Soil mineral nitrogen availability was unaffected by elevated atmospheric pCO2 in a four year old field experiment (Swiss FACE)

The effect of elevated (60 Pa) atmospheric carbon dioxide partial pressure (p_CO2) and N fertilisation on the availability of mineral N and on N transformation in the soil of a Lolium perenne L. monoculture was investigated in the Swiss FACE (Free Air Carbon dioxide Enrichment) experiment. The apparent availability of nitrate and ammonium for plants was estimated during a representative, vegetative re-growth period at weekly intervals from the sorption of the minerals to mixed-bed ion-exchange resin bags at a soil depth of 5 cm. N mineralisation was measured using sequential coring and in situ exposure of soil cores in the top 10 cm of the soil before and after the first cut in spring 1997. High amounts of mineral N were bound to the ion exchange resin during the first week of re-growth. This was probably the combined result of the fertiliser application, the weak demand for N by the newly cut sward and presumably high rates of root decay and exudation after cutting the sward. During the first 2 weeks after the application of fertiliser N at the first cut, there was a dramatic reduction in available N; N remained low during the subsequent weeks of re-growth in all treatments. Overall, nitrate was the predominant form of mineral N that bound to the resin for the duration of the experiment. Apparently, there was always more nitrate than ammonium available to the plants in the high N fertilisation treatment for the whole re-growth period. Apparent N availability was affected significantly by elevated p_CO2 only in the first week after the cut; under high N fertilisation, elevated p_CO2 increased the amount of mineral N that was apparently available to the plants. Elevated p_CO2 did not affect apparent net transformation of N, loss of N or uptake of N by plants. The present data are consistent with earlier results and suggest that the amount of N available to plants from soil resources does not generally increase under elevated atmospheric p_CO2. Thus, a possible limiting effect of N on primary production could become more stringent under elevated atmospheric p_CO2 as the demand of the plant for N increases. This revised version was published online in June 2006 with corrections to the Cover Date.     

Changes in spectral reflectance of a foliar lichen <Emphasis Type="Italic">Umbilicaria hirsuta</Emphasis> during desiccation

Water potential (ψ_w) and water saturation deficit (WSD), and several reflectance (R) indexes were assessed in an aerophytic lichen Umbilicaria hirsuta (Sw. ex Westr.) Hoffm. The water index (WI, R₉₀₀/_R970) and normalized difference vegetation index, NDVI [(R₉₀₀-R₆₈₀)/(R₉₀₀+R₆₈₀)] were strongly correlated both with the ψ_w and the WSD of lichen thalli. No significant changes during desiccation were found in structural independent pigment index, SIPI [(R₈₀₀-R₄₄₅)/(R₈₀₀-R₆₈₀)]. Sensitivity of the spectral detection of water status was rather small at high hydration level (WSD < 25 %, or ψ_w > −1 MPa), but this is not much limiting its value and potential use, because physiological processes in lichens are usually inhibited at much lower values of ψ_w than in leaves of vascular plants.     

Signalling mechanisms involved in the response of two varieties of Humulus lupulus L. to soil drying: II. changes in the concentration of abscisic acid catabolites and stress-induced phytohormones

Abscisic acid (ABA) is one of the most common stress signals that appear in plant organs in response to soil drying. Equilibrium between ABA biosynthesis and catabolism regulates ABA accumulation in plants under water stress. The aim of our work was to explore the dynamics of changes in ABA metabolites as well as other stress-induced phytohormones such as jasmonic acid, indole-3-acetic acid, and their respective metabolites in hop [Humulus lupulus (L.)] plants during drying and to identify among them potential signals involved in drought signalling. We showed that the concentrations of all ABA metabolites (except the concentration of ABA glucosyl ester in leaves) increased in the same manner in leaves and xylem sap approximately at the same level of soil water content when the relative water content of leaves decreased. The predominant metabolites in leaves and xylem sap were phaseic acid and dihydroxyphaseic acid. ABA glucosyl ester was not a source of the increased concentration of ABA in leaves and xylem sap because of its considerably lower concentration compared to ABA. The concentration of jasmonates decreased in leaves of hop plants. Changes in auxin concentration suggest that this hormone is involved in the response of hop plants to soil drying.     

