilization that was statistically significant stronger than during stimulation with a square (¯X _S), i.e.¯X _A>¯X _S. Thus, in comparison between right and left hemisphere as well as between brains the following ratios were obtained:Optic tectum:¯X _W>¯X _A>¯X _S; nucleus isthmi:¯X _W>¯X _A-¯X _s; posterodorsal lateral thalamic nucleus:¯X _S>¯X _A>¯X _W; posteroventral lateral thalamic nucleus:¯X _S>¯X _A¯X _W; posterior thalamic nucleus:¯X _W>¯X _A¯X _S; anteripr division of the lateral thalamic nucleus:¯X _W>¯X _A¯X _S; anterior thalamic nucleus:¯X _A>¯X _S>¯X _W; nucleus of Bellonci and dorsal division of the ventrolateral thalamic nucleus:¯X _W¯X _A¯X _S; cerebellum:¯X _S¯X _W>¯X _A.Abbreviations A anterior thalamic nucleus - Cb cerebellum - Hyp hypothalamus - Ist nucleus isthmi - cl. Ist contralateral Ist - La lateral thalamic nucleus, anterior division - Lpd lateral thalamic nucleus, posterodorsal division - Lpv lateral thalamic nucleus, posteroventral division - MP medial pallium - NB/VLd nucleus of Bellonci and ventrolateral thalamic nucleus, dorsal division - P posterior thalamic nucleus - PO preoptic area - Sna snapping evoking area=ventrolateral tectum - Str striatum - Tec tectum opticum     

Vertical diffusion and nutrient transport in a tropical lake (Lake McIlwaine,Rhodesia)

Measurements of the vertical temperature in tropical Lake McIlwaine were used to calculate the time-averaged ( 6 months) vertical diffusivity coefficient (K_z) in the metalimnion and hypolimnion. The mean value of K_z (0.21 cm² s^–1) was correlated with the lake surface area. The mass transport rates of PO₄-P and NH₄-N, upward from the hypolimnion to the metalimnion, were calculated using K_z and measured values of the nutrient concentration gradients. During a period of 4.5 months when the water was stably stratified, PO₄-P was transported upward at a mean rate of 42 kg day^–1 and NH₄-N at a mean rate of 162 kg day^–1 over the entire lake.     

Growth,photosynthesis and photorespiration of Lemna gibba: response to variations in CO2 and O2 concentrations and photon flux density

Dry weight and Relative Growth Rate of Lemna gibba were significantly increased by CO₂ enrichment up to 6000 l CO₂ l^–1. This high CO₂ optimum for growth is probably due to the presence of nonfunctional stomata. The response to high CO₂ was less or absent following four days growth in 2% O₂. The Leaf Area Ratio decreased in response to CO₂ enrichment as a result of an increase in dry weight per frond. Photosynthetic rate was increased by CO₂ enrichment up to 1500 l CO₂ l^–1 during measurement, showing only small increases with further CO₂ enrichment up to 5000 l CO₂ l^–1 at a photon flux density of 210 mol m^–2 s^–1 and small decreases at 2000 mol m^–1 s^–1. The actual rate of photosynthesis of those plants cultivated at high CO₂ levels, however, was less than the air grown plants. The response of photosynthesis to O₂ indicated that the enhancement of growth and photosynthesis by CO₂ enrichment was a result of decreased photorespiration. Plants cultivated in low O₂ produced abnormal morphological features and after a short time showed a reduction in growth.     

Nitrogen fixation in a large shallow lake: rates and initiation conditions

The fixation of molecular nitrogen (N₂fix) by cyanobacteria in situ and in PO₄-P enrichment experiments was investigated in large shallow Lake Võrtsjärv in 1998–2000. In this lake, N₂fix started when TN/TP mass ratio was about 20, which is much higher than Redfield mass ratio 7. The rate of N₂fix varied between 0.81 and 2.61 gN l^–1 d^–1 and maximum rate (2.61 gN l^–1 d^–1) was measured in 15.08.2000. In L. Võrtsjärv a lag period of a couple of weaks occurred between the set-up of favourable conditions for N₂fix as the appearance of N₂-fixing species and depletion of mineral nitrogen, and the real N₂fix itself. However, if the favorable conditions for N₂fix occurred in the lake, N₂fix started after enrichment with PO₄-P in mesocosms even then when no N₂fix was detected in the lake. N₂fix in mesocosms was also more intensive than in lake water. In our experiments PO₄-P concentrations higher than 100 gP l^–1started to inhibit N₂fix.     

