Field metabolic rates of black-browed albatrosses Thalassarche melanophrys during the incubation stage

Field metabolic rates (FMR) and activity patterns of black-browed albatrosses Thalassarche melanophrys were measured while at sea and on nest during the incubation stage at Kerguelen Island, southwestern Indian Ocean. Activity-specific metabolic rates of five albatrosses at sea (FMR_at-sea) were measured using doubly labeled water (DLW), and by equipping birds with wet-dry activity data loggers that determined when birds were in flight or on the water. The metabolic rates of four birds incubating their eggs (FMR_on-nest) were also measured using DLW. The mean±SD FMR_at-sea of albatrosses was 611±96 kJ kg⁻¹ d⁻¹ compared to FMR_on-nest of 196±52 kJ kg⁻¹ d⁻¹. While at sea, albatrosses spent 52.9±8.2% (N=3) of their time in flight and they landed on the water 41.2±13.9 times per day. The FMR of black-browed albatrosses appear to be intermediate to that of three other albatross species. Based on at-sea activity, the power requirement of flight was estimated to be 8.7 W kg⁻¹ (or 4.0×predicted BMR), which is high compared to other albatross species, but may be explained by the high activity levels of the birds when at sea. The FMR_at-sea of albatrosses, when scaled with body mass, are lower than other seabirds of similar body size, which probably reflects the economical nature of their soaring flight.     

Water potential and plant metabolism: comments on Dr P. J. Kramer's article 'Changing concepts regarding plant water relations', Volume 11, Number 7, pp. 565–568, and Dr J. B. Passioura's Response, pp. 569–571

Abstract. Kramer (1988) and Passioura (1988) highlight an important principle in plant physiology, namely that roots affect the activity of shoots. It is safe to say that anyone who has observed plants could cite many examples. What is in contention, however, is the interpretation of the water potential (Ψ_w) after some investigators (Bates & Hall, 1981; Blackman & Da vies, 1985; Eavis & Taylor, 1979; Gollan, Passioura & Munns, 1986; Termaat, Passioura & Munns, 1985; Turner, Schulze & Gollan, 1985) observed that roots in water deficient media can affect shoot physiology in ways not involving the Ψ_w of the shoot. As a result, some investigators (Sinclair & Ludlow, 1985; Passioura, 1988) question the Ψ_w concept on the grounds indicated by Passioura (1988): if roots affect shoot activity by means other than by changing shoot Ψ_w, the Ψ_w concept must be wrong. This is unfortunate. It has been known for years that metabolic reactions generally do not respond directly to the Ψ_w or its components. Nevertheless, the shoot Ψ_w, and its components play important roles in the physiology and metabolism of plants. Often these roles are interactive with roots. In what follows, I will review some of the evidence for these principles.     

Physiological differences between strains of Tribolium castaneum selected for resistance to hypoxia and hypercarbia, and the unselected strain

Abstract. The metabolic rates, as expressed by oxygen (O₂) consumption, carbon dioxide (CO₂) production, and losses in wet and dry weights, were examined for adults of three strains of the red flour beetle Tribolium castaneum (Herbst), during exposure to two modified atmospheres (MAs). Exposure of a strain selected for resistance over twenty-one generations to an atmosphere of 65% CO₂, 20% O₂ and the balance nitrogen (N₂), termed a high carbon dioxide concentration atmosphere (HCC) and exposure of an unselected strain to HCC, showed considerable levels of aerobic metabolism during exposure. For the unselected strain water loss and mobilization of energy reserves were rapid and mortality was followed by rapid desiccation. For the HCC-resistant strain water balance was maintained and energy reserves were utilized more slowly over a prolonged period. Exposure of a strain selected for resistance over twenty-one generations to a low oxygen concentration atmosphere (LOC) of 0.5% O₂ in N₂, and an unselected strain to LOC, revealed that even at 0.5% O₂, metabolism was largely aerobic in both strains. Maintenance of water balance was not a major factor causing mortality of either strain during exposure to LOC. In air, metabolic rates of both the resistant strains were lower than that of the unselected strain.     

