Thermal dependence of contractile properties of single skinned muscle fibres from Antarctic and various warm water marine fishes including Skipjack Tuna (Katsuwonus pelamis) and Kawakawa (Euthynnus affinis)

Summary Single fast fibres and small bundles of slow fibres were isolated from the trunk muscles of an Antarctic (Notothenia neglecta) and various warm water marine fishes (Blue Crevally,Carangus melampygus; Grey Mullet,Mugil cephalus; Dolphin Fish,Coryphaena hippurus; Skipjack-tuna,Katsuwonus pelamis and Kawakawa,Euthynuus affinis). Fibres were chemically skinned with the nonionic detergent Brij 58.For warm water species, maximum Ca²⁺-activated tension (P ₀) almost doubled between 5–20°C with little further increase up to 30°C. However, when measured at their normal body temperatures,P ₀ values for fast fibres were similar for all species examined, 15.7–22.5 N · cm^–2. Ca²⁺-regulation of contraction was disrupted at temperatures above 15°C in the Antarctic species, but was maintained at up to 30°C for warm water fish.Unloaded (maximum) contraction speeds (V _max) of fibres were determined by the slacktest method. In general,V _max was approximately two times higher in white than red muscles for all species studied, except Skipjack tuna. For Skipjack tuna,V _max of superficial red and white fibres was similar (15.7 muscle lengths · s^–1 (L ₀ · s^–1)) but were 6.5 times faster than theV _max of internal red muscle fibres (2.4±0.2L ₀ · s^–1) (25°C). V _max forN. neglecta fast fibres at 0–5°C (2–3L ₀ · s^–1) were similar to that of warm water species measured at 10–20°C. However, when measured at their normal muscle temperatures, theV _max for the fast muscle fibres of the warm water species were 2–3 times higher than that forN. neglecta.In general,Q _{10(15–30°C)} values forV _max were in the range 1.8–2.0 for all warm water species studied except Skipjack tuna.V _max for the internal red muscle fibres of Skipjack tuna were much more temperature dependent (Q _{10(15–30°C)}=3.1) (P<0.01) than for superficial red or white muscle fibres. The proportion of slower red muscle fibres in tuna (28% for 1 kg Skipjack) is 3–10 times higher than for most teleosts and is related to the tuna's need to sustain high cruising speeds. We suggest that the 8–10°C temperature gradient that can exist in Skipjack tuna between internal red and white muscles allows both fibre types to contract at the same speed. Therefore, in tuna, both red and white muscle may contribute to power generation during high speed swimming.     

Larviculture of the fairy shrimp,Streptocephalus proboscideus (Crustacea: Anostraca): effect of food concentration and physical and chemical properties of the culture medium

Food concentration (0.5 × 10³ – 5 × 10⁵ Scenedesmus cells m1^–1) significant influenced the somatic growth, maturation and survivorship ofS. proboscideus larvae. A density of 5 × 10⁴ cells m1^–1 was optimal for early larval stages. Of four temperature tested (20–35 °C), 30 °C resulted in the best growth and survival. Maturation time was inversely related to temperature, and was size- rather that age-dependent. Larvae were tolerant of a wide conductivity range, but optimal growth and survival were observed at 260 µS cm^–1. Nitrate-Nitrogen (NO₂-N) caused a larval mortality of 50% after 24 h at 0.58 mg1^–1.     

Effects of temperature on the properties of primary auditory fibres of the spectacled caiman,Caiman crocodilus (L.)

