Interactions of blue light and inorganic carbon supply in the control of light-saturated photosynthesis in brown algae

Photosynthetic capacities of five species of brown algae in red light were found to be strongly limited by the inorganic carbon supply of natural sea water. Under these conditions, pH 8·2 and dissolved inorganic carbon concentration (DIG) of 2·1 mol m^?3, a short pulse of blue light was found to increase the subsequent rate of photosynthesis in saturating red light. The degree of blue light stimulation varied between species, ranging from an increase of over 200% of the original rate in Colpomenia peregrins to only 10% in Dictyota dichotoma. Increasing the DIG concentration of sea water by bicarbonate addition resulted in carbon saturation of photosynthesis in all five species. Blue light stimulation was greatly reduced at these higher DIG concentrations. The response in Laminaria digitata was examined in more detail by manipulation of pH and DIG to produce solutions with different concentrations of dissolved CO₂. At a CO₂ concentration typical of normal sea water (12·4 mmol m^?3), blue light treatment increased photosynthetic rate by approximately 50%. Blue light stimulation was increased to over 150% at CO₂ concentrations below that of sea water, whereas at concentrations above that of sea water, the effect was diminished. Therefore, the effect of blue light on photosynthetic capacity appears to involve an increase in the rate of supply of carbon dioxide to the plant.     

The role of acidification in gibberellic acid- and fusicoccin-induced elongation growth of lettuce hypocotyl sections

The roles of gibberellic acid (GA₃) and fusicoccin (FC) in the elongation growth and acidification of the medium by excised hypocotyl sections of lettuce (Lactuca sativa L.) were investigated. Hypocotyl sections incubated in buffer without GA₃ elongate optimally at pH 4.0–4.25 while sections incubated with GA₃ show the same growth between pH 4.25 and 6.0. Preincubation of sections at pH 6.0 for 6 h does not affect the subsequent elongation response to acidic medium (pH 4.25); however, the sections become refractory to further acid treatment after their initial burst of growth in response to pH 4.25. Sections made refractory to acid are responsive to GA₃ application, however, and the rate of growth in response to GA₃ of sections pretreated for 6 h at pH 4.25 is 85% of that of sections pretreated at pH 6.0. Although preincubation of sections for 48 h in medium at pH 6.0 abolishes the GA₃ response, it does not affect the response to buffer at pH 4.25. FC stimulates elongation growth in letuce hypocotyls at an optimal concentration of 1 M, and pretreatment of sections at pH 4.25 does not affect this elongation response. Although both GA₃ and FC increase elongation of the section, neither causes appreciable acidification of the medium. Addition of KCl or NaCl to FC-treated sections causes rapid medium acidification but addition of salts to GA₃-treated tissue does not cause acidification. Abrasion of the hypocotyl to remove the cuticle does not enhance acidification of the medium by the sections nor deos it affect elongation of the sections in response to GA₃ or FC. Medium acidification by the sections is not a passive process since it is abolished both by low temperature (2° C) and metabolic inhibitors (carbonyl cyanide-m-chlorophenyl-hydrazone, azide). The acidification of the medium by barley (Hordeum vulgare L.) roots in response to FC is also dependent on the presence of KCl. We conclude that the acid-growth hypothesis does not explain GA₃- or FC-induced elongation in lettuce hypocotyls.Abbreviations FC tusicoccin - GA₃ gibberellic acid - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid - CCCP carbonyl cyanide-m-chlorophenyl-hydrazone - MES 2-(N-morpholino)ethanesulphonic acid - Tris tris-(hydroxymethyl)aminomethane     

Structure and function of the elongation sink in the stems of higher plants.*

Abstract. Application of an acid aerosol generated from an aqueous HC1 or HNO₃ solution (pH 1-2) to the hypocotyl segment of Vigna sesquipedalis, excised from the elongation zone and abraded with alumina gel, induced rapid elongation growth comparable with that induced by aerosol generated from neutral 1 mol m^?3 1AA aqueous solution. The activity of the first electrogenic ion pump, whose activity is known to be stimulated by IAA aerosol in advance of the increase in growth rate, was little affected by acids. The latent period of the growth response to acids was only 1 min shorter than that to IAA (mean value: 12min), or than the period from the stimulation of the electrogenic ion pump activity by IAA to the beginning of growth acceleration (mean value: 4 min). The growth rate, together with the activities of the first and the second ion pump, was reduced by anoxia in the presence of acid. The acid N₂-sol was ineffective to stimulate the elongation under anoxia. The acid aerosol was ineffective to stimulate the elongation of a non-abraded segment with intact cuticle layer on its surface.     

