Emission of volatile sulfur compounds from spruce trees

Spruce (Picea Abies L.) trees from the same clone were supplied with different, but low, amounts of plant available sulfate in the soil (9.7-18.1 milligrams per 100 grams of soil). Branches attached to the trees were enclosed in a dynamic gas exchange cuvette and analyzed for the emission of volatile sulfur compounds. Independent of the sulfate supply in the soil, H₂S was the predominant reduced sulfur compound continuously emitted from the branches with high rates during the day and low rates in the night. In the light, as well as in the dark, the rates of H₂S emission increased exponentially with increasing water vapor flux from the needles. Approximately 1 nanomole of H₂S was found to be emitted per mole of water. When stomata were closed completely, only minute emission of H₂S was observed. Apparently, H₂S emission from the needles is highly dependent on stromatal aperture, and permeation through the cuticle is negligible. In several experiments, small amounts of dimethylsulfide and carbonylsulfide were also detected in a portion of the samples. However, SO₂ was the only sulfur compound consistently emitted from branches of spruce trees in addition to H₂S. Emission of SO₂ mainly proceeded via an outburst starting before the beginning of the light period. The total amount of SO₂ emitted from the needles during this outburst was correlated with the plant available sulfate in the soil. The diurnal changes in sulfur metabolism that may result in an outburst of SO₂ are discussed.     

Sulfur dynamics in mineral horizons of two northern hardwood soils. A column study with 35S

Sulfur dynamics of two Spodosols were ascertained using soil columns constructed from homogenized mineral soil from nothern hardwood ecosystems at the Huntington Forest (HF) in the Adirondack Mountains of New York and Bear Brook Watershed in Maine (BBWM). Columns were leached for 20 weeks with a simulated throughfall solution with³⁵SO₄ ^2-. Sulfur constituents were similar to those of other Spodosols, with the organic S fractions (C-bonded S and ester sulfate) constituting over 90% of total S. HF soil columns had higher total S (14.9 mol S g^-1) than that for the BBWM soil columns (7.4 mol g^-1) primarily due to higher C-bonded S in the former.Initially, adsorbed SO₄ ^- accounted for 5 and 4% of total S for the BBWM and HF soil columns, respectively. After 20 weeks, adsorbed SO₄ ^2- decreased (81%) in BBWM and increased (33%) in HF soil columns. For both HF and BBWM soil columns, C-bonded S increased and ester sulfate decreased, but only for HF columns was there a net mineralization of organic S (5.6% of total S). The greatest decrease in ester sulfate occurred at the top of the columns.Leaching of³⁵S was less than 0.5% of the³⁵S added due to its retention in various S constituents. There was an exponential decrease in³⁵S with column depth and most of the radioisotope was found in C-bonded S (70–88 and 70–91% for BBWM and HF, respectively). The rapid turnover of adsorbed SO^2- ₄ was reflected in its high specific activity (834 and 26 kBq mol^-1 S for BBWM and HF, respectively). The lower specific activity of adsorbed SO₄ ^2- in HF was attributable to greater isotopic dilution by non-radioactive SO^2- ₄ derived from greater organic S mineralization in the HF versus the BBWM columns.Both soil columns initially had high levels of NO^- ₃ which resulted in the generation of H⁺ and net retention of SO₄ ^2- in the early phase of the experiment due to pH dependent sulfate adsorption; later NO₃ ^- decreased and SO₄ ^2- was desorbed. Leaching of NIO₃ ^- and SO₄ ^2- was correlated with losses of Mg²⁺ and Ca²⁺ of which the latter was the dominant cation.Analyses using both S mass balances and radioisotopes corroborate that for BBWM soil columns, SO^2- ₄ adsorption-desorption dominated the S biogeochemistry while in HF soil columns, organic S mineralization-immobilization processes were more important. It is suggested that similar techniques can be applied to soils in the field to ascertain the relative importances of SO₄ ^2- adsorption processes and organic S dynamics.     