Summary The effect of temperature on the response properties of primary auditory fibres in caiman was studied. The head temperature was varied over the range of 10–35 ° C while the body was kept at a standard temperature of 27 °C (T_s). The temperature effects observed on auditory afferents were fully reversible. Below 11 °C the neural firing ceased.The mean spontaneous firing rate increased nearly linearly with temperature. The slopes in different fibres ranged from 0.2–3.5 imp s^–1 °C^–1. A bimodal distribution of mean spontaneous firing rate was found (<20 imp s^–1 and >20 imp s^–1 at T_s) at all temperatures.The frequency-intensity response area of the primary fibres shifted uniformly with temperature. The characteristic frequency (CF) increased nearly linearly with temperature. The slopes in different fibres ranged from 3–90 Hz °C^–1. Expressed in octaves the CF-change varied in each fibre from about O.14oct °C^–1 at 15 °C to about 0.06 oct °C^–1 at 30 °C, irrespective of the fibre's CF at T_s. Thresholds were lowest near T_s. Below T_s the thresholds decreased on average by 2dB°C^–1, above T_s the thresholds rose rapidly with temperature. The sharpness of tuning (Q_10db) showed no major change in the temperature range tested.Comparison of these findings with those from other lower vertebrates and from mammals shows that only mammalian auditory afferents do not shift their CF with temperature, suggesting that a fundamental difference in mammalian and submammalian tuning mechanisms exists. This does not necessarily imply that there is a single unifying tuning mechanism for all mammals and another one for non-mammals.Abbreviations BF best frequency: frequency of maximal response at an intensity 10 dB above the CF-threshold - CF characteristic frequency - FTC frequency threshold curve, tuning curve - T _s standard temperature of 27 °C     

Microbiological degradation of the herbicide dicamba

Summary Pseudomonas paucimobilis was isolated from a consortium which was capable of degrading dicamba (3,6-dichloro-2-methoxybenzoic acid) as the sole source of carbon. The degradation of dicamba byP. paucimobilis and the consortium was examined over a range of substrate concentration, temperature, and pH. In the concentration range of 100–2000 mg dicamba L^–1 (0.5–9.0 mM), the degradation was accompanied by a stoichiometric release of 2 mol of Cl^– per mol of dicamba degraded. The cultures had an optimum pH 6.5–7.0 for dicamba degradation. Growth studies at 10°C, 20°C, and 30°C yielded activation energy values in the range of 19–36 kcal mol^–1 and an average Q₁₀ value of 4.0. Compared with the pure cultureP. paucimobilis, the consortium was more active at the lower temperature.     

Radiochemical investigation of the respiration of spores of Bacillus cereus

Summary The endogenous respiration of ¹⁴C-labelled spores of B. cereus was measured through the ¹⁴CO₂ produced, and the rate expressed as Q (l CO₂/hxmg). New upper limits for respiration in various conditions have been set.Dry spores had no measurable activity; Q<10^–4 at room temperature and <10^–3 at 35° C. For wet spores of different harvests, at 30°C, Q lay between 0.0013 to 0.067. Near 40° C, respiration showed a maximum. Thermal history has a great influence on Q. CO₂ production by heat-killed spores is attributed largely to infection.Water or 10^–3 m sodium phosphate buffer (pH=6.5) gave equal spore respiration, in strong NaCl it was less. Azide enhanced respiration dramatically. A temporary increase was also found with non-radioactive glucose. Exogenous respiration of spores in glucose exceeded endogenous respiration.Endogenous and exogenous respiration of vegetative forms were much larger than those of spores and were time-dependent. The ratio of minimum (endogenous, dry spores) and maximum (exogenous, wet vegetative cells) respiration was at least 3x10⁵.     

Oxygen consumption rate in rotifers

The oxygen consumption rate (OCR) is a cumulative index of metabolic losses during aerobic metabolism. The generalized relationship of oxygen consumption rate (R, n1 O₂ ind^–1 h^–1) and dry body mass (M, µg) for rotifers is described by the equation: R = 9.15M^0.716. The level of rotifer metabolism is slightly lower than that of multicellular poikilothermic animals. Differences of OCR values in ontogenesis are substantial. Embryos and senile individuals are characterized by minimal OCR values. The OCR of oviparous females in the beginning of reproduction exceeds 2–3 times OCR values of juveniles. Differences in oxygen consumption intensity (OCI) are not so essential. OCR depends on food concentration. An increase of food concentration from 1.4 to 7.0 µg dry mass m1^–1 resulted in Brachionus calyciflorus in an OCR escalation of 2.5 times at 30°C, and 0.5 times at 25°C. Maximal OCR values occur at food concentration close to the saturation concentration for population growth rate. An exponential equation is adequate to describe R-t dependence for animals, long-term adapted to different constant temperatures (2 < Q₁₀ < 3). Acclimation effects observed during sharp temperature changes are determined by peculiarities of compensation reactions in species and separate populations. The formation of a zone of relative temperature independence of OCR (Q¹⁰ 1) at fluctuating temperature is observed. It is necessary to study enzymatic activities parallel to OCR and OCI measurements.     

