Ionic regulation and Na+,K+-ATPase activity in gills and kidney of the Antarctic aglomerular cod icefish exposed to dilute sea water

When Notothenia neglecta was exposed to diluted, half strength, sea water for 6 h or 10 days, serum concentrations of Cl^-, Na⁺, K⁺ and Mg²⁺ did not differ from those of sea water controls. This indicates that the fish were capable of both short- and long-term regulation. Renal Na⁺,K⁺-ATPase activity decreased after a 6 h exposure to diluted sea water, but there were no differences between diluted sea water and controls after 10 days of exposure.     

Does the 13C of foliage‐respired CO2 and biochemical pools reflect the 13C of recently assimilated carbon?

Isotopic labelling experiments were conducted to assess relationships among ¹³C of recently assimilated carbon ( δC _A), foliage respiration ( δC _F), soluble carbohydrate ( δC _SC), leaf waxes ( δC _LW) and bulk organic matter ( δC _OM). Slash pine, sweetgum and maize were grown under ¹³C depleted CO₂ to label biomass and then placed under ambient conditions to monitor the loss of label. In pine and sweetgum, δC _F of labelled plants (∼−44 and −35‰, respectively) rapidly approached control values but remained depleted by ∼4–6‰ after 3–4 months. For these tree species, no or minimal label was lost from δC _SC, δC _LW and δC _OM during the observation periods. δC _F and δC _SC of labelled maize plants rapidly changed and were indistinguishable from controls after 1 month, while δC _LW and δC _OM more slowly approached control values and remained depleted by 2–6‰. Changes in δC _F in slash pine and sweetgum fit a two-pool exponential model, with the fast turnover metabolic pool (∼3–4 d half-life) constituting only 1–2% of the total. In maize, change in δC _F fits a single pool model with a half-life of 6.4 d. The ¹³C of foliage respiration and biochemical pools reflect temporally integrated values of δC _A, with change in isotopic composition dampened by the size of metabolic carbon reserves and turnover rates.     

Purification and characterization of the major β-1,4-endoglucanase from Thermomonospora curvata

The major β-1,4-endoglucanase (EG) of the thermophilic actinomycete, Thermomonospora curvata , contributed over 80% of the total EG activity recovered from cell-free culture fluid after growth on cellulose. The enzyme was purified to electrophoretic homogeneity by ammonium sulphate precipitation, ion-exchange chromatography and size exclusion HPLC. This monomeric enzyme had a specific activity of 750 IU mg⁻¹ when assayed with 2.5% (w/v) carboxymethyl cellulose (CMC) at 70°C, pH 6.0. Highest activity was observed on CMC with a degree of polymerization of 3200. The EG was stable for 48 h at 60°C, pH 6.0 and had a half-life of 30 min at 80°C; temperature and pH optima were 70–73°C and 6.0–6.5, respectively. The mol. wt was 100000 and the pI was 4.0. The K _m and V _max values were 7.33 mg ml⁻¹ and 833 μmol min⁻¹, respectively. EG activity was inhibited by Fe^{2 +}, Hg^{2 +}, Ag⁺ and Pb^{2 +}, and enhanced by dithiothreitol and Zn^{2 +}. The first 12 amino acid residues at the N -terminus were: Asp-Glu-Val-Asp-Glu-Ile-Arg-Asn-Gly-Asp-Phe-Ser. Glutamic and aspartic acid constituted 24% of the total amino acid composition; no amino sugar was found.     

The acquisition and accumulation of inorganic carbon by the unicellular green alga Chlorella ellipsoidea