Influence of anions on the potassium status and productivity of kiwifruit (Actinidia deliciosa) vines

The effects of K fertiliser (160 kg ha^-1) applied with Cl^- or SO₄ ^2- as the accompanying anion on the K nutrition of kiwifruit (Actinidia deliciosa var. deliciosa) were assessed in a field experiment, using vines with varying degrees of K deficiency. Leaf K concentrations in spring were significantly higher for vines receiving KCl, compared to those receiving K₂SO₄. This effect did not interact significantly with the degree of K deficiency, and persisted for about 6 weeks. Subsequently there was no significant difference between the leaf K concentrations for the vines receiving KCl or K₂SO₄. Applying K as KCl increased the leaf Cl concentration, especially in spring, while applying K as K₂SO₄ had no significant effect on the leaf S concentration at that time. These results implied a greater requirement for organic acid anions for K⁺ uptake from K₂SO₄ than from KCl, and the importance of organic acid anions for K⁺ uptake from different sources of K fertiliser is discussed. This transient effect of the accompanying anion on leaf K status was associated with large effects on flowering, and fruit yields were about 28% higher for plants receiving KCl rather than K₂SO₄.The effects on growth and tissue nutrient composition of varying the concentrations of Cl^-, NO₃ ^-, SO₄ ^2- and H₂PO₄ ^- around the roots of kiwifruit vines were examined in a solution culture experiment. For H₂PO₄ ^-, plant growth was very similar over a wide range of rates of addition. For the other anions, the range between deficiency and toxicity was clearly delineated. For Cl^- and NO₃ ^-, toxicity was associated with high tissue concentrations of Cl and N, respectively, and was consistent with competition for uptake between Cl^- and NO₃ ^-. However, for SO₄ ^2-, toxicity was associated with only a small increase in the tissue S concentration relative to that associated with maximum growth, and appeared to result more from effects on uptake of other anions and cations rather than from direct effects of high tissue S concentrations.It is concluded that the sensitivity of kiwifruit to the anion accompanying K⁺ in fertiliser may be related to the unusually high requirement for Cl previously reported for this species.     

Leaching of solutes by the action of acidic rain: a comparison of efflux from twigs and single needles of Picea abies (L. Karst.)

Abstract. Leaching of inorganic cations (K⁺, Mg²⁺) and in some cases of inorganic anions and sugars from detached twigs and single needles of spruce Picea abies L. Karst.) in the presence of acid rain (H₂SO₄, 1 mol m^?3) or salt solutions (Na₂ SO₄, 1 mol m^?3) was examined under laboratory conditions. Cation leaching (as percentage of the total water soluble ion content of the tissue per hour) was: K⁺: 0.01-0.02%; Mg²⁺: 0.005-0.01%; Ca²⁺: 0.1-0.2%. Leaching rates of anions were even lower than that and concentrations in the leachate were often below the detection limit of anion chromatography. Spraying with H₂SO₄ (pH 2.95, 1 mol m^?3) increased leaching only transiently. Similar effects were found when Na₂SO₄ was used instead of H₂SO₄. The transiently enhanced leaching was apparently due to H⁺/cation or cation/cation exchange at the twig or leaf surfaces. Feeding of K⁺ or Al³⁺ through the stems increased leaching of all cations within a few hours, again demonstrating rapid ion exchange in the apoplast. Leaching of potassium and magnesium from single needles occurred at similar relative rates as from twigs. Loss of Ca²⁺ ions, however, was even smaller from needles than from twigs. Apparently, a large part of the Ca²⁺ lost from twigs originated from the bark and not from the needles. Efflux of ions from longitudinal needle sections was about 1000 times taster than the rates obtained with intact needles, indicating that the cuticle was the main barrier Preventing solute loss. In relation to the total amount of mineral nutrients in trees, leaching is considered to be too small to be the primary cause of damage to trees stressed by acid rain, as has been suggested in the literature.     

Actions of Hydrogen Sulfide and ATP-Sensitive Potassium Channels on Colonic Hypermotility in a Rat Model of Chronic Stress

Objective

To investigate the potential role of hydrogen sulphide (H₂S) and ATP-sensitive potassium (K_ATP) channels in chronic stress-induced colonic hypermotility.

