H. Harry Taylor

The aerobic scope of an antarctic fish, Pagothenia borchgrevinki and its significance for metabolic cold adaptation

SummaryResting weight-specific oxygen consumption of the cryopelagic Antarctic nototheniid Pagothenia borchgrevinki at 0°C was 39.6 ml kg-1 · h-1 for a 50 g fish, with oxygen consumption being described by the regression equation: log10 VO2(ml/h)=−1.104+0.825 log10 Mb (g). These values are considerably below those raported by Wohlschlag (1964a,b). VO2 max. in forced swimming was described by the regression equation: log10 VO2 max = −0.507+0.823 log10 Mb. Despite low basal metabolism, factorial aerobic scope is similar to that reported for most other teleost fish, as is the cost of net transport. Myotomal muscles were used only at the highest swimming speeds and once they were recruited the fish fatigued rapidly. After swimming, oxygen debt was repaid rapidly, with a half-time of 20 min.

Chemical composition of seminal and ovarian fluids of chinook salmon (Oncorhynchus tshawytscha) and their effects on sperm motility traits

The relationships between the compositions of ovarian, seminal fluids and sperm function are not well known in teleostean fish species. The objective of the present study was to determine the concentration of the major inorganic ions (Na(+), K(+), Ca(2+), Mg, Cl(-)), osmolality, and pH of ovarian and seminal fluid of sexually mature chinook salmon (Oncorhynchus tshawytscha), and to determine if the composition of these fluids influences sperm motility traits (swimming speed, duration of forward mobility, swimming path trajectory, and percent motility). Cation concentrations and osmolality were significantly different in the two fluids. The ionic composition of ovarian fluid differed among individual females, and also among samples collected at different times through the spawning season. Carbonate and bicarbonate were the principal buffer ions in ovarian fluid, and its viscosity was considerably greater than that of water and was shear-dependent. The duration of forward motility (longevity) of spermatozoa, swimming speed, percent motility, and path trajectory were measured using milt from 10 males activated in the ovarian fluid from 7 females whose ion concentrations were known. No significant correlations were observed between the composition of the seminal fluid and sperm traits. However, in ovarian fluid, sperm longevity was negatively correlated with variation in [Ca(2+)] and [Mg(2+)], while percent motility increased with increasing [Mg(2+)]. These observations provide a possible chemical basis for cryptic female mate choice whereby female ovarian fluid differentially influences the behaviour of sperm from different males, and thus their fertilization success.

Recovery from exhausting exercise in an Antarctic fish, Pagothenia borchgrevinki

SummaryPagothenia borchgrevinki, an Antarctic teleost fish was swum to exhaustion and changes in lactic acid levels and blood haematocrit were monitored during recovery. The fish did not perform well at high swimming speeds due to an inability of the white myotomal muscle to produce ATP by anaerobic glycolysis. Consequently, low levels of lactic acid were produced which were fairly rapidly broken down. Haematocrit values were low in non-exercised fish, and these increased by over 100% during exercise, falling back to control levels over many hours. This is probably related to the increased oxygen demand during exercise.

The subcutaneous sinus of the hagfish, Eptatretus cirrhatus and its relation to the central circulating blood volume

Abstract 1. 1. Using a combination of indicator dilution techniques ( 125 I-HSA, Evans Blue dye and 51 Cr labelled RBCs), the total blood volume of the hagfish, Eptatretus cirrhatus was estimated to be 177.4 ml/kg body weight with a plasma volume of 163.5 ml/kg. 2. 2. Approximately 30% of the blood volume is contained within the subcutaneous sinus (SCS) and exchange of RBCs and plasma markers between the two compartments is slow, taking 8 hr or more to reach equilibrium. 3. 3. SCS blood has a lower haematocrit than that in the central circulation, providing further evidence of plasma skimming at site(s) of entry.