The effects of temperature and IAA concentration on the latent period for IAA-induced rapid growth of Avena coleoptile segments

Summary Indoleacetic acid buffered at pH 7.0 induces a high growth rate in Avena coleoptile segments after a latent period, the duration of which is dependent upon both IAA concentration and temperature. A minimum latent period of 7.3 min is observed at 25° C with 10^-3 M IAA in phosphate buffer at pH 7.0.In contrast, 5×10^-3 M IAA made up in 0.01 M KH₂PO₄ alone, promotes elongation almost immediately, regardless of whether the segments have been previously incubated in 0.01 M KH₂PO₄ at pH 4.7, or phosphate buffer at pH 7.0. This immediate response is unaffected by 10^-4 M KCN which abolishes the rapid growth induced by 5×10^-3 M IAA buffered at pH 7.0 but does not affect the immediate appearance of low-pH-induced growth. Since we consistently find solutions of 5×10^-3 M IAA in 0.01 M KH₂PO₄ to have a pH of 3.5, our results indicate that the immediate growth response elicited by this solution is attributable to its low pH rather than to the presence of IAA as previously reported in the literature.     

Short-term kinetics of elongation growth of gibberellin-responsive lettuce hypocotyl sections

The short-term kinetics of growth of the excised lettuce (Lactuca sativa L.) hypocotyl were characterized with respect to the effects of gibberellic acid (GA₃), indole-3-acetic acid (IAA), KCl and pH. A Hall-device-based, miniaturized, linear displacement transducer was developed to measure the growth of 2-mm hypocotyl sections with 1-m resolution. Following treatment with GA₃, a lag time of less than 10 min was typically followed by an increase in growth rate with two acceleration phases, reaching a final elevated rate within about 1 h. The kinetics of the response to GA₁, a mixture of GA₄ and GA₇, and GA₉ were similar to the response to GA₃. There was no response to IAA treatment either in the presence or absence of GA₃. KCl alone had no effect on the growth rate, but caused an increase in rate when added after GA₃, with a lag time of usually less than 1 h. Responses to pH changes had lag times of a few minutes in all cases. A shift from H₂O to pH 6 buffer inhibited growth, while a shift from H₂O to pH 4 buffer resulted in a transient increase to a rate comparable to that induced by GA₃. A shift from pH 6 to pH 5 caused an increase in growth rate, followed by a gradual decline to an H₂O control rate after more than an hour. The responses to GA₃ at pH 4 and pH 5 were similar to that found for addition of GA₃ to water controls.Abbreviations GA gibberellin - GA₃ gibberellic acid - GA₁, GA₄₊₇, GA₉ gibberellins A₁, A₄₊₇, A₉ - IAA indole-3-acetic acid     

The effects of pH and calcium on the growth ofLeucaena leucocephala in an oxisol and ultisol soil

Leucaena was grown for eleven weeks in a pH and calcium amended oxisol and ultisol to determine whether poor growth in acid soils is related to calcium deficiency or low pH induced effects, such as aluminium toxicity. Soil pH was ameliorated by the addition of either CaCO₃, or SrCO₃, while CaCO₃ or Ca(NO₃)₂ were used to modify calcium supply. In both soils, CaCO₃, and SrCO₃ application resulted in an increase in pH and a reduction in exchangeable aluminium although the response of leucaena to the applied amendment varied between the two soils. In the oxisol there was little effect of increased pH on growth, but a marked response to Ca application. In the ultisol, growth was improved by increasing pH but there was no response to increased calcium. The effects of liming on these soils are discussed in relation to alternative strategies available for utilising leucaena and other tree legumes.     