Methods

Male Wistar rats were submitted daily to 1 h of water avoidance stress (WAS) or sham WAS (SWAS) for 10 consecutive days. Organ bath recordings, H₂S production, immunohistochemistry and western blotting were performed on rat colonic samples to investigate the role of endogenous H₂S in repeated WAS-induced hypermotility. Organ bath recordings and western blotting were used to detect the role of K_ATP channels in repeated WAS.

Results

Repeated WAS increased the number of fecal pellets per hour and the area under the curve of the spontaneous contractions of colonic strips, and decreased the endogenous production of H₂S and the expression of H₂S-producing enzymes in the colon devoid of mucosa and submucosa. Inhibitors of H₂S-producing enzymes increased the contractile activity of colonic strips in the SWAS rats. NaHS concentration-dependently inhibited the spontaneous contractions of the strips and the NaHS IC₅₀ for the WAS rats was significantly lower than that for the SWAS rats. The inhibitory effect of NaHS was significantly reduced by glybenclamide. Repeated WAS treatment resulted in up-regulation of Kir6.1 and SUR2B of K_ATP channels in the colon devoid of mucosa and submucosa.

Conclusion

The colonic hypermotility induced by repeated WAS may be associated with the decreased production of endogenous H₂S. The increased expression of the subunits of K_ATP channels in colonic smooth muscle cells may be a defensive response to repeated WAS. H₂S donor may have potential clinical utility in treating chronic stress- induced colonic hypermotility.     

Stable sulfur isotope analysis of SO2 pollution impact on vegetation

Summary The ³⁴S value of SO₂ emitted by natural gas refineries is about +25, which is higher than that for non-industrial sulfur sources in our study areas. Terrestrial mosses absorb SO₂ from the atmosphere and have a ³⁴S value which is directly related to the degree of SO₂ stress to which they are subjected. The ³⁴S values for conifer needles are lower than for mosses at the same collection site, which indicates that trees obtain sulfur from both atmospheric and soil sources.Potted conifers were transferred to sites differing in their degree of SO₂ stress. This difference is reflected by the change of ³⁴S values of their needles. SO₂ absorbant pot covers, such as charcoal and moss, reduce the amount of airborne sulfur which is available to tress. Moss also may reduce SO₂ absorbed by soils in forest stands. We have used analysis of ³⁴S values to (1) help define SO₂ dispersion patterns; (2) reveal the rates at which plants accumulate this pollutant; and (3) associate suspected SO₂ injury more closely to an emission source.     

Soil organic sulfur dynamics in a coniferous forest

Sulfate microbial immobilization and the mineralization of organic S were measured in vitro in soil horizons (LFH, Ae, Bhf, Bf and C) of the Lake Laflamme watershed (47°17 N, 71°14 O) using ³⁵SO₄. LFH samples immobilized from 23 to 77% of the added ³⁵SO₄ within 2 to 11 days. The ³⁵SO₄ microbial immobilization increased with temperature and reached an asymptote after a few days. The mineral soil generally immobilized less than 20% of the added ³⁵SO₄, and an asymptote was reached after 2 days. An isotopic equilibrium was rapidly reached in mineral horizons. A two-compartment (SO₄ and organic S) model adequately described ³⁵SO₄ microbial immobilization kinetics. The active organic reservoir in the whole soil profile represented less than 1% of the total organic S. The average concentrations of dissolved organic S (DOS) in the soil solutions leaving the LFH, Bhf and Bf horizons were respectively 334, 282 and 143 µgL^–1. Assuming that the DOS decrease with soil depth corresponded to the quantities adsorbed in the B horizons, we estimated that 12 800 kgha^–1 of organic S could have been formed since the last glaciation, which is about 13 times the size of the actual B horizons reservoirs. Our results suggest that the organic S reservoirs present in mineral forest soils are mostly formed by the DOS adsorption resulting from incomplete litter decomposition in the humus layer. The capability of these horizons to immobilize SO₄ from the soil solution would be restricted to a 1% active fraction composed of microorganisms. Despite their refractory nature, these reservoirs can, however, be slowly decomposed by microorganisms and contribute to the S-SO₄ export from the watershed in the long term.     