Compared thermoluminescence characteristics of pea thylakoids studied in vitro and in situ (in leaves). The effect of photoinhibitory treatments

Characteristics of thermoluminescence (TL) glow curves were studied in thylakoids (isolated from pea leaves) or in intact pea leaves after an exposure to very high light for 2 min in the TL device. The inhibition of photosynthesis was detected as decreases of oxygen evolution rates and/or of variable fluorescence.In thylakoids exposed to high light, then dark adapted for 5 min, a flash regime induced TL glow curves which can be interpreted as corresponding to special B bands since: 1) they can be fitted by a single B band (leaving a residual band at –5°C) with a lower activation energy and a shift of the peak maximum by –5 to –6°C and, 2) the pattern of oscillation of their amplitudes was normal with a period of 4 and maxima on flashes 2 and 6. During a 1 h dark adaptation, no recovery of PS II activity occurred but the shift of the peak maximum was decreased to –1 to –2°C, while the activation energy of B bands increased. It is supposed that centers which remained active after the photoinhibitory treatment were subjected to reversible and probably conformational changes.Conversely, in intact leaves exposed to high light and kept only some minutes in the dark, TL bands induced by a flash regime were composite and could be deconvoluted into a special B band peaking near 30°C and a complex band with maximum at 2–5°C. In the case of charging bands by one flash, this low temperature band was largely decreased in size after a 10 min dark adaptation period; parallely, an increase of the B band type component appeared. Whatever was the flash number, bands at 2–5°C were suppressed by a short far red illumination given during the dark adaptation period and only remained a main band a 20°C; therefore, the origin of the low temperature band was tentatively ascribed to recombinations in centers blocked in state S₂Q_A ^–Q_B ^2–. In vivo, the recovery of a moderately reduced state in the PQ pool, after an illumination, would be slow and under the dependence of a poising mechanism, probably involving an electron transfer between cytosol and chloroplasts or the so-called chlororespiration process.Abbreviations E_a- activation energy - FR- far-red - MV- methylviologen - pBQ- p-benzoquinone - PQ- plastoquinone - PS II- Photosystem II - Q_A- primary quinone electron acceptor of PS II - Q_B- secondary quinone electron acceptor of PS II - TL- thermoluminescence     

Invertebrate muscle performance at high latitude: swimming activity in the Antarctic scallop, Adamussium colbecki

The escape swimming performance of the Antarctic scallop, Adamussium colbecki, was measured in animals acclimated for 6 weeks to –1, 0 or 2°C and tested at –1.5 to +1.5°C. Clap duration and swimming velocity were significantly related to temperature, but were not affected by acclimation, demonstrating no phenotypic plasticity. Comparisons of the mean swimming velocity of A. colbecki with the published data for temperate and tropical species showed little evidence for evolutionary compensation for temperature, with all data fitting to a single exponential relationship with a Q₁₀ of 2.08 (0–20°C). The contraction kinetics of the isolated fast adductor muscle of A. colbecki were determined and the times to 50% peak tension and 50% relaxation had Q₁₀s (0–4°C) of 3.6 and 4.7, respectively. The Q₁₀ of the overall relationship for pooled time to peak twitch data for four scallop species was 2.05 (0–20°C). Field studies revealed low mobility and poor escape performance in wild A. colbecki. A combination of thermodynamic constraints, reduced food supply, and lower selective pressure probably explains the low levels of swimming performance seen in A. colbecki.     