The protective effect of sodium nitroprusside (SNP) treatment on Arabidopsis thaliana seedlings exposed to toxic level of Pb is not linked to avoidance of Pb uptake

The effects of 100 μM Pb(NO₃)₂ on 7-day-old Arabidopsis thaliana seedlings grown from seeds pretreated with a nitric oxide donor, sodium nitroprusside (SNP), or a nitric oxide scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) were investigated. Physiological stress induced by Pb (reduced root growth) was less evident in seedlings grown from seeds pretreated with SNP. However, SNP pretreatment of seeds did not affect Pb accumulation in the seedlings. Pb exposure caused oxidative stress by elevating hydrogen peroxide (H₂O₂) and lipid hydroperoxide contents of the seedlings. SNP pretreatment of seeds counteracted Pb toxicity by reducing the H₂O₂ and lipid hydroperoxide contents of Pb-exposed seedlings. Additionally, Pb-induced rises in antioxidative enzyme activities were reversed by SNP pretreatment of seeds. It was concluded that the ameliorating effects of SNP pretreatment were associated with the release of nitric oxide because cPTIO reversed these effects of SNP pretreatment of seeds and more importantly SNP pretreatment did not trigger an avoidance mechanism.

Correlation of growth inhibition with accumulation of Pb in cell wall and changes in response to oxidative stress in Arabidopsis thaliana seedlings

Uptake of the non-essential element, lead (Pb), by 7-days-old Arabidopsis thaliana seedlings caused inhibition of root growth. Pb accumulated mainly in the root and only a small proportion of the total uptake was transported to the shoot. At the ultrastructural level, Pb was localized mainly in the cell walls, intercellular spaces and vacuoles, which may serve to minimize Pb toxicity to vital functions of the cytosol. Pb exposure induced the generation of reactive oxygen species (ROS) and increased the level of lipid hydroperoxide. These changes were accompanied by up-regulation of the activities of antioxidative enzymes in a dose-dependent manner. Although no major destructive changes to the cytoplasm and vital organelles were observed, it is postulated that at least part of the cost of Pb exposure to A. thaliana seedlings is reflected in reduced root growth associated with increased free radical production by cell wall-accumulated Pb.

The control of vascular resistance in the southern rock lobster, Jasus edwardsii (Decapoda: Palinuridae)

In Jasus edwardsii (Hutton) the vascular resistance of each of the seven major arterial systems leaving the heart was increased in response to several of the following neurotransmitters and neurohormones: acetylcholine, adrenalin, serotonin, dopamine, octopamine and peptides proctolin and FLRFamide-related peptide F(1). The resistance to flow through the infrabranchial sinus (IBS), part of the venous system, was also sensitive to these drugs. Unexpectedly, the responses of the IBS continued after removal of the gills. Differences in the profiles of responses of the arteries to individual hormones and in the magnitudes and the time courses of back pressure changes, eliminate a common downstream location such as the venous sinuses or gills, as the source of the arterial responses. Vasoactive drugs were effective when applied either via the lumen or, with longer delay, to the basal side of an artery via the IBS. It is concluded that the resistance of each of these sections of the vascular system is independently controllable by hormones.

Ontogeny of osmoregulation in embryos of intertidal crabs (Hemigrapsus sexdentatus and H. crenulatus, Grapsidae, Brachyura): putative involvement of the embryonic dorsal organ.

