Carbon Dioxide and Ethylene Control of Spore Germination in Onoclea sensibilis L

Regulation of spore germination in the fern Onoclea sensibilis L. was investigated by applying CO₂ alone and in combination with ethylene. Sterile spores were sown aseptically on Knops solution in loosely capped culture tubes, enclosed individually in 2-liter chambers, and grown under continuous white light. When maintained in enclosed containers with the ethylene-absorbent mercuric perchlorate and with atmospheres enriched up to 2% CO₂ (v/v), spores germinated without any inhibition. Higher levels of applied CO₂ were progressively inhibitory. Inhibition by CO₂ was reversible. When CO₂ was permitted to escape and spores were exposed subsequently to ambient laboratory air, recovery from inhibition occurred within 48 hours. Also, inhibition by CO₂ was specific, since the same degree of inhibition resulted regardless of whether spores were treated with exogenous CO₂ for 48, 72, or 96 hours. The effect on germination of 1 μl/l added ethylene depended upon the amount of applied CO₂. When containers of KOH were enclosed and ambient CO₂ was absorbed, inhibition of germination by 1 μl/l exogenous ethylene was 90%. When CO₂ was applied in concentrations from 0.25 to 1.0% (v/v), CO₂ increasingly antagonized the inhibitory action of 1 μl/l added ethylene. Thus, photoinduced germination of spores was regulated by competitively interacting levels of CO₂ and ethylene.     

Effects of ethylene and carbon dioxide on the germination of osmotically inhibited lettuce seed

Lettuce seeds (Lactuca sativa L.) used in this study germinated 98% at 25 C in light or dark. Their germination was completely inhibited by 0.20 m NaCl, 0.35 m mannitol, or polyethylene glycol 6000 (−7 bars) under continuous light when germination tests were made in Petri dishes. Approximately 50% germination occurred in sealed flasks due to endogenously produced C₂H₄ and CO₂. Removal of either or both gases prevented germination. In the presence of endogenous CO₂, addition of C₂H₄ (0.5 to 16 microliters/liter) stimulated 95 to 100% germination (after 5 days) only in the light, but the rate of germination was dependent on C₂H₄ concentration. At 16 microliters/liter C₂H₄, full germination occurred within 72 hours. Addition of up to 3.2% CO₂ had no adverse effect on the C₂H₄ action. Higher concentrations or the complete absence of CO₂ reduced both rate and total germination. CO₂ alone was ineffective.     

Investigation of factors influencing spore germination of Paenibacillus polymyxa ACCC10252 and SQR-21

Bioorganic fertilizer containing Paenibacillus polymyxa SQR-21 showed very good antagonistic activity against Fusarium oxysporum. To optimize the role of P. polymyxa SQR-21 in bioorganic fertilizer, we conducted a study of spore germination under various conditions. In this study, l-asparagine, glucose, fructose and K⁺ (AGFK), and sugars (glucose, fructose, sucrose, and lactose) plus l-alanine were evaluated to determine their ability to induce spore germination of two strains; P. polymyxa ACCC10252 and SQR-21. Spore germination was measured as a decrease in optical density at 600 nm. The effect of heat activation and germination temperature were important for germination of spores of both strains on AGFK in Tris–HCl. l-Alanine alone showed a slight increase in spore germination; however, fructose plus l-alanine significantly induced spore germination, and the maximum spore germination rate was observed with 10 mmol l⁻¹ l-alanine in the presence of 1 mmol l⁻¹ fructose in phosphate-buffered saline (PBS). In contrast, fructose plus l-alanine hardly induced spore germination in Tris–HCl; however, in addition of 10 mmol l⁻¹ NaCl into Tris–HCl, the percentages of OD₆₀₀ fall were increased by 19.6% and 24.3% for ACCC10252 and SQR-21, respectively. AGFK-induced spore germination was much more strict to germination temperature than that induced by fructose plus l-alanine. For both strains, fructose plus l-alanine-induced spore germination was not sensitive to pH. The results in this study can help to predict the effect of environmental factors and nutrients on spore germination diversity, which will be beneficial for bioorganic fertilizer storage and transportation to improve the P. polymyxa efficacy as biological control agent.     

