2,056 research outputs found
Non-autonomy of AGAMOUS function in flower development: use of a Cre/loxP method for mosaic analysis in Arabidopsis
Angiosperms use a multi-layered meristem (typically L1, L2 and L3) to produce primordia that then develop into plant organs, A number of experiments show that communication between the cell layers is important for normal development. We examined whether the function of the flower developmental control gene AGAMOUS involves communication across these layers. We developed a mosaic strategy using the Cre/loxP site-specific recombinase system, and identified the sector structure for mosaics that produced mutant flowers. The major conclusions were that (1) AGAMOUS must be active in the L2 for staminoid and carpelloid tissues, (2) that AGAMOUS must be active in the L2 and the L3 for floral meristem determinacy, and (3) that epidermal cell identity can be communicated by the L2 to the L1 layer
A lunar base reference mission for the phased implementation of bioregenerative life support system components
Previous design efforts of a cost effective and reliable regenerative life support system (RLSS) provided the foundation for the characterization of organisms or 'biological processors' in engineering terms and a methodology was developed for their integration into an engineered ecological LSS in order to minimize the mass flow imbalances between consumers and producers. These techniques for the design and the evaluation of bioregenerative LSS have now been integrated into a lunar base reference mission, emphasizing the phased implementation of components of such a BLSS. In parallel, a designers handbook was compiled from knowledge and experience gained during past design projects to aid in the design and planning of future space missions requiring advanced RLSS technologies. The lunar base reference mission addresses in particular the phased implementation and integration of BLS parts and includes the resulting infrastructure burdens and needs such as mass, power, volume, and structural requirements of the LSS. Also, operational aspects such as manpower requirements and the possible need and application of 'robotics' were addressed
A genetic and molecular model for flower development in Arabidopsis thaliana
Cells in developing organisms do not only differentiate, they differentiate in defined patterns. A striking example is the differentiation of flowers, which in most plant families consist of four types of organs: sepals, petals, stamens and carpels, each composed of characteristic cell types. In the families of flowering plants in which these organs occur, they are patterned with the sepals in the outermost whorl or whorls of the flower, with the petals next closest to the center, the stamens even closer to the center, and the carpels central. In each species of flowering plant the disposition and number (or range of numbers) of these organs is also specified, and the floral 'formula' is repeated in each of the flowers on each individual plant of the species. We do not know how cells in developing plants determine their position, and in response to this determination differentiate to the cell types appropriate for that position. While there have been a number of speculative proposals for the mechanism of organ specification in flowers (Goethe, 1790; Goebel, 1900; Heslop-Harrison, 1964; Green, 1988), recent genetic evidence is inconsistent with all of them, at least in the forms in which they were originally presented (Bowman et al. 1989; Meyerowitz et al. 1989). We describe here a preliminary model, based on experiments with Arabidopsis thaliana. The model is by and large consistent with existing evidence, and has predicted the results of a number of genetic and molecular experiments that have been recently performed
Programmed Cell Death During Female Gametophyte Development
Endosperm is a storage tissue in the angiosperm seed that is important both biologically and agriculturally. Endosperm is biologically important because it provides nutrients to the embryo during seed development and agriculturally important because it is a significant source of food, feed, and industrial raw materials. Approximately two-thirds of human calories are derived from endosperm, either directly or indirectly through animal feed. Furthermore, endosperm is used as a raw material for numerous industrial products including ethanol. A major event in endosperm development is the transition between the syncytial phase, during which the endosperm nuclei undergo many rounds of mitosis without cytokinesis, and the cellularized phase, during which cell walls form around the endosperm nuclei. Understanding how the syncytial-cellular transition is regulated is agriculturally important because it influences seed size, seed sink strength, and grain weight. However, the molecular processes controlling this transition are not understood. This project led to the identification of the AGL62 gene that regulates the syncytial-cellular transition during endosperm development. AGL62 is expressed during the syncytial phase and suppresses endosperm cellularization during this period. AGL62 most likely does so by suppressing the expression of genes required for cellularization. At the end of the syncytial phase, the FIS PcG complex suppresses AGL62 expression, which allows expression of the cellularization genes and triggers the initiation of the cellularized phase. Endosperm arises following fertilization of the central cell within the female gametophyte. This project also led to the identification of the AGL80 gene that is required for development of the central cell into the endosperm. Within the ovule and seed, AGL80 is expressed exclusively in the central cell and uncellularized endosperm. AGL80 is required for expression of several central cell-expressed genes, including DEMETER and DD46. Together, these data suggest that AGL80 functions as a transcription factor within the central cell gene regulatory network and controls the expression of downstream genes required for central cell development and function