SUMMARY This study examined whether the existence of hyperosmotic internal fluids in embryos of euryhaline crabs (Hemigrapsus sexdentatus and H. crenulatus) in dilute seawater reflects osmotic isolation due to impermeability of the egg envelope, as proposed for other decapods, or active osmoregulation. When ovigerous crabs with eggs at gastrula stage were transferred from 100% seawater (osmolality 1000 mmol kg–1) to 50% seawater, embryogenesis and hatching of zoea were completed normally, but were delayed. Hatching failed if the transfer to 50% seawater occurred before gastrulation, and embryogenesis was abnormal in 25% seawater. In 100% seawater, embryos at all stages were internally hyperosmotic by 150–250 mmol kg–1. On transfer to 50% seawater, osmolality initially decreased but remained 200–350 mmol kg–1 hyperosmotic to the medium for several weeks until hatching. High efflux rates of tritium-labelled water (t1/2 16–75 min) and 22Na (t1/2 109–374 min) from H. crenulatus embryos were inconsistent with the osmotic isolation hypothesis. It is concluded that post-gastrula embryos were actively hyper-osmoregulating. The diffusional water permeability of the embryos decreased during development while the sodium efflux rate increased 10-fold. Very rapidly exchanging pools of water and sodium (t1/2 a few seconds to minutes) probably corresponded to peri-embryonic fluid and implied that the egg envelope was a negligible barrier to diffusion of water and salts. Higher Na+/K+-ATPase activities in late embryos of H. crenulatus incubated in 50% seawater than in embryos incubated in full strength seawater were consistent with an acclimation response. An area of the embryonic surface located over the yolk in the region of the embryonic dorsal organ stained with AgNO3. Staining appeared at gastrulation, persisted throughout development and was lost at hatching. Deposits of AgCl between the outer and inner membranes, identified by X-ray microanalysis, suggest that the dorsal organ was a site of chloride extrusion. A model for osmoregulation in post-gastrula embryos is proposed: osmotic uptake of water is balanced by excretion of water and salts via the dorsal organ and salt loss is balanced by active uptake over the general embryonic ectoderm.

Heterogeneous perfusion of the paired gills of the abalone Haliotis iris Martyn 1784: an unusual mechanism for respiratory control.

SUMMARY The abalone Haliotis iris retains the ancestral gastropod arrangement of a pair of bipectinate gills (ctenidia). The gills share a single branchial chamber, are supplied from a common haemolymph sinus and effectively support the whole of oxygen uptake by the animal. Using chronic indwelling cannulae and pulsed Doppler probes, post-branchial haemolymph oxygen partial pressures (PaO2) and haemolymph flow rates were measured in the left and right efferent ctenidial veins. During periods of internal hypoxia following emersion and handling, total branchial haemolymph flow (24.4±3.6 ml kg-1 min-1) was partitioned nearly equally between the left and right gills (13.3±2.6 and 10.8±1.4 ml kg-1 min-1, respectively) and their PaO2 values were similar (81.9±6.1 and 87.3±4.7 mmHg, respectively). In animals settled for >24 h, branchial haemolymph flow decreased to 9.1±2.1 ml kg-1 min-1, primarily resulting from a virtual shutdown of the left gill flow to only 4.6% of total flow (left, 0.41±0.34 ml kg-1 min-1; right, 8.6±2.0 ml kg-1 min-1). At rest, right gill PaO2 (85.5±6.8 mmHg) was essentially unchanged while PaO2 of the slowly perfused left gill rose to 105.3±10.2 mmHg, close to the PO2 of the exhalant seawater (104.5±3.1 mmHg). The aerobic metabolic scope of H. iris therefore appears to be met primarily by circulatory adjustments at the left gill, which at rest is highly perfusion limited (left Ldiff, 0.14±0.07; right Ldiff, 0.44±0.08).

EDTA reduces lead accumulation in Symphytum officinale L. (comfrey) roots

The addition of EDTA in phytoextraction studies has been reported to increase heavy metal accumulation in above-ground parts or to have no negative impact on the overall (root/shoot) accumulation levels in terrestrial plants. At a purely quantitative level, this study assessed the phytoextraction potential of a previously untested high-biomass terrestrial plant, Symphytum officinale L. (comfrey), in the presence of Pb and EDTA. In this hydroponic-based study, we report a small increase in shoot accumulation of Pb with EDTA but, conversely, the presence of EDTA in the nutrient medium markedly reduced the overall quantity of Pb in the plant root by at least 80%. The loss does not appear to be explained by EDTA acting alone, increased transport of Pb to the shoots, or anionic charge repulsion of the [PbEDTA]2− complex. The elusive action and negative effect of EDTA on Pb accumulation in S. officinale provides additional reasons towards a growing trend away from the use of EDTA as a chelating agent in phytoextraction.