Emission of Hydrogen Sulfide by Leaf Tissue in Response to l-Cysteine

Leaf discs and detached leaves exposed to l-cysteine emitted a volatile sulfur compound which was proven by gas chromatography to be H₂S. This phenomenon was demonstrated in all nine species tested (Cucumis sativus, Cucurbita pepo, Nicotiana tabacum, Coleus blumei, Beta vulgaris, Phaseolus vulgaris, Medicago sativa, Hordeum vulgare, and Gossypium hirsutum). The emission of volatile sulfur by cucumber leaves occurred in the dark at a similar rate to that in the light. The emission of leaf discs reached the maximal rate, more than 40 picomoles per minute per square centimeter, 2 to 4 hours after starting exposure to l-cysteine; then it decreased. In the case of detached leaves, the maximum occurred 5 to 10 h after starting exposure. The average emission rate of H₂S during the first 4 hours from leaf discs of cucurbits in response to 10 millimolar l-cysteine, was usually more than 40 picomoles per minute per square centimeter, i.e. 0.24 micromoles per hour per square decimeter. Leaf discs exposed to 1 millimolar l-cysteine emitted only 2% as much as did the discs exposed to 10 millimolar l-cysteine. The emission from leaf discs and from detached leaves lasted for at least 5 and 15 hours, respectively. However, several hours after the maximal emission, injury of the leaves, manifested as chlorosis, was evident. H₂S emission was a specific consequence of exposure to l-cysteine; neither d-cysteine nor l-cystine elicited H₂S emission. Aminooxyacetic acid, an inhibitor of pyridoxal phosphate dependent enzymes, inhibited the emission. In a cell free system from cucumber leaves, H₂S formation and its release occurred in response to l-cysteine. Feeding experiments with [³⁵S]l-cysteine showed that most of the sulfur in H₂S was derived from sulfur in the l-cysteine supplied and that the H₂S emitted for 9 hours accounted for 7 to 10% of l-cysteine taken up. ³⁵S-labeled SO₃²⁻ and SO₄²⁻ were found in the tissue extract in addition to internal soluble S²⁻. These findings suggest the existence of a sulfur cycle which converts l-cysteine to SO₄²⁻ through cysteine desulfhydration.     

Possible interference of fertilization in the natural recovery of a declining sugar maple stand in southern Quebec

A five year study was conducted in a 100–120 year old even-aged sugar maple stand in southern Quebec (46°07N 73° 56W; 305 m altitude) to explore the effect of different fertilization formulations aimed at 1) correcting the most common nutrient deficiencies observed in declining maple stands (K and Mg), 2) decreasing soil acidity, and 3) simulating enrichment with atmospheric N. Seven fertilizer mixtures were applied in the spring of 1987: 400 kg ha^-1 of K₂SO₄, CaCO₃, CaMg(CO₃)₂, (NH₄)₂SO₄, complete fertilizer (Maplegro) and 800 kg ha^-1 of an equal mixture of K₂SO₄+CaCO₃ or K₂SO₄+CaMg(CO₃)₂. The site was divided into twenty-four 25×25 m plots and treatments including control were replicated three times. Leaves and soils (organic and mineral) were sampled in 1987, 1988 and 1991. Trees were cored at 1.2 m to measure their response in diameter growth. The application of K₂SO₄+CaMg(CO₃)₂ was the only treatment that significantly increased (+13%) the average growth rate over the five year period after fertilization. The application of (NH₄)₂SO₄, Maplegro, CaMg(CO₃)₂ and K₂SO₄ reduced growth relative to the control for the five year period by 29, 24, 20 and 12 %, respectively. Positive and negative effects on growth can be explained mainly in terms of changes in leaf K. Both the application of Maplegro and (NH₄)₂SO₄ increased soil P availability. Overall, the rate of growth showed a cubic pattern of change over the 5 year period with peaks in 1988 and 1991. Trees in control plots went from a limiting foliar status of Ca and Mg, and surplus N in 1987 to a surplus of Ca and Mg, and lower N concentration in 1991. Our results suggest that nutrient deficiencies observed at our site were associated with a disturbance of the biogeochemical cycle of nutrients rather than soil nutrient depletion.Abbreviations BS base saturation - CEC cation exchange capacity - DRIS diagnosis and recommendation integrated system     

