1,721,025 research outputs found
Embryo-patterning genes and reinforcement cues determine cell fate in the Arabidopsis thaliana root
No full textThe majority of plant organs arise from groups of continuously dividing cells, the meristems. Little is known about mechanisms of cell specification in meristems. Within the Arabidopsis root meristem, the fate of every cell can be predicted accurately, and the origin of these cells during the formation of the embryonic root primordium is known. Laser ablations reveal that, despite the regularity in cell lineage, position remains important to reinforce cell specification. Genetic analysis has revealed that many genes involved in the specification of the main cell types in the root act early, during embryogenesis, and an important question is whether the same or other genes are involved in the reinforcement of specification. Sub-specification of cell types, as exemplified by epidermal root hair cell specification, involves two pathways, one of which may act to reinforce earlier patterning events mediated by the other
Cell signaling in root development
No full textCell signaling has recently been shown to be of major importance in cell specification during Arabidopsis root development. In the ground tissue, cues of unknown molecular nature convey positional information and two genes provide an interesting link between asymmetric cell division and the determination of cell fate. In the root epidermis, cell specification involves ethylene signaling and transcription
factors of which at least two are also required for cell fate decisions in the shoot epidermis
Root development: new meanings for root canals?
No full textDuring Arabidopsis root development, a radial pattern of tissues is extended by the meristem. These tissues form continuous layers and recent data suggest that tissue
continuity is instrumental for constraining the direction of signaling in a process termed channeling. In the ground tissue, fate-determining signals originate from contiguous cells of the same layer, possibly due to specific symplastic connections. Mutant analysis supports the hypothesis that
vascular tissue continuity may facilitate and depend on the directional transport of a vascular fate-determining signal, possibly the phytohormone auxin
The Arabidopsis root as a model to study plant development
No full textWith its straightforward amenability to genetic approaches, Arabidopsis thaliama proves to be a powerful system to study biological processes in plants. The root of Arabidopsis has several additional features which make it a good model system to study developmental processes. It has a largely invariant ontogeny and fixed cellular organization. Continuous cellular differentiation in the root meristematic region allows monitoring of developmental
processes after embryogenesis. The Arabidopsis root is also amenable for experimental manipulation. The simplicity of its organization allows large-scale mutant screens covering several aspects of root formation and growth. Experimental manipulations have uncovered the existence of positional cues important for pattern formation. Together with the several classes of mutants and the ongoing identification of genes these findings contribute to a better understanding of developmental processes at the cellular level
A LEAFY link from outer space
No full textThe beautiful shape and colour patterns
of flowers attract almost everybody,
including developmental biologists.
Studies of floral patterning have shown that
the identity of floral organs is determined
by a combinatorial code of homeotic genes,
termed A, B and C, expressed in three separate
regions of the flower. This knowledge
allows scientists (and biotech companies) to
manipulate flowers to form organs at any
position, yet the secret of how the three
activities are put into the right place remains
hidden. But on page 561 of this issue, Parcy et
al. bring new insights to this matter. They
show that the LEAFY (LFY) protein is
directly involved in activating the transcription
of homeotic genes, together with at
least one co-regulator, UNUSUAL FLORAL
ORGANS (UFO). The genes that encode
these proteins were originally isolated as
floricaula and fimbriata in a flower that
almost all of us have manipulated as
children, the snapdragon
Moleculaire inzichten vergroten sturingsmogelijkheden wortelgroei : Auxine speelt een sleutelrol
No full textHet wortelstelsel van gewassen is vaak ‘de verborgen helft’ genoemd. Lange tijd bestond er een enorm gebrek aan kennis over wortelgroei. Dat maakt het moeilijk er op te veredelen of om er in de teelt anders mee om te gaan. De afgelopen jaren is het inzicht belangrijk gegroeid, met name op genetisch en moleculair niveau
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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