Untersuchungen über die Redoxregulation der Glutathionsynthese und Charakterisierung von Glutaredoxinen in Spinat

Die an der Glutathionsynthese im Chloroplasten von Spinatblättern beteiligten Enzyme sind auf eine lichtabhängige Regulation durch Thioredoxine (Trx) und Glutaredoxine (Grx) hin untersucht worden. Dazu wurde eine neue, vereinfachte Methode zur Aktivitätsbestimmung für die gamma-Glutamylcystein- und Glutathionsynthetase auf der Kapillarelektrophorese entwickelt. Untersuchungen mit den homologen Thioredoxinen Trx m und Trx f aus Spinatchloroplasten und mit dem E.coli Trx und E.coli Grx 1 zeigten, dass bei beiden Enzymen keine Redoxmodulation durch diese Proteine stattfindet. Weitere Untersuchungen mit der Glutathionsynthetase zeigten keinen Einfluss von Dithiothreit, Sulfit-Ionen und Ascorbat auf die Enzymaktivität. Nur H2O2, in unphysiologischen Konzentrationen, bewirkte eine leichte Abnahme der Ausgangsaktivität. Im Fall der gamma-Glutamylcysteinsynthetase konnten verschiedene Einflüsse ausgemacht werden. So war mit Dithiothreit und H2O2 bei niedrigen Konzentrationen eine Stimulation und bei höheren Konzentration eine Inhibition der Enzymaktivität festzustellen: Sulfit-Ionen zeigten eine starke Stimulierung der gamma-Glutamylcysteinsynthetase über einen weiten Konzentrationsbereich, wobei eine starke pH-Wert-Abhängigkeit der Stimulation zu beobachten war. Ascorbat zeigte, wie bei der Glutathionsynthetase, keinen Einfluss auf die Enzymaktivität der gamma-Glutamyl-cysteinsynthetase. In einem zweiten Teil der Arbeit über die Glutaredoxine des Spinats konnte ein 12,4 kDa Protein mit Thioltransferase-Aktivität, das bisher als cytosolisches Glutaredoxin beschrieben wurde, aufgereinigt und mittels N-terminaler Sequenzierung eindeutig als ein Glutaredoxin identifiziert werden. Überdies konnte ein noch nicht beschriebenes 12,8 kDa Protein mit Thioltransferase-Aktivität aus Spinatchloroplasten aufgereinigt werden. Durch Peptid-Sequenzierung gelang es dieses Protein auch als ein Glutaredoxin zu identifizieren. Beide pflanzlichen Glutaredoxine zeigten keine Modulation der Aktivitäten der chloroplastidären Fructosebisphosphatase (FbPase) und NADPH-Malatdehydrogenase (NADPH-MDH). Auch war mit beiden Glutaredoxinen keine Dehydroascorbatreduktase-Aktivität, oder eine Stimulation der Ribonucleotidreduktase aus Lactobacillus leichmannii festzustellen.

On the transition from localized to delocalized electronic states in divalent-metal clusters

The transition from van der Waals to covalent bonding, which is expected to occur in divalent-metal clusters with increasing cluster size, is discussed. We propose a model which takes into account, within the same electronic theory, the three main competing contributions, namely the kinetic energy of the electrons, the Coulomb interactions between electrons, and the s \gdw p intraatomic transitions responsible for van der Waals like bonding. The model is solved by taking into account electron correlations using a generalized Gutzwiller approximation (slave boson method). The occurrence of electron localization is studied as a function of the interaction parameters and cluster size.

Effects of grassland renovation on carbon concentrations and aggregate distribution in temperate grassland soils