Seasonal Effects in the Hormonal Control of Growth in the Submerged Aquatic Macrophyte Ceratophyllum demersum

The season dependent changes in growth response to treatment with auxin or gibberellin were studied in the aquatic macrophyte Ceratophyllum demersum. Control plants show, under experimental conditions, a maximum growth in length in February. In the same period most of the lateral buds appear. Growth of the lateral buds occurs later. IAA causes a stimulation of growth in length from late November or December until February, in concentrations of 10^?9M and 10^?6M. There is almost no stimulation of lateral bud formation by IAA, only a slight increase from late November until December occurs by the lowest concentrations used. The highest concentration used, 10^?4M, is in most cases supraoptimal for lateral bud formation; only when plants become dormant (August), this high dose may stimulate the process. GA₃, in concentrations of 10^?9, 10^?6 or 10^?4M, exhibits a dose dependent increase of the response with respect to growth in length and lateral bud formation. The response occurs earlier than that for IAA: already early in November, or December, until February. Growth of the lateral buds may show only a slight stimulation by IAA as well as GA in winter. From February until April all GA concentrations used could cause a small increase of the growth of sprouts. In the case of IAA, however, only the lowest concentration could cause a small increase.     

PREY CAPTURE AND FACTORS CONTROLLING TRAP NARROWING IN DIONAEA (DROSERACEAE)

Traps of Dionaea which have captured prey by a rapid closure mechanism continue to close with the lobes of the trap assuming a tightly appressed condition called the narrowed phase. Traps fed ants, which make up about one-third of the prey captured in the field, assumed the narrowed condition within about 7 h of feeding. Ants were alive and capable of delivering mechanical stimulation to the trigger hairs until about 8 h after feeding when they were apparently killed by acid fluid (pH 2–3) secreted by the trap at that time. That stimulation of trigger hairs delivered by the insect during this period is sufficient to cause both the narrowing and acid secretion was demonstrated by laboratory experiments in which both of these responses were initiated within 5 h by stroking the trigger hairs with clean, dry nylon bristles. Such purely mechanical stimuli, delivered to the trigger hairs, produced action potentials in the trap throughout the period of stimulation. Chemicals such as Na⁺, NH₄⁺, urea, and amino acids were capable of producing the narrowing response within one or two days. There was a 50% response to NaCl and NH₄Cl solutions of about 6 mM and a 90% response to 34 mm solutions. Urea, L-lysine, and glycine produce a significant response at 50 mm but can cause necrosis of the trap tissue at concentrations above 50 mm . Salt-free ovalbumen (0.5 and 5.0 g/l) and KCl, CaCl₂, and D-glucose were ineffective in initiating the narrowing response. The level of Na⁺, NH₄⁺, and amino acids necessary to elicit the narrowing response is within the range of concentrations previously demonstrated to exist in the haemolymph and tissues of prey known to be captured by Dionaea in the field. The data is consistent with the hypothesis that narrowing and secretion are initiated by mechanical stimulation and maintained by chemical stimulation after the death of the prey.     

Inhibition of cell growth by bafilomycin A1, a selective inhibitor of vacuolar H+-ATPase

Summary Bafilomycin A₁, a potent selective inhibitor of vacuolar H⁺-ATPase, inhibited the growth of a variety of cultured cells dose-dependently, including golden hamster embryo and NIH-3T3 fibroblasts, whether or not they were transformed, and PC12 and HeLa cells. The concentration of bafilomycin A₁ for 50% inhibition of cell growth ranged from 10 to 50 nM. The dose response was nearly parallel with that of the bafilomycin A₁-induced lysosomal pH increase. The degree of pH increase for growth inhibition produced by bafilomycin A₁ was similar to that produced by NH₄Cl in which little difference was recognized in effect among cell types.     

pH-Dependent electrical properties and buffer permeability of theNecturus renal proximal tubule cell