Exchange of oxygen and its role in energy dissipation during drought stress in tomato plants

To elucidate how excess light energy is dissipated during water deficit, net photosynthesis (P_N), stomatal conductance (g_s), intercellular CO₂ concentration (c_i) and Chl a fluorescence were investigated in control and drought-stressed tomato plants ( Lycopersicon esculentum ). Gross O₂ evolution (E_o) and gross O₂ uptake (U_o) were determined by a mass spectrometric ¹⁶O/¹⁸O₂ isotope technique. Under drought stress P_N, g_s, c_i and U_o decline. While photochemical fluorescence quenching decreases under water deficit, non-photochemical quenching rises. The maximal efficiency of PSII measured in the dark is not affected by drought; however, in the light, E_o decreases under water deficit. The ratio P_N/E_o falls under stress while the ratio U_o/E_o increases. We conclude that tomato plants follow a double strategy to avoid photodamage under drought stress conditions: (1) a substantial portion of light energy is emitted as heat and PSII activity is downregulated. This results in a decrease in E_o as well as P_N and U_o. Despite reduced charge separation at PSII, the decline of CO₂ assimilation because of lowered stomatal conductance and metabolic changes results in the need of degrading excessive photosynthetic electrons. (2) Oxygen is used as an alternative electron acceptor in photorespiration or Mehler reaction and U_o rises relative to E_o.     

Direct measurements of metabolism, activity and feeding behaviour of pike, Esox Zucius L., in the wild, by the use of heart rate telemetry

Heart rate telemetry records of up to 5 days duration were obtained from pike living in Lochs Kinord and Davan, Scotland. Applying metabolic rate correlations it was found that mean metabolic rate (R) was 1.5 times standard metabolic rate (R_a), The fish rarely worked near their metabolic limits. Activity metabolism (R_a) was much higher than estimates based on mean swimming speed and comprised up to 10% of R. Most activity metabolism was the result of localized bursts of activity. Less than 10% of activity showed evidence of oxygen debt. Specific Dynamic Action or feeding metabolism (R_f) comprised 15–25% of R. Food intake estimated from heart rate was 1.5% wet body weight day⁻¹, consumed in the form of small items captured during the day and digested during the afternoon and night.     

Inhibitory Effect of Omeprazole, a Specific Inhibitor of H+, K+-ATPase, on Spicule Formation in Sea Urchin Embryos and in Cultured Micromere-Derived Cells.

Embryos kept with omeprazole, a specific H⁺, K⁺-ATPase inhibitor, in a period of development between the mesenchyme blastula and the pluteus corresponding stage became abnormal plutei having quite small spicules, somewhat poor pluteus arms and apparently normal archenterons. In micro-mere-derived cells, kept with omeprazole at pH 8.2 in a period between 15 and 40 hr of culture at 20°C, omeprazole strongly inhibited spicule formation but did not block the outgrowth of pseudopodial cables, in which spicule rods were to be formed. These indicate that omeprazole probably exerts no obvious inhibitory effects other than spicule rods formation. Omeprazole-sensitive H⁺, K⁺-ATPase, an H⁺pump, seems to be indispensable for CaCO₃ deposition (formation of spicule rod) in these spicule forming cells. H⁺, produced in overall reaction for CaCO₃ formation: Ca²⁺+ CO₂+H₂O°CaCO₃+2H⁺, is probably released from the cells by this H⁺pump and hence, this reaction tends to go to CaCO₃ production to form spicule rods. Omeprazole, known to become effective following its conversion to a specific inhibitor of H⁺, K⁺-ATPase at acidic pH, is able to inhibit formation of spicule rod at alkaline pH in sea water. This is probably due to an acidification of sea water near the cell surface by H⁺ejection in H⁺, K⁺-ATPase reaction.     