Separation and characterization of the complexes constituting the cellulolytic enzyme system of Clostridium thermocellum

Clostridium thermocellum, strain JW20 (ATCC 31449) when growing in cellulose produces a cellulolytic enzyme system, that at the early stage of the fermentation is largely bound to the substrate. As cellulose is consumed the bound enzyme is released as free enzyme to the culture fluid. The bound enzyme fraction extracted with distilled water from the cellulose contains two major components, a large complex (M_r100×10⁶) and a small complex M_r4.5×10⁶) which were separated by gel filtration and sucrose solved by affinity chromatography into a complex that binds to the column and into a non-bindable mixture of proteins. All four fractions have endo--glucanase activity but only the two bound complexes and the free bindable complex hydrolyze crystalline cellulose with cellobiose as the main product. These three complexes are qualitatively similar in that they each contain about 20 different polypeptides (M_r values from 45,000 to 200,000) of which about ten are major components. However, the relative amounts of some of the peptides in the complexes differ. At least four polypeptides of the complexes have endo--glucanase activity.Abbreviations CM cellulose, carboxymethyl cellulose - CMCase carboxymethyl cellulase cosidered endo--1,4-glucanase - SDS sodium dodecyl sulfate - YAS yellow affinity substance - YAS-cellulose yellow affinity substance-cellulose complex     

Stimulation of insulin release from pancreatic islets by quinones

Coenzyme Q (CoQ₀) and other quinones were shown to be potent insulin secretagogues in the isolated pancreatic islet. The order of potency was CoQ₀benzoquinonehydroquinonemenadione. CoQ₆ and CoQ₁₀ (ubiquinone), duroquinone and durohydroquinone did not stimulate insulin release. CoQ₀'s insulinotropism was enhanced in calcium-free medium and CoQ₀ appeared to stimulate only the second phase of insulin release. CoQ₀ inhibited inositol mono-, bis- and trisphosphate formation. Inhibitors of mitochondrial respiration (rotenone, antimycin A, FCCP and cyanide) and the calcium channel blocker verapamil, did not inhibit CoQ₀-induced insulin release. Dicumarol, an inhibitor of quinone reductase, did not inhibit CoQ₀-induced insulin release, but it did inhibit glucose-induced insulin release suggesting that the enzyme and quinones play a role in glucose-induced insulin release. Quinones may stimulate insulin release by mimicking physiologically-occuring quinones, such as CoQ₁₀, by acting on the plasma membrane or in the cytosol. Exogenous quinones may bypass the quinone reductase reaction, as well as many reactions important for exocytosis.     

The effect of low oxygen uptake rate on the fatty acid profile of the oleaginous yeast Apiotrichum curvatum

Summary The effect of limiting the available oxygen on the fatty acid profile of Apiotrichum curvatum ATCC 20509 during growth on sulphuric acid casein whey was studied. At oxygen uptake rates (OUR) lower than 7 mmol O₂/l per hour, applied during the oil accumulating phase of the fermentation, a decrease in total unsaturated fatty acids was observed. It was possible to decrease the unsaturated fatty acids (oleate from 55% to 41% and linoleate from 9% to 3%) by limiting the OUR of the culture to <3 mmol O₂/l per hour. However at this low OUR, a lower oil coefficient (a measure of the efficiency of lactose substrate conversion to oil) was recorded. Furthermore the fermentation time was increased. An OUR of 5 mmol O₂/l per hour appeared to be the limit below which adverse effects on oil yields and increased fermentation times occurred. At this OUR, the accumulated oil contained 45% oleate and 5% linoleate. These effects were demonstrated in a 20-l air-lift fermentor and confirmed in a scaled down 500-l industrial type bubble column fermentor. Offprint requests to: R. J. Davies     