Factors affecting soil acidification under legumes I. Effect of potassium supply

This study examined the effect of K (as K₂SO₄) supply on acid production under N₂-fixing plants of lupin (Lupinus angustifolius L. cv. Gungurru) and clover (Trifolium subterraneum L. cv. Dalkeith) grown in a K-deficient soil with a low pH buffer capacity for 55 days in the glasshouse at 20/12 °C (day/night). Increasing K supply up to 240 mg K kg^-1 soil markedly increased plant growth of both species but clover growth was more responsive than lupin. Growing plants for 55 days decreased soil pH by 0.65–0.85 units under lupin and 0.45–0.83 units under clover. The amounts of H⁺ produced per kg biomass (specific acid production) were the highest at the nil K supply, generally decreased with increasing K level up to 30 mg K kg^-1 under lupin and up to 120 mg K kg^-1 soil under clover and only slightly increased with further increasing K under lupin. Increasing K₂SO₄ supply proportionally increased plant uptake of K and SO ₄ ^2- but generally decreased concentrations of Ca, Mg, Na, P and Cl. Specific acid production correlated well with concentrations of excess cations and ash alkalinity, and total acid production was strongly correlated with total excess cations and total ash alkalinity in plants. These relationships were not affected by K treatment and species. Specific acid production also correlated with plant Ca concentration but not with K concentration. In addition, lupin and clover extruded similar amounts of H⁺ per kg biomass produced. It is suggested that application of K₂SO₄ does not have a significant impact on acid production by lupin and clover.     

Stomatal SO2 uptake and sulfate accumulation in needles of Norway spruce stands (Picea abies) in Central Europe

Monthly uptake rates and the annual deposition of gaseous SO₂ via the stomata of six Norway spruce canopies (Picea abies (L.) Karst.) in Germany (Königstein im Taunus, Witzenhausen, Grebenau, Frankenberg, Spessart, Fürth im Odenwald) were calculated (i) from statistical response functions of stomatal aperture depending on meteorological data, and (ii) from the synchronously measured SO₂ immission at these stands. The stomatal response functions had been derived on the basis of thorough stomatal water conductance measurements in the field. Calculations of the SO₂ conductance of spruce twigs and SO₂ uptake rates via stomata need continuously measured complete data sets of the (i) light intensity, (ii) air temperature, (iii) air humidity and (iv) SO₂ concentration in spruce forests from all the year. These data were recorded half hourly in different German spruce forests. The apparent needle water vapour pressure difference and transpiration rates were calculated from meteorological data. Additional use of canopy through flow data in dry years allowed the estimation of the mean stomatal conductance for H₂O and SO₂ of whole spruce canopies. The annual SO₂ uptake of a mean unit needle surface in spruce forests was 32% of the SO₂ uptake rate of exposed needles at the top of spruce crowns. There is significant SO₂ uptake all the year. The mean SO₂ dose at all sites and years received through the stomata was (0.25±0.07) mol SO₂ m^-2 (total needle surface) (nPa Pa^-1)^-1 (annual mean of SO₂ immission; 1 nPa (SO₂) Pa^-1 (air) = 1 ppb) day^-1 (vegetation period per year). Comparison of calculated SO₂ uptake rates into needles with measured SO₄ ^2- accumulation rates in needles from the mentioned sites and additionally from Würzburg, Schneeberg (Fichtelgebirge) and from three sites in the eastern Erzgebirge (Höckendorf, Kahleberg, Oberbärenburg) revealed that oxidative SO₂ detoxification (SO₄ ^2- formation) dominates only at sites with high SO₂ immission and short vegetation periods. Under these conditions 70 to 90% of the annual stomatal SO₂ uptake is detoxified via SO₄ ^2- accumulation in needles. Cations are needed for neutralization of accumulating SO₄ ^2- which are inavailable to support growth. Thus, SO₂ induces a dominant and competitive additional nutrient cation demand, cation deficiency symptoms and enhanced needle loss (spruce decline symptoms) mainly at sites, where the ratio R=(SO₂ immission): (length of the vegetation period) is higher than R=0.07 nPa Pa^-1 day^-1. Correlation analysis of the relative needle loss versus the SO₂-dependent SO₄ ^2- formation rate revealed a significant increase of needle loss at the 98% level (Student). At sites with small SO₂ immission and long vegetation periods (R<0.07 nPa Pa^-1 day^-1) reductive SO₂ detoxification via growth (and/or phloem export of SO₄ ^2-) is not kinetically overburdened. Under these conditions only 30% of the annual SO₂ uptake is detoxified via SO₄ ^2- formation and spruce decline is small or absent. On the basis of the critical value R0.07 nPa Pa^-1 day^-1 recommended SO₂ immission limits can be deduced on a mere ecophysiological basis. These deduced values are close to the proposed SO₂ immission limits of the IUFRO, WHO and the UNECE.     

