Yearbook 2004

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We seek to understand the evolutionary forces which influence genetic variation of ecologically important traits within and among species. Following our earlier functional genomics studies in the model organism Arabidopsis thaliana, evolutionary inquiries are now focused on wild, perennial species of Arabidopsis and Boechera growing in natural populations in Europe and North America. more
Experimental investigations by means of 3-dimensional scanning microscopy together with diffraction techniques as well as numerical simulations such as the Texture Component Crystal Plasticity Finite Element Method are used for the microstructure analysis and the development of new steels. more

Preparation of Nanostructures from Directionally Solidified Eutectics

Max-Planck-Institut für Eisenforschung GmbH Hassel, Achim Walter; Bello Rodriguez, Belen; Milenkovic, Srdjan; Schneider, André
The production of nanostructured materials is possible by directional solidification. Metals as well as semiconductors can be employed in the eutectics. An appropriate etching allows either the production of short standing wires or of longer wires organised in domains. Furthermore the preparation of isolated nanowires becomes possible by a complete dissolution of the matrix. The system shows a remarkable high degree of order and a uniform crystallographic orientation. Anodic polarisation in a neutral buffer allows a simultaneous passivation of the host phase and selective oxidising dissolution of the wires. Other metals such as gold can be deposited in the so formed cavities. The different strategies for a structuring of these materials and their applications as nanostructured materials and in sensors are discussed. more
Photosynthesis in green plants and some bacteria is based on the efficient function of most sophisticated molecular machines. Like in a factory assembly line, sunlight is captured, stabilized and converted into chemical energy - which then is used for chemical reactions and to oxidize water. Particularly the last step is very difficult and the most demanding task in chemical terms. The whole process of photosynthesis is based on charge separation at specific redox centers of the photosystem and careful charge conduction and control. To avoid immediate loss of the energy by 'electrical short circuit' (and thus charge recombination) the redox potentials of the redox-active centers and the spatial arrangement of the elements in the charge transfer path were carefully tuned by evolution. We are particularly interested in the interaction and mutual control of specific redox-active groups in the so-called "reaction center" (which is the site of water oxidation) and how one could measure their interaction by physical means. The final goal of such a research program is understanding the natural systems in full detail and depth so that blueprints for technical designs and applications can be deduced. In the project presented here a series of isostructural dimeric manganese complexes with tethered organic radicals was synthesized. For the first time these compounds could mimic the paramagnetic interaction of the manganese cluster and a tyrosin Yz radical in the S2Yz state of photosystem PS II. The state S2Yz is an artificially stabilized intermediate in the chain of oxidation events in the reaction center of PS II which may control the flow of electrons during catalysis. Since both sites, the manganese cluster and the radicals in S2Yz as well as in the models, carry spin and magnetic moment, their magnetic dipole interaction could be detected by using electron paramagnetic resonance techniques (EPR spectroscopy) and susceptibility measurements. For the first time the conditions of long-range interactions between mixed-valence manganese clusters and organic radicals like in PS II could be systematically explored as a function of known molecular structures. The EPR results are most relevant for the understanding of real systems and EPR distance measurements in biochemical molecules. more
While there is ample experimental evidence for a role of species diversity in ecosystem performance, the functional significance of genetic diversity is less clear. In fact, many aquatic plant communities are highly productive although they consist of only a few or a single dominant species. In order to shed light on this apparent contradiction, scientists at the MPI of Limnology manipulated the genotypic diversity in the field in the seagrass species Zostera marina. The experiment took place in the Baltic Sea in 2003. During that year, a heat wave caused surface water temperatures to rise above 25°C, leading to widespread heat stress related mortality among shallow water animals and plants. Such conditions may serve as a model for predicted increases in climatic extremes. After the heat wave, genotypically diverse seagrass areas recovered faster, had more shoots and biomass and harboured more associated invertebrates at the end of the experimental period. Positive effects of genotypic diversity were due to true biodiversity effects (complementarity) and not due to the dominance of particularly resistant genotypes. These results provide experimental evidence that not only species diversity but also genetic diversity should be preserved. Genotypic diversity had a similar function as species diversity. This way, the level of genetic diversity can be incorporated into existing ecological theory on biodiversity at the level of species. more
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