Identification of transcription-factor genes expressed in the Arabidopsis female gametophyte
Dongfang Wang, Changqing Zhang, David J. Hearn, Il-HO Kang, megan I. Skaggs, Karen S. Schumaker, and Ramin Yadegari are with the School of Plant Sciences, University of Arizona, Tucson, Arizona 85721-0036, USA -- Il-Ho Kang, Jayson A. Punwani, and Gary N. Drews are with the Department of Biology, University of Utah, Salt Lake City, Utah 84112-0840, USA -- Changqing Zhang is with The Section of Molecular, Cell and Developmental Biology, University of Texas at Austin, Austin, Texas 78712-0159, USA -- David J. Hearn is with the Department of Biological Sciences, Towson University, Towson, Maryland 21252-0001, USA -- Il-Ho Kang is with the Department of Horticulture, Iowa State University, Ames, Iowa 50011-1100, USA --Jayson A. Punwani is with the Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3280, USABackground
In flowering plants, the female gametophyte is typically a seven-celled structure with four cell types: the egg cell, the central cell, the synergid cells, and the antipodal cells. These cells perform essential functions required for double fertilization and early seed development. Differentiation of these distinct cell types likely involves coordinated changes in gene expression regulated by transcription factors. Therefore, understanding female gametophyte cell differentiation and function will require dissection of the gene regulatory networks operating in each of the cell types. These efforts have been hampered because few transcription factor genes expressed in the female gametophyte have been identified. To identify such genes, we undertook a large-scale differential expression screen followed by promoter-fusion analysis to detect transcription-factor genes transcribed in the Arabidopsis female gametophyte.
Results
Using quantitative reverse-transcriptase PCR, we analyzed 1,482 Arabidopsis transcription-factor genes and identified 26 genes exhibiting reduced mRNA levels in determinate infertile 1 mutant ovaries, which lack female gametophytes, relative to ovaries containing female gametophytes. Spatial patterns of gene transcription within the mature female gametophyte were identified for 17 transcription-factor genes using promoter-fusion analysis. Of these, ten genes were predominantly expressed in a single cell type of the female gametophyte including the egg cell, central cell and the antipodal cells whereas the remaining seven genes were expressed in two or more cell types. After fertilization, 12 genes were transcriptionally active in the developing embryo and/or endosperm.
Conclusions
We have shown that our quantitative reverse-transcriptase PCR differential-expression screen is sufficiently sensitive to detect transcription-factor genes transcribed in the female gametophyte. Most of the genes identified in this study have not been reported previously as being expressed in the female gametophyte. Therefore, they might represent novel regulators and provide entry points for reverse genetic and molecular approaches to uncover the gene regulatory networks underlying female gametophyte development.Cellular and Molecular [email protected]
Evolution of Derwael Ice Rise in Dronning Maud Land, Antarctica, over the last millennia
Ice rises situated in the ice-shelf belt around Antarctica have a spatially confined flow regime with local ice divides. Beneath the divides, ice stratigraphy often develops arches with amplitudes that record the divide's horizontal residence time andsurface elevation changes. To investigate the evolution of Derwael Ice Rise, Dronning Maud Land, Antarctica, we combine radar and GPS data from three consecutive surveys, with a two-dimensional, full Stokes, thermomechanically-coupled, transient ice-flow model. We find that the surface mass balance (SMB) is higher on the upwind and lower on the downwind slopes. Near the crest, the SMB is anomalously low and causes arches to form in the shallow stratigraphy, observable by radar. In deeper ice, arches are consequently imprinted by both SMB and ice rheology (Raymond effect). The data show how arch amplitudes decrease as along-ridge slope increases, emphasizing that the lateral positioning of radar cross-sections is important for the arch interpretation. Using the model with three rheologies (isotropic with n = 3,4.5 and anisotropic with n = 3), we show that Derwael Ice Rise is close to steady-state, but is best explained using ice anisotropy and moderate thinning. Our preferred, albeit notunique, scenario suggests that the ice divide has existed for at least 5000 years and lowered at approximately 0.03 m a−1 over the last 3400 years. Independent of the specific thinning scenario, our modeling suggests that Derwael Ice Rise has exhibited a local flow regime at least since the Mid-Holocene
Influence of urban land cover changes and climate change for the exposure of European cities to flooding during extreme precipitation
The optimal form of the scanning near-field optical microscopy probe
A theoretical approach to determine the optimal form of the near-field
optical microscope probe is proposed. An analytical expression of the optimal
probe form with subwavelength aperture has been obtained. The advantages of the
probe with the optimal form are illustrated using numerical calculations. The
conducted calculations show 10 times greater light throughput and the reception
possibility of the more compactly localized light at the output probe aperture
which could indicate better spatial resolution of the optical images in
near-field optical technique using optimal probe.Comment: 12 pages, 6 figure
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