Abstract. The uptake and accumulation of inorganic carbon has been investigated in Chlorella ellipsoidea cells grown at acid or alkaline pH. Carbonic anhydrase (CA) was detected in ceil extracts but not in intact cells and CA activity in acid-grown cells was considerably less than that in alkali-grown cells. Both cell types demonstrates low K_1/2 (CO₂) values in the range pH 7.0–8.0 and these were unaffected by O₂ concentration. The CO₂ compensation concentrations of acid- and alkali-grown cells suspended in aqueous media were not significantly different in the range of pH 6.0–8.0, but at pH 5.0, the CO₂ compensation concentrations of acid-grown cells (57.4cm³ m⁻³) were lower than those of alkali-grown cells (79.2cm³ m⁻³). The rate of photo-synthetic O₂ evolution in the range pH 7.5–8.0 exceeded the calculated rate of CO₂ supply two- to three-fold, in both acid- and alkali-grown cells, indicating that HCO₃⁻ was taken up by the cells. Accumulation of inorganic carbon was measured at pH 7.5 by silicone-oil centri-fugation, and the concentration of unfixed inorganic carbon was found to be 5.1 mol m⁻³ in acid-grown and 6.4mol m⁻³ in alkali-grown cells. These concentrations were 4.6- and 5.9-fold greater than in the external medium. These results indicate that photorespiration is suppressed in both acid- and alkali-grown cells by an intracellular accumulation of inorganic carbon due, in part, to an active uptake of bicarbonate.     

The Measurement of Spinal Cord Tissue pH Using a Diffusible, Lipid-Soluble, pH-Sensitive Fluorescent Indicator

Abstract: Spinal cord tissue pH was measured in cats at normocapnia, hypocapnia, hypercapnia and death from anoxia using a pH-sensitive fluorescent indicator (umbelliferone) with both molecular and ionic fluorophors. A ratio analysis of the indicator's calibrated 450 nm fluorescent tissue clearance curves from 340 and 370 nm excitation permitted direct in vivo tissue pH determinations. Fifteen animals were divided into three equal groups according to different arterial carbon dioxide tensions (P_a co₂):five animals at P_a co₂ 20, five animals P_a co₂ 40 and five animals P_a co₂ 60 torr. Spinal cord tissue pH varied linearly with arterial pH, but within narrower limits. These values (arterial versus cord pH) were: 7.46 versus 7.15; 7.21, 7.09; and 7.04, 7.00. At death from hypoxemia the arterial pH fell to 6.99 and spinal cord to 6.67. The clearance curves of umbelliferone in spinal cord varied according to P_a co₂ and appeared to reflect spinal cord blood flow.     

Respiratory and acid-base disturbances in rainbow trout blood during exposure to chloramine-T under hypoxia and hyperoxia

Rainbow trout Oncorhynchus mykiss were exposed acutely to chloramine-T at a therapeutic concentration (9mg l⁻¹) under moderately hypoxic (water P o₂: l00 mmHg) or hyperoxic (water P o₂: 430mmHg) conditions and arterial blood gas tensions ( P ao₂ and P aco₂) and pH were monitored using an extracorporeal circulation. Hypoxia, alone, resulted in an increased ventilation frequency, a decrease in both arterial P co₂ and P o₂ and an increase in arterial pH. There was no effect of chloramine-T exposure on the measured variables as compared with pre-exposure (hypoxia baseline) values. Hyperoxia, alone, resulted in a decrease in ventilation frequency, an increase in arterial P co₂ and P o₂, and a decrease in arterial pH. Chloramine-T exposure under these conditions caused a significant increase in ventilation frequency, but no significant effect on arterial blood gases or pH as compared with the hyperoxia baseline values. Despite the increase in ventilation caused by chloramine-T during hyperoxia, there was no reduction in P co₂ or increase in P o₂. Although these results were of little pathological significance, this study suggests that chloramine-T, although stimulating ventilation, was impairing the diffusion of co₂ across the gill probably by the secretion of branchial mucus and enhancing the gill boundary layer.     

Ecophysiological characterization of common food-borne fungi in relation to pH and water activity under various atmospheric compositions

The combined effects of pH, water activity (a_w), oxygen (O₂) and carbon dioxide (CO₂) levels on growth and sporulation of 10common food-borne fungi were studied. The use of a multivariate statistical method (PLS) for the analysis of data showed that the fungi could be grouped according to their physiological response to changes in the four tested factors. Carbon dioxide, a_w and pH were found to be the most significant factors describing differences and similarities among the fungi. Maximal inhibitory effect of elevated levels of CO₂ (5–25%) and decreased a_w (0·99–0·95) varied among the 10 species from 6 to 77% and from 52 to 100%, respectively. Sporulation of the fungi was sensitive to all tested factors. Furthermore, interaction of CO₂ and a_w displayed a significant effect on sporulation. It was shown that different fungal species associated with the same ecosystem responded similarly to changes in the tested factors. Thus, fungi which are not phylogenetically related may be physiologically related or show a common strategy of life.     

