Braun-Blanquet meets EcoVeg: a formation and division level classification of European phytosociological units

Aims: To link the Braun-Blanquet units of the EuroVegChecklist (EVC) with the upper levels of the International Vegetation Classification (IVC), and to propose a division level classification for Europe. Study area: Europe. Methods: We established a tabular linkage between EVC classes and IVC formations and identified mismatches between these two levels. We then proposed IVC division level units to organize EVC classes. Results: We organized the EVC classes into 21 formations and 30 divisions. We flagged classes that did not fit comfortably within an existing formation, either because its content corresponded to more than one formation or because it did not fit any formation description. In a few cases, we split EVC classes because they seemed too heterogenous to be assigned to a single formation. Conclusions: The IVC approach adds a set of physiognomic and ecological criteria that effectively organizes the EVC classes, which are already being increasingly informed by physiognomy. Therefore, the formation concepts are relatively natural extensions of concepts already embedded in the classes. However, physiognomic placement of Braun-Blanquet classes can be difficult when the sampling of the vegetation is at finer grain than usual in the respective formation (tall-scrub, annual pioneer communities). Some EVC classes seem too heterogenous to fit into the IVC formation system. Delimitation of these classes has often been a matter of debate for many decades, and the IVC perspective might help to solve these intricate issues. In other cases, mismatches between phytosociological classes and IVC formations might better be solved by emending the current formation concepts. Abbreviations: BB = Braun-Blanquet; EVC = EuroVegChecklist; IVC = International Vegetation Classification.

La producción de líderes políticos situados en dos comunidades políticas mexicanas

En este escrito reflexionamos sobre las condiciones históricas que influyeron para que en dos espacios geográficos, organizativos y económicos distintos existan importantes similitudes en la producción de complejos liderazgos agrarios. Por un lado, la comunidad agraria de Zirahuén en Michoacán, nos centraremos en la figura política de Marcos Paz Calvillo; por el otro el ejido de Campos, Colima con Armín Núñez Meza. Estas organizaciones son analizadas como comunidades políticas perennes, en las cuales su propia historia y las biografías de los sujetos estudiados estuvieron en constante producción y disputa. Con base en nuestros resultados etnográficos proponemos la noción de liderazgos políticos situados, cuyo rango de influencia depende, en gran medida, de los objetivos, espacios, públicos y condiciones históricas específicas de sus respectivas formaciones. Abstract This paper analyzes the historical conditions that allowed two very different geographic, organizational and economic spaces to develop important similarities in the production of complex agrarian leaderships; on one hand, the agrarian community of Zirahuén in Michoacán, centered in the political figure of Marcos Paz Calvillo; on the other, the Campos ejido in Colima with its leader, Armín Núñez Meza. These organizations are examined as perennial political communities in which local history and the biographies of the subjects studied emerged through an ongoing process of production and dispute. Based on our ethnographic results we propose the notion of situated political leadership in these communities; the degree of influence exerted by such leaderships depends largely on the objectives, spaces, publics and specific historical conditions of their respective formation.

Basis of Arginine Sensitivity of Microbial N-Acetyl-l-Glutamate Kinases: Mutagenesis and Protein Engineering Study with the Pseudomonas aeruginosa and Escherichia coli Enzymes

ABSTRACT N-Acetylglutamate kinase (NAGK) catalyzes the second step of arginine biosynthesis. In Pseudomonas aeruginosa, but not in Escherichia coli, this step is rate limiting and feedback and sigmoidally inhibited by arginine. Crystal structures revealed that arginine-insensitive E. coli NAGK (EcNAGK) is homodimeric, whereas arginine-inhibitable NAGKs, including P. aeruginosa NAGK (PaNAGK), are hexamers in which an extra N-terminal kinked helix (N-helix) interlinks three dimers. By introducing single amino acid replacements in PaNAGK, we prove the functionality of the structurally identified arginine site, as arginine site mutations selectively decreased the apparent affinity for arginine. N-helix mutations affecting R24 and E17 increased and decreased, respectively, the apparent affinity of PaNAGK for arginine, as predicted from enzyme structures that revealed the respective formation by these residues of bonds favoring inaccessible and accessible arginine site conformations. N-helix N-terminal deletions spanning ≥16 residues dissociated PaNAGK to active dimers, those of ≤20 residues decreased the apparent affinity for arginine, and complete N-helix deletion (26 residues) abolished arginine inhibition. Upon attachment of the PaNAGK N-terminal extension to the EcNAGK N terminus, EcNAGK remained dimeric and arginine insensitive. We concluded that the N-helix and its C-terminal portion after the kink are essential but not sufficient for hexamer formation and arginine inhibition, respectively; that the N-helix modulates NAGK affinity for arginine and mediates signal transmission between arginine sites, thus establishing sigmoidal arginine inhibition kinetics; that the mobile αH-β16 loop of the arginine site is the modulatory signal receiver; and that the hexameric architecture is not essential for arginine inhibition but is functionally essential for physiologically relevant arginine control of NAGK.

Zoned, birefringent garnets from Thera Island, Santorini Group (Aegean Sea)

SummaryA garnetite that occurs locally in phyllitic schists exposed by the Santorini caldera consists mainly of euhedral garnet crystals showing alternating isotropic and birefringent lamellae. X-ray diffraction revealed two garnets with unit cell dimensions a of 12·052±0·002 and 11·984±0·005 Å, corresponding respectively to almost pure andradite and a granditic phase. Mean compositions determined by microprobe analysis are An97Sp1Alm2 for the isotropic and about An63Gr33Sp1Alm3 for the birefringent layers.The garnets are deduced to have been produced mainly by thermal metamorphism of the schists. Although cyclic variations in the composition of circulating fluids could have brought about the zoning, this may just as well be the result of temperature fluctuations, individual garnet compositions being indicative of the respective formation temperature.