Browsing by Subject "Aufnahme"

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Abgabe von bodenbürtigem Lachgas über Pflanzen
(2003) Ferch, Norbert-Jakob; Römheld, Volker
The aim of this work was to explore and to rank the different ways and forms of transition of N2O through plants (dissolved in water and transported with the transpiration or gaseous through aerenchyma). To achieve this goal an experimental set-up had to be realized that allowed the determination of possible N2O emissions by plants, the determination of different ways of transition of N2O through the plant and the determination of different influencing factors (e.g. N2O concentration) on the N2O emissions. In the beginning experiments with closed chambers and with ?controlled opened chambers? were conducted in comparison to each other. In the experiments with closed chambers samples were drawn by means of molecular sieves and vacutainers. N2O concentrations of the samples were measured with a GC (gas chromatograph type HP 5890) equipped with an ECD (electron capture detector). Besides the two methods mentioned above in order to determine the N2O concentrations within the experiments with the ?controlled opened chambers? a third method was used for N2O measurement by means of a photo acoustic online measuring machine. The accuracy of the photo acoustic measurement was evaluated with the GC. For the questions of interest the photo acoustic measurement showed to be the best to determine differences of N2O emissions between different experimental treatments. The experiments that were taken in consideration were conducted in a ?controlled opened system? because in closed chambers CO2 concentration decreased rapidly. Additionally, the air in the closed chambers became saturated in water vapour within a few minutes. These two factors lead to inhibited growth of the plants and to undesired influences on the N2O measurements. The ?controlled opened system? consisted of a root and a shoot compartment. Both compartments were separated airtight from each other and from the surroundings. The root compartments were enriched with a definite amount of N2O. The N2O concentrations measured in the shoot compartments of the systems with N2O enrichment in the root compartment were compared with measurements of systems without N2O enrichment and measurements of ambient air. The necessity to divide the root compartment from the shoot compartment airtight was realised with a material on the basis of silicone that is usually used to make prints of teeth (Optosil, from Haereus) and a sealing mass (Prestik AE hellgrau, from Bostik GmbH). To determine the different factors potentially influencing the N2O emission through plants a hydroponical culture system was established that allowed controlling the following factors: concentration of nutrients, pH-factor, concentration of different water soluble gases (e. g. N2O, CO2) and the ratio between water and gas filled space in the root compartment. As experimental plants sunflower (Helianthus annuus cv. Frankasol), barley (Hordeum vulgare cv. Scarlet), rice (Oryza sativa cv. 94D-22) and corn (Zea mays cv. Helix) were used. For the experiment with sunflower (no aerenchyma, N2O dissolved in water available only) a relationship between N2O concentration in the root compartment, the emitted amount of N2O by the shoots and the intensity of transpiration in a diurnal pattern was found. In systems with gaseous availability of N2O in the root compartment the observed emissions were higher than in systems with availability of N2O dissolved only in water. From this it could be concluded, that gaseous N2O is better available for plants than N2O dissolved in water. Similar results were obtained from experiments with barley. The only difference was that the highest N2O emissions were observed in systems with availability of N2O dissolved in water only. The possible N2O emission through aerenchyma was checked with rice plants. In these experiments a pronounced diurnal pattern of the N2O emissions was also found. This lead to the conclusion that aerenchyma only have a small influence on the N2O emissions out of the root compartment through rice plants. Because the N2O emission in the three experiments described above followed the diurnal pattern of the transpiration, it was concluded that N2O was transported with the transpiration water flow from the root (compartment) to the shoot (compartment). The experiments with corn showed for all treatments (control and availability of N2O in gaseous form or dissolved in water) a net N2O depletion in the shoot compartment for night (darkness) and day (light) respectively, thus leading to the conclusion that N2O can be metabolised and used as a nitrogen source. All in all the experiments showed that the main way of transition of N2O through plants is water dissolved with the transpiration water flow and not gaseous (through aerenchyma).
Membrane transport and long-distance translocation of urea in Arabidopsis thaliana
(2011) Bohner, Anne; von Wirén, Nicolaus
Urea is a soil nitrogen (N) form available to plant roots and a secondary N metabolite liberated in plant cells by protein degradation, especially during senescence. Despite the fact that urea also represents the most widespread form in N fertilizers used in agricultural plant production, membrane transporters that might contribute to urea uptake in plant roots or urea retranslocation in senescent leaves have so far been characterized only in heterologous systems. The first part of the thesis investigated a role of the H+/urea cotransporter AtDUR3 in N nutrition of Arabidopsis thaliana plants. T-DNA insertion lines with a defective expression in AtDUR3 showed impaired growth on urea as a sole nitrogen source. In transgenic lines expressing an AtDUR3-promoter-GFP construct, promoter activity was upregulated under N deficiency and localized to the rhizodermis, including root hairs, as well as to the cortex in more basal root zones. The AtDUR3 protein accumulated in plasma membrane-enriched protein fractions, and AtDUR3 gene expression in N-deficient roots was repressed by ammonium and nitrate but induced after supply of urea. Higher urea accumulation in roots of wild-type plants relative to the T-DNA insertion lines confirmed that urea was the transported substrate of AtDUR3. Influx of 15N-labeled urea allowed the calculation of an affinity constant of 4 µM. These results indicated that AtDUR3 is the major transporter for high-affinity urea uptake in Arabidopsis roots and suggested that the high substrate affinity of AtDUR3 reflects an adaptation to the low urea levels usually found in unfertilized soils. A physiological function of urea and its transporters in leaves was investigated in the second part of the thesis. Currently it is unclear whether transport and metabolism of urea might limit the overall retranslocation of N during senescence. AtDUR3 transcript levels were only slightly de-repressed under N starvation, but strongly increased in senescent leaves. Urea concentrations in leaf samples of different plant and leaf age showed a strong increase after plants turned into generative growth. In parallel, mRNA as much as the protein abundance of AtDUR3 increased with leaf age. The analysis of leaf petiole exudates revealed that urea was indeed a translocated N form and urea-N represented approx. 13% of the total amino acid-N irrespective of the N status of the plant. Urea concentrations determined in apoplastic wash fluids supported a role of AtDUR3 in urea retrieval from the leaf apoplast, and transgenic AtDUR3-promoter-GUS lines indicated a localization of AtDUR3 promoter activity in the vasculature of old leaves. Thus, AtDUR3 might keep internal urea in the cytosol by urea retrieval from the apoplast, allowing urea to be transported to the vascular bundle, where it is either passively loaded to the phloem or converted into amino acids for long-distance N translocation. A strong daytime-dependent phenotype with shorter leaf petioles of an Arabidopsis line overexpressing AtDUR3 led to an in silico analysis of the AtDUR3 promoter sequence revealing that salicylic acid (SA) appears to induce AtDUR3 gene expression in senescent leaves. SA is well known for its involvement in the initiation of senescence. A strongly enhanced uptake capacity for 15N-labeled urea in N-sufficient Arabidopsis roots after SA pretreatment indicated that SA might be able to mimic N-deficiency conditions, paving the way to the possibility that SA builds a regulatory link between developmental and N deficiency-induced senescence.