Soils contain two different activities for oxidation of hydrogen

Abstract Hydrogen oxidation rates were measured in a neutral compost soil and an acidic sandy loam at H₂ mixing ratios of 0.01 to 5000 ppmv. The kinetics were biphasic showing two different K _m values for H₂, one at about 10–40 nM dissolved H₂, the other at about 1.2–1.4 μM H₂. The low- K _m activity was less sensitive to chloroform fumigation than the high- K _m activity. If sterile soil was amended with Paracoccus denitrificans or a H₂-oxidizing strain isolated from compost soil, it exhibited only a high- K _m (0.7–0.9 μM) activity. It also failed to utilize H₂ mixing ratios below a threshold of 1.6–3.0 ppmv H₂ (160–300 mPa). A similar result was obtained when fresh soil samples were suspended in water, and H₂ oxidation was determined from the decrease of dissolved H₂. However, H₂ was again utilized to mixing ratios lower than 0.05 ppmv, if the supernatant of the soil suspension or the settled soil particles were dried onto sterile soil or purified quarz sand. Obviously, soils contain two different activities for oxidation of H₂: (1) a high- K _m, high-threshold activity which apparently is due to aerobic H₂-oxidizing bacteria, and (2) a low- K _m, low-threshold activity whose origin is unknown but presumably is due to soil enzymes.     

Diel variations in carbonate incorporation into otoliths in goldfish

When D-[¹⁴C-U]-glucose was administered intraperitoneally into goldfish Carassius amatus at 20° C and 12L: 12D (dark period 1800–0600 hours) at 0600, 1200, 1800, 2400 and 0600 hours on the following day, glucose was metabolized to release ¹⁴CO₂ and then it was incorporated into otoliths as carbonate. The rate of metabolic activity, judging from the ratio of inorganic to organic radiocarbon in plasma, was low during the dark period. Carbon incorporation into otoliths was also minimized during 1800–2400 h. When fish were exposed to ambient water containing NaH¹⁴CO₃, plasma radioactivity was lowest during 1800–2400 hours, during which time carbon incorporation into otoliths was lowest. Plasma total CO₂ levels markedly increased during the dark period. These results clearly indicate that carbonate formation in otoliths has a diel variation with a nadir lasting 6 h from 1800 to 2400 hours under the photoperiod used.     

Matrix composition and community structure analysis of a novel bacterial pyrite leaching community

Here we describe a novel bacterial community that is embedded in a matrix of carbohydrates and bio/geochemical products of pyrite (FeS₂) oxidation. This community grows in stalactite-like structures – snottites – on the ceiling of an abandoned pyrite mine at pH values of 2.2–2.6. The aqueous phase in the matrix contains 200 mM of sulfate and total iron concentrations of 60 mM. Micro-X-ray diffraction analysis showed that jarosite [(K,Na,H₃O)Fe₃(SO₄)₂(OH)₆] is the major mineral embedded in the snottites. X-ray absorption near-edge structure experiments revealed three different sulfur species. The major signal can be ascribed to sulfate, and the other two features may correspond to thiols and sulfoxides. Arabinose was detected as the major sugar component in the extracellular polymeric substance. Via restriction fragment length polymorphism analysis, a community was found that mainly consists of iron oxidizing Leptospirillum and Ferrovum species but also of bacteria that could be involved in dissimilatory sulfate and dissimilatory iron reduction. Each snottite can be regarded as a complex, self-contained consortium of bacterial species fuelled by the decomposition of pyrite.     

Uptake regions of inorganic nitrogen in roots of carob seedlings

Three-week-old seedlings of carob ( Ceratonia siliqua L. cv. Mulata) were grown for 9 weeks under different root temperatures (20, 30 and 40°C) at pH values of 5, 7 and 9 with nitrate or ammonium as nitrogen source. Nitrogen uptake rates were determined by depletion from the medium and decreased with distance from the apex. The decline of nitrogen uptake rates along the roots depended on the form of inorganic nitrogen in the medium as well as on pH and temperature, such that the NO⁻₃ and NH⁺₄ ions were taken up essentially by the root tips (0–2 cm) through processes requiring energy. The uncharged NH₃ species entered passively, through the mature parts of the root (2–10 cm). Root zone temperature and pH affect the NH⁺₄/NH³ equilibrium in the nutrient solution and, consequently, the uptake areas of the root for these ions. Furthermore. while root tip uptake of nitrogen is energy dependent, uptake through mature root areas is essentially passive and seems to depend on a well developed apparent free space.     