The role of carbon dioxide in glucose metabolism of Bacteroides fragilis

The effect of CO₂ concentration on growth and glucose fermentation of Bacteroides fragilis was studied in a defined mineral medium. Batch culture experiments were done in closed tubes containing CO₂ concentrations ranging from 10% to 100% (with appropriate amounts of bicarbonate added to maintain the pH at 6.7). These experiments revealed that CO₂ had no influence on growth rate or cell yield when the CO₂ concentration was above 30% CO₂ (minimum available CO₂–HCO ₃ ^- , 25.5 mM), whereas a slight decrease in these parameters was observed at 20% and 10% CO₂ (available CO₂–HCO ₃ ^- , 17 and 8.5 mM, respectively). If CO₂–HCO ₃ ^- concentrations were below 10 mM, the lag phase lengthened and a decrease in maximal growth rate and cell yield were observed. The amount of acetate made decreased, while d-lactate concentration increased. A net production of CO₂ allowed growth under conditions of extremely low concentrations of added CO₂.When B. fragilis was grown in continuous culture with 100% CO₂ or 100% N₂, the dilution rate influenced the concentrations of acetate, succinate, propionate, d-lactate, l-malate and formate formed. Decreasing the dilution rate favored propionate and acetate production under both conditions. When the organism was grown with 100% N₂, the amount of propionate formed was greater than the amount of succinate formed at all dilution rates. Except at slow dilution rates the reverse was true when 100% CO₂ was used. B. fragilis was unable to grow at dilution rates faster than 0.154 h^-1 when grown with 100% N₂; the Y _glc ^max was 67.9 g DW cells/mol glucose and m _s was 0.064 mmol glucose/g DW·h. If the gas atmosphere was 100% CO₂ the organism was washed out of the culture when the dilution rate exceeded 0.38 h^-1; the Y _glc ^max was 59.4 g DW cells/mol glucose and m _s was 0.094 mmol glucose/g DW·h.Measurement of the phosphoenolpyruvate (PEP) carboxykinase (E.C. 4.1.1.49) with whole, permeabilized cells of B. fragilis showed an increase of specific enzyme activity with decreasing CO₂ concentrations. The mechanisms used by B. fragilis to adjust to low levels of CO₂ are discussed.     

Land plants of amphibious Littorella uniflora (L.) Aschers. maintain utilization of CO2 from the sediment

Summary Submerged macrophytes of the isoetid life form derive the majority of their CO₂ for photosynthesis from the sediment. The experiments described here were designed to test the hypothesis that root uptake of CO₂ is important also in the terrestrial form of Littorella uniflora. The results of ¹⁴CO₂ experiments showed that sediment CO₂ contributed 56% of the total fixation at 0.1mm CO₂ in the rhizosphere, 83% at 0.5mm and 96% at 2.5mm. Sediment CO₂ in emergent Littorella stands ranged from 0.1 to 1.0mm and averaged 0.5mm. Measurements of the net CO₂ exchange over the leaves showed an even higher dependence of the sediment as CO₂ source. Littorella leaves had no stomata at the base and densities (ca. 100 mm^–2) typical of terrestrial plants at the tip, allowing sediment-derived CO₂ to be supplied along the length of the leaf. The stomata permit supply of CO₂ from the air during periods of reduced sediment CO₂ concentrations (e.g. if the sediment dries up) and regulate transpiration.     

Development of dependence on aerial respiration in Polypterus senegalus (Cuvier)

The respiratory behaviour and partitioning of O₂ uptake between air and water were investigated in Polypterus genegalus using continuous-flow and two-phase respirometers and lung gas replacement techniques P. senegalus rarely resorts to aerial respiration under normal conditions. Partitioning of O₂ consumption depends on the activity and age of fish and the availability of aquatic oxygen. Immature fish (12–22 g) cannot utilize aerial O₂ but older fish exhibit age-dependent reliance on aerial respiration in hypoxic and hypercarbic waters. Pulmonary respiration accounts for 50% of the total requirement at aquatic O₂ concentrations of about 3.5 mg · l^–1 (or CO₂ of about 5%) and fish rely exclusively on aerial respiration at O₂ concentrations of less than 2.5 mg · l^–1. Branchial respiration is initially stimulated by hypercarbia (CO₂: 0.5–0.8%) but increased hypercarbia (CO₂ – 1%) greatly depresses (by over 90%) brancial respiration and initiates (CO₂: 0.5%) and sustains pulmonary respiration.     