A malic Acid permease in isolated vacuoles of a crassulacean Acid metabolism plant

Pine (Pinus silvestris L.) trees subjected to relatively low concentration of SO₂ in the field emit H₂S from the needles, as demonstrated by gas chromatographic analysis after preconcentration on a molecular sieve. H₂S is the only reduced sulfurous compound emitted from SO₂ fumigated leaves. The emission is light and SO₂ concentration dependent. Pine trees in the field and in laboratory experiments continue to emit H₂S several hours after the termination of prolonged SO₂ fumigation. The maximum emission rates observed from pine trees in the field and in laboratory experiments, 14 and 20 nanomoles per milligram chlorophyll per hour respectively, are about the activity expected for the sulfur assimilation pathway in the chloroplasts.     

Re-assessment of Wundsch's (1940) ‘H2S-Oscillatoria-Lake’ type using the eutrophic Lake Scharmützel (Brandenburg, NE Germany) as an example

Thienemann's 1922 biological lake classification indicates the increase in the trophic level of lakes. It is based on the sucession of the disappearance of certain benthic indicator organisms in relation to the gradient of a decreasing O₂concentration in the deep water, i.e. from O₂-sensitive Chironomidae spp. (non-biting midges) to the less sensitive Chaoboridae (phantom midges) larvae. As early as the mid 1930s, several lakes in Brandenburg, e.g. Lake Scharmützel, belonged to the last category of this classification. They were O₂-deficient in deep water during summer and lacked the Chironomidae larvae. Simultaneously, filamentous cyanobacteria (Oscillatoriales) appeared. This lead to the replacement of Thienemann's indicators, i.e. O₂ by H₂S and Chironomidae by Oscillatoriales, and to Wundsch's 1940 new H₂S-Oscillatoria-Lake type. Since H₂S and Oscillatoriales were not clearly identified as symptoms of eutrophication, it is not justified to use them to characterise a separate lake type. However, these indicators are of ecological importance, since the regional and common creeping increase in SO₄ ^2- concentration favoures the current high H₂S formation. The successive deterioration in O₂ conditions, the increase in the extent of H₂S formation related to the decrease in species diversity clearly indicates that Lake Scharmützel reached a qualitatively new state of eutrophication within 60 years.     

Localization and capacity of proton pumps in roots of intact sunflower plants

Proton extrusion by roots of intact sunflower plants (Helianthus annuus L.) was studied in nutrient solutions or in agar media with a pH indicator. Proton extrusion was enhanced by either iron deficiency, addition of fusicoccin, or single salt solutions of ammonium or potassium salts. The three types of proton extrusion differ in both localization along the roots and capacity. From their sensitivity to ATPase inhibitors it seems justified to characterize them as proton pumps driven by plasma membrane APTases.

Enhanced proton extrusion induced by preferential cation uptake from (NH₄)₂SO₄ or K₂SO₄ was uniformly distributed over the whole root system. In contrast, the enhancement effect of fusicoccin was confined to the basal root zones and that of iron deficiency to the apical root zones. Also the rates of proton extrusion per unit of root fresh weight differed remarkably and increased in the order: Fusicoccin K₂SO₄ < (NH₄)₂SO₄ < iron deficiency.

