Stress response in two Antarctic teleosts (Notothenia coriiceps Richardson andChaenocephalus aceratus Lönnberg) following capture and surgery

Blood chemistry and haematological parameters have been determined in two Antarctic teleosts,Notothenia coriiceps Richardson andChaenocephalus aceratus Lönnberg, held at around 1°C.Notothenia coriiceps has a low haemoglobin content compared to tem-perate-zone species, whereasC. aceratus apparently lacks respiratory pigments. Blood samples were obtained by cardiac puncture following landing or using chronically implanted post-branchial arterial cannulae. Although both species showed a similar acidosis on capture (arterial pH as low as 7.5 versus the final recovery value of around 7.9),C. aceratus took 48 h to reestablish baseline values whileN. coriiceps recovered within 12 h, despite initially showing a greater degree of hypercapnic hypoxia. Surgery led to a more severe disturbance of acid-base regulation inN. coriiceps thanC. aceratus (arterial pH of 7.5 versus 7.8) but needed only half as long for recovery. A progressive decrease in arterial oxygen tension and increase in arterial carbon dioxide tension (both more pronounced inN. coriiceps) with level of acidosis was observed down to arteria pH 7.2 InC. aceratus this was accompanied by a rise in blood lactate (up to 10 mmol·1^-1 in some individuals), whileN. coriiceps showed only a modest and transient lactacidosis. Stress inN. coriiceps therefore induces primarily a respiratory, rather than a metabolic acidosis, whereas inC. aceratus both components are present. A differential response to stress is also indicated by an elevated, though low noradrenaline titre inN. coriiceps following surgery and capture, whileC. aceratus was little affected by surgery. However, both species show an unusually weak catecholamine response to induced stress.Abbreviations pH/T °C thermal sensitivity of pH - Ad adrenaline - bw body weight - C.CO₂ total carbon dioxide content - C.O₂ total oxygen content - ED ₅₀ Median effective dose - EDTA ethylenediaminetertra-acetic acid - Hb haemoglobin - Hct haematocrit - HPLC high-performance liquid chromatography - lac lactate - MCH mean corpuscular haemoglobin content - MCHC mean corpuscular haemoglobin concentration - MCV mean cell volume - MS222 tricaine methane sulphonate - NAd noradrenaline - P _aCO₂ arterial carbon dioxide tension - P _aO₂ arterial oxygen tension - pHa arterial blood pH - RBCC red blood cell count - SW sea water - T _a ambient air temperature - VO₂ oxygen consumption     

The role of adrenaline as a modulator of cardiac performance in two Antarctic fishes

The present work was performed to test the hypothesis that Antarctic teleosts rely mostly on cholinergic inhibition for autonomic modulation of the heart. The effects of adrenaline on the inotropic properties on paced, isometrically contracting muscle strips were examined in two distinct Antarctic teleosts, the haemoglobinless icefish Chaenocephalus aceratus and the red-blooded Notothenia coriiceps. All tissues examined revealed a negative force-frequency relationship. Under baseline conditions C. aceratus contracted with a force twice as great as that of N. coriiceps. While the degree to which ventricular tissues responded to adrenaline varied between species, adrenergic stimulation significantly increases myocyte contraction force in this group of fishes. Contraction and relaxation times were not significantly affected by adrenaline concentration while absolute rates of contraction were. Adrenergic stimulation does not enable tissues to achieve higher contraction frequencies, but is shown to be a potent modulator of contraction force.     