Effect of oxygen concentration on intracellular pH, glucose-6-phosphate and NTP content in rice (Oryza sativa) and wheat (Triticum aestivum) root tips: in vivo 31P-NMR study

Hypoxic pretreatment is known to induce anoxia tolerance in plant species sensitive to oxygen deprivation. However, we still do not have detailed information on changes in cytoplasmic and vacuolar pH (pH_cyt and pH_vac) in plants under low-oxygen availability (hypoxia) and under anoxia. To investigate this, we have studied the influence of hypoxia and anoxia on pH_cyt and pH_vac, glucose-6-phosphate (Glc-6-P) and nucleotide triphosphate (NTP) contents in rice ( Oryza sativa L.) root tips in comparison with those of wheat ( Triticum aestivum L.) with in vivo ³¹P-nuclear magnetic resonance. Both cereals responded to hypoxia similarly, by rapid cytoplasmic acidification (from pH 7.6–7.7 to 7.1), which was followed by slow partial recovery (0.3 units after 6 h). Anoxia led to a dramatic pH_cyt drop in tissues of both species (from pH 7.6–7.7 to less than 7.0) and partial recovery took place in rice only. In wheat, the acidification continued to pH 6.8 after 6 h of exposure. In both plants, NTP content followed the dynamics of pH_cyt. There was a strong correlation between NTP content and cytoplasmic H⁺ activity ([H⁺]_cyt= 10^−pHcyt) for both hypoxic and anoxic conditions. Glc-6-P content increased in rice under anoxia and hypoxia. In wheat, Glc-6-P was not detectable under anoxia but increased under hypoxia. In this study, rice root tips were shown to behave as anoxia tolerant tissues. Our results suggest that the initial cytoplasmic acidification and subsequent pH_cyt are differently regulated in anoxia tolerant and intolerant plants and depend on the external oxygen concentration.     

The controlling influence of cell-surface electrical potential on the uptake and toxicity of selenate (SeO42–)

Root elongation in wheat seedlings ( Triticum aestivum L. cv. Atlas 66) was inhibited by micromolar activities of SeO₄^2–. SeO₄^2– inhibition was enhanced by supplementation of the rooting medium with CaCl₂, MgCl₂, SrCl₂, or the reduction of pH. These solute treatments, as well as the addition of tris (ethylenediamine)cobalt³⁺, enhanced the uptake of Se by the roots. The results are interpreted to reflect an elevated PM-surface activity of SeO₄^2– caused by solute-induced reductions of plasma membrane (PM) surface negativity. (PM-surface electrical potential is sometimes measured electrophoretically as the zeta potential.) This study complements an extensive literature documenting the suitability of an electrostatic model (Gouy-Chapman-Stern), based almost entirely upon experiments with cations rather than anions. The close correspondence among uptake, intoxication, and model-computed SeO₄^2– activity at the PM surface adds credibility to the model and its evaluated parameters. The model may be useful for the interpretation of other plant-anion interactions, and phosphate and sulphate nutrition in acidic soils are considered as examples.     

Availability, uptake and turnover of glycerol in hypersaline environments

Abstract A sensitive assay for glycerol and other polyols was developed, based on periodate oxidation to formaldehyde, followed by a colorimetric assay with 3-methyl-2-benzothiazolone hydrazone. Apparent glycerol concentrations thus measured in saltern crystallizer ponds were around 20–36 μM, while in the Dead Sea, during a Dunaliella bloom, values were up to 27 μM. However, these values probably overestimate the glycerol concentrations present, as shown by labeled glycerol uptake experiments. Values of [K + S_n] (natural concentration + affinity constant) in saltern ponds were as low as 0.76–1.4 μM, with V_max values of 193–303 nmol 1⁻¹h⁻¹, and turnover times between 2.6–7.2 h at 35°C. Similar measurements in the Dead Sea were: [K + S_n] 0.07–1.41 μM, V_max values 160–426 nmol 1⁻¹h⁻¹, and turnover times in the range of 0.45–3.3 h.     