H<Subscript>2</Subscript>-Producing bacterial communities from a heat-treated soil inoculum

Hydrogen gas (60% H₂) was produced in a continuous flow bioreactor inoculated with heat-treated soil, and fed synthetic wastewater containing glucose (9.5 g l^–1). The pH in the bioreactor was maintained at 5.5 to inhibit consumption of H₂ by methanogens. The objective of this study was to characterize bacterial communities in the reactor operated under two different hydraulic retention times (HRTs of 30-h and 10-h) and temperatures (30°C and 37°C). At 30-h HRT, the H₂ production rate was 80 ml h^–1 and yield was 0.91 mol H₂/mol glucose. At 10-h HRT, the H₂ production rate was more than 5 times higher at 436 ml h^–1, and yield was 1.61 mol H₂/mol glucose. Samples were removed from the reactor under steady-state conditions for PCR-based detection of bacterial populations by ribosomal intergenic spacer analysis (RISA). Populations detected at 30-h HRT were more diverse than at 10-h HRT and included representatives of Bacillaceae, Clostridiaceae, and Enterobacteriaceae. At 10-h HRT, only Clostridiaceae were detected. When the temperature of the 10-h HRT reactor was increased from 30°C to 37°C, the steady-state H₂ production rate increased slightly to 463 ml h^–1 and yield was 1.8 mol H₂/mol glucose. Compared to 30°C, RISA fingerprints at 37°C from the 10-h HRT bioreactor exhibited a clear shift from populations related to Clostridium acidisoli (subcluster Ic) to populations related to Clostridium acetobutylicum (subcluster Ib).     

Temperature dependence of violaxanthin de-epoxidation and non-photochemical fluorescence quenching in intact leaves ofGossypium hirsutum L. andMalva parviflora L.

The temperature dependence of the rate of de-epoxidation of violaxanthin to zeaxanthin was determined in leaves of chilling-sensitive Gossypium hirsutum L. (cotton) and chilling-resistant Malva parviflora L. by measurements of the increase in absorbance at 505 nm (A ₅₀₅) and in the contents of antheraxanthin and zeaxanthin that occur upon exposure of predarkened leaves to excessive light. A linear relationship between A ₅₀₅ and the decrease in the epoxidation state of the xanthophyll-cycle pigment pool was obtained over the range 10–40° C. The maximal rate of de-epoxidation was strongly temperature dependent; Q₁₀ measured around the temperature at which the leaf had developed was 2.1–2.3 in both species. In field-grown Malva the rate of de-epoxidation at any given measurement temperature was two to three times higher in leaves developed at a relatively low temperature in the early spring than in those developed in summer. Q₁₀ measured around 15° C was in the range 2.2–2.6 in both kinds of Malva leaves, whereas it was as high as 4.6 in cotton leaves developed at a daytime temperature of 30° C. Whereas the maximum (initial) rate of de-epoxidation showed a strong decrease with decreased temperature the degree of de-epoxidation reached in cotton leaves after a 1–2 · h exposure to a constant photon flux density increased with decreased temperature as the rate of photosynthesis decrease. The zeaxanthin content rose from 2 mmol · (mol chlorophyll)^–1 at 30° C to 61 mmol · (mol Chl)^–1 at 10° C, corresponding to a de-epoxidation of 70% of the violaxanthin pool at 10° C. The degree of de-epoxidation at each temperature was clearly related to the amount of excessive light present at that temperature. The relationship between non-photochemical quenching of chlorophyll fluorescence and zeaxanthin formation at different temperatures was determined for both untreated control leaves and for leaves in which zeaxanthin formation was prevented by dithiothreitol treatment. The rate of development of that portion of non-photochemical quenching which was inhibited by dithiothreitol decreased with decreasing temperature and was linearly related to the rate of zeaxanthin formation over a wide temperature range. In contrast, the rate of development of the dithiothreitol-resistant portion of non-photochemical quenching was remarkably little affected by temperature. Evidently, the kinetics of the development of non-photochemical quenching upon exposure of leaves to excessive light is therefore in large part determined by the rate of zeaxanthin formation. For reasons that remain to be determined the relaxation of dithiothreitolsensitive quenching that is normally observed upon darkening of illuminated leaves was strongly inhibited at low temperatures.Abbreviations and Symbols Chl chlorophyll - DTT dithiothreitol - EPS epoxidation state - NPQ non-photochemical chlorophyll fluorescence quenching - PFD photon flux density - PSII photosystem II - F, F_m fluorescence emission at the actual, full closure of the PSII centers C.I.W.-D.P.B. Publication No. 1092We thank Connie Shih for skillful assistance in growing the plants, for conducting the HPLC analyses, and for preparing the figures. A Carnegie Institution Fellowship and a Feodor-Lynen-Fellowship by the Alexander von Humboldt-Foundation to W.B. is gratefully acknowledged. This work was supported by Grant No. 89-37-280-4902 of the Competitive Grants Program of the U.S. Department of Agriculture to O.B.     