The physiology of spore-negative and spore-positive nodules ofMyrica gale

The physiology of spore-negative and spore-positive root nodules was investigated inMyrica gale L. grown in water culture in a growth chamber. Spore(–) nodules were induced withFrankia cultures and spore(+) nodules with crushed nodules. Gas exchange was measured in a flow-through system.The time course of acetylene reduction following addition of acetylene was essentially the same in both spore(–) and spore(+) nodules with a stable maximum between 2 and 4 minutes followed by a steep decline to a minimum (37% of the maximum) between 9 and 30 minutes depending on the plant. The minimum was followed by a partial recovery. Nodule CO₂ evolution showed a similar pattern but the minimum rate (83% of the maximum) was not nearly as low.Plants nodulated with one spore(–) and one spore(+) strain were compared at 6, 8 and 10 weeks after inoculation. At 6 weeks the spore(–) plants had 52% greater specific nitrogenase activity and 46% more biomass than the spore(+) plants. At 8 and 10 weeks, however, the differences between plants with spore(–) and spore(+) nodules became smaller.Plants nodulated with 4 spore(–) and 5 spore(+) strains were compared at 8 weeks after inoculation. Collectively the spore(–) plants exhibited a 32% greater specific nitrogenase activity, a 15% lower energy cost of nitrogenase activity (CO₂/C₂H₄), and invested 31% less biomass in nodules than the spore(+) plants. The spore(–) plants also produced 16% more biomass indicating that spore(–) strains are generally more desirable than spore(+) strains. However, two spore(+) strains were as effective as the spore(–) strains.     

Communicating junctions and calmodulin: Inhibition of electrical uncoupling inXenopus embryo by calmidazolium

Summary This paper reports the inhibitory effects of calmidazolium (CDZ), a calmodulin inhibitor, on electrical uncoupling by CO₂. Membrane potential and coupling ratio (V ₂/V₁) are measured in two neighboring cells ofXenopus embryos (16 to 64 cell stage) for periods as long as 5.5 hr. Upon exposure to 100% CO₂, control cells consistently uncouple even if the CO₂ treatments are repeated every 15 min for 2.5 hr. CDZ (5×10^–8–1×10^–7 m) strongly inhibits uncoupling. The inhibition starts after 30, 50 and 60 min of treatment with 1×10^–7, 7×10^–8 and 5×10^–8 m CDZ, respectively, is concentration-dependent and partially reversible. In the absence of CO₂, CDZ also improves electrical coupling. CDZ has no significant effect on membrane potential and nonjunctional membrane resistance. These data suggest that calmodulin or a calmodulin-like protein participates in the uncoupling mechanism.     

Spatial and temporal variations of dissolved gases (CH4, CO2, and O2) in peat cores

Spatial and temporal variations in the concentrations of dissolved gases (CH₄, CO₂, and O₂) in peat cores were studied using membrane inlet mass spectrometry (MIMS). Variations in vertical gas profiles were observed between random peat cores taken from hollows on the same peat bog. Methane concentrations in profiles (0–30 cm) generally increased with depth and reached maximum values in the range of 200–450 m CH₄ below about 13-cm depth. In some profiles, a peak of dissolved methane was observed at 7-cm depth. Oxygen penetrated to approximately 2-cm depth in the hollows. The sampling probe was used to continuously monitor CH₄, CO₂, and O₂ concentrations at fixed depths in peat cores over periods of several days. The concentration of dissolved CO₂ and O₂ at 1-cm depth oscillated over a 24-h period with the maximum of CO₂ concentration corresponding with the minimum of 0₂. Diurnal variations in CO₂ but not CH₄ were measured at 15-cm depth; dissolved CO₂ levels decreased during daylight hours to a constant minimum concentration of 4.85 mm. This report also describes the application of MIMS for the measurement of gaseous diffusion rates in peat using an inert gas (argon); the value of D, the diffusion coefficient, was 2.07 × 10^–8 m² s^–1. Correspondence to: D. Lloyd     

Dependence of cell membrane conductances on bathing solution HCO 3 − /CO2 inNecturus gallbladder