Effects of ambient water vapor pressure and temperature on evaporative water loss inPeromyscus maniculatus andMus musculus

Summary Oxygen equilibria, ligand-binding kinetics and some other physicochemical properties are reported for erythrocruorins of two intertidal polychaetes:Marphysa sanguinea, which inhabits simple, relatively stagnant burrows, andDiopatra cuprea, which inhabits impermeable, parchment-like tubes that are vigorously ventilated.Marphysa erythrocruorin has a higher O₂ affinity, which is less pH dependent (at pH 7.3 and 20°C, half-saturation O₂ tension,P ₅₀, and Bohr factor, =logP ₅₀/pH, are 0.8 mm Hg and –0.25, respectively) than the corresponding parameters (P ₅₀=5.5; =–0.86) inDiopatra (Figs. 1 and 2). In contrast to vertebrate haemoglobins, inorganic salts increase erythrocruorin O₂ affinity (Fig. 3). The kinetic rates of ligand binding and dissociation ofMarphysa andDiopatra erythrocruorins (Tables 1 and 2) correlate well with the measured O₂ affinities and appear to illustrate basic molecular adaptations of the two species to their respective micro-environmental conditions.     

Postglacial loss of microsatellite variation in the landlocked Lake Saimaa ringed seal

The Lake Saimaa ringed sealPhoca hispida saimensis has lived as anisolated landlocked population in easternFinland since the early post-glacial. In thelast century, the population crashed down to c.200 individuals, and is under a constant threatof extinction. We evaluated the genetic historyof the Saimaa population through a comparisonwith the conspecific sister populations in theArctic Ocean and the Baltic Sea, which haveretained high levels of variation since thedeglaciation. At eight microsatellite loci, thecurrent gene diversity (heterozygosity) of theSaimaa seal was 69% lower than in thereference populations. Allowing reasonablemutation rates ( = 10^–4), thisimplies a long-term post-glacial effectivepopulation size of N _e 350,and a slow average rate of inbreeding F 0.15% per generation during the c.860 generations (9 500 years) of isolation. Thecurrent N _e is an order of magnitudesmaller and F correspondinglylarger. Whereas the additional loss of markervariation in the short term will not be highrelative to that already taken place, it seemsunwarranted to suppose that the past, slowinbreeding would have effectively purged thepopulation of genetic load and reduced thegenetic risks from small population size.Although the population is now clearlygeographically subdivided in the complex lakesystem, we found little genetic differentiationbetween main breeding areas (F _ST =0.02). However, at the current low populationdensities, the subdivision may markedly furtherincrease the future rate of inbreeding.     

Oxygen evolving membranes and particles from the transformable cyanobacterium Synechocystis sp. PCC6803

Membranes and PS II particles retaining high rates of O₂-evolving activity have been isolated from the transformable cyanobacterium, Synechocystis sp. PCC6803. Membranes from cells grown under red light exhibit rates of O₂-evolution ranging from 500–700 mole O₂/mg chl/h. PS II particles are prepared by a simple procedure involving DEAE column chromatography of detergent extracts obtained by simultaneous treatment of membranes with octylglucoside and dodecylmaltoside. The isolated PS II fraction is enriched in polypeptides immunologically cross-reactive with polypeptides present in core reaction center preparations of spinach, exhibits 77 K fluorescence emission maxima at 685 and 696 nm, but not emission and absorption due to phycobilines and is capable of rates of O₂-evolution exceeding 1000 mole O₂/mg chl/h.Abbreviations DM dodecyl--D-maltoside - OG octyl--D-glucoside     

Purification and characterization of an NADH oxidase from extremely thermophilic anaerobic bacterium Thermotoga hypogea

