Influences of different nitrogen sources on nitrogen- and water-use efficiency, and carbon isotope discrimination, in C3 Triticum aestivum L. and C4 Zea mays L. plants

The impacts of various nitrogen sources, i.e. NO⁻ ₃, NH₄ ⁺ or NH₄NO₃ in combination with gaseous NH₃, on nitrogen-, carbon- and water-use efficiency and ¹³C discrimination (δ¹³C) by plants of the C₃ species Triticum aestivum L. (wheat) and the C₄ species Zea mays L. (maize) were studied. Triticum aestivum and Z. mays were hydroponically grown with 2 mol · m⁻³ of N supplied as NO⁻ ₃, NH₄ ⁺ or NH₄NO₃ for 21 and 18 d, respectively, and thereafter exposed to gaseous NH₃ at 320 μg · m⁻³ or to ambient air for 7 d. In T. aestivum and Z. mays over a 7-d growth period, nitrogen-use efficiency (NUE) values were influenced by N-sources in the decreasing order NH₄NO₃-N > NO⁻ ₃-N > NH₄ ⁺-N and NO⁻ ₃-N > NH₄NO₃-N > NH₄ ⁺-N, respectively. Fumigation with NH₃ decreased the NUE values of plants grown with any of the N-forms. During 28- and 7-d growth periods, N-sources affected water-use efficiency (WUE) values in the decreasing order of NH₄ ⁺-N > NO⁻ ₃-N≈NH₄NO₃-N in non-fumigated T. aestivum, while fumigation with NH₃ increased the WUE of NO⁻ ₃-grown plants. There were insignificant effects of N-sources on WUE values of Z. mays over 25- and 7-d growth periods. Furthermore, δ¹³C values in plant tissues (leaves, stubble and roots) were higher (less negative) in NH₄ ⁺-grown plants of T. aestivum and Z. mays than in those supplied with NH₄NO₃ or NO⁻ ₃. Regardless of the N-form supplied to the roots of the plant species, exposure to NH₃ caused more-positive δ¹³C values in the plant tissues. These results indicate that the variations in N-source were associated with small but significant variations in δ¹³C values in plants of T. aestivum and Z. mays. These differences in δ¹³C values are in the direction expected from differences in WUE values over long or short growth periods and with differences in the extent of non-Rubisco (ribulose-1,5-bisphosphate carboxylase-oxygenase, EC 4.1.1.39) carboxylate contribution to net C acquisition, as a function of N-source. Received: 12 September 1997 / Accepted: 13 January 1998     

Estimating the cost of flowering in a grapefruit tree

The objective of the present study is to evaluate a Citrus tree's investment in the flowering process in relation to its photoassimilate resources, as a part of its annual reproductive effort. The overall requirement for carbohydrate of a single flower of grapefruit ( Citrus paradisi Macf. cv. 'Marsh seedless') is evaluated as 8·33 × 10^–3 mol C over 3 weeks. The direct cost of production of a single flower is estimated to be 5·75 × 10^–3 mol C, most of which is allocated to the petals, anthers and style — organs designated to abscise. About 2·58 × 10^–3 mol C is consumed by respiration not associated with growth processes. Growth respiration ( R _g) occurs mostly during early stages of flower growth and development. However, the total respiration rate increases sharply during anthesis, when growth processes have almost ceased. Ethylene evolution also reaches remarkably high rates during anthesis. High temperatures increase the rate of flower respiration ( Q ₁₀ = 2·12) but shorten the duration of flowering. A grapefruit tree may bear each year 20 000–50 000 flowers, only 0·5–2·5% of which develop into mature fruit. The amount of carbohydrate invested each year in bloom at the whole-tree level is 166–400 mol C per tree (depending on the number of flowers), amounting to 10–20% of the carbohydrate consumed for fruit growth. The overall daily demand for carbohydrate by the flowers of a grapefruit tree during anthesis may exceed the daily carbohydrate production by the leaves. High temperatures lead to a further increase in the daily demand for carbohydrate. In such cases, the management of flowering must rely on carbohydrate reserves recruited from other tree organs. The ecophysiological and evolutionary aspects of Citrus flowering are discussed.     