Effects of aerobic exercise on the torque-velocity relationship in cycling

The kinetics of the torque-velocity (T-ω) relationship after aerobic exercise was studied to assess the effect of fatigue on the contractile properties of muscle. A group of 13 subjects exercised until fatigued on a cycle ergometer, at an intensity which corresponded to 60% of their maximal aerobic power for 50 min (MAP60%); ten subjects exercised until fatigued at 80% of their maximal aerobic power for 15 min (MAP80%). Of the subjects 7 exercised at both intensities with at least a 1-week interval between sessions. Pedalling rate was set at 60 rpm. The T-ω relationship was determined from the velocity data collected during all-out sprints against a 19 N · m braking torque on the same ergometer, according to a method proposed previously. Maximal theoretical velocity (ω₀) and maximal theoretical torque (T ₀) were estimated by extrapolation of the linear T-ω relationship. Maximal power (P _max) was calculated from the values of T ₀ and ω₀ (P _max = 0.25 ω₀ T ₀). The T-ω relationships were determined before, immediately after and 5 and 10 min after the aerobic exercise. The kinetics of ω₀, T ₀ and P _max was assumed to express the effects of fatigue on the muscle contractile properties (maximal shortening velocity, maximal muscle strength and maximal power). Immediately after exercise at MAP60% a 7.8% decrease in T ₀ and 8.8% decrease in P _max was seen while the decrease in ω₀ was nonsignificant, which suggested that P _max decreased in the main because of a loss in maximal muscle strength. In contrast, MAP80% induced a 8.1% decrease in ω₀ and 12.8% decrease in P _max while the decrease in T ₀ was nonsignificant, which suggested that the main cause of the decrease in P _max was probably a slowing of maximal shortening velocity. The short recovery time of the T-ω relationship suggests that the causes of the decrease of torque and velocity are processes which recover rapidly. Accepted: 25 November 1996     

Effects of short-term thermal stress on the plasma biochemical profiles of two Antarctic nototheniid species

Thermal elevation records in the Austral Ocean have raised questions about the physiological impacts on Antarctic organisms which have evolved under cold and stable water temperatures. Some notothenioid fishes exhibit species-specific responses to elevated temperature, yet the mechanisms involved in restoring homeostasis are unclear. Our study focused on the physiological effects of short-term (2–144 h) exposure to water temperatures of 8 °C on the plasma biochemical profiles of Notothenia coriiceps and Notothenia rossii, species that are abundant in Admiralty Bay, King George Island, Antarctic Peninsula, a region where increasing temperatures have been detected. Despite being phylogenetically similar, these species responded differently to thermal stress. N. rossii showed no changes in cortisol levels, and transient hyperglycemia was likely triggered by elevated catecholamine levels; conversely, metabolic and antioxidant defense parameters were unaffected. Increased gill Na⁺/K⁺-ATPase activity was observed only in N. rossii after 24 h at 8 °C, which assists in maintaining ionic homeostasis. In N. coriiceps, cortisol accurately indicated thermal stress. Increased cortisol levels in N. coriiceps additionally resulted in transient secondary responses such as hyperglycemia and hyperlactemia, as well as reduced levels of total protein, globulins and triglycerides. Unlike in N. rossii, catalase activity in N. coriiceps was modulated at 8 °C, and this parameter is thus considered a good biomarker of thermal stress. Results suggest that N. coriiceps is more sensitive to thermal stress than is N. rossii and that the former is a potential bioindicator for Admiralty Bay.     

The effect of a thiamin derivative on exercise performance

The purpose of this study was to investigate the effect of a thiamin derivative, thiamin tetrahydrofurfuryl disulfide (TTFD), on oxygen uptake (˙VO₂), lactate accumulation and cycling performance during exercise to exhaustion. Using a randomized, double-blind, cross-over design with a 10-day washout between trials, 14 subjects ingested either 1 g · day⁻¹ of TTFD or a placebo (PL) for 4 days. On day 3, subjects performed a progressive exercise test to exhaustion on a cycle ergometer for the determination of ˙VO_2submax, ˙VO_2peak, lactate concentration ([La⁻ ]), lactate threshold (Th_La) and heart rate ( f _c). On day 4, subjects performed a maximal 2000-m time trial on a cycle ergometer. A one-way analysis of variance (ANOVA) with repeated measures was used to determine significant differences between trials. There were no significant differences detected between trials for serial measures of ˙VO_2submax, [La⁻] or f _c. Likewise, ˙VO_2peak [PL 4.06 (0.19) TTFD 4.12 (0.19) l · min⁻¹, P = 0.83], Th_La [PL 2.47 (0.17), TTFD 2.43 (0.16) l · min⁻¹, P = 0.86] and 2000-m performance time [PL 204.5 (5.5), TTFD 200.9 (4.3) s, P = 0.61] were not significantly different between trials. The results of this study suggest that thiamin derivative supplementation does not influence high-intensity exercise performance. Accepted: 19 December 1996     