Under iron deficiency the average values of proton extrusion for the whole root system are 5.6 micromoles H⁺ per gram fresh weight per hour; however, for the apical root zones values of about 28 micromoles H⁺ can be calculated. This high capacity is most probably related to the iron deficiency-induced formation of rhizodermal transfer cells in the apical root zones. It can be assumed that the various types of root-induced acidification of the rhizosphere are of considerable ecological importance for the plant-soil relationships in general and for mobilization of mineral nutrients from sparingly soluble sources in particular.

     

Carbon disulfide oxidation by a microbial consortium from a trickling filter

Biological oxidation rates of CS₂ with a mixed microbial culture obtained from a trickling filter were optimal with 3 mM CS₂, pH 7, 30°C and SO₄ ^2– below 25 g l^–1. Degradation rates were 3.4 mg CS₂/g_proteinmin and 13.8 mg H₂S/g_proteinmin. The concentrations of intermediates (H₂S, COS and S°) and the product (SO₄ ^2–) of CS₂ oxidation were measured. The biological oxidation was due principally to Gram negative bacteria.     

On the dependence of salt tolerance of beans (Phaseolus vulgaris L.) on soil water matric potentials

Summary Bean plants (Kora cv) were grown in potted soil artificially salinized by adding NaCl and CaCl₂ to the irrigation water to obtain an electrical conductivity of the soil saturation extract (EC_e) thirty days after emergence of 0.1, 0.3, 0.5 and 0.7 S/m at 25°C and a sodium adsorption ratio (SAR) of 4 (mmol/l)². Thereafter, plants were irrigated when soil water matric potential (_M) was in the range of –20 to –30 kPa (wet treatment) and when _M was in the range of –40 to –60 kPa (dry treatment).Transpiration rates (Tr) and leaf extension rates (LER) per plant or per unit of leaf area were decreased by increasing soil salinity and by decreasing soil moisture. However, a given decrement of _M produced a considerable larger decrement in Tr of LER than an equivalent decrement of soil water osmotic potential (₀). Absolute yields of green pods under wet treatments were from twice to one and a half time as large under the wet than under the dry treatment at equivalent values of ₀. Relative yields were reduced by 25% when EC_e were about 0.5 S/m and 0.7 S/m in the dry and wet treatment respectively. Salt tolerance data of crops may not have a quantitative interest when soil irrigation regimes under which they were obtained are not specified.     

Evidence for two functionally distinct hydrogenases in Anacystis nidulans

The effect of growth conditions on aerobic and anaerobic hydrogenase activities of Anacystis nidulans was studied. It was found that the two hydrogenase activities both of which were confined to the particulate fraction of cell-free extracts correlated in an opposite way with growth temperature: The algae were always grown photoautotrophically in presence of H₂ but after growth at 25° C a significant oxyhydrogen reaction contrasted with negligible photoreduction rates while the opposite was true after growth at 40°C. A similar correlation between incubation temperature and induction of the respective hydrogenase activity was also observed with resting cells.Kinetic analysis of the two different types of hydrogenase — catalysed reactions with Anacystis membranes yielded the following Michaelis-Mentenparameters: K _M=55 M H₂ and v _max=0.12 mol H₂ per min and mg protein for the oxyhydrogen reaction, and K _M=170 M H₂ and v _max=0.3 mol H₂ per min and mg protein for the photoreductions. Also the dependences of oxyhydrogen and of photoreduction activities on pH and on temperature were measured; both pH and temperature profiles were found to be markedly different for each type of H₂-supported reaction.The results are discussed as pointing to the possible occurrence of two functionally distinct hydrogenase enzymes which can be synthesized by Anacystis in response to the conditions of induction.Abbreviations BO p-benzoquinone - CAP chloramphenicol - chl chlorophyll - cytc horse heart cytochrome c - DCMU 3-(34-dichlorophenyl)-1,1-dimethylurea - DCPIP 2,6-dichlorophenolindophenol - fd ferredoxin - FeCy ferricyanide - MB methylene blue - MV methyl viologen - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid - MES 2-(N-morpholino)-ethanesulfonic acid - PIPES piperazine-N,N-bis-(2-ethanesulfonic acid) - tricine N-tris-(hydroxymethyl)-methylglycine - Tris tris-(hydroxymethyl)-aminomethan     