Phytoplankton primary production in a eutrophic cooling water pond

The seasonal variation of phytoplankton photosynthesis was measured with ¹⁴C-method in a warmed ice-free pond in central Finland. Simultaneously with in situ measurements the photosynthesis was also measured in an incubator with different water temperatures and constant light (ca. 16 W m^–2). The total annual photosynthesis was 57.2 C m^–2 a^–1. The portion of the winter and spring production of the annual photosynthesis was 18.4%, that of the autumn production ws 17.4%. Thus 64.3% of the total annual phytoplankton photosynthesis occurred in the three summer months. The range of the daily integrated photosynthesis per unit area was 1.9—563 mg C m^–2d^–1. The photosynthetic rate per unit chlorophyll a varied in situ from 0.94 to 33.1 mg C (mg chl. a)^–1 d^–1. The highest value was measured in the beginning of July and the lowest in mid-January. The photosynthetic rate increased in situ exponentially with increasing water temperature. In the incubator the highest photosynthetic rate values were also found in July and August (at+20 °C) when the phytoplankton population was increasing and the minimum values occurred after every diatom maximum both in spring and autumn. Light was a limiting factor for photosynthesis from September to Mid-January, low water temperature was a limiting factor from late January through May. The efficiency of the photosynthesis varied between 0.1 and 0.7% of P.A.R. According to the incubator experiments the Q₁₀ values for the photosynthesis were 2.45 and 2.44 for the winter population between 1 and 10° C and for the summer population between 5 and 15° C, respectively, but the Q₁₀ values decrease at the higher temperatures. The main effect of the warm effluents on the yearly photosynthesis was the increase of production in spring months due to the lack of ice cover. However, the increase of total annual phytoplankton photosynthesis was only ca. 10–15%, because the water temperature was during the spring months below 10° C.     

Treatment of simulated wastewater containing toxic amides by immobilized <Emphasis Type="Italic">Rhodococcus rhodochrous</Emphasis> NHB-2 using a highly compact 5-stage plug flow reactor

Biodegradation of toxic amides by immobilized Rhodococcus rhodochrous NHB-2 has been studied to generate data for future development of reactors for the treatment of simulated wastewater containing various toxic amides. The whole resting cells were immobilized in different matrices like agar, polyacrylamide and alginate. Agar gel beads were selected for the treatment of simulated wastewater containing 100mM each acetamide, propionamide, and 10mM of acrylamide and packed in a highly compact five-stage plug flow reactor. The immobilized bacterium worked well in a broad pH range from 5 to 10, with an optimum at 8.7. The apparent K _m-value for the turnover of acetamide for the resting cells was determined to be around 40mM at pH 8.5 and 55°C, whereas the K _m-value of the purified amidase was predicted to be about 20 mM. This organism exhibited greater turnover of aliphatic amides as compared to aromatic amides. Although these cells showed maximal amide-degrading activity at 55°C, simulated wastewater treatment was carried out at 45°C, because of the greater stability of the amidase activity at that temperature. Of note, indices for overall temperature stability, based on the temperature dependence of apparent first order kinetic temperature denaturation constants, were determined to be –7.9±1.1×10^–4, and –13.7±1.3×10^–4, –14.5±0.7×10^–4, and –13.7±0.8×10^–4°Cmin, for free cells and cells immobilized in alginate, agar and polyacrylamide respectively. After 250min the reactor showed maximum degradation of acetamide, propionamide and acrylamide of about 97, 100 and 90%, respectively by using 883 enzyme activity units per reactor stage. The results of this investigation showed that R. rhodochrous NHB-2 expressing thermostable amidase could be used for the efficient treatment of wastewater containing toxic amides. Therefore, we suggest that this microbe has a very high potential for the detoxification of toxic amides from industrial effluents and other wastewaters.     