The influence of maximal aerobic power on recovery of skeletal muscle following anaerobic exercise

Phosphorus magnetic resonance spectroscopy (³¹P-MRS) was used to investigate the influence of maximal aerobic power (˙VO _2max) on the recovery of human calf muscle from high-intensity exercise. The (˙VOO_2max) of 21 males was measured during treadmill exercise and subjects were assigned to either a low-aerobic-power (LAP) group (n = 10) or a high-aerobic-power (HAP) group (n = 11). Mean (SE) ˙VO _2max of the groups were 46.6 (1.1) and 64.4 (1.4) ml · kg⁻¹ · min⁻¹, respectively. A calf ergometry work capacity test was used to assign the same relative exercise intensity to each subject for the MRS protocol. At least 48 h later, subjects performed the rest (4 min), exercise (2 min) and recovery (10 min) protocol in a 1.5 T MRS scanner. The relative concentration of phosphocreatine (PCr) was measured throughout the protocol and intracellular pH (pH_i) was determined from the chemical shift between inorganic phospate (P_i) and PCr. End-exercise PCr levels were 27 (3.4) and 25 (3.5)% of resting levels for LAP and HAP respectively. Mean resting pH_i was 7.07 for both groups, and following exercise it fell to 6.45 (0.04) for HAP and 6.38 (0.04) for LAP. Analysis of data using non-linear regression models showed no differences in the rate of either PCr or pH_i recovery. The results suggest that ˙VO_2max is a poor predictor of metabolic recovery rate from high-intensity exercise. Differences in recovery rate observed between individuals with similar ˙VO_2max imply that other factors influence recovery. Accepted: 17 December 1996     

Characterization of the intestinal microbiota of two Antarctic notothenioid fish species

The fish fauna of the Southern Ocean is dominated by species of the perciform suborder Notothenioidei, which constitute 46% of fish species and 90% of biomass. Notothenioids have undergone rapid morphological and ecological diversification and developed physiological adaptations to a cold, highly oxygenated environment. Microbes inhabiting animal intestines include those that perform essential nutritional functions, but notothenioid gut microbial communities have not been investigated using cultivation-independent approaches. We analyzed bacterial 16S rRNA gene sequences obtained from the intestinal tract of Notothenia coriiceps and Chaenocephalus aceratus, which differ in their pelagic distribution and feeding strategies. Both samples showed dominance of Gammaproteobacteria (mostly Vibrionaceae), as has been reported for temperate teleost species. Both samples showed low diversity relative to that reported for other fish microbiota studies, with C. aceratus containing fewer OTUs than N. coriiceps. Despite the small sample size of this preliminary study, our findings suggest that Antarctic notothenioids carry a gut microbiota similar in composition to that of temperate fish, but exhibiting lower species-level diversity. The omnivorous N. coriiceps individual exhibited greater diversity than the exclusively carnivorous C. aceratus individual, which may indicate that increasing herbivory in fish leads to gut microbe diversification, as found in mammals. Lastly, we detected members of taxa containing known microbial pathogens, which have not been previously reported in Antarctic notothenioid fish.     

