scholarly journals Mutants of Arabidopsis thaliana Hypersensitive to DNA-Damaging Treatments

Genetics ◽  
1997 ◽  
Vol 146 (1) ◽  
pp. 401-407
Author(s):  
Jean E Masson ◽  
Patrick J King ◽  
Jerzy Paszkowski
Keyword(s):  
Arabidopsis Thaliana ◽  
Root Meristem ◽  
Screening Method ◽  
Shoot Meristem ◽  
Recombinational Repair ◽  
X Rays ◽  
X Ray ◽  
Interstrand Crosslinks ◽  
Sublethal Doses ◽  
Simple Screening

A simple screening method was developed for the isolation of Arabidopsis thaliana mutants hypersensitive to X-ray irradiation. The root meristem was used as the target for irradiation with sublethal doses of X rays, while protection of the shoot meristem by a lead cover allowed the rescue of hypersensitive individuals. We isolated nine independent X-ray-hypersensitive mutants from 7000 M2 seedlings. Analysis of three chosen mutants (xrs4, xrs9 and xrs11) showed that alterations in single recessive alleles are responsible for their phenotypes. The mutations are not allelic but linked and map to chromosome 4, suggesting mutations in novel genes as compared to previously mapped mutant alleles. Importantly, hypersensitivity to X rays was found to correlate with hypersensitivity to the DNA-alkylating agent mitomycin C, which provokes interstrand crosslinks, and/or to methyl methanesulfonate, which is known as a radiomimetic chemical. These novel phenotypes suggest that the mutants described here are altered in the repair of DNA damage, most probably by recombinational repair.

Identification of Lead and Other Elements in Ceramic Glazes and Housewares by 109Cd-Induced X-Ray Fluorescence Emission Spectrometry

1995 ◽  
Vol 78 (2) ◽  
pp. 407-412 ◽  
Author(s):  
David L Anderson ◽  
William C Cunningham ◽  
Tyler R Lemdstrom ◽  
Ilhan Olmez
Keyword(s):  
Limit Of Detection ◽  
Screening Method ◽  
Fluorescence Emission ◽  
The Other ◽  
Fluorescence Spectrometry ◽  
Emission Spectrometry ◽  
X Rays ◽  
Nondestructive Analysis ◽  
X Ray ◽  
Lower Count

Abstract Radioisotope x-ray fluorescence spectrometry was investigated as a potential screening method for Pb and other elements in housewares. Thirty-six commercial houseware items and 87 ceramic test tiles (85 fired with hobby glazes and 2 blank bisques) were examined qualitatively for the presence of Pb by using 109Cd-induced L x-ray fluorescence emission spectrometry. For the housewares, the technique provided fast, nondestructive analysis of areas with about 10 cm diameters (general regions) to about 4 mm diameters (isolated design regions). Pb was found in 25 of 28 ceramicware items, in all 8 other housewares, and in all the testtile glazes above the limit of detection of 1 count per second (cps) for Pb Lβ x-rays. For housewares, Pb identification did not always correspond to Pb leachability. For 68 test-tile glazes labeled as containing Pb (39 of which were also labeled ‘dinnerware safe’ or ‘safe for food containers’), count rates ranged from 290 to 730 cps, whereas for the other 17 glazes labeled (with one exception) ‘nontoxic,’ much lower count rates (5–61 cps) were obtained. Other elements found in the housewares or test glazes were As, Au, Ca, Co, Cr, Cu, Fe, Mn, Nb, Ni, Rb, Sr, Y, Zn, and Zr.

Cell fate in the shoot apical meristem of Arabidopsis thaliana

Development ◽  
1992 ◽  
Vol 115 (3) ◽  
pp. 755-764 ◽  
Author(s):  
J. Furner I ◽  
J. E. Pumfrey
Keyword(s):  
Arabidopsis Thaliana ◽  
Cell Fate ◽  
Apical Meristem ◽  
Higher Plants ◽  
Great Majority ◽  
Shoot Meristem ◽  
X Rays ◽  
Developmental Fate ◽  
Axillary Meristems ◽  
Cell Layers

Seeds of Arabidopsis thaliana, heterozygous for the alb1 mutation were treated with X-rays to generate sectors of albino tissue in the mature plants. Sectors were observed in tissues derived from L2 and L3 layers of the shoot meristem. Altogether 324 sectors were obtained affecting 512 leaves or the inflorescence. The majority of sectors affected only one or other of the first leaf pair. In later leaves, sectors were less frequent, and often affected more than one leaf. Sectors seen in the flowers almost invariably included some of the cauline leaves. Sectors in any region of the plant were of variable length and width. The axillary meristems of Arabidopsis were found to be clonally related to two or more cells near the centre of the subtending leaf. Overall the data are compatible with the idea that there are few, if any, restrictions on cell fate within the cell layers of the dry seed meristem. As in other higher plants, developmental fate could only be predicted in a general and probabilistic way. Such a pattern might be generated if the acquisition of cell fate occurred continuously as the plant grows, in a position-dependent, lineage-independent fashion. A general model of the meristem has been produced to accommodate the observations concerning the great majority of the sectors.