Photosystem II reaction centres stay intact during low temperature photoinhibition

Photoinhibition of photosynthesis was studied in intact barley leaves at 5 and 20°C, to reveal if Photosystem II becomes predisposed to photoinhibition at low temperature by 1) creation of excessive excitation of Photosystem II or, 2) inhibition of the repair process of Photosystem II. The light and temperature dependence of the reduction state of Q_A was measured by modulated fluorescence. Photon flux densities giving 60% of Q_A in a reduced state at steady-state photosynthesis (300 mol m^–2s^–1 at 5°C and 1200 mol m^–2s^–1 at 20°C) resulted in a depression of the photochemical efficiency of Photosystem II (F_v/F_m) at both 5 and 20°C. Inhibition of F_v/F_m occurred with initially similar kinetics at the two temperatures. After 6h, F_v/F_m was inhibited by 30% and had reached steady-state at 20°C. However, at 5°C, F_v/F_m continued to decrease and after 10h, F_v/F_m was depressed to 55% of control. The light response of the reduction state of Q_A did not change during photoinhibition at 20°C, whereas after photoinhibition at 5°C, the proportion of closed reaction centres at a given photon flux density was 10–20% lower than before photoinhibition.Changes in the D1-content were measured by immunoblotting and by the atrazine binding capacity during photoinhibition at high and low temperatures, with and without the addition of chloramphenicol to block chloroplast encoded protein synthesis. At 20°C, there was a close correlation between the amount of D1-protein and the photochemical efficiency of photosystem II, both in the presence or in the absence of an active repair cycle. At 5°C, an accumulation of inactive reaction centres occurred, since the photochemical efficiency of Photosystem II was much more depressed than the loss of D1-protein. Furthermore, at 5°C the repair cycle was largely inhibited as concluded from the finding that blockage of chloroplast encoded protein synthesis did not enhance the susceptibility to photoinhibition at 5°C.It is concluded that, the kinetics of the initial decrease of F_v/F_m was determined by the reduction state of the primary electron acceptor Q_A, at both temperatures. However, the further suppression of F_v/F_m at 5°C after several hours of photoinhibition implies that the inhibited repair cycle started to have an effect in determining the photochemical efficiency of Photosystem II.Abbreviations CAP D-threochloramphenicol - F₀ and F ₀ fluorescence when all Photosystem II reaction centres are open in dark- and light-acclimated leaves, respectively - F_m and F _m fluorescence when all Photosystem II reaction centres are closed in dark- and light-acclimated leaves, respectively - F_s fluorescence at steady state - Q_A the primary, stable quinone acceptor of Photosystem II - q_N non-photochemical quenching of fluorescence - q_P photochemical quenching of fluorescence     