Thermotoga hypogea is an extremely thermophilic anaerobic bacterium capable of growing at 90°C. It was found to be able to grow in the presence of micromolar molecular oxygen (O₂). Activity of NADH oxidase was detected in the cell-free extract of T. hypogea, from which an NADH oxidase was purified to homogeneity. The purified enzyme was a homodimeric flavoprotein with a subunit of 50 kDa, revealed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It catalyzed the reduction of O₂ to hydrogen peroxide (H₂O₂), specifically using NADH as electron donor. Its catalytic properties showed that the NADH oxidase had an apparent V_max value of 37 mol NADH oxidized min^–1 mg^–1 protein. Apparent K_m values for NADH and O₂ were determined to be 7.5 M and 85 M, respectively. The enzyme exhibited a pH optimum of 7.0 and temperature optimum above 85°C. The NADH-dependent peroxidase activity was also present in the cell-free extract, which could reduce H₂O₂ produced by the NADH oxidase to H₂O. It seems possible that O₂ can be reduced to H₂O by the oxidase and peroxidase, but further investigation is required to conclude firmly if the purified NADH oxidase is part of an enzyme system that protects anaerobic T. hypogea from accidental exposure to O₂.     

Respiratory adaptations to diving in the nile monitor lizard,Varanus niloticus

Summary The objectives of this study included directin vivo measurements of circulating blood gases, pH, heart rate, and blood pressure during voluntary dives of unrestrained Nile monitor lizards. A Radiometer flow-through cuvette was employed for continuous recording of arterial PO₂, PCO₂ and pH. Hematological properties revealed no particular adaptations for diving. Mean values were: hematocrit = 24%; hemoglobin concentration = 7.1 g %; oxygen capacity = 9.3 vol %; red cell dimensions = 22×12 ; red cell count = 0.67 million/l. The respiratory properties of the blood, studiedin vitro andin vivo, show distinct adaptations to habitual diving. Oxygen affinity of blood is low (P₅₀ = 42.4 mm Hg at pH 7.45, 25 °) and the dissociation curve is markedly sigmoid (n = 3.1). These features, coupled with a Bohr factor ( logP ₅₀/pH) of –0.48, ensure increased utilization of oxygen while maintaining relatively high tissue PO₂. Arterial pH decreases during diving from about 7.5 to 7.1 due to combined respiratory and metabolic acidosis. High plasma bicarbonate (30 mM/l at PCO₂ = 25 mm Hg) and a buffering capacity of H C₃ ^–O/ pH = 18.9 mM/l increase the tolerance to this acidosis and prolong diving time. Thein vivo oxygen dissociation curve shows a 90 % depletion of arterial oxygen content during typical dives. Diving elicited a rapidly developing bradycardia with maximum of 85 % reduction in heart rate. The temperature sensitivity of HbO₂ binding was very low (H = –3kcal). This would minimize the HbO₂ affinity increase accompanying the decrease in body temperature likely to occur in lizards going from sun basking to submergence in water.Supported by a grant from the Danish Natural Science Research Council.     

Photosynthesis and apparent affinity for dissolved inorganic carbon by cells and chloroplasts of Chlamydomonas reinhardtii grown at high and low CO2 concentrations

Chloroplasts with high rates of photosynthetic O₂ evolution (up to 120 mol O₂· (mg Chl)^-1·h^-1 compared with 130 mol O₂· (mg Chl)^-1·h^-1 of whole cells) were isolated from Chlamydomonas reinhardtii cells grown in high and low CO₂ concentrations using autolysine-digitonin treatment. At 25° C and pH=7.8, no O₂ uptake could be observed in the dark by high- and low-CO₂ adapted chloroplasts. Light saturation of photosynthetic net oxygen evolution was reached at 800 mol photons·m^-2·s^-1 for high- and low-CO₂ adapted chloroplasts, a value which was almost identical to that observed for whole cells. Dissolved inorganic carbon (DIC) saturation of photosynthesis was reached between 200–300 M for low-CO₂ adapted chloroplasts, whereas high-CO₂ adapted chloroplasts were not saturated even at 700 M DIC. The concentrations of DIC required to reach half-saturated rates of net O₂ evolution (K_m(DIC)) was 31.1 and 156 M DIC for low- and high-CO₂ adapted chloroplasts, respectively. These results demonstrate that the CO₂ concentration provided during growth influenced the photosynthetic characteristics at the whole cell as well as at the chloroplast level.Abbreviations Chl chlorophyll - DIC dissolved inorganic carbon - K_m(DIC) coneentration of dissolved inorganic carbon required for the rate of half maximal net O₂ evolution - PFR photon fluence rate - SPGM silicasol-PVP-gradient medium     

Leaf cavity CO2 concentrations and CO2 exchange in onion,Allium cepa L.

