University of Tübingen

About: University of Tübingen is a education organization based out in Tübingen, Germany. It is known for research contribution in the topics: Population & Transplantation. The organization has 40555 authors who have published 84108 publications receiving 3015320 citations. The organization is also known as: Eberhard Karls University & Eberhard-Karls-Universität Tübingen.

Neuron-specific contribution of the superior colliculus to overt and covert shifts of attention.

Abstract: The analysis of a peripheral visual location can be improved in two ways: either by orienting one's gaze (usually by making a foveating saccade) or by 'covertly' shifting one's attention to the peripheral location without making an eye movement. The premotor theory of attention holds that saccades and spatial shifts of attention share a common functional module with a distinct neuronal basis. Using single-unit recording from the brains of trained rhesus monkeys, we investigated whether the superior colliculus, the major subcortical center for the control of saccades, is part of this shared network for attention and saccades. Here we show that a distinct type of neuron in the intermediate layer of the superior colliculus, the visuomotor neuron, which is known to be centrally involved in the preparation of saccades, is also active during covert shifts of attention.

XMM-EPIC observation of MCG-6-30-15: direct evidence for the extraction of energy from a spinning black hole?

Abstract: We present XMM-Newton European Photon Imaging Camera (EPIC) observations of the bright Seyfert 1 galaxy MCG 6-30-15, focusing on the broad Fe Kline at � 6keV and the associated reflection continuum, which is believed to originate from the inner accretion disk. We find these reflection features to be extremely broad and red-shifted, indicating its origin from the very most central regions of the accretion disk. It seems likely that we have caught this source in the "deep minimum" state first observed by Iwasawa et al. (1996). The implied central concentration of X-ray illumination is difficult to understand in any pure accretiondisk model. We suggest that we are witnessing the extraction and dissipation of rotational energy from a spinning black hole by magnetic fields connecting the black hole or plunging region to the disk.

Role of the ZWILLE gene in the regulation of central shoot meristem cell fate during Arabidopsis embryogenesis

Abstract: Postembryonic development in higher plants is marked by repetitive organ formation via a self‐perpetuating stem cell system, the shoot meristem. Organs are initiated at the shoot meristem periphery, while a central zone harbors the stem cells. Here we show by genetic and molecular analyses that the ZWILLE ( ZLL ) gene is specifically required to establish the central–peripheral organization of the embryo apex and that this step is critical for shoot meristem self‐perpetuation. zll mutants correctly initiate expression of the shoot meristem‐specific gene SHOOT MERISTEMLESS in early embryos, but fail to regulate its spatial expression pattern at later embryo stages and initiate differentiated structures in place of stem cells. We isolated the ZLL gene by map‐based cloning. It encodes a novel protein, and related sequences are highly conserved in multicellular plants and animals but are absent from bacteria and yeast. We propose that ZLL relays positional information required to maintain stem cells of the developing shoot meristem in an undifferentiated state during the transition from embryonic development to repetitive postembryonic organ formation.

Geomicrobiological cycling of iron

Abstract: Iron is the most abundant element on Earth and the most frequently utilized transition metal in the biosphere. It is a component of many cellular compounds and is involved in numerous physiological functions. Hence, iron is an essential micronutrient for all eukaryotes and the majority of prokaryotes. Prokaryotes that need iron for biosynthesis require micromolar concentrations, levels that are often not available in neutral pH oxic environments. Therefore, prokaryotes have evolved specific acquisition molecules, called siderophores, to increase iron bioavailability. Acquisition of iron by siderophores is a complex process and is discussed in detail by Kraemer et al. (2005). Here we focus on prokaryotes that generate energy for growth by oxidation or reduction of iron. In both processes single electron transfers are involved. Hence, for a significant extent of energy generation, turnover of iron in the millimolar rather than the micromolar range is necessary. Iron metabolizing organisms have therefore a strong influence on iron cycling in the environment. Microbial iron oxidation and reduction will be discussed, with emphasis on circumneutral pH environments that prevail on Earth. The active metabolic processes outlined above have to be distinguished from indirect biologically induced iron mineral formation in which prokaryotic cell surfaces simply act as passive templates (“passive iron biomineralization”) (e.g., Konhauser 1997). ### General aspects of the iron cycle On our planet, iron is ubiquitous in the hydrosphere, lithosphere, biosphere and atmosphere, either as particulate ferric [Fe(III)] or ferrous [Fe(II)] iron-bearing minerals or as dissolved ions. Redox transformations of iron, as well as dissolution and precipitation and thus mobilization and redistribution, are caused by chemical and to a significant extent by microbial processes (Fig. 1⇓). Microorganisms catalyze the oxidation of Fe(II) under oxic or anoxic conditions as well as the reduction of Fe(III) in anoxic habitats. Microbially influenced transformations of iron are often much faster than the …