Inorganic carbon limitation of photosynthesis in lake phytoplankton

1. Inorganic carbon availability influences species composition of phytoplankton in acidic and highly alkaline lakes, whereas the overall influence on community photosynthesis and growth is subject to debate.
2. The influence of total dissolved inorganic carbon (DIC) and free CO₂ on community photosynthesis was studied in six Danish lakes during the summer of 1995. The lakes were selected to ensure a wide range of chlorophyll a concentrations (1–120 μg l^–1), pH (5.6–9.6) and DIC concentration (0.02–2.5 m m ). Photosynthesis experiments were performed using the ¹⁴C technique in CO₂-manipulated water samples, either by changing the pH or by adding/removing CO₂.
3. Lake waters were naturally CO₂ supersaturated during most of the experimental period and inorganic carbon limitation of photosynthetic rates did not occur under ambient conditions. However, photosynthesis by phytoplankton in lakes with low and intermediate DIC concentrations was seriously restricted when CO₂ concentrations declined. Similarly, photosynthesis was limited by low CO₂ concentrations during phytoplankton blooms in the hardwater alkaline lakes.     

The effect of different growth conditions on dark and light carbon assimilation in Littorella uniflora

The effect of long-term exposure to different inorganic carbon, nutrient and light regimes on CAM activity and photosynthetic performance in the submerged aquatic plant, Littorella uniflora (L.) Aschers was investigated. The potential CAM activity of Littorella was highly plastic and was reduced upon exposure to low light intensities (43 μmol m⁻² s⁻¹), high CO₂ concentrations (5.5 mM, pH 6.0) or low levels of inorganic nutrients, which caused a 25–80% decline in the potential maximum CAM activity relative to the activity in the control experiments (light: 450 μmol m⁻² s⁻¹; free CO₂: 1.5 mM). The CAM activity was regulated more by light than by CO₂, while nutrient levels only affected the activity to a minor extent. The minor effect of low nutrient regimes may be due to a general adaptation of isoetid species to low nutrient levels.
The photosynthetic capacity and CO₂ affinity was unaffected or increased by exposure to low CO₂, irrespective of nutrient levels. High CO₂, low nutrient and low light, however, reduced the capacity by 22–40% and the CO₂ affinity by 35-45%, relative to control.
The parallel effect of growth conditions on CAM activity and photosynthetic performance of Littorella suggest that light and dark carbon assimilation are interrelated and constitute an integrated part of the carbon assimilation physiology of the plant. The results are consistent with the hypothesis that CAM is a carbon-conserving mechanism in certain aquatic plants. The investment in the CAM enzyme system is beneficial to the plants during growth at high light and low CO₂ conditions.     

Protein aggregation in neurons following OGD: a role for Na+ and Ca2+ ionic dysregulation

In this study, we investigated whether disruption of Na⁺ and Ca²⁺ homeostasis via activation of Na⁺-K⁺-Cl⁻ cotransporter isoform 1 (NKCC1) and reversal of Na⁺/Ca²⁺ exchange (NCX_rev) affects protein aggregation and degradation following oxygen–glucose deprivation (OGD). Cultured cortical neurons were subjected to 2 h OGD and 1–24 h reoxygenation (REOX). Redistribution of ubiquitin and formation of ubiquitin-conjugated protein aggregates occurred in neurons as early as 2 h REOX. The protein aggregation progressed further by 8 h REOX. There was no significant recovery at 24 h REOX. Moreover, the proteasome activity in neurons was inhibited by 80–90% during 2–8 h REOX and recovered partially at 24 h REOX. Interestingly, pharmacological inhibition or genetic ablation of NKCC1 activity significantly decreased accumulation of ubiquitin-conjugated protein aggregates and improved proteasome activity. A similar protective effect was obtained by blocking NCX_rev activity. Inhibition of NKCC1 activity also preserved intracellular ATP and Na⁺ homeostasis during 0–24 h REOX. In a positive control study, disruption of endoplasmic reticulum Ca²⁺ with thapsigargin triggered redistribution of free ubiquitin and protein aggregation. We conclude that overstimulation of NKCC1 and NCX_rev following OGD/REOX partially contributes to protein aggregation and proteasome dysfunction as a result of ionic dysregulation.     