Renal basolateral membrane anion transporter characterized by a fluorescent disulfonic stilbene

Summary The fluorescence enhancement of 4,4-dibenzamido-2,2-disulfonic stilbene (DBDS) upon binding to membranes was used to examine proximal tubule stilbene binding sites. Equilibrium binding studies of DBDS to renal brush border (BBMV) and basolateral membrane vesicles (BLMV) were performed using a fluorescence enhancement technique developed for red blood cells (A.S. Verkman, J.A. Dix and A.K. Solomon,J. Gen. Physiol. 81:421–449, 1983). In the absence of transportable anions, DBDS bound reversibly to a single class of sites on BLMV isolated from rabbit (K _d =3.8 m) and rat (3.2 m); 100 m dihydro-4,4-diisothiocyano-2,2-disulfonic stilbene (H₂DIDS) blocked >95% of binding. H₂DIDS inhibitable DBDS binding was not detected using rat or rabbit BBMV. In rabbit BLMV, DBDSK _d doubled with 10mm SO₄, 50mm HCO₃ and 100mm Cl, but was not altered by Na or pH (6–8). In stopped-flow experiments the exponential time constant for DBDS binding slowed with SO₄, HCO₃ and Cl, but was unaffected by Na. These results are consistent with competitive binding of DBDS and anions at an anion transport site. To relate DBDS binding data to anion transport inhibition we used³⁵SO₄ uptake to characterize several modes of rabbit BLM anion transport: H/SO₄ and Na/SO₄ cotransport, and Cl/SO₄ countertransport. Each transport process was electroneutral and was inhibited by H₂DIDS, furosemide, probenecid, chlorothiazide and DBDS. The apparentK _t 's for DBDS (3–20 m) were similar toK _d for DBDS binding. These studies define a class of anion transport sites on the proximal tubule basolateral membrane measureable optically by a fluorescent stilbene.     

Electrochemical identification of microbially mediated hydrogen sulfide oxidation

The process of H₂S oxidation by the phototrophic bacteriaThiocapsa roseopersicina andChlorobium phaeobacteroides, respectively, was monitored using a Pt-glass-Ag⁰, Ag₂S electrode combination without liquid junction. Due to the resulting pe(pH) and pH₂S plottings three steps can be distinguished: oxidation of H₂S to an S(0) state, oxidation of S (0) to SO₄ ^2–, and oxidation of the remaining H₂S directly to SO₄ ^2–. Differences between the investigated bacteria exist with respect to their individual oxidation strategies.Thiocapsa apparently stops oxidizing H₂S at pH₂S 7.5 (e.g. 10^–7.5M H₂S) and shifts to the utilization of the intracellularly stored S (0). In contrastChlorobium utilizes its extracellularly stored sulfur parallel to the extracellular H₂S fraction. The corresponding Pt-sensor responses (pe₇ values) were found to be similar to the corresponding partial redox equilibria (p₇ values) of H₂S oxidation stoichiometries as proposed by Van Niel (1931) and Trüper (1964). It is concluded that the recording of pe enables investigators to understand (and control) in situ redox processes, independent of their thermodynamic equilibration, only bound to changes of electroactivity vs. sensor.     

The effect of calcium carbonate and potassium sulphate on the efficiency of ammonium as tested by barley seedlings

Summary Using the Neubauer technique and the slope ratio, it was found that efficiency of (NH₄)₂SO₄ in the presence of 12.5 or 25.0 g CaCO₃ per pot relative to its efficiency without CaCO₃ was 0.6 and 0.47, respectively.Application of 4 or 6 mg K/pot, the efficiency of (NH₄)₂SO₄ was 0.56 and 0.33, respectively, relative, to its efficiency without K application.The Dean's a value was found to vary with percent CaCO₃ or K₂SO₄ application.