The effects of continuous tillage on the distribution of soil organic matter (SOM) and aggregates have been well studied for arable soils. However, less is known about the effects of sporadic tillage on SOM and aggregate dynamics in grassland soils. The objectives of the present thesis were (I) to study the longer-term effects of sporadic tillage of grassland on organic carbon (Corg) stocks and the distribution of aggregates and SOM, (II) to investigate the combined effects of sporadic tillage and fertilization on carbon and nitrogen dynamics in grassland soils, and (III) to study the temporal dynamics of Corg stocks, aggregate distribution and microbial biomass in grassland soils. Soil samples were taken in three soil depths (0 – 10 cm; 10 – 25 cm; 25 – 40 cm) from a field trial with loamy sandy soils (Cambisols, Eutric Luvisols, Stagnosols, Anthrosols) north of Kiel, Germany. For Objective I we have sampled soil two and five years after one or two tillage operation(s). Treatments consisted of (i) permanent grassland, (ii) tillage of grassland followed by a re-establishment of grassland and (iii) tillage of grassland followed by a re-establishment of grassland with one season of winter wheat in between. The tillage in grassland led to a reduction in Corg stocks, large macroaggregates (>2000 µm) and SOM in the top 10 cm soil depth. These findings were still significant two years after tillage; however, five years after tillage no longer present. Regarding the soil profile (0 – 40 cm) no significant differences in the mentioned parameters between the tilled plots and the permanent grassland existed. A second tillage event and the insertion of one season of winter wheat did not lead to any further effects on Corg stocks as well as aggregate and SOM concentrations in comparison with a single tillage event in these grassland soils. Treatments adapted for Objective II included (i) long-term grassland and (ii) tillage of grassland followed by a re-establishment of grassland with one season of winter wheat in between. The plots were split and received either 240 kg N ha-1 year-1 in the form of cattle slurry or no cattle slurry application. The application of slurry within a period of four years had no effects on the Corg and total nitrogen stocks or the aggregate distribution, but led to a reduction of free and not physically protected SOM. However, the application of cattle slurry and the grassland renovation seems to change the plant species composition and therefore generalizations on the direct effects are not yet possible. For studying Objective III a further field trial was initiated in September 2010. Soil samples were taken six times within one year (from October 2010 to October 2011) (i) after the conversion from arable land into grassland, (ii) after the tillage of grassland followed by a re-establishment of grassland and (iii) in a permanent grassland. We found an increase in the microbial and fungal biomass after the conversion of arable land into grassland, but no effect on aggregate distribution and Corg stocks. A one-time tillage operation in grassland led to a reduction in large macroaggregates and Corg stocks in the top 10 cm soil depth with no effect on the sampled soil profile. However, we found large variations in the fungal biomass and aggregate distribution within one year in the permanent grassland, presumably caused by environmental factors. Overall, our results suggest that a single tillage operation in grassland soils markedly decreased the concentrations of Corg, larger aggregates and SOM. However, this does not result in long-lasting effects on the above mentioned parameters. The application of slurry cannot compensate the negative effects of a tillage event on aggregate concentrations or Corg stocks. However, while the Corg concentration is not subject to fluctuations within a year, there are large variations of the aggregate distribution even in a permanent grassland soil. Therefore conclusions of results from a single sampling time should be handled with care.

Optical Antennas for Biosensing Applications

The aim of the thesis is to theoretically investigate optical/plasmonic antennas for biosensing applications. The full 3-D numerical electromagnetic simulations have been performed by using finite integration technique (FIT). The electromagnetic properties of surface plasmon polaritons (SPPs) and the localized surface plasmons (LSPs) based devices are studied for sensing purpose. The surface plasmon resonance (SPR) biosensors offer high refractive index sensitivity at a fixed wavelength but are not enough for the detection of low concentrations of molecules. It has been demonstrated that the sensitivity of SPR sensors can be increased by employing the transverse magneto-optic Kerr effect (TMOKE) in combination with SPPs. The sensor based on the phenomena of TMOKE and SPPs are known as magneto-optic SPR (MOSPR) sensors. The optimized MOSPR sensor is analyzed which provides 8 times higher sensitivity than the SPR sensor, which will be able to detect lower concentration of molecules. But, the range of the refractive index detection is limited, due to the rapid decay of the amplitude of the MOSPR-signal with the increase of the refractive indices. Whereas, LSPs based sensors can detect lower concentrations of molecules, but their sensitivity is small at a fixed wavelength. Therefore, another device configuration known as perfect plasmonic absorber (PPA) is investigated which is based on the phenomena of metal-insulator-metal (MIM) waveguide. The PPA consists of a periodic array of gold nanoparticles and a thick gold film separated by a dielectric spacer. The electromagnetic modes of the PPA system are analyzed for sensing purpose. The second order mode of the PPA at a fixed wavelength has been proposed for the first time for biosensing applications. The PPA based sensor combines the properties of the LSPR sensor and the SPR sensor, for example, it illustrates increment in sensitivity of the LSPR sensor comparable to the SPR and can detect lower concentration of molecules due to the presence of nanoparticles.