Morphology and diet are decoupled in nearshore notothenoids from King George Island,West Antarctica

Antarctic notothenioid fishes show wide adaptive morphological radiation, linked to habitat preferences and food composition. However, direct comparisons of phenotypic variability and feeding habits are still lacking, particularly in stages inhabiting nearshore areas. To assess these relationships, we collected juveniles and adults of the most common benthic species inhabiting shallow waters off the South Shetland Islands within a similar size range, the plunderfish Harpagifer antarcticus, the black rockcod Notothenia coriiceps, and the marbled rockcod Notothenia rossii. Individual size ranges varied from 44.0 to 98.9 mm standard length (LS) (H. antarcticus), from 95.8 to 109.3 mm LS (N. coriiceps), and from 63.0 to 113.0 mm LS (N. rossii). Notothenioid fish showed different morphospace variability, being larger for H. antarcticus than the other Notothenia species and associated with the position of the posterior end of the operculum, along with the location and relative size of the eye. The evolutionary allometry was low, but the static allometry was much higher, especially for H. antarcticus and N. rossii. The diet was mainly carnivorous, consisting of amphipods and euphausiids. Macroalgae were scarce or totally absent in the gut contents of all species. Only H. antarcticus showed an increase in the prey number and ingested prey volume with fish size. Finally, there was a significant covariation between shape changes and LS in all species (allometric effects), however, not with prey composition, probably due to the small size range or ontogenetic stage and the relative similarity (or lack of contrast) in the benthic environment that they utilized.     

Populus tremuloides photosynthesis and crown architecture in response to elevated CO2 and soil N availability

We tested the hypothesis that elevated CO₂ would stimulate proportionally higher photosynthesis in the lower crown of Populus trees due to less N retranslocation, compared to tree crowns in ambient CO₂. Such a response could increase belowground C allocation, particularly in trees with an indeterminate growth pattern such as Populus tremuloides. Rooted cuttings of P. tremuloides were grown in ambient and twice ambient (elevated) CO₂ and in low and high soil N availability (89 ± 7 and 333 ± 16 ng N g⁻¹ day⁻¹ net mineralization, respectively) for 95 days using open-top chambers and open-bottom root boxes. Elevated CO₂ resulted in significantly higher maximum leaf photosynthesis (A _max) at both soil N levels. A _max was higher at high N than at low N soil in elevated, but not ambient CO₂. Photosynthetic N use efficiency was higher at elevated than ambient CO₂ in both soil types. Elevated CO₂ resulted in proportionally higher whole leaf A in the lower three-quarters to one-half of the crown for both soil types. At elevated CO₂ and high N availability, lower crown leaves had significantly lower ratios of carboxylation capacity to electron transport capacity (V _cmax/J _max) than at ambient CO₂ and/or low N availability. From the top to the bottom of the tree crowns, V _cmax/J _max increased in ambient CO₂, but it decreased in elevated CO₂ indicating a greater relative investment of N into light harvesting for the lower crown. Only the mid-crown leaves at both N levels exhibited photosynthetic down regulation to elevated CO₂. Stem biomass segments (consisting of three nodes and internodes) were compared to the total A _leaf for each segment. This analysis indicated that increased A _leaf at elevated CO₂ did not result in a proportional increase in local stem segment mass, suggesting that C allocation to sinks other than the local stem segment increased disproportionally. Since C allocated to roots in young Populus trees is primarily assimilated by leaves in the lower crown, the results of this study suggest a mechanism by which C allocation to roots in young trees may increase in elevated CO₂. Received: 12 August 1996 / Accepted: 12 November 1996     

Effect of exercise-induced hyperventilation on airway resistance and cycling endurance