Metabolic adjustments of an air-breathing teleost, Channa maculata, to acute and prolonged exposure to hypoxic water

Plasma and tissue metabolite levels were measured in the air-breathing Channa maculata during acute and prolonged exposure to normoxic and hypoxic water. Exposure of the fish to hypoxic water (water oxygen partial pressure, PwO ₂= 50 mmHg) for 1 h caused increases in plasma glucose and lactate, liver and brain lactate, liver a-amino acid, heart and brain alanine and brain succinate levels. The metabolic changes in heart, brain and muscle could only be detected when Pw O₂ was 30 or 10 mmHg. Heart glycogen and liver lipid decreased during acute exposure. Prolonged exposure to hypoxic water ( Pw O₂= 30 mmHg) for 3 days caused an increase in plasma glycerol and liver lactate dehydrogenase activity, and a depletion of glycogen store in all tissues investigated. However, metabolite levels which had been elevated during acute hypoxic exposure were observed to return to their normoxic values after prolonged exposure. It was concluded that anaerobic metabolism was triggered by acute exposure to hypoxic water. Prolonged exposure to hypoxic water induced a metabolic readjustment involving mobilisation of lipid and glycogen stores, which is probably a reflection of the high metabolic load of aerial respiration imposed on the fish during exposure to hypoxic water.     

Responses of juvenile rainbow trout, under food limitation, to chronic low pH and elevated summer temperatures, alone and in combination

Rainbow trout were exposed (90 days) in synthetic soft water to sublethal low pH (5.2) and a simulated climate warming scenario (+2°C above the control summer temperature range of 16.5–21° C), alone and in combination, under conditions of limited food (∼4% dry body weight day⁻¹). Weight specific oxygen consumption rates ( M o₂) were ∼55% of M o_2(max), in contrast to ∼75% of M o_2(max) found in trout fed an unlimited ration. This is likely due to a reduction in food quantity and thus feeding activity. However, the trout exposed to low pH at control temperatures exhibited higher conversion efficiencies and increased growth. In contrast, trout exposed to +2°C had reduced growth rates. No ionoregulatory disturbance occurred in any treatment, suggesting that this ration was sufficient to provide a replacement salt load in the diet. Energy budgets indicated that the limited ration resulted in a lowered optimum temperature for growth, with a greater proportion of the energy intake dissipated for metabolic expenditure, resulting in reduced conversion efficiencies. A fourfold reduction in faecal and unaccounted energy losses indicated higher absorption efficiencies than in satiation-fed trout.     

Variation in routine metabolism of juvenile muskellunge: evidence for seasonal metabolic compensation in fishes

Metabolic rate of age 0 muskellunge Esox masquinongy ranged from 0·10 at 5° C to 0·24 mg O₂ g^-1 h^-1 at 25° C and was significantly higher in spring and autumn than during winter months at comparable water temperatures. Reduced metabolic rate in winter was consistent with the metabolic compensation hypothesis, implying that metabolism of muskellunge varies independently of acclimation temperature and gonadogenesis. Moreover, seasonal variation in metabolic rate has important implications for energy budget studies. Single-season estimates of esocid metabolism may be inadequate to describe annual energy requirements; the magnitude of errors will depend on the time of year metabolic rate was measured. As a result, it is suggested that seasonal variation in metabolic rate be incorporated into energy budget determinations for fishes.     