Nutrient concentration in shape Sphagna at increased N-deposition rates and raised atmospheric CO2 concentrations

Sphagnum fuscum, S. magellanicum, S. angustifolium and S. warnstorfii were treated with N deposition rates (0, 10, 30 and 100 kg ha^-1 a^-1) and with four atmospheric CO₂ concentrations (350, 700, 1000 and 2000 ppm) in greenhouse for 71–120 days. Thereafter, concentrations of total N, P, K, Ca and Mg in the capitulae of the Sphagna were determined. The response of each species to N deposition was related to ecological differences. With increasing N deposition treatments, moss N concentrations increased and higher N:P-ratios were found, the increase being especially clear at the highest N load. Sphagnum fuscum, which occupies ombrotrophic habitats, was the most affected by the increased nitrogen load and as a consequence the other elements were decreased. Oligotrophic S. magellanicum, wide nutrient status tolerant S. angustifolium and meso-eutrophic S. warnstorfii tolerated better increased N deposition, though there were increased concentrations of Ca and Mg in S. warnstorfii and Mg in S. magellanicum. Nitrogen and P concentrations decreased with raised CO₂ concentrations, except for S. magellanicum. This seems to be the first time this kind of response in nutrient concentrations to enhanced CO₂ concentration has been shown to exist in bryophytes. The concentration of K clearly decreased in S. fuscum as did the concentration of Mg in the other Sphagna with increasing CO₂. Sphagnum angustifolium and S. magellanicum, which are the less specialized species, were the least affected by the CO₂ treatments.     

Characterization of a model cyanobacterium Synechocystis sp. PCC 6803 autotrophic growth in a flat‐panel photobioreactor

We characterized the photoautotrophic growth of glucose‐tolerant Synechocystis sp. PCC 6803 in a flat‐panel photobioreactor running on a semicontinuous regime under various lights, temperatures, and influx carbon dioxide concentrations. The maximum reached growth rate was 0.135 h^?1, which corresponds to a doubling time of 5.13 h—a growth speed never reported for Synechocystis before. Saturating red light intensity for the strain was 220–360 μmol(photons) m^?2 s^?1, and we did not observe any photoinhibition up to 660 μmol(photons) m^?2 s^?1. Synechocystis was able to grow under red light only; however, photons of wavelengths 405–585 and 670–700 nm further improved its growth. Optimal growth temperature was 35°C. Below 32°C, the growth rates decreased linearly with temperature coefficient (Q₁₀) 1.70. Semicontinuous cultivation is known to be efficient for growth characterization and optimization. However, the assumption of correct growth rates calculation—culture exponential growth—is often not fulfilled. The semicontinuous setup in this study was operated as a turbidostat. Accurate online OD measurements with high time‐resolution allowed fast and reliable growth rates determination. Repeating diluting frequencies (up to 18 dilutions per day) were essential for rapid growth stability evaluation. The presented setup provides improvement to previously published semicontinuous characterization strategies by decreasing experimental time requirements and maintaining the culture in exponential growth phase throughout the entire characterization procedure.     

Predator‐driven elemental cycling: the impact of predation and risk effects on ecosystem stoichiometry

Empirical evidence is beginning to show that predators can be important drivers of elemental cycling within ecosystems by propagating indirect effects that determine the distribution of elements among trophic levels as well as determine the chemical content of organic matter that becomes decomposed by microbes. These indirect effects can be propagated by predator consumptive effects on prey, nonconsumptive (risk) effects, or a combination of both. Currently, there is insufficient theory to predict how such predator effects should propagate throughout ecosystems. We present here a theoretical framework for exploring predator effects on ecosystem elemental cycling to encourage further empirical quantification. We use a classic ecosystem trophic compartment model as a basis for our analyses but infuse principles from ecological stoichiometry into the analyses of elemental cycling. Using a combined analytical‐numerical approach, we compare how predators affect cycling through consumptive effects in which they control the flux of nutrients up trophic chains; through risk effects in which they change the homeostatic elemental balance of herbivore prey which accordingly changes the element ratio herbivores select from plants; and through a combination of both effects. Our analysis reveals that predators can have quantitatively important effects on elemental cycling, relative to a model formalism that excludes predator effects. Furthermore, the feedbacks due to predator nonconsumptive effects often have the quantitatively strongest impact on whole ecosystem elemental stocks, production and efficiency rates, and recycling fluxes by changing the stoichiometric balance of all trophic levels. Our modeling framework predictably shows how bottom‐up control by microbes and top‐down control by predators on ecosystems become interdependent when top predator effects permeate ecosystems.     