The purpose of the present study was to investigate the effect of exercise induced hyperventilation and hypocapnia on airway resistance (R _aw), and to try to answer the question whether a reduction of R _aw is a mechanism contributing to the increase of endurance time associated with a reduction of exercise induced hyperventilation as for example has been observed after respiratory training. Eight healthy volunteers of both sexes participated in the study. Cycling endurance tests (CET) at 223 (SD 47) W, i.e. at 74 (SD 5)% of the subject's peak exercise intensity, breathing endurance tests and body plethysmograph measurements of pre- and postexercise R _aw were carried out before and after a 4-week period of respiratory training. In one of the two CET before the respiratory training CO₂ was added to the inspired air to keep its end-tidal concentration at 5.4% to avoid hyperventilatory hypocapnia (CO₂-test); the other test was the control. The pre-exercise values of specific expiratory R _aw were 8.1 (SD 2.8), 6.8 (SD 2.6) and 8.0 (SD 2.1) cm H₂O · s and the postexercise values were 8.5 (SD 2.6), 7.4 (SD 1.9) and 8.0 (SD 2.7) cm H₂O · s for control CET, CO₂-CET and CET after respiratory training, respectively, all differences between these tests being nonsignificant. The respiratory training significantly increased the respiratory endurance time during breathing of 70% of maximal voluntary ventilation from 5.8 (SD 2.9) min to 26.7 (SD 12.5) min. Mean values of the cycling endurance time (t _cend) were 22.7 (SD 6.5) min in the control, 19.4 (SD 5.4) min in the CO₂-test and 18.4 (SD 6.0) min after respiratory training. Mean values of ventilation ( _E) during the last 3␣min of CET were 123 (SD 35.8) l · min⁻¹ in the control, 133.5 (SD 35.1) l · min⁻¹ in the CO₂-test and 130.9 (SD 29.1) l · min⁻¹ after respiratory training. In fact, six subjects ventilated more and cycled for a shorter time, whereas two subjects ventilated less and cycled for a longer time after the respiratory training than in the control CET. In general, the subjects cycled longer the lower the _E, if all three CET are compared. It is concluded that R _aw measured immediately after exercise is independent of exercise-induced hyperventilation and hypocapnia and is probably not involved in limiting t _cend, and that t _cend at a given exercise intensity is shorter when _E is higher, no matter whether the higher _E occurs before or after respiratory training or after CO₂ inhalation. Accepted: 11 September 1996     

Walking performance and economy in chronic heart failure patients pre and post exercise training

The effect of a 3-week exercise programme on performance and economy of walking was analysed in 16 male patients with chronic heart failure [mean age 51.8 (SD 6.9) years, height 174.9 (SD 6.3) cm, body mass 75.3 (SD 11.5) kg, ejection fraction 20.8 (SD 5.0)%]. They were submitted to a cardiopulmonary exercise test on a cycle ergometer and a 6-min walking test on a treadmill before and after the period of exercise training. The training programme consisted of interval cycle (five times a week for 15 min), and treadmill ergometer training (three times a week for 10 min) at approximately 70% cycling peak oxygen uptake (O_2peak) and supplementary exercises (three times a week for 20 min). Compared to the pre values cycling O_2peak [11.9 (SD 2.9) vs 14.0 (SD 2.3) ml ·  kg^–1 · min^–1], maximal self paced walking speed [0.68 (SD 0.33) vs 1.16 (SD 0.30) m · s^–1], and net walking power [2.16 (SD 0.89) vs 2.73 (SD 0.91) W · kg^–1] had increased (P < 0.01) while net energy cost [3.31 (SD 0.66) vs 2.33 (SD 0.38) J · kg^–1 ·  m^–1] had decreased (P < 0.001) after the training period. Approximately 42% of the increase of walking speed resulted from a higher walking power output, whereas approximately 58% corresponded to a positive effect on walking economy. The improvement in walking economy was a function of an increase in walking velocity itself and a result of a more efficient walking technique. These results would indicate that in patients with marked exercise intolerance, adequate exercise training programmes could contribute to favourable metabolic changes with positive effects on the economy of motion. Accepted: 29 August 1996     

Heart structure and ventricular ultrastructure of hemoglobin- and myoglobin-free icefish Channichthys rhinoceratus

Summary The structural and ultrastructural characteristics of the heart of Channichthys rhinoceratus, an antarctic teleost devoid of respiratory pigments, are described and compared with those obtained from the red-blooded related species Notothenia rossii.The heart of the icefish is characterized by a spongy myocardium supplied with a highly developed arterial coronary system. This vasculature includes a subepicardial system and an extensive intratrabecular capillary network. Arterial hilar network and Thebesian vessels may also be present. The bulbus arteriosus shows unusually large spheroid structures located in the middle layer of the wall.Both white- and red-blooded species display comparable myocardial cell morphology and organelle distribution. However, the mitochondrial cristae of the former are more densely packed and the sarcolemma possesses numerous caveolae. A large proportion of non-contractile cells is also found in the icefish ventricular wall.     