Summary Necturus kidneys were perfused with Tris-buffered solutions at three different pH values, i.e. 7.5, 6.0 and 9.0. A significant drop in fluid absorption occurred at pH 6.0, whereas pH 9.0 did not increase volume flow significantly. When acute unilateral, i.e. either in the lumen or the peritubular capillaries, and bilateral pH changes were elicited in both directions from 7.5 to 9.0 at a constant Tris-butyrate buffer concentration, both peritubular membrane potential differenceV ₁ and transepithelial potential differenceV ₃ hyperpolarized, independently of the side where the change in pH was brought about. Acid perfusions at pH 6.0 caused a similar response but of opposite sign. Analysis of the potential changes shows that pH influences not only the electromotive force and resistance of the homolateral membrane, but also the electrical properties of the paracellular path. Interference of pH with Na, Cl or K conductance was assessed. Any appreciable role for sodium or chloride was excluded, whereas the potassium transference number (t _K) of the peritubular membrane increased 16% in alkaline pH. However, this increase accounts only for 19 to 36% of the observed hyperpolarization. Since changes in Tris-butyrate buffer concentration at constant pH do not affect V₁ or V₃ considerably, the hyperpolarization in pH 9 cannot be explained by an elevation in internal pH only, or by a Tris-H⁺ ion diffusion potential only. The role of the permeability of the buffers: bicarbonate, butyrate and phosphate, in determining electrical membrane parameters was evaluated. Transport numbers of the buffer anions ranked as follows:t _HCO3>t _butyrate>t _phosphate. It is concluded that modulation of membrane potential by extracellular pH is mediated primarily by a change in peritubular cell membranet _K and additionally by membrane currents carried by buffer anions.     

Boric acid stimulates the plasma membrane H+-ATPase of ungerminated lily pollen grains

The stimulation of the plasma membrane (PM) H⁺-ATPase by boric acid was studied on a microsomal fraction (MF) obtained from ungerminated, boron-dependent pollen grains of Lilium longiflorum Thunb. which usually need boron for germination and tube growth. ATP hydrolysis and H+ transport activity increased by 14 and 18%, respectively, after addition of 2-4 mM boric acid. The optimum of boron stimulation was at pH 6.5-8.5 for ATP hydrolysis and at pH 6.5-7.5 for H⁺ transport. No boron stimulation was detected when vanadate was added to the MF, whereas an increase of 10-20% in ATP hydrolysis and H⁺ transport was still measured in the presence of inhibitors specific for V -type ATPase (nitrate and bafilomycin) and F-type ATPase (azide), respectively. A vanadate-sensitive increase in ATP hydrolysis activity was also observed in partially permeabilized vesicles (0.001%[w/v] Triton X-100) suggesting a direct interaction between borate and the PM H⁺-ATPase rather than a weak acid-induced stimulation. Additionally, we measured the effect of boron on membrane voltage (V_m) of ungerminated pollen grains and observed small hyperpolarizations in 48% of all experiments. Exposing pollen grains to a more acidic pH of 4 caused a depolarization, followed in some experiments by a repolarization (21%). In the presence of 2 mM boron such hyperpolarizations, perhaps caused by an enhanced activity of the H⁺-ATPase, were measured in 58% of all tested pollen grains. The effects of boron on V_m may be reduced by additional stimulation of a K⁺ inward current of opposite direction to the H⁺-ATPase. All experiments indicate that boron stimulates an electrogenic transport system in the plasma membrane which is sensitive to vanadate and has a pH optimum around 7, i.e. the plasma membrane H⁺-ATPase. A boron-increased PM H⁺-ATPase activity in turn may stimulate germination and growth of pollen tubes.     

Cell elongation in the grass pulvinus in response to geotropic stimulation and auxin application

Summary Horizontally-placed segments of Avena sativa L. shoots show a negative geotropic response after a period of 30 min. This response is based on cell elongation on the lower side of the leaf-sheath base (pulvinus). Triticum aestivum L., Hordeum vulgare L. and Secale cereale L. also show geotropic responses that are similar to those in Avena shoots. The pulvinus is a highly specialized organ with radial symmetry and is made up of epidermal, vascular, parenchymatous and collenchymatous tissues. Statoliths, which are confined to parenchyma cells around the vascular bundles, sediment towards the gravitational field within 10–15 min of geotropic stimulation. Collenchymatous cells occur as prominent bundle caps, and in Avena, they occupy about 30% of the volume of the pulvinus. Geotropic stimulation causes a 3- to 5-fold increase in the length of the cells on the side nearest to the center of the gravitational field. Growth can also be initiated in vertically-held pulvini by the application of indole-3-acetic acid, 1-naphthaleneacetic acid or 2.4-dichlorophenoxyacetic acid. 2.3.5.-triiodobenzoic acid interferes with growth response produced by geotropic stimulation as well as with the response caused by auxin application. Gibberellic acid and kinetin have no visible effect on the growth of the pulvinus. Polarization microscopy shows a unique, non-uniform stretching of the elongating collenchymatous cells. Nonelongated collenchymatous cells appear uniformally anisotropic. After geotropic stimulation or auxin application, they appear alternately anisotropic and almost isotropic. Such a pattern of cell elongation is also observed in collenchyma cells of geotropically-stimulated shoots of Rumex acetosa L., a dicotyledon.Abbreviations 2.4-D 2.4-dichlorophenoxyacetic acid - GA₃ gibberellic acid - IAA indole-3-acetic acid - NAA l-naphthaleneacetic acid - TIBA 2.3.5-triiodobenzoic acid     