scholarly journals Nucleotide sequence and transcriptional regulation of the yeast recombinational repair gene RAD51

1992 ◽  
Vol 12 (7) ◽  
pp. 3235-3246 ◽  
Author(s):  
G Basile ◽  
M Aker ◽  
R K Mortimer
Keyword(s):  
Cell Cycle ◽  
Transcriptional Regulation ◽  
Recombinational Repair ◽  
X Rays ◽  
Repair Gene ◽  
Sequence Element ◽  
Rad51 Protein ◽  
Transcript Levels ◽  
X Ray ◽  
Significant Homology

The RAD51 gene of Saccharomyces cerevisiae is required both for recombination and for the repair of DNA damage caused by X rays. Here we report the sequence and transcriptional regulation of this gene. The RAD51 protein shares significant homology (approximately 50%) over a 70-amino-acid with the RAD57 protein (J.A. Kans and R.K. Mortimer, Gene 105:139-140, 1991), the product of another yeast recombinational repair gene, and also moderate (approximately 27%), but potentially significant, homology with the bacterial RecA protein. The homologies cover a region that encodes a putative nucleotide binding site of the RAD51 protein. Sequences upstream of the coding region for RAD51 protein share homology with the damage response sequence element of RAD54, an upstream activating sequence required for damage regulation of the RAD54 transcript, and also contain two sites for restriction enzyme MluI; the presence of MluI restriction sites has been associated with cell cycle regulation. A 1.6-kb transcript corresponding to RAD51 was observed, and levels of this transcript increased rapidly after exposure to relatively low doses of X-rays. Additionally, RAD51 transcript levels were found to that of a group of genes involved primarily in DNA synthesis and replication which are thought to be coordinately cell cycle regulated. Cells arrested in early G1 were still capable of increasing levels of RAD51 transcript after irradiation, indicating that increased RAD51 transcript levels after X-ray exposure are not solely due to an X-ray-induced cessation of the cell cycle at a period when the level of RAD51 expression is normally high.

scholarly journals Nucleotide sequence and transcriptional regulation of the yeast recombinational repair gene RAD51.

1992 ◽  
Vol 12 (7) ◽  
pp. 3235-3246 ◽  
Author(s):  
G Basile ◽  
M Aker ◽  
R K Mortimer
Keyword(s):  
Cell Cycle ◽  
Transcriptional Regulation ◽  
Recombinational Repair ◽  
X Rays ◽  
Repair Gene ◽  
Sequence Element ◽  
Rad51 Protein ◽  
Transcript Levels ◽  
X Ray ◽  
Significant Homology

The RAD51 gene of Saccharomyces cerevisiae is required both for recombination and for the repair of DNA damage caused by X rays. Here we report the sequence and transcriptional regulation of this gene. The RAD51 protein shares significant homology (approximately 50%) over a 70-amino-acid with the RAD57 protein (J.A. Kans and R.K. Mortimer, Gene 105:139-140, 1991), the product of another yeast recombinational repair gene, and also moderate (approximately 27%), but potentially significant, homology with the bacterial RecA protein. The homologies cover a region that encodes a putative nucleotide binding site of the RAD51 protein. Sequences upstream of the coding region for RAD51 protein share homology with the damage response sequence element of RAD54, an upstream activating sequence required for damage regulation of the RAD54 transcript, and also contain two sites for restriction enzyme MluI; the presence of MluI restriction sites has been associated with cell cycle regulation. A 1.6-kb transcript corresponding to RAD51 was observed, and levels of this transcript increased rapidly after exposure to relatively low doses of X-rays. Additionally, RAD51 transcript levels were found to that of a group of genes involved primarily in DNA synthesis and replication which are thought to be coordinately cell cycle regulated. Cells arrested in early G1 were still capable of increasing levels of RAD51 transcript after irradiation, indicating that increased RAD51 transcript levels after X-ray exposure are not solely due to an X-ray-induced cessation of the cell cycle at a period when the level of RAD51 expression is normally high.

White-Light Coronal Structures: Streamers and CMEs

1994 ◽  
Vol 144 ◽  
pp. 82
Author(s):  
E. Hildner
Keyword(s):  
Emission Line ◽  
Electron Density ◽  
White Light ◽  
Coronal