Summary The effects of bathing solution HCO ₃ ^– /CO₂ concentrations on baseline cell membrane voltages and resistances were measured inNecturus gallbladder epithelium with conventional intracellular microelectrode techniques. Gallbladders were bathed in either low HCO ₃ ^– /CO₂ Ringer's solutions (2.4mm HCO ₃ ^– /air or 1mm HEPES/air) or a high HCO ₃ ^– /CO₂ Ringer's (10mm HCO ₃ ^– /1% CO₂). The principal finding of these studies was that the apical membrane fractional resistance (fR _a) was higher in tissues bathed in the 10mm HCO ₃ ^– /CO₂ Ringer's, averaging 0.87±0.06, whereasfR _a averaged 0.63±0.07 and 0.48±0.08 in 2.4mm HCO ₃ ^– and 1mm HEPES, respectively. Intraepithelial cable analysis was employed to obtain estimates of the individual apical (R _a) and basolateral membrane (R _b) resistances in tissues bathed in 10mm HCO ₃ ^– /1% CO₂ Ringer's. Compared to previous resistance measurements obtained in tissues bathed in a low HCO ₃ ^– /CO₂ Ringer's, the higher value offR _a was found to be due to both an increase inR _a and a decrease inR _b. The higher values offR _a and lower values ofR _b confirm the recent observations of others. To ascertain the pathways responsible for these effects, cell membrane voltages were measured during serosal solution K⁺ and Cl^– substitutions. The results of these studies suggest that an electrodiffusive Cl^– transport mechanism exists at the basolateral membrane of tissues bathed in a 10mm HCO ₃ ^– /1% CO₂ Ringer's, which can explain in part the fall inR _b. The above observations are discussed in terms of a stimulatory effect of solution [HCO ₃ ^– /PCO₂ on transepithelial fluid transport, which results in adaptive changes in the conductive properties of the apical and basolateral membranes.     

Responses of N fluxes and pools to elevated atmospheric CO2 in model forest ecosystems with acidic and calcareous soils

The objectives of this study were to estimate how soil type, elevated N deposition (0.7 vs. 7 g N m^–2y^–1) and tree species influence the potential effects of elevated CO₂ (370 vs. 570 mol CO₂ mol^–1) on N pools and fluxes in forest soils. Model spruce-beech forest ecosystems were established on a nutrient-rich calcareous sand and on a nutrient-poor acidic loam in large open-top chambers. In the fourth year of treatment, we measured N concentrations in the soil solution at different depths, estimated N accumulation by ion exchange resin (IER) bags, and quantified N export in drainage water, denitrification, and net N uptake by trees. Under elevated CO₂, concentrations of N in the soil solution were significantly reduced. In the nutrient-rich calcareous sand, CO₂ enrichment decreased N concentrations in the soil solution at all depths (–45 to –100%). In the nutrient-poor acidic loam, the negative CO₂ effect was restricted to the uppermost 5 cm of the soil. Increasing the N deposition stimulated the negative impact of CO₂ enrichment on soil solution N in the acidic loam at 5 cm depth from –20% at low N inputs to –70% at high N inputs. In the nutrient-rich calcareous sand, N additions did not influence the CO₂ effect on soil solution N. Accumulation of N by IER bags, which were installed under individual trees, was decreased at high CO₂ levels under spruce in both soil types. Under beech, this decrease occurred only in the calcareous sand. N accumulation by IER bags was negatively correlated with current-years foliage biomass, suggesting that the reduction of soil N availability indices was related to a CO₂-induced growth enhancement. However, the net N uptake by trees was not significantly increased by elevated CO₂. Thus, we suppose that the reduced N concentrations in the soil solution at elevated CO₂ concentrations were rather caused by an increased N immobilisation in the soil. Denitrification was not influenced by atmospheric CO₂ concentrations. CO₂ enrichment decreased nitrate leaching in drainage by 65%, which suggests that rising atmospheric CO₂ potentially increases the N retention capacity of forest ecosystems.     