Analysis of acid-soil stress in sorghum genotypes with emphasis on aluminium and magnesium interactions

Acid-soil stress in 12 sorghum (Sorghum bicolor (L.) Moench) genotypes was attributed mainly to aluminium (Al) toxicity. Root damage and magnesium (Mg) deficiency are two independent aspects of plant sensitivity to Al, either in acid soil or in nutrient solution. At moderate soil acidity, Mg deficiency dominantly limited growth whilst at high acidity root damage overruled the effect of Mg deficiency on the growth response. In nutrient solutions containing Al, increased Mg supply improved both root development and Mg nutrition of plants, whereas increased calcium (Ca) supply, or nutrition with ammonium (NH₄) instead of nitrate (NO₃), alleviated root damage but amplified Mg deficiency. At lowered pH the syndrome of Al toxicity was more profound. The implications of Mg-Al interactions, root damage, Mg supply and genotype selection are elucidated.     

Interspecific variation in the growth response of plants to an elevated ambient CO2 concentration

The effect of a doubling in the atmospheric CO₂ concentration on the growth of vegetative whole plants was investigated. In a compilation of literature sources, the growth stimulation of 156 plant species was found to be on average 37%. This enhancement is small compared to what could be expected on the basis of CO₂-response curves of photosynthesis. The causes for this stimulation being so modest were investigated, partly on the basis of an experiment with 10 wild plant species. Both the source-sink relationship and size constraints on growth can cause the growth-stimulating effect to be transient.Data on the 156 plant species were used to explore interspecific variation in the response of plants to high CO₂. The growth stimulation was larger for C₃ species than for C₄ plants. However the difference in growth stimulation is not as large as expected as C₄ plants also significantly increased in weight (41% for C₃ vs. 22% for C₄). The few investigated CAM species were stimulated less in growth (15%) than the average C₄ species. Within the group of C₃ species, herbaceous crop plants responded more strongly than herbaceous wild species (58%vs. 35%) and potentially fast-growing wild species increased more in weight than slow-growing species (54%vs. 23%). C₃ species capable of symbiosis with N₂-fixing organisms had higher growth stimulations compared to other C₃ species. A common denominator in these 3 groups of more responsive C₃ plants might be their large sink strength. Finally, there was some tendency for herbaceous dicots to show a larger response than monocots. Thus, on the basis of this literature compilation, it is concluded that also within the group of C₃ species differences exist in the growth response to high CO₂.Abbreviations LAR leaf area ratio - LWR leaf weight ratio - NAR net assimilation rate - PS_a rate of photosynthesis per unit leaf area - RGR relative growth rate - RWR root weight ratio - SLA specific leaf area     

Growth,toxicity and oxidative stress of a cultured cyanobacterium (Dolichospermum sp.) under different CO2/pH and temperature conditions

Cyanobacteria blooms are a worldwide nuisance in fresh, brackish and marine waters. Changing environmental conditions due to upwelling, changed mixing conditions or climate change are likely to influence cyanobacteria growth and toxicity. In this study, the response of the toxic cyanobacterium Dolichospermum sp. to lowered pH (?0.4 units by adding CO₂) and elevated temperature (+4°C) in an experimental set‐up was examined. Growth rate, microcystin concentration and oxidative stress were measured. The growth rate and intracellular toxin concentration increased significantly as a response to temperature. When Dolichospermum was exposed to the combination of elevated temperature and high CO₂/low pH, lipid peroxidation increased and antioxidant levels decreased. Microcystin concentrations were significantly correlated with growth rates. Our results show, although oxidative stress increases when exposed to a combination of high CO₂/low pH and high temperature, that growth and toxicity increase at high temperature, suggesting that the cyanobacterium in general seems to be fairly tolerant to changes in pH and temperature. Further progress in identifying biological responses and predicting climate change consequences in estuaries experiencing cyanobacteria blooms requires a better understanding of the interplay between stressors such as pH and temperature.     