Location of tyrosine phenol-lyase in some Gram-negative bacteria

Abstract From various habitats (plant material, fruits, soil), yeasts belonging to the species of Pichia kluyveri and Hanseniaspora uvarum were isolated that showed killer activity. According to the activity spectrum against other yeasts these strains belonged to 11 different groups that were distinguishable from the killer strains K₁-K₁₀. The isoelectric points of the killer proteins were in the range of pH 3.5–3.9, the activity optimum was observed at pH 4.2–4.6. Above pH 5 and above a temperature of 25–35°C the killer proteins were inactivated.     

The presence of two types of β-cyanoalanine synthase in germinating seeds and their responses to ethylene

Germinating seeds of many species contain two types of β-cyanoalanine synthase (CAS, EC 4.4.1.9) that convert HCN to β-cyanoalanine. One is cytoplasmic CAS (cyt-CAS), which is precipitated by 50 to 60% (NH₄)₂SO₄ and has a pH optimum of 10.5. Cytoplasmic CAS is present at high levels in dry seed and its activity does not increase during imbibition. The activity of cyt-CAS is not affected by exogenously applied ethylene (C₂H₄), except in rice ( Oryza sativa cv. Sasanishiki). The second type of CAS found in seed is mitochondrial CAS (mit-CAS), which is precipitated by 60 to 70% (NH₄)₂SO₄ and has a pH optimum of 9.5. Mitochondrial CAS is present at low levels in dry seed, and its activity increases greatly during imbibition in the seeds of all species tested. Exposure to C₂H₄ stimulated mit-CAS activity in seeds of rice, barley ( Hordeum vulgare cv. Hadakamugi). cucumber ( Cucumis sativus cv. Kagafushinari) and cocklebur ( Xanthium pennsylvanicum ). The increase in the mit-CAS activity in cocklebur in response to C₂H₄ commenced alter a lag period of 2 to 3 h when the duration of soaking was short (16 h), but commenced without a lag period when the seeds were soaked for three months. Application of both chloramphenicol and cycloheximide to the axial and cotyledonary tissues of cocklebur seeds strongly inhibited growth as well as the increase in mit-CAS activity. It is postulated that the mit-CAS is synthesized de novo during imbibition and that its activity is regulated by C₂H₄, CO₂ which also promotes seed germination in some species, was ineffective m stimulating mit-CAS activity in cocklebur seeds.     

Endocrine, osmoregulatory, respiratory and haematological parameters in flounder exposed to the water soluble fraction of crude oil

Flounders Pleuronectes flesus with an implanted vascular catheter were exposed to a 50% dilution of the water soluble fraction (WSF) of Omani crude oil (c. 6ppm total aromatic hydrocarbons) and serial blood samples taken to determine their endocrine status (cortisol, catecholamines and thyroid hormones) and the resultant and/or causal physiological (haematological, ionoregulatory and respiratory) disturbances. This resulted in a progressive increase in plasma cortisol concentrations from 3 h onwards (rising from 18 to 51 ng ml⁻¹ after 48-h exposure), and increased plasma glucose concentrations indicating a generalized stress response. Plasma T3 and T4 concentrations of both control and WSF-exposed groups declined progressively over the experimental period; exposure to the WSF of crude oil further depressed plasma T4 concentrations but not plasma T₃ concentrations relative to those of control fish. Plasma osmolality and sodium and chloride concentrations were stable in WSF-exposed fish, however, plasma potassium concentrations were increased significantly at the 24-and 48-h sampling points. The most profound physiological disturbance in WSF-exposed fish was a dramatic decline in blood oxygen content (CvO₂) (from 2–8 to 0–8 ml 100 ml⁻¹ after 48-h exposure), which is likely to be the cause of the increased plasma noradrenaline concentrations from 3 h onwards. Increased noradrenaline is likely in turn to have been responsible for the significant increase in blood haematocrit and blood haemoglobin at the 3-h sampling point, although the dominant effect in the longer-term was a significant decline in both of these haematological parameters.