Nitrogen and base cation uptake in seedlings of Acer pseudoplatanus and Calamagrostis villosa exposed to an acidified environment

The effects of solution acidity and form of nitrogen on net nutrient uptake rates in Acer pseudoplatanus and Calamagrostis villosa seedlings were examined as part of a complex ecological study. Uptake rates were measured by the depletion method under controlled conditions (temperature 20 °C, irradiance 400 mol m^–2 s^–1 PAR) from a nutrient solution containing 1.5 mM nitrogen in the form of nitrate or ammonium or an equimolar mixture of both. The solution acidity was kept constant at pH 5.5 (control treatment), 4.5 or 3.5 (low pH treatments). Strongly acid pH decreased or stopped the uptake rates of NO₃ ^–, Mg²⁺ and Ca²⁺, but the uptake of NH₄ ⁺ was not changed in both species. Ammonium ions reduced the uptake rate of NO₃ ^– in Acer but increased the uptake rate in Calamagrostis. Ammonium as the sole source of nitrogen had a strong negative impact on the uptake rates of calcium and magnesium and this effect was independent of the media acidification usually connected with NH₄ ⁺ uptake and assimilation. However, the negative effect of ammonium ions on the base cation uptake was more pronounced at low pH values.     

Novel Ubiquitin-derived High Affinity Binding Proteins with Tumor Targeting Properties

Targeting effector molecules to tumor cells is a promising mode of action for cancer therapy and diagnostics. Binding proteins with high affinity and specificity for a tumor target that carry effector molecules such as toxins, cytokines, or radiolabels to their intended site of action are required for these applications. In order to yield high tumor accumulation while maintaining low levels in healthy tissues and blood, the half-life of such conjugates needs to be in an optimal range. Scaffold-based binding molecules are small proteins with high affinity and short systemic circulation. Due to their low molecular complexity, they are well suited for combination with effector molecules as well as half-life extension technologies yielding therapeutics with half-lives adapted to the specific therapy. We have identified ubiquitin as an ideal scaffold protein due to its outstanding biophysical and biochemical properties. Based on a dimeric ubiquitin library, high affinity and specific binding molecules, so-called Affilin® molecules, have been selected against the extradomain B of fibronectin, a target almost exclusively expressed in tumor tissues. Extradomain B-binding molecules feature high thermal and serum stability as well as strong in vitro target binding and in vivo tumor accumulation. Application of several half-life extension technologies results in molecules of largely unaffected affinity but significantly prolonged in vivo half-life and tumor retention. Our results demonstrate the utility of ubiquitin as a scaffold for the generation of high affinity binders in a modular fashion, which can be combined with effector molecules and half-life extension technologies.     

Does the Response of Perennial Ryegrass to Elevated CO2 Concentration Depend on the Form of the Supplied Nitrogen?

To test whether different nitrogen form (nitrate or ammonium) in substrate can alter the response to elevated partial pressure of CO₂ (pCO₂) plants of perennial ryegrass (Lolium perenne cv. Bastion) were grown from seeds in growth chambers under pCO₂ of either 35 Pa (ambient, CA) or 70 Pa (elevated, CE) in a hydroponic system (with nutrient and pH control) for 24 d. Nitrogen was supplied as ammonium, nitrate or an equimolar mixture of both N forms. Under CE plants grew faster than their counterparts under CA during the first 14 d but after 23 d of cultivation stimulation disappeared. Despite the strong positive effect of mixed forms of N on plant growth, the beneficial effect of CE was similar to that in the other two N treatments. However, the almost alike final growth response to CE had different underlying mechanisms in different N treatments. Plants supplied with nitrate as a sole source of nitrogen had lower leaf mass ratio but much higher specific leaf area compared to plants supplied with ammonium. The decrease in the content of leaf organic N (per unit of structural dry mass) under CE was found only in leaves of plants supplied with ammonium on day 14. Nevertheless, the available form of N evidently contributes to changes of leaf N content under CE. The high levels of N and non-structural saccharides in plants supplied with ammonium at CE suggest that the CO₂ response of these plants was controlled by factors other than amount of available carbon and nitrogen.