Comparison of growth stimulation of HeLa cells,HL-60 cells,and mouse fibroblasts by coenzyme Q10

Summary The addition of coenzyme Q₁₀ to culture media stimulates the serum-free growth of HeLa, HL-60 cells, and mouse fibroblasts (Balb/3T3). With HeLa cells, the stimulation by coenzyme Q₁₀ is additive to the stimulation by ferricyanide, an impermeable electron acceptor for the transplasma membrane electron transport. This combined response to coenzyme Q₁₀ and ferricyanide is enhanced with insulin. -Tocopherylquinone can also stimulate the growth of HeLa cells, but vitamin K₁ is inactive. Specificity of quinone effects is indicated. Serum-free growth of Balb/3T3 and SV 40 transformed BaIb/3T3 (SV/T2) cells is also stimulated by coenzyme Qio with stimulation similar to HeLa cells. However, Balb/3T3 cells are not stimulated by ferricyanide, which does not increase the response to coenzyme Q₁₀. The transformed cells (SV/T2) respond better to ferricyanide alone, but the effects of coenzyme Qio and ferricyanide are not additive. Serum-free growth of HL-60 cells is stimulated dramatically by coenzyme Q₁₀. The extent of growth stimulation on HL-60 cells is almost six-fold that of HeLa or Balb/3T3 cells. The stimulation of NADH-ferricyanide reductase (a transmembrane redox enzyme) by coenzyme Q₁₀ with HL-60 cells is similar to their growth pattern in response to coenzyme Q₁₀. Unlike HL-60, HeLa and Balb/3T3 cells show little stimulation of ferricyanide reduction by coenzyme Q₁₀. The stimulatory effect on both ferricyanide reduction and cell growth by the short side-chain coenzyme Q₂ is much less than that of the long side-chain coenzyme Q₁₀. Ferricyanide reduction by HeLa cells is inhibited by coenzyme Q analogs such as 2,3-dimethoxy-5-chloro-6-naphthyl-mercapto-coenzyme Q and 2-methoxy-3-ethoxyl-5-methyl-6-hexadecyl-mercapto-coenzyme Q. However, these inhibitions are reversed by coenzyme Q₁₀. The growth inhibition of HL-60 cells by other coenzyme Q analogs, such as capsiacin can also be reversed by coenzyme Q₁₀. These data indicate that plasma membrane-based NADH oxidation or modification of the membrane quinone redox balance may be a basis for the growth stimulation.     

Differential effects of prazosin and rauwolsin on the release of prostaglandins I2 and E2 from the perfused mesenteric arterial bed of the rabbit following nerve stimulation

Sympathetic nerve stimulation of the perfused mesenteric arterial bed of the rabbit, , increase the secretion of prostaglandin (PG)I₂ and PGE₂. Prazosin (4.8 × 10⁻⁶), and α₁ adrenergic receptor antagonist, inhibited this inrease in release of PGI₂ but not of PGE₂ whereas rauwolsin (10⁻⁷ M), an α₂ adrenergic receptor antagonist, inhibited the increase in release of PGE₂ but not of PGI₂. Prazosin (10⁻⁶ M) completely blocked the vasoconstrictor response to nerve stimulation, and to norepinephrine and phenylephrine administration, suggesting there to be little of an α₂ adrenergic receptor component in this response. It is concluded that the increase in PGI₂ release follows the activation of α₁ adrenergic receptors and is therefore post-junctional in origin, whereas the increase in PGE₂ release follows the activation of α₂ adrenergic receptors and may be pre- and/or post-junctional in origin.Indomethacin (2.8 × 10⁻⁷, 5.6 × 10⁻⁷ and 1.12 × 10^{−6 M} did not affect the vasoconstrictor responses to nerve stimulation at 10 Hz, whereas rauwolsin (10⁻⁷ M) in the presence of indomethacin substantially increased them. These results indicate that PGE₂ does not regulate norepinephrine release following nerve stimulation at 10 Hz to rabbit mesenteric arteries, and that the inhibition of norepinephrine release following stimulation of α₂ pre-junctional receptors is independent of PG involvement.     