Metabolic Precursors and Compartmentation of Cerebral GABA in Vigabatrin-Treated Rats

Abstract: The metabolic precursors and cerebral compartmentation of the augmented GABA pool induced by vigabatrin, an irreversible inhibitor of GABA transaminase, have been investigated by ¹³C NMR. Adult rats receiving rat chow ad libitum were given either drinking water only or drinking water containing 2.5 g/L vigabatrin for 7 days. Both groups of animals were infused either with [1,2-¹³C₂]acetate (15 µmol/min/100 g body weight), an exclusive precursor of GABA formation through the glial glutamine pathway, or with [1,2-¹³C₂]glucose (15 µmol/min/100 g body weight), a substrate that can produce GABA through the glial glutamine pathway or by direct metabolism in the neurons. The brains were frozen in situ, extracted with perchloric acid, and analyzed by ¹³C NMR. In vigabatrin-treated animals [¹³C]glutamine, a common intermediate for [¹³C]GABA synthesis from glucose or acetate, was accumulated to similar amounts during infusions with [1,2-¹³C₂]glucose or [1,2-¹³C₂]acetate. However, [¹³C]GABA accumulation was sevenfold higher during [1,2-¹³C₂]glucose infusions or twofold higher during [1,2-¹³C₂]acetate infusions. These results show that the direct pathway of GABA formation by neuronal metabolism of glucose predominates over the alternative pathway through glial glutamine. Near-equilibrium relationships of the aminotransferases of GABA and aspartate imply that the observed [¹³C]GABA accumulation occurs initially in the neuronal compartment.     

The link between respiratory capacity and changing metabolic demands during growth of northern pike, Esox lucius L.

The relationship between metabolic rate of pike (Y, mgO2) and body weight (X, g) over the range 40–1291 gat 15° C is of the form: Y=aX^b. For resting metabolic rate (V_o2, rest), the scaling coefficient, b , is 0.80 and for maximum metabolic rate measured after exhaustive swimming (V₀₂, max), b is 0.99. Factorial metabolic scope (V₀₂, max/ V₀₂, rest) increases with body weight. Peak postprandial oxygen consumption (V₀₂, ASDA) is a constant multiple of V₀₂ rest for any discrete meal (expressed as % of body weight) up to 10% body weight. V₀₂ASDA after a single meal can utilize the entire metabolic scope (V₀₂, max—V₀₂, rest) of juvenile but not adult pike.     

PYRUVATE METABOLISM IN THE LOBSTER NERVE AS AFFECTED BY THE PARTIAL PRESSURE OF CARBON DIOXIDE: OBSERVATIONS ON THE SYNTHESIS OF ACETYLCHOLINE AND ON METABOLIC COMPARTMENTATION

Abstract— In the lobster nerve the fixation of CO, at various levels of _pCO2 was studied by the incorporation of [l-¹⁴C]pyruvate. Incorporation of ¹⁴C was solely dependent on CO₂ fixation since the C-1 was decarboxylated in the formation of acetyl-CoA. Paired-nerve studies with [2-¹⁴C]pyruvate afforded a study of pyruvate metabolism in the lobster nerve. [I¹⁴C]Pyruvate was incorporated to nearly the same extent at all levels of pCO₂ including zero pCO₂, a finding that suggested metabolic recycling of CO₂. The magnitude of the metabolic recycling of C-1 of pyruvate or pyruvate dismutation was estimated to be nearly 20 per cent of total CO₂ fixation. Re-evaluation of the relative contributions of the CO₂ fixation. and acetyl-CoA pathways on the basis of more extensive data gave a ratio of 2:3.
The pCO₂ affected synthesis of ACh and the level of citrate. With increasing pCO₂, the specific radioactivity of ACh decreased much more than the content of ACh. The decrease in the specific radioactivity of ACh but not that of citrate further suggested metabolic compartmentation. The implication of these findings is discussed.
Alanine functioned as a metabolic sink for the incorporated pyruvate. Pyruvate levels were estimated to be approximately 0.1 nmol/mg of protein.     