Methodische Studien zur Cytochemie der Leukozytenphosphatasen

Zusammenfassung Es werden mehrere Techniken angeführt, die für den Phosphatasenachweis an Ausstrich- und Tupfpräparaten entwickelt wurden und hier sicher reproduzierbare Ergebnisse liefern. Im Prinzip handelt es sich um die Gomori-Technik des Nachweises der sauren Phosphatase (Bleisulfid-Methode). Benutzt wurden folgende Substrate: 1. Glycerophosphat beiph 6,6, 2. Aneurinpyrophosphat beiph 7,2, 3. Adenosin-3-monophosphorsäure beiph 6,0, 4. Adenosin-5-monophosphorsäure beiph 6,0. Die Inkubationszeit betrug 2–3 Std bei 37° C. Bei allen Substraten konnte die Reaktion durch vorhergehende Cyanidbehandlung komplett gehemmt werden.Auf die Reaktion der verschiedenen Blutzellen wird hingewiesen. Die starke Aktivität der Kapillaren und Retikulumzellen wird ausdrücklich betont. Die angeführten Methoden erscheinen besonders geeignet zum Studium der Retikulumzellen in bioptischen Knochenmarkspunktaten.

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Summary Several cytochemical techniques are described demonstrating the activity of phosphatases in blood and bone marrow smears. All theses methods are a modification of the lead-sulfide principle ofGomori for the demonstration of acid phosphatase. The following substrates were being used: 1. Sodium--Naphthylphosphate,ph 9,2. 2. Aneurinpyrophosphate (Cocarboxylase),ph 7,2. 3. Adenosine-3-monophosphoric acid,ph 6,0. 4. Adenosine-5-monophosphoric acid,ph 6,0. 5. Sodium-glycerophosphate,ph 6,6. The incubation time was 2–3 hours at 37° C. With all substrates the reaction was completely inhibited by preceding incubation in a 0,1 m cyanide solution.The reaction of different bone marrow cells is shortly described. The very strong activity of capillaries and reticulum cells is pointed out. The methods described seem especially useful for the study of reticulum cells in bone marrow smears.

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Mit 6 Textabbildungen     

Ouabain-induced cell swelling in rabbit cortical collecting tubule: NaCl transport by principal cells

Summary Ouabain had no effect on the volume of intercalated cells of DOCA-stimulated rabbit cortical collecting tubules, but caused principal cells to swell rapidly at an initial rate of 67% min., Principal cells swelled 133% then activated regulatory volume decrease mechanisms and shrank at an initial rate of –3%/min to a new volume 13% above control. The initial rate of ouabain swelling was completely inhibited by perfusate Na⁺ removal or reduced 95% by luminal addition of 10^–5 m amiloride. Luminal peritubular, or bilateral Cl^– removal each caused cell shrinkages of 10% and reduced the rate of ouabain swelling by 70, 85, and 99%, respectively. The presence of an apical Cl^– transport step in principal cells was confirmed by increasing luminal K⁺ from 5 to 53mm, which caused cell swelling of 22%. This volume increase was completely blocked by luminal Cl^– removal, but was unaffected by peritubular Cl^– substitution. Perfusion of CCT with 0.1mm acetazolomide, 0.1mm DPC or 0.5mm SITS caused principal cell shrinkages of 7–9% and reduced the rate of ouabain swelling by 60, 70, and 40%, respectively. The initial rate of ouabain swelling was inhibited 70% by bilateral CO₂/HCO₃ removal and 50% by whole animal acid loading. Taken together these results demounstrate that ouabain swelling is due to cellular NaCl accumulation and that Na⁺ enters the cell primarily through apical Na⁺ channels. Cellular Cl^– entry occurs at least partially through the apical membrane and may be mediated by a Cl^–/HCO ₃ ^– exchanger. Brief (45–90 sec) exposure of principal cells to ouabain is associated with a rapid inhibition of Na⁺ and/or Cl^– entry steps, whereas long-term (>5min) ouabvain exposure completely blocks one or both of these transport pathways.     

Role of vacuolar adenosine triphosphatase in the regulation of cytosolic pH in hepatocytes

