Multi-Disciplinary North-South Collaboration in Participatory Action Research on Food Value Chains: a German-Tanzanian Case Study on Perceptions,Experiences and Challenges

Systemic Practice and Action Research - Upgrading local food value chains is a promising approach to invigorating African food systems. This endeavour warrants multi-disciplinary North-South...     

Local and Global Properties of the World

The essence of the method of physics is inseparably connected with the problem of interplay between local and global properties of the universe. In the present paper we discuss this interplay as it is present in three major departments of contemporary physics: general relativity, quantum mechanics and some attempts at quantizing gravity (especially geometrodynamics and its recent successors in the form of various pregeometry conceptions). It turns out that all big interpretative issues involved in this problem point towards the necessity of changing from the standard space-time geometry to some radically new, most probably non-local, generalization. We argue that the recent noncommutative geometry offers attractive possibilities, and gives us a conceptual insight into its algebraic foundations. Noncommutative spaces are, in general, non-local, and their applications to physics, known at present, seem very promising. One would expect that beneath the Planck threshold there reigns a "noncommutative pregeometry", and only when crossing this threshold does the usual space-time geometry emerges.     

Rat sternothyroid muscle: Dissection and preparation for electrophysiologic and electronmicrographic studies

Summary The sternothyroid muscle of the rat is described. The ease of dissection and localization of end-plate regions within the sternothyroid muscle by direct visualization of nerve supply provides a convenient mammalian muscle preparation for electrophysiological and ultrastructural research.This research was supported in part by the following grants: PHS 5429-16-20 (to C. M. Poser), NIH grant NS-07740 (to R. L. Parsons).We express our appreciation to Drs C. M. Poser and R. L. Parsons for providing us with laboratory space and equipment to conduct these experiments in addition to much helpful advice and criticism.     

Modification de métabolisme des ARN induites par l'adrénaline dans les cellules animales

Summary The effects of adrenalin were studied on mice liver RNA, with different concentrations and action times. It was found that, after the incorporation of the radioactive precursor, the activity increased rapidly, followed almost immediately by an inhibition, which itself decreased progressively.     

Newly synthesized lithium in the interstellar medium

Astronomical observations of elemental and isotopic abundances provide the means to determine the source of elements and to reveal their evolutionary pathways since the formation of the Galaxy some 15 billion years ago. The abundance of lithium is particularly interesting because, although some of it is thought to be primordial, most results from spallation reactions (in which Galactic cosmic rays break apart larger nuclei in the interstellar medium). Spallation reactions are crucial for the production of other light elements, such as beryllium and boron, so observations of lithium isotopic abundances can be used to test model predictions for light-element synthesis in general. Here we report observations of 7Li and 6Li abundances in several interstellar clouds lying in the direction of the star o Persei. We find the abundance ratio 7Li/6Li to be about 2, which is significantly lower than the average Solar System value of 12.3 (refs 6, 7). An abundance ratio of 2 is clear evidence that the observed lithium must have resulted entirely from spallation, confirming a basic tenet of light-element synthesis. The total lithium abundance, however, is not enhanced as expected.     

Lipid packing sensed by ArfGAP1 couples COPI coat disassembly to membrane bilayer curvature

Protein coats deform flat lipid membranes into buds and capture membrane proteins to form transport vesicles. The assembly/disassembly cycle of the COPI coat on Golgi membranes is coupled to the GTP/GDP cycle of the small G protein Arf1. At the heart of this coupling is the specific interaction of membrane-bound Arf1-GTP with coatomer, a complex of seven proteins that forms the building unit of the COPI coat. Although COPI coat disassembly requires the catalysis of GTP hydrolysis in Arf1 by a specific GTPase-activating protein (ArfGAP1), the precise timing of this reaction during COPI vesicle formation is not known. Using time-resolved assays for COPI dynamics on liposomes of controlled size, we show that the rate of ArfGAP1-catalysed GTP hydrolysis in Arf1 and the rate of COPI disassembly increase over two orders of magnitude as the curvature of the lipid bilayer increases and approaches that of a typical transport vesicle. This leads to a model for COPI dynamics in which GTP hydrolysis in Arf1 is organized temporally and spatially according to the changes in lipid packing induced by the coat.     

Nuclear DNA sequences detect species limits in ancient moa

Ancient DNA studies have typically used multi-copy mitochondrial DNA sequences. This is largely because single-locus nuclear genes have been difficult to recover from sub-fossil material, restricting the scope of ancient DNA research. Here, we have isolated single-locus nuclear DNA markers to assign the sex of 115 extinct moa and, in combination with a mitochondrial DNA phylogeny, tested competing hypotheses about the specific status of moa taxa. Moa were large ratite birds that showed extreme size variation both within and among species. For some taxa, this large variation was hypothesized to represent sexual dimorphism, while for others it was argued to reflect the existence of different species. Our results show that moa were characterized by extreme reverse sexual dimorphism and as a result we have been able to clarify the number of moa species. For example, we show that the three recognized 'species' of Dinornis comprised only two monophyletic groups and that two of these 'species' comprised individuals of one sex only. This study also illustrates that single-locus nuclear DNA sequences can be consistently recovered from ancient material.     

A cytoplasmic region determines single-channel conductance in 5-HT3 receptors

5-hydroxytryptamine type 3 (5-HT3) receptors are cation-selective transmitter-gated ion channels of the Cys-loop superfamily. The single-channel conductance of human recombinant 5-HT3 receptors assembled as homomers of 5-HT3A subunits, or heteromers of 5-HT3A and 5-HT3B subunits, are markedly different, being 0.4 pS (refs 6, 9) and 16 pS (ref. 7), respectively. Paradoxically, the channel-lining M2 domain of the 5-HT3A subunit would be predicted to promote cation conduction, whereas that of the 5-HT3B subunit would not. Here we describe a determinant of single-channel conductance that can explain these observations. By constructing chimaeric 5-HT3A and 5-HT3B subunits we identified a region (the 'HA-stretch') within the large cytoplasmic loop of the receptor that markedly influences channel conductance. Replacement of three arginine residues unique to the HA-stretch of the 5-HT3A subunit by their 5-HT3B subunit counterparts increased single-channel conductance 28-fold. Significantly, ultrastructural studies of the Torpedo nicotinic acetylcholine receptor indicate that the key residues might frame narrow openings that contribute to the permeation pathway. Our findings solve the conundrum of the anomalously low conductance of homomeric 5-HT3A receptors and indicate an important function for the HA-stretch in Cys-loop transmitter-gated ion channels.