Osmotic water permeabilities of human placental microvillous and basal membranes

Summary Literature data suggest that water accumulation by the human fetus is driven by osmotic gradients of small solutes. However, the existence of such gradients has not been supported by prior measurements. Attempts to estimate the size of the gradient necessary to drive net water movement have been seriously hampered by the lack of permeability data for the syncytiotrophoblast membranes. Stopped-flow light scattering techniques were employed to measure the osmotic water permeability (P _f )of microvillous (MVM) and basal membrane (BM) vesicles isolated from human term placenta. At 37°C, the P _f was determined to be 1.9±0.06 × 10^+–3 cm/sec for MVM and 3.1±0.20 × 10^+–3 cm/sec for BM (mean ±SD, n = 6). At 23°C, P _f was reduced to 0.7±0.04 × 10^+–3 cm/sec in MVM and 1.6±0.05 × 10^+–3 cm/sec in BM. These P _f values are comparable to those observed in membranes where water has been shown to permeate via a lipid diffusive mechanism. Arrhenius plots of P _f over the range 20–40°C were linear, with activation energies of 13.6 ± 0.6 kcal/mol for MVM and 12.9±1.0 kcal/mol for BM. Water permeation was not affected by mercurial sulfhydryl agents and glucose transport inhibitors. These data clearly suggest that water movement across human syncytiotrophoblast membranes occurs by a lipid diffusion pathway. As noted in several other epithelial tissues, the basal membrane has a higher water permeability than the microvillous membrane. It is speculated that water accumulation by the human fetus could be driven by a solute gradient small enough to be within the error of osmolarity measurements.We thank the staff of the labor and delivery ward at University of San Francisco Medical Center for help in obtaining placental tissue. This work was supported by NIH grant HD 26392. Dr. Jansson was supported by the Sweden-America Foundation, The Swedish Society of Medicine, The Swedish Society for Medical Research, and the Swedish Medical Research Council.     

Respiration of individual honeybee larvae in relation to age and ambient temperature

The CO₂ production of individual larvae of Apis mellifera carnica, which were incubated within their cells at a natural air humidity of 60–80%, was determined by an open-flow gas analyzer in relation to larval age and ambient temperature. In larvae incubated at 34 °C the amount of CO₂ produced appeared to fall only moderately from 3.89±1.57 µl mg^–1 h^–1 in 0.5-day-old larvae to 2.98±0.57 µl mg^–1 h^–1 in 3.5-day-old larvae. The decline was steeper up to an age of 5.5 days (0.95±1.15 µl mg^–1 h^–1). Our measurements show that the respiration and energy turnover of larvae younger than about 80 h is considerably lower (up to 35%) than expected from extrapolations of data determined in older larvae. The temperature dependency of CO₂ production was determined in 3.5-day-old larvae, which were incubated at temperatures varying from 18 to 38 °C in steps of 4 °C. The larvae generated 0.48±0.03 µl mg^–1 h^–1 CO₂ at 18 °C, and 3.97±0.50 µl mg^–1 h^–1 CO₂ at 38 °C. The temperature-dependent respiration rate was fitted to a logistic curve. We found that the inflection point of this curve (32.5 °C) is below the normal brood nest temperature (33–36 °C). The average Q₁₀ was 3.13, which is higher than in freshly emerged resting honeybees but similar to adult bees. This strong temperature dependency enables the bees to speed up brood development by achieving high temperatures. On the other hand, the results suggest that the strong temperature dependency forces the bees to maintain thermal homeostasis of the brood nest to avoid delayed brood development during periods of low temperature.Abbreviations m body mass - R rate of development or respiration - T_I inflexion point of a logistic (sigmoid) curve - T_L lethal temperature - T_O temperature of optimum (maximum) developmentCommunicated by G. Heldmaier     

Dependence of temperature on loss rates of rotifers,lipids, and ω3 fatty acids in starved Brachionus plicatilis cultures

Rotifer cultures of Brachionus plicatilis (SINTEF-strain, length 250 m) rich in 3 fatty acids were starved for > 5 days at variable temperature (0–18 °C). The net specific loss rate of rotifer numbers were 0.04 day^–1 (range 0–0.08 day^–1) at 5–18 °C, but reached values up to 0.25 day^–1 at 0–3 °C. The loss rate was independent on culture density (range 40–1000 ind ml^–1), but was to some extent dependent on the initial physiological state of the rotifers (i.e., egg ratio).The loss rate of lipids was 0.02–0.05 day^–1 below 10 °C, where the potential growth rate of the rotifer is low (0–0.09 day^–1). The loss rate of lipids increased rapidly for higher temperatures where the rotifer can maintain positive growth, and reached 0.19 day^–1 at 18 °C. The Q₁₀ for the lipid loss rate versus temperature was higher than the Q₁₀ for respiration found in other strains. This may suggest that other processes than respiration were involved in lipid catabolism. The content of 3 fatty acids became reduced somewhat faster than the lipids (i.e. in particular 22:6 3), but the fatty acid per cent distribution remained remarkably unaffected by the temperature during starvation.The results showed that rotifer cultures could be starved for up to 4 days at 5–8 °C without essential quantitative losses of lipids, 3 fatty acids, and rotifers. The rotifers exhausted their endogenous lipids through reproduction (anabolism) and respiration (including enhanced locomotion) at higher temperatures. At lower temperatures, the mortality rate became very high.     