Net nitrogen mineralization and net nitrification rates in soils following deforestation for pasture across the southwestern Brazilian Amazon Basin landscape

Previous studies of the effect of tropical forest conversion to cattle pasture on soil N dynamics showed that rates of net N mineralization and net nitrification were lower in pastures compared with the original forest. In this study, we sought to determine the generality of these patterns by examining soil inorganic N concentrations, net mineralization and nitrification rates in 6 forests and 11 pastures 3 years old or older on ultisols and oxisols that encompassed a wide variety of soil textures and spanned a 700-km geographical range in the southwestern Brazilian Amazon Basin state of Rondônia. We sampled each site during October-November and April-May. Forest soils had higher extractable NO₃ ^?-N and total inorganic N concentrations than pasture soils, but substantial NO₃ ^?-N occurred in both forest and pasture soils. Rates of net N mineralization and net nitrification were higher in forest soils. Greater concentrations of soil organic matter in finer textured soils were associated with greater rates of net N mineralization and net nitrification, but this relationship was true only under native forest vegetation; rates were uniformly low in pastures, regardless of soil type or texture. Net N mineralization and net nitrification rates per unit of total soil organic matter showed no pattern across the different forest sites, suggesting that controls of net N mineralization may be broadly similar across a wide range of soil types. Similar reductions in rates of net N transformations in pastures 3 years old or older across a range of textures on these soils suggest that changes to soil N cycling caused by deforestation for pasture may be Basin-wide in extent. Lower net N mineralization and net nitrification rates in established pastures suggest that annual N losses from largely deforested landscapes may be lower than losses from the original forest. Total ecosystem N losses since deforestation are likely to depend on the balance between lower N loss rates from established pastures and the magnitude and duration of N losses that occur in the years immediately following forest clearing.     

The surface structure of Antarctic fish eggs and its use in identifying fish eggs from the Southern Ocean

Summary The surface structure of eggs of Notothenia neglecta, Nototheniops larseni, Nototheniops nudifrons (Nototheniidae), Champsocephalus gunnari and Chaenocephalus aceratus (Channichthyidae), collected near Elephant Island (Atlantic sector of the Southern Ocean) and of Notothenia rossii rossii (Nototheniidae) from Kerguelen waters (Indian sector of the Southern Ocean) was studied by scanning electron microscopy (SEM). Eggs of N. larseni differed from the other species by containing a micropyle with two micropyle pits. External morphological characteristics of the egg envelope such as the ultrastructure of the zona radiata, its interpore distances and the diameter of the micropyle were species-specific and could aid in the identification of fish eggs collected from the Southern Ocean.     

Regulation of splenic contraction persists as a vestigial trait in white-blooded Antarctic fishes

In fishes, the spleen can function as an important reservoir for red blood cells (RBCs), which, following splenic contraction, may be released into the circulation to increase haematocrit during energy-demanding activities. This trait is particularly pronounced in red-blooded Antarctic fishes in which the spleen can sequester a large proportion of RBCs during rest, thereby reducing blood viscosity, which may serve as an adaptation to life in cold environments. In one species, Pagothenia borchgrevinki, it has previously been shown that splenic contraction primarily depends on cholinergic stimulation. The aim of the present study was to investigate the regulation of splenic contraction in five other Antarctic fish species, three red-blooded notothenioids (Dissostichus mawsoni Norman, 1937, Gobionotothen gibberifrons Lönnberg, 1905, Notothenia coriiceps Richardson 1844) and two white-blooded “icefish” (Chaenocephalus aceratus Lönnberg, 1906 and Champsocephalus gunnari Lönnberg, 1905), which lack haemoglobin and RBCs, but nevertheless possess a large spleen. In all species, splenic strips constricted in response to both cholinergic (carbachol) and adrenergic (adrenaline) agonists. Surprisingly, in the two species of icefish, the spleen responded with similar sensitivity to red-blooded species, despite contraction being of little obvious benefit for releasing RBCs into the circulation. Although the icefish lineage lost functional haemoglobin before diversifying over the past 7.8–4.8 millions of years, they retain the capacity to contract the spleen, likely as a vestige inherited from their red-blooded ancestors.     