Onion (Allium cepa L.) plants were examined to determine the photosynthetic role of CO₂ that accumulates within their leaf cavities. Leaf cavity CO₂ concentrations ranged from 2250 L L^–1 near the leaf base to below atmospheric (<350 L L^–1) near the leaf tip at midday. There was a daily fluctuation in the leaf cavity CO₂ concentrations with minimum values near midday and maximum values at night. Conductance to CO₂ from the leaf cavity ranged from 24 to 202 mol m^–2 s^–1 and was even lower for membranes of bulb scales. The capacity for onion leaves to recycle leaf cavity CO₂ was poor, only 0.2 to 2.2% of leaf photosynthesis based either on measured CO₂ concentrations and conductance values or as measured directly by ¹⁴CO₂ labeling experiments. The photosynthetic responses to CO₂ and O₂ were measured to determine whether onion leaves exhibited a typical C₃-type response. A linear increase in CO₂ uptake was observed in intact leaves up to 315 L L^–1 of external CO₂ and, at this external CO₂ concentration, uptake was inhibited 35.4±0.9% by 210 mL L^–1 O₂ compared to 20 mL L^–1 O₂. Scanning electron micrographs of the leaf cavity wall revealed degenerated tissue covered by a membrane. Onion leaf cavity membranes apparently are highly impermeable to CO₂ and greatly restrict the refixation of leaf cavity CO₂ by photosynthetic tissue.Abbreviations C_a external CO₂ concentration - C_i intercellular CO₂ concentration - CO₂ compensation concentration - PPFR photosynthetic photon fluence rate     

Prolongation of MGE 412 Transposition Induction after γ-Irradiation in an Isogenic Line of Drosophila melanogaster

The dose dependence of the rate of -induced transpositions and consequent dynamics of the MGE 412pattern after -irradiation were investigated in isogenic line 49 in generations F₁, F₁₂, F₁₄₀, and F₁₇₀. It was shown that the results on dose dependence of transpositions was very similar with the corresponding results of the classic works by Timofeeff-Ressovsky et al.(1935). It is suggested that the transcribed copies of retrotransposon 412cure -radiation-induced double-strand DNA breaks. The phenomenon of prolongation of MGE transposition induction during early generations after treatment was shown. In this period (F₁–F₁₂), the maximum transposition rate ( 2 × 10^–2events per MGE copy, per haploid genome, per generation) and the maximum number of heterozygous MGE copies were achieved. In the late generations (F₁₄₀–F₁₇₀), the reduced induction level ( 10^–3) was established. In the population of effective size N _e= 2000 individuals, this corresponds to the state when 1/4N _e, i.e., when the transposition flow prevails over the MGE copy loss by genetic drift. These data together with some indirect evidence argue for the hypothesis that the spontaneous transposition rate is proportional to the average number of heterozygous MGE copies per diploid genome.     

Ion channels in the membrane ofChara inflata

Summary Voltage-clamped steps in the electric potential difference (PD) across the membrane in cells of the green alga,Chara inflata, cause voltage- and time-dependent current flows, interpreted to arise from opening and closing of various types of ion channel in the membrane. With cells in the light, these channels are normally closed, and the resting PD is probably determined by the operation of an H⁺ efflux pump. Positive steps in PD from the resting level often caused the opening of K⁺ channels with sigmoid kinetics. The channels began to show opening when the PD–120 mV for an external concentration of K⁺ of 1.0mm. Return of the PD to the resting level caused closing of the channels with complex kinetics. Various treatments of the cell could cause these K⁺ channels to open, and remain open continuously, with the PD then lying closer to the Nernst PD for K⁺. The K⁺ channels have been identified by the blocking effects of TEA⁺. Another group of channels, probably Cl^– and Ca²⁺ associated with the action potential open when the PD is stepped to values less negative than –50 mV. Negative steps from the resting PD cause the slow opening, with a time course of seconds, of yet another type of channel, probably Cl^–.