The responses of the cytosolic pH of hepatocytes in suspension to agents affecting the activity of vacuolar adenosine triphosphatase (V-ATPase) and Na/H exchange have been studied. Changes of cytosolic pH were determined both with dual-wavelength excitation (500/440 nm) of the fluorescence of 2,7-bis-(2-carboxyethyl)-5(and 6)-carboxyfluorescein and from the distribution of ¹⁴C-dimethyloxazolidinedione; both methods gave very similar results. Changes of vesicular pH were determined by comparing the fluorescence of fluorescein isothiocyanate-dextran and rhodamine B isothiocyanate-dextran taken up by endocytosis. Nitrate, which inhibits V-ATPase in isolated organelles, induced a concentration-dependent acidification of the cytosol and alkalinization of vesicles, with maximal effects at 25–37.5 mm in each case, indicating that V-ATPase contributes to removal of cytosolic protons. On continued exposure to nitrate, the acidification underwent an amiloride-inhibitable reversal. At the higher concentrations of NO ₃ ^– , both cytosolic acidification and vesicular alkalinization were reduced or absent. Bafilomycin A₁ caused alkalinization of vesicular pH; cytosolic acidification was not observed, possibly because of other ionic exchanges. Recovery of cytosolic pH from an acid load (2 min exposure to 5% CO₂) was sensitive to both 25 mm NO ₃ ^– and to ouabain. The pH dependence of the nitrate effect was tested with media of different pH; the activity was negligible at cytosolic pH 6.2 and rose to a maximum at cytosolic pH 7.3. Treatment of hepatocytes with 0.5–1.0 mm ouabain resulted in an initial alkalinization (0.5–2 min duration) of the cytosol, followed by a spontaneous reversal and, on occasion, further acidification. The alkalinization was blocked by 25 mm NO ₃ ^– , but not by 25 mm gluconate. The results suggest that the cytosolic alkalinization is caused by a stimulation of H⁺ uptake by V-ATPase activity. We conclude that V-ATPases make an important contribution to the regulation of the cytosolic pH of hepatocytes.This work was supported in part by National Institutes of Health B.R.S. Grant 507 RR05417 to Temple University.     

Nutritional requirements of keratinophilic fungi and dermatophytes for conidial germination

Germination of spores of Chrysosporium crassitunicatum, Nannizzia fulva (+), Nannizzia fulva (–) and Trichophyton equinum was studied in the presence of various carbon and nitrogen sources. Effect of different temperatures on spore germination was also determined. Maximum spore germination within 24 hours was recorded when glucose was used as a carbon source for all the test fungi. Except sodium nitrate all the inorganic nitrogen sources enhanced the spore germination at 0.05% concentration. Most of the organic nitrogen sources used were found to be stimulatory for the spore germination of test fungi. Optimum temperature i.e. 28 °C supported maximum spore germination of all the test fungi within 24 hours. C. Crassitunicatum, N. fulva(+), N. fulva(–) could germinate upto 35 °C but beyond that no spore germination was noticed in these fungi. T. equinum could germinate at a higher temperature of 40 °C but the percentage of germination was very low.     

6-Phosphogluconate dehydrogenase in cell free extracts of Escherichia coli K-12

Summary Investigations into the properties of 6-PG dehydrogenase in cell free extracts of Escherichia coli revealed a pH optimum at pH 9.5 with a sharp decline on both sides of the optimum. The addition of 1.0×10^-2 m MgCl₂ produced maximal activity, whereas higher concentrations caused inhibition. The K _m values were 2.5×10^-4 m for 6-phosphogluconate and 2.5×10^-5 m for NADP⁺ as substrate. The enzyme was extremely stable for at least 5 hours if stored at 4°C in Tris–NaCl–MgCl₂ buffer at pH 7.5. 6-PG dehydrogenase activity was shown to be proportional to cell free extract concentration over the range 0–0.3 mg protein. An assay method based on the new optimal conditions has been established and has been shown to be 33% more sensitive than a number of commonly used methods.Meinem hochverehrten Lehrer Herrn Professor A. Rippel zum 80. Geburtstage.     

Determination of volatile nematode exudates and their effects on a nematode-trapping fungus

Volatile compounds exuded from axenically grown free-living nematodes were determined with gas chromatographic and mass spectrometric techniques. Carbon dioxide evolved from 5–200 nematodes was determined with an ampoule technique, whereas total ammonia (NH₃ + NH₄ ⁺) and acetic and propionic acids were determined by direct injection of water in which nematodes had been suspended for 1–3 days. CO₂ amounted to about 80 ng nematode^–1 d^–1, total ammonia to 1–5 ng, and acetic and propionic acids to 0.5 and 1.0 pg nematode^–1 d^–1.The effects of these compounds on induction of trap formation in the nematodetrapping fungusArthrobotrys oligospora were tested. CO₂ inhibited trap formation at 5–10% CO₂ in air (v/v), whereas ammonia stimulated trap formation in a certain concentration range. No effects of acetic and propionic acids were noted for the concentrations tested. The combined effects of these volatiles in the aqueous environment are discussed on the basis of stoichiometric considerations.     

