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Distribution by Scientific Domains

Life Sciences	50%
Humanities and Social Sciences	50%

Selected Abstracts

The evolution of the protonephridial terminal organ across Rotifera with particular emphasis on Dicranophorus forcipatus, Encentrum mucronatum and Erignatha clastopis (Rotifera: Dicranophoridae)

ACTA ZOOLOGICA, Issue 2 2010
Ole Riemann
Abstract Riemann, O. and Ahlrichs, W.H. 2009. The evolution of the protonephridial terminal organ across Rotifera with particular emphasis on Dicranophorus forcipatus, Encentrum mucronatum and Erignatha clastopis (Rotifera: Dicranophoridae). ,Acta Zoologica (Stockholm) 91: 199,211 We report on the ultrastructure of the protonephridial terminal organ in three species of dicranophorid rotifers (Dicranophorus forcipatus, Encentrum mucronatum and Erignatha clastopis). Differences between the three species relate to shape and size, the morphology of the filter region and the number of microvilli and cilia inside the terminal organ. A comparison across Rotifera indicates that the terminal organs in D. forcipatus display a number of plesiomorphic characters, but are modified in E. mucronatum and Er. clastopis. This is in accordance with the results of phylogenetic analyses suggesting a basal position of D. forcipatus compared with the more derived species E. mucronatum and Er. clastopis. Moreover, we survey available data on the terminal organ in Rotifera and discuss its evolutionary transformations. The protonephridial terminal organ in the common ancestor of Rotifera consisted of a cytoplasmic cylinder with cilia united into a vibratile flame and a single circle of circumciliary microvilli. Depending on the topology on which characters are optimized, the site of ultrafiltration was formed by longitudinal cytoplasmic columns spanned by a fine filter diaphragm or by pores in the wall of the terminal organ. In several taxa of Rotifera, the terminal organ , probably independently , lost its circumciliary microvilli. [source]

Cytokinins negatively regulate the root iron uptake machinery in Arabidopsis through a growth-dependent pathway

THE PLANT JOURNAL, Issue 2 2008
Mathilde Séguéla
Summary Plants display a number of biochemical and developmental responses to low iron availability in order to increase iron uptake from the soil. The ferric-chelate reductase FRO2 and the ferrous iron transporter IRT1 control iron entry from the soil into the root epidermis. In Arabidopsis, expression of IRT1 and FRO2 is tightly controlled to maintain iron homeostasis, and involves local and long-distance signals, as well as transcriptional and post-transcriptional events. FIT encodes a putative basic helix-loop-helix (bHLH) transcription factor that regulates iron uptake responses in Arabidopsis. Here, we uncover a new regulation of the root iron uptake genes. We show that IRT1, FRO2 and FIT are repressed by the exogenous addition of cytokinins (CKs), and that this repression acts at the level of transcript accumulation, and depends on the AHK3 and CRE1 CK receptors. The CKs and iron-deficiency signals act through distinct pathways to regulate the soil iron uptake genes, as (i) CK repression is independent of the iron status, (ii) IRT1 and FRO2 downregulation is unchanged in a fit loss-of-function mutant, indicating that FIT does not mediate CK repression, and (iii) the iron-regulated genes AtNRAMP3 and AtNRAMP4 are not downregulated by CKs. We show that root growth-inhibitory conditions, such as abiotic stresses (mannitol, NaCl) and hormonal treatments (auxin, abscissic acid), repress the iron starvation response genes. We propose that CKs control the root iron uptake machinery through a root growth dependent pathway in order to adapt nutrient uptake to the demand of the plant. [source]

Portugal as a Semi-peripheral Country in the Global Migration System

INTERNATIONAL MIGRATION, Issue 3 2009
Pedro Góis
Although Portugal has traditionally produced many emigrants, the last 30 years have also shown increasing immigration. This increase in immigration has drawn attention away from the fact that significant emigration from Portugal continues. In this article, some of the main characteristics of migrations to and from Portugal are highlighted from a systemic perspective. The article shows that Portugal is both a receiving country and a sending country in the global migration system, and that it integrates several of the main migration systems at different levels. It is suggested that Portugal's participation in existing migration systems is best captured and explained by conceptualizing it as a semi-peripheral society, one that is part of a core region of the world system (the European Union) and displays a number of characteristics of both central and peripheral countries. The concept of semi-periphery enables one to recognize the existence of what could be termed a quasi or emergent migratory system: the Lusophone migration system, which one can conceive as communicating intensively with other macro migratory systems. Observing the country's migratory dynamics from the last two decades, and especially the migration flows that bond the Portuguese-speaking countries, one may view the Lusophone migration system as able to combine different levels of centers that (in some moments, and given certain conditions) could evolve into a bicephalous, or even tricephalous, center. These centers function as bonds among several other migration systems, and it is in the middle of this Lusophone migration system that the semi-peripheral role of Portugal becomes evident, as it can be core and periphery at the same time. [source]

A Stereotype, Wrapped in a Cliché, Inside a Caricature: Russian Foreign Policy and Orientalism

POLITICS, Issue 3 2010
James D.J. Brown
This article distils Edward Said's celebrated critique of Orientalism and applies it to the mainstream Western discourse on Russian foreign policy. It finds that the literature in this field, while not as afflicted as the material towards which Said's strident criticism was originally directed, displays a number of the characteristic symptoms of Orientalism , the exaggeration of difference, assumption of Western superiority and resort to clichéd analytical models. To overcome this malaise, it is proposed that scholars make greater efforts to break free of these ,mind-forg'd manacles' and reflect more deeply upon the assumptions underpinning their scholarship. [source]