1,721,195 research outputs found
SUPERMANprevents class B gene expression and promotes stem cell termination in the fourth whorl ofArabidopsis thalianaflowers
No full textThe molecular and genetic networks underlying the determination of floral organ identity are well studied, but much less is known about how the flower is partitioned into four developmentally distinct whorls. The SUPERMAN gene is required for proper specification of the boundary between stamens in whorl 3 and carpels in whorl 4, as superman mutants exhibit supernumerary stamens but usually lack carpels. However, it has remained unclear whether extra stamens in superman mutants originate from an organ identity change in whorl 4 or the overproliferation of whorl 3. Using live confocal imaging, we show that the extra stamens in superman mutants arise from cells in whorl 4, which change their fate from female to male, while floral stem cells proliferate longer, allowing for the production of additional stamens
Genetic Control of Cell Division Patterns in Developing Plants
No full textUnderstanding the control of the patterns and numbers of cell divisions in developing plants and animals is central to understanding the mechanisms of development. However, we know almost nothing about this control: we have no idea how a particular organ realizes its eventual cell number (and thus size) and have little idea of how the regional patterns of cell division that are a critical part of organogenesis are established or maintained. These problems can be studied in a very straightforward manner in flowering plant development: plants do not use the standard animal mechanisms of cell migration and migration of sheets of cells, and although plants use programmed cell death in many ways, they do not appear to use it to achieve appropriate cell numbers in developing organs or stem cell populations. Furthermore, plant cells do not slide or slip relative to one another. Organogenesis in flowering plants thus results almost entirely from patterned control of the numbers, places, and planes of cell divisions, coupled with regulated and coordinated cellular expansion
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Pattern formation in plant development: four vignettes
No full textIn their development, plants precisely control the patterns of cell size, cell shape and cell division, the position of differentiation of cell types, and the position and number of organs. In the past year, progress has been made in understanding four of these five levels of control of plant pattern formation, including specification of cell fate by cell size in the alga Volvox carteri, genetic control of cell shape in the leaf hairs of the flowering plant Arabidopsis thaliana, precise control of cell division and cellular enlargement in Arabidopsis root meristems, and control of cell number in meristems of Arabidopsis, tobacco, and maize. These examples indicate that both the fate and shape of differentiated plant cells can be determined by the size of their undifferentiated precursors, and that the primary effect of mutations that alter cell fate and cellular shape can be on cell size. Furthermore, specific genes have been found that are necessary for normal patterns and numbers of cell divisions. Molecular cloning of these genes is revealing the molecular basis of plant cell division control
Flower development and evolution: New answers and new questions
Full text linkCertain genes have a way of rewarding continued study, as can be seen from the long histories of discoveries that have
resulted from work on mammalian hemoglobin genes, on the Escherichia coli lacZ gene, and on many others. A plant gene
that may fit this mold is the homeotic flower-development gene AGAMOUS (AG). In the past few years, study of the genetics and molecular genetics of this Arabidopsis thaliana gene and of its orthologues in other plant species has led to a stream of discoveries that have revealed some of the mechanisms and some of the complexity of flower development. Two recent papers (1, 2), one in this issue, describe a new level of regulation of AG and raise new questions about the function and evolutionary history of this gene
Variations on the Author
Full text link“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
Today we have naming of parts
No full textAlthough we share the planet with plants
and depend on them for food, raw
materials and energy, we know very
little about them. But this is beginning to
change. On pages 761 and 769 of this issue,
Lin et al. and Wambutt et al. report the
DNA sequences of chromosomes 2 and 4,
respectively, from Arabidopsis thaliana. The
sequences include about 30% of the plant’s
genes, and show that although many plant
genes are familiar homologues of known
animal and fungal genes, many others are
plant specific. The sequences also show an
evolving genome, with evidence for ancient
and recent duplications of both single genes
and large chromosomal regions
From genome to phenotype: Modeling the interaction of physical and chemical signals in plant meristems
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