Genetic variation in Arabidopsis thaliana for night-time leaf conductance

Night-time leaf conductance ( g _night) and transpiration may have several adaptive benefits related to plant water, nutrient and carbon relations. Little is known, however, about genetic variation in g _night and whether this variation correlates with other gas exchange traits related to water use and/or native habitat climate. We investigated g _night in 12 natural accessions and three near isogenic lines (NILs) of Arabidopsis thaliana . Genetic variation in g _night was found for the natural accessions, and g _night was negatively correlated with native habitat atmospheric vapour pressure deficit (VPD_air), suggesting lower g _night may be favoured by natural selection in drier habitats. However, there were also significant genetic correlations of g _night with daytime gas exchange traits expected to affect plant fitness [i.e. daytime leaf conductance, photosynthesis and intrinsic water-use efficiency (WUE_i)], indicating that selection on daytime gas exchange traits may result in indirect selection on g _night. The comparison of three NILs to their parental genotypes identified one quantitative trait locus (QTL) contributing to variation in g _night. Further characterization of genetic variation in g _night within and among populations and species, and of associations with other traits and native habitats will be needed to understand g _night as a putatively adaptive trait.     

Implications of non-uniform stomatal closure on gas exchange calculations

Abstract. This paper discusses the consequences of non-uniform (= patchwise) stomatal closure on the estimation of gas exchange parameters. The estimation of the partial pressure of internal CO₂ (c_i) appears to be little sensitive to complete non-uniform stomatal closure. During the process of closure of these patches, however, a lower c_i will be calculated. For gas exchange measurements done at low wind speeds, it can be shown that an error is made in the partitioning of the total vapour transfer resistance into boundary layer and stomatal resistance. This error influences the calculated total transfer resistance of gases other than water vapour (e.g. CO₂). The apparent negative internal gas concentrations that have sometimes been found in fumigation experiments with SO₂ can possibly be explained by this error.     

Seasonal changes of thyroid hormones in field-collected Atlantic cod in relation to condition indices, water temperature and photoperiod

Serum T₄ and T₃ in wild Atlantic cod Gadus morhua ranged from 1 to 12 ng ml⁻¹ and from 2 to 27 ng ml⁻¹ respectively over a 3-year period. In general, the concentrations increased from summer (T₃) or early autumn (T₄) to maxima in mid-winter and declined abruptly during spring. The T₄/T₃ monthly means were lowest in summer and highest in winter. The seasonal patterns of thyroid hormones were weakly correlated with changes in water temperature. However, both T₄ and T₃ co-varied simultaneously with photoperiod. In addition, T₃ was correlated with the hepatosomatic index and condition factor during summer and autumn. It is suggested that the seasonal changes in the release of T₄ from the thyroid were photoperioddriven, and that the course of T3 was regulated by the metabolic state of the fish during the somatic growth period.     

Thermoregulation, energy metabolism, and torpor in blossom-bats, Syconycteris australis (Megachiroptera)

Since little information is available on torpor in bats of the suborder Megachiroptera, we investigated whether the small (18 g) blossom-bat Syconycteris australis displays torpor in the laboratory. Bats entered daily torpor when food and water were withheld for one night and the air temperature (T_a) was below about 26°. Torpor began shortly after lights went on in the morning and lasted for a maximum of 12 hours. During torpor at T_a18°, metabolic rates fell to a minimum of about 15% of that in resting individuals at the same T_a, and to about 40% of the basal metabolic rate. The body temperature (T_b) during torpor was metabolically defended at or above about T_b 18°. Individuals that did not enter torpor in the morning reduced their T_b from about 34.5°, observed in resting individuals that had been fed during the previous night, to values between 30.2 and 32.8°, and the resting metabolic rate fell by about 25%. The ability to undergo short periods of torpor may explain why the distribution range of S. australis extends much further south than that of other small Australian megachiropteran bats.     