Effects of hydration state on hormonal and renal responses during moderate exercise in the heat

The effects of hydromineral hormones and catecholamines on renal concentrating ability at different hydration states were examined in five male volunteers while they performed three trials. Each of these trials comprised a 60-min exercise bout on a treadmill (at 50% of maximal oxygen uptake) in a warm environment (dry bulb temperature, 35°C; relative humidity, 20–30%). In one session, subjects were euhydrated before exercise (C). In the two other sessions, after thermal dehydration (loss of 3% body mass) which markedly reduced plasma volume (PV) and increased plasma osmolality (osm_pl), the subjects exercised either not rehydrated (Dh) or rehydrated (Rh) by drinking 600 ml of mineral water before and 40 min after the onset of exercise. During exercise in the Dh compared to C state, plasma renin, aldosterone, arginine vasopressin (AVP), noradrenaline and adrenaline concentrations were increased (P < 0.05). A reduction in creatinine clearance and urine flow was also observed (P < 0.05) together with a decrease in urine osmolality, osmolar clearance and sodium excretion, while free water clearance increased (P < 0.05). However, compared to Dh, Rh partially restored PV and osm_pl and induced a marked reduction in the time courses of both the plasma AVP and catecholamine responses (P < 0.05). Values for renal water and electrolyte excretion were intermediate between those of Dh and C. Plasma atrial natriuretic peptide presented similar changes whatever the hydration state. These results demonstrate that during moderate exercise in the heat, renal concentrating ability is paradoxically reduced by prior dehydration in spite of high plasma AVP levels, and might be the result of marked activation of the sympatho-adrenal system. Rehydration, by reducing this activation, could partially restore the renal concentrating ability despite the lowered plasma AVP. Accepted: 23 April 1997     

Nitrogen storage forms in nine boreal understorey plant species

Storage forms of N were studied in below-ground structures of nine boreal forest understorey plants. The ericaceous shrubs Vacciniumvitis-idaea and V.myrtillus, the fern Gymnocarpium dryopteris, the grass Deschampsia flexuosa, and the herbs Epilobium angustifolium, Maianthemum bifolium, Solidago virgaurea, Geranium sylvaticum and Trientalis europaea were sampled in early summer and late autumn from plots fertilised with a complete mixture of nutrients and from non-fertilised control plots. Concentrations of total nitrogen, insoluble and soluble proteins, free amino acids and nitrate were measured, and changes in absolute and relative concentrations of these N fractions between early summer and late autumn were used to identify the forms in which the plants store N. In all species studied, the concentration of free amino acids increased both between summer and autumn and in response to fertilisation, while the concentration of protein N increased only in response to fertilisation. Thus, free amino acids appear to have a central role in N storage. In all of the species except G. dryopteris, D. flexuosa and S. virgaurea, arginine dominated the pool of free amino acids and thus arginine was the major form of stored N in most species. In D. flexuosa and S. virgurea, however, asparagine and arginine together were the major forms of stored N, while glutamine was the major free amino acid, and N storage form, in G. dryopteris. Received: 10 March 1996 / Accepted: 22 December 1996     

Triacylglycerol lipase activities in tissues of Antarctic fishes

. The activity of the lipolytic enzyme, triacylglycerol lipase (TAG lipase; E.C. 3.1.1.3) was measured in heart ventricle, liver, oxidative skeletal muscle, and adipose tissue of four species of Antarctic fishes (Chaenocephalus aceratus, Notothenia coriiceps, Trematomus newnesi, Gobionotothen gibberifrons). Estimates of weight-specific activities at 0°C in tissues of the Antarctic fishes were broadly comparable to those reported for temperate-zone fish species assayed at their physiological temperature. Within each species, liver tissue displayed the highest weight-specific activity of TAG lipase in C. aceratus, T. newnesi, and G. gibberifrons, while adipose tissue of N. coriiceps showed the highest activity within that species. Combining these estimates with carefully measured somatic indices of the tissues, permitted assessment of the relative importance of different tissues to overall lipolytic capacity on an organismal level. On this basis, liver tissue displays the greatest capacity of TAG lipase per 100 g body weight in each of the species studied.     