Temperature dependence of inorganic nitrogen uptake and assimilation in Antarctic sea-ice microalgae

Summary The influence of temperature on NO ₃ ^- and NH ₄ ⁺ uptake, and the activity of the assimilatory enzyme NO ₃ ^- reductase (NR) was compared to inorganic C uptake (photosynthesis) in natural assemblages of Antarctic sea-ice microalgae. NO ₃ ^- and NH ₄ ⁺ uptake reached a maximum between 0.5°–2.0°C and 2.0°–3.0°C, respectively, which was close to that for photosynthesis (2.5°–3.0°C). NR showed a distinctly higher temperature maximum (10.0°–12.0°C) and a lower Q₁₀ value than inorganic N and C transport. Our data imply that, owing to differential temperature characteristics between N transport and N assimilation at in situ temperature (-1.9°C), the incorporation of extracellular NO ₃ ^- into cellular macromolecules, may be limited by transport of NO ₃ ^- into the cell rather than the intracellular reduction of NO ₃ ^- to NH ₄ ⁺ . Despite differences in temperature maxima between N transport and N assimilation, the overall low temperature maxima of inorganic N metabolism characterizes Antarctic sea-ice microalgae as psychrophilic. Our study is the first to examine the temperature dependence of inorganic N uptake and assimilation in sea-ice microbial communities.     

The basal permeability to water of human red blood cells evaluated by a nuclear magnetic resonance technique

The characteristics of water diffusional permeability (P) of human red blood cells were studied on isolated erythrocytes by a doping nuclear magnetic resonance technique. In order to estimate the basal permeability the maximal inhibition of water diffusion was induced by exposure of red blood cells to p-chloromercuribenzene sulfonate (PCMBS) under various conditions (concentration, duration, temperature). The lowest values of P were around 0.7×10^–3 cm s^–1 at 10°C, 1.2×10^–3 cm s^–1 at 15°C, 1.4×10^–3 cm s^–1 at 20°C, 1.8×10^–3 cm s^–1 at 25°C, 2.1×10^–3 cm s^–1 at 30°C and 3.5×10^–3 cm s^–1 at 37°C. The mean value of the activation energy of water diffusion (E_a,d) was 25 kJ/mol for control and 43.7 kJ/mol for PCMBS-inhibited erythrocytes. The values of P and E_a,d obtained after induction of maximal inhibition of water diffusion by PCMBS can be taken as references for the basal permeability to water of the human red blood cell membrane.     

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     

Towards an understanding of human impact upon the hydrology of Lake Naivasha,Kenya

The growth of a strain of Moina macrocopa (Straus 1820) isolated from an experimental stabilization pond in Marrakesh, was examined at seven concentrations of algae (6.25–6.25 × 10⁵ cells ml^–1 and at 5 different temperatures (15–30 °C)). Feeding conditions influenced the growth rate as well as the maximum size that reached 1.8 mm at 25 °C and at the highest algal concentration (6.25 × 10⁵ cell ml^–1). The life span and number of moltings reached a maximum (17.4 days and 13 moltings) at average nutrient concentrations (6.25 × 10⁵ cell ml^–1). Juvenile stages varied from 1 to 3 and adult ones from 6 to 8. In the temperature interval tested, growth rate increased with temperature while longevity decreased. Temperature had less effect on maximal size than nutrient availability. Population density (but not crowding) influenced longevity and survival but had no effect on growth.