Metal Reduction at Low pH by a Desulfosporosinus species: Implications for the Biological Treatment of Acidic Mine Drainage

We isolated an acid-tolerant sulfate-reducing bacterium, GBSRB4.2, from coal mine-derived acidic mine drainage (AMD)-derived sediments. Sequence analysis of partial 16S rRNA gene of GBSRB4.2 revealed that it was affiliated with the genus Desulfosporosinus. GBSRB4.2 reduced sulfate, Fe(III) (hydr)oxide, Mn(IV) oxide, and U(VI) in acidic solutions (pH 4.2). Sulfate, Fe(III), and Mn(IV) but not U(VI) bioreduction led to an increase in the pH of acidic solutions and concurrent hydrolysis and precipitation of dissolved Al³⁺. Reduction of Fe(III), Mn(IV), and U(VI) in sulfate-free solutions revealed that these metals are enzymatically reduced by GBSRB4.2. GBSRB4.2 reduced U(VI) in groundwater from a radionuclide-contaminated aquifer more rapidly at pH 4.4 than at pH 7.1, possibly due to the formation of poorly bioreducible Ca-U(VI)-CO₃ complexes in the pH 7.1 groundwater.     

Responses of the red blood cells from two high-energy-demand teleosts, yellowfin tuna (Thunnus albacares) and skipjack tuna (Katsuwonus pelamis), to catecholamines

In fishes, catecholamines increase red blood cell intracellular pH through stimulation of a sodium/proton (Na⁺/H⁺) antiporter. This response can counteract potential reductions in blood O₂ carrying capacity (due to Bohr and Root effects) when plasma pH and intracellular pH decrease during hypoxia, hypercapnia, or following exhaustive exercise. Tuna physiology and behavior dictate exceptionally high rates of O₂ delivery to the tissues often under adverse conditions, but especially during recovery from exhaustive exercise when plasma pH may be reduced by as much as 0.4 pH units. We hypothesize that blood O₂ transport during periods of metabolic acidosis could be especially critical in tunas and the response of rbc to catecholamines elevated to an extreme. We therefore investigated the in vitro response of red blood cells from yellowfin tuna (Thunnus albacares) and skipjack tuna (Katsuwonus pelamis) to catecholamines. Tuna red blood cells had a typical response to catecholamines, indicated by a rapid decrease in plasma pH. Amiloride reduced the response, whereas 4,4′diisothiocyanatostilbene-2,2′-disulphonic acid enhanced both the decrease in plasma pH and the increase in intracellular pH. Changes in plasma [Na⁺], [Cl⁻], and [K⁺] were consistent with the hypothesis that tuna red blood cells have a Na⁺/H⁺ antiporter similar to that described for other teleost red blood cells. Red blood cells from both tuna species were more responsive to noradrenaline than adrenaline. At identical catecholamine concentrations, the decrease in plasma pH was greater in skipjack tuna blood, the more active of the two tuna species. Based on changes in plasma pH, the response of red blood cells to catecholamines from both tuna species was less than that of rainbow trout (Oncorhynchus mykiss) red blood cells, but greater than that of cod (Gadus morhua) red blood cells. Noradrenaline had no measurable influence on the O₂ affinity of skipjack tuna blood and only slightly increased the O₂ affinity of yellowfin tuna blood. Our results, therefore, do not support our original hypothesis. The catecholamine response of red blood cells from high-energy-demand teleosts (i.e., tunas) is not enhanced compared to other teleosts. There are data on changes in cardio-respiratory function in tunas caused by acute hypoxia and modest increases in activity, but there are no data on the changes in cardio-respiratory function in tunas accompanying the large increases in metabolic rate seen during recovery from exhaustive exercise. However, we conclude that during those instances where high rates of O₂ delivery to the tissues are needed, tunas' ability to increase cardiac output, ventilation volume, blood O₂ carrying capacity, and effective respiratory (i.e., gill) surface area are probably more important than are the responses of red blood cells to catecholamines. We also use our data to investigate the extent of the Haldane effect and its relationship to blood O₂ and CO₂ transport in yellowfin tuna. Yellowfin tuna blood shows a large Haldane effect; intracellular pH increases 0.20 units during oxygenation. The largest change in intracellular pH occurs between 40–100% O₂ saturation, indicating that yellowfin tuna, like other teleosts, fully exploit the Haldane effect over the normal physiological range of blood O₂ saturation. Accepted: 27 March 1998