Highly sensitive electrochemical aptasensor for immunoglobulin E detection based on sandwich assay using enzyme-linked aptamer

Here, we describe the fabrication of an electrochemical immunoglobulin E (IgE) aptasensor using enzyme-linked aptamer in the sandwich assay method and thionine as redox probe. In this protocol, 5′-amine-terminated IgE aptamer and thionine were covalently attached on glassy carbon electrode modified with carbon nanotubes/ionic liquid/chitosan nanocomposite. Furthermore, another IgE aptamer was modified with biotin and enzyme horseradish peroxidase (HRP), which attached to the aptamer via biotin–streptavidin interaction. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry were performed at each stage of the chemical modification process to confirm the resulting surface changes. The presence of IgE induces the formation of a double aptamer sandwich structure on the electrode, and the electrocatalytic reduction current of thionine in the presence of hydrogen peroxide was measured as the sensor response. Under optimized conditions and using differential pulse voltammetry as the measuring technique, the proposed aptasensor showed a low detection limit (6 pM) and high sensitivity (1.88 μA nM⁻¹). This aptasensor also exhibited good stability and high selectivity for IgE detection without an interfering effect of some other proteins such as bovine serum albumin (BSA) and lysozyme. The application of the aptasensor for IgE detection in human serum sample was also investigated. The proposed protocol is quite promising as an alternative sandwich approach for various protein assays.     

PSII-efficiency,polysaccharide production,and phenotypic plasticity of Scenedesmus obliquus in response to changes in metabolic carbon flux

To investigate the response of Scenedesmus obliquus to changes in metabolic carbon flux, S. obliquus was cultured in medium with different concentrations of glyoxylate over 9 days. Results showed that growth rates were not affected in the lower concentration glyoxylate (0.25 and 0.5 mM). However, growth rate of S. obliquus was inhibited in the higher concentration glyoxylate (0.85 and 1.25 mM) during the early phase before recovering at higher densities. Changes in growth rates in different glyoxylate concentrations were in line with changes in F_v/F_m and Φ_PSII. Colony formation was observed in S. obliquus in the four glyoxylate treatments. As a consequence, the mean number of cells per particle of S. obliquus in the glyoxylate treatments were significantly higher than those in the control. The total polysaccharide content of S. obliquus cells increased with increased glyoxylate concentrations. The increased glyoxylate-stimulated polysaccharide levels were directly correlated with colony size of S. obliquus.     

Novel rhamnolipid biosurfactants produced by a polycyclic aromatic hydrocarbon-degrading bacterium Pseudomonas aeruginosa strain NY3

A novel rhamnolipid biosurfactant-producing and Polycyclic Aromatic Hydrocarbon (PAH)-degrading bacterium Pseudomonas aeruginosa strain NY3 was isolated from petroleum-contaminated soil samples. Strain NY3 was characterized by its extraordinary capacity to produce structurally diverse rhamnolipids. A total of 25 rhamnolipid components and 37 different parent molecular ions, representing various metal ion adducts (Na⁺, 2Na⁺ and K⁺), were detected by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Among these compounds are ten new rhamnolipids. In addition to its biosurfactant production, strain NY3 was shown to be capable of efficient degradation of PAHs as well as synergistic improvement in the degradation of high molecular weight PAHs by its biosurfactant. These findings have added novel members to the rhamnolipid group and expanded current knowledge regarding the diversity and productive capability of rhamnolipid biosurfactants from a single specific strain with variation of only one carbon source. Additionally, this paper lays the foundation for improvement in the yield of NY3BS and study of the degradation pathway(s) of PAHs in P. aeruginosa strain NY3.     

Brief exposure to carbon monoxide preconditions cardiomyogenic cells against apoptosis in ischemia-reperfusion

We examined whether and how pretreatment with carbon monoxide (CO) prevents apoptosis of cardioblastic H9c2 cells in ischemia-reperfusion. Reperfusion (6 h) following brief ischemia (10 min) induced cytochrome c release, activation of caspase-9 and caspase-3, and apoptotic nuclear condensation. Brief CO pretreatment (10 min) or a caspase-9 inhibitor (Z-LEHD-FMK) attenuated these apoptotic changes. Ischemia-reperfusion increased phosphorylation of Akt at Ser472/473/474, and this was enhanced by CO pretreatment. A specific Akt inhibitor (API-2) blunted the anti-apoptotic effects of CO in reperfusion. In normoxic cells, CO enhanced generation, which was inhibited by a mitochondrial complex III inhibitor (antimycin A) but not by a NADH oxidase inhibitor (apocynin). The CO-enhanced Akt phosphorylation was suppressed by an scavenger (Tiron), catalase or a superoxide dismutase (SOD) inhibitor (DETC). These results suggest that CO pretreatment induces mitochondrial generation of , which is then converted by SOD to H₂O₂, and subsequent Akt activation by H₂O₂ attenuates apoptosis in ischemia-reperfusion.