Genetic evidence for 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) as a negative effector of cytochrome terminal oxidase cbb 3 production in Rhizobium etli

A Rhizobium etli Tn5mob-induced mutant (CFN035) exhibits an enhanced capacity to oxidize N,N,N′,N′, tetramethyl-p -phenylenediamine (TMPD), a presumptive indicator of elevated cytochrome c terminal oxidase activity. Sequencing of the mutated gene in CFN035 revealed that it codes for the amidophosphoribosyl transferase enzyme (PurF) that catalyzes the first step in the purine biosynthetic pathway. Two c-type cytochromes with molecular weights of 32 and 27 kDa were produced in strain CFN035, which also produced a novel CO-reactive cytochrome (absorbance trough at 553 nm), in contrast to strain CE3 which produced a single 32 kDa c-type protein and did not produce the 553 nm CO-reactive cytochrome. A wild-type R. etli strain that expresses the Bradyrhizobium japonicum fixNOQP genes, which code for the symbiotic cytochrome terminal oxidase cbb ₃, produced similar absorbance spectra (a trough at 553 nm in CO-difference spectra) and two c -type proteins similar in size to those of strain CFN035, suggesting that CFN035 also produces the cbb ₃ terminal oxidase. The expression of a R. etli fixN-lacZ gene fusion was measured in several R. etli mutants affected in different steps of the purine biosynthetic pathway. Our analysis showed that purF, purD, purQ, purL, purY, purK and purE mutants expressed three-fold higher levels of the fixNOQP operon than the wild-type strain. The derepressed expression of fixN was not observed in a purH mutant. The purH gene product catalyzes the conversion of 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) to 5-formaminoimidazole-4-carboxamide ribonucleotide (FAICAR) and inosine. Supplementation with AICA riboside lowered the levels of fixN expression in the purF mutants. These data are consistent with the possibility that AICAR, or a closely related metabolite, is a negative effector of the production of the symbiotic terminal oxidase cbb ₃ in R. etli. Received: 21 November 1996 / Accepted: 22 January 1997     

Specific immunity proteomic profile of the skin mucus of Antarctic fish Chionodraco hamatus and Notothenia coriiceps

The white-blooded Antarctic icefish is the only known vertebrate lacking oxygen-transporting haemoglobins. Fish skin mucus, as the first line of defence against pathogens, can reflect fish welfare. In this study, we analysed the skin mucus proteome profiles of the two Antarctic fish species, the white-blooded Antarctic icefish, Chionodraco hamatus, and the red-blooded Antarctic fish, Notothenia coriiceps, unfolding the different proteins by liquid chromatography coupled with tandem mass spectrometry isobaric tags for relative and absolute quantitation (iTRAQ) technology. Of the 4444 totally identified proteins, 227 differentially expressed proteins (DEPs) were found in the comparison between C. hamatus and N. coriiceps, of which 121 were upregulated and 106 were downregulated in the icefish. In the Kyoto Encyclopedia of Genes and Genomes pathway annotation, we found two pathways “Legionellosis” and “Complement and coagulation cascades” were significantly enriched, among of which innate immune candidate proteins such as C3, CASP1, ASC, F3 and C9 were significantly upregulated, suggesting their important roles in C. hamatus immune system. Additionally, the DEP protein–protein interaction network analysis and “Response to stress” GO category provided candidate biomarkers for deep understanding of the distinct immune response of the two Antarctic fish underlying the cold adaptation.