The effects of temperature, body mass and feeding on metabolic rate in the tsetse fly Glossina morsitans centralis

Abstract.  Metabolic rate variation with temperature, body mass, gender and feeding status is documented for Glossina morsitans centralis . Metabolic rate [mean ± SE; VCO₂= 19.78 ± 3.11 μL CO₂ h⁻¹ in males (mean mass = 22.72 ± 1.41 mg) and 27.34 ± 3.86 μL CO₂ h⁻¹ in females (mean mass = 29.28 ± 1.96 mg) at 24 °C in fasted individuals] is strongly influenced by temperature, body mass and feeding status, but not by gender once the effects of body mass have been accounted for. A significant interaction between gender and feeding status is seen, similar to patterns of metabolic rate variation documented in Glossina morsitans morsitans . Synthesis of metabolic rate-temperature relationships in G. m. centralis , G. m. morsitans and Glossina pallidipes indicate that biting frequency as well as mortality risks associated with foraging will probably increase with temperature as a consequence of increasing metabolic demands, although there is little evidence for variation among species at present. Furthermore, metabolic rate–body mass relationships appear to be similarly invariant among these species. These data provide important physiological information for bottom-up modelling of tsetse fly population dynamics.     

Fluoride inhibits root water transport and affects leaf expansion and gas exchange in aspen (Populus tremuloides) seedlings

The effects of sodium fluoride (0.3, 5 and 10 m M NaF) on root hydraulic conductivity, and gas exchange processes were examined in aspen ( Populus tremuloides Michx.) seedlings grown in solution culture. A long-term exposure of roots to NaF significantly decreased root hydraulic conductivity ( L _p) and stomatal conductance ( g _s). Root absorbed NaF significantly affected electrolyte leakage in leaf tissues and substantially restricted leaf expansion. NaF did not significantly affect leaf chlorophyll contents but decreased net photosynthesis ( P _n). A short-term exposure of excised roots to 5 m M NaF and KF significantly decreased root water flow ( Q _v) with a concomitant decline in root respiration and reduced g _s when applied through intact roots or excised stems. The same molar concentration of NaCl also decreased Q _v and g _s in intact seedlings, but to a lesser extent than NaF or KF, and did not significantly affect root respiration. The results suggest that fluoride metabolically inhibited Q _v or L _p, probably by affecting water channel activity. We suggest that the metabolic inhibition of L _p by root-absorbed fluoride affected gas exchange and leaf expansion in aspen seedlings.     

Metabolic rate, growth and aggressiveness in three Atlantic salmon Salmo salar populations

Standard metabolic rate ( R _S), specific growth rate ( G ) and aggressiveness were investigated in three Finnish populations of Atlantic salmon Salmo salar (Neva, Saimaa and Teno), which were reared in identical hatchery conditions. The populations differed in their geographical origin and native habitat. There was a significant difference between populations in R _S: the southernmost Neva population had higher values in R _S than the northernmost Teno population. No difference was found in G or aggressiveness between the populations. G was found to have a significant positive association with aggressiveness and R _S among the three populations, however, these results were not statistically significant after correction for multiple tests. There was no significant association between R _S and aggressiveness. Higher metabolic rate of the most southern population Neva is suggested to be an adaptation to the more abundant food sources of the southern stream.     

Effects of atmospheric SO2 on Azolla and Anabaena symbiosis

The water fern Azolla pinnata R. Br. was fumigated for 1 week with either 25, 50 or 100 nl 1⁻¹ SO₂. The symbiosis of Azolla with Anabaena azollae (spp.) was severely damaged by atmospheric SO₂ even at concentrations as low as 25 nl 1⁻¹, with significant reductions in growth, reduction of C₂H₂, NH₃ assimilation, protein synthesis, and heterocyst development. These disturbances appear to be mainly responsible for the extreme sensitivity of this fern to atmospheric SO₂. Changes in violaxanthin/antheraxanthin and epoxy-lutein/lutein ratios also indicate that free radical products are induced by atmospheric SO₂. These results suggest that the Azolla-Anabaena symbiotic system is a very responsive and reliable lower plant model to study the detailed effects of total sulphur deposition upon the balances between various important plant metabolic processes.