The decomposition of organic compounds in soil

Summary The course of the CO₂ evolution rates of soil samples has been followed continuously in the absence and in the presence of various organic compounds. After an incubation period of 300 hours at 13 and 20°C the CO₂ evolution from pasture soil (containing 1.76% soil organic carbon) amounted to 0.13 and 0.44g CO₂–C.g soil^–1.h^–1, respectively. For arable soil (containing 1.20% soil organic carbon) the rates amounted to 0.04 and 0.09 g CO₂–C.g soil^–1.h^–1, respectively.At 20°C larger amounts of the organic substrates added to the soil supplied with 20 g NH₄NO₃–N.g soil^–1 were lost as CO₂ than at 13°C, indicating a higher efficiency of the growth of microorganisms at lower temperatures. In the absence of NH₄NO₃ the respiration rates were initially higher than in its presence, suggesting that a part of the soil microflora is inhibited by low concentrations of NH₄NO₃. The amounts of carbon lost were low for phenolcarboxylic acids with OH groups in the ortho position. The replacement of one of these groups by a methoxyl group resulted in a larger amount of the C lost as CO₂. The replacement of the COOH group by a C=C–COOH group had a decreasing effect on the decomposition of the phenolic acids tested. The decomposition of vanillic acid,p-hydroxybenzoic acid, and of the benzoic acids with OH groups in the meta position was as complete as that of glucose, amino acids or casein. The decomposition of bacterial cells to CO₂ was considerably less than that of glucose.No evidence could be obtained that the low percentage of substrate converted to CO₂ at the time of maximal respiration rate was due to the decreasing diffusion rate of substrate to the microbial colonies in the soil during the consumption of substrate.     

An improved method for somatic plantlet production in hybrid larch (Larix × leptoeuropaea): Part 2. Control of germination and plantlet development

Germination and plantlet development in somatic embryos of Larix x leptoeuropaea were affected by the duration of the maturation treatment and the concentrations of sucrose and abscisic acid in the maturation media. Extension of the maturation period from 3 weeks to 4 weeks resulted in a significant decrease in germination and plantlet development frequencies. There was no significant effect of abscisic acid concentration on either the number of somatic embryos germinated or the number of plantlets obtained, but it affected the rapidity of the epicotyl development. Sucrose at 0.2 M, applied during maturation, was significantly more beneficial in attaining high germination rates than at 0.1 M. High germination rates (92 and 93%) and plantlet development rates (74 and 80%) were achieved when somatic embryos were matured for a 3-week period on media with either 40 or 60 M abscisic acid, respectively, and 0.2 M sucrose prior to transfer to the growth regulator-free germination medium. Two acclimatization methods were applied: the first required 10 to 12 weeks and ensured 97% plantlet survival under greenhouse conditions; the second required 2–3 weeks and ensured 86% plantlet survival. This represents the first detailed study of the effects of maturation regimes on the recovery of somatic embryo-derived plants of Larix.Abbreviations ABA abscisic acid - IBA indolebutyric acid - 2,4-d 2,4-dichlorophenoxyacetic acid - EM embryonal mass     

The effect of elevated CO2 concentrations in the atmosphere on plant transpiration and water use efficiency. A study with potted carnation plants

Transpiration rates of potted spray carnation plants Cerise Royalette decreased about 0.04% per vpm CO₂ between ambient atmospheric CO₂ concentration and 1500 vpm CO₂ at several light flux densities and leaf temperatures. Measurements of daily water losses of potted spray carnation plants placed under high solar radiation conditions in two minigreenhouses with 300 and 5000 vpm CO₂ demonstrated that elevated CO₂ concentrations reduced water losses by 20–30%. The effect of the increase in global CO₂ concentration on stomatal closure was calculated to have decreased the yearly transpiration rate of an outdoor crop by 1.6% in this century and is expected to cause a decrease of 10% within the next 50 years if all other factors remain unchanged. From a model of CO₂ uptake of carnation plants it was calculated that the expected water use efficiency (net photosynthesis rate/transpiration rate) will increase by about 40–50% over the next 50 years due to the expected increase in global CO₂ concentration.Contribution No. 205-E, 1979 series.Presented at the Eighth International Congress of Biometeorology 8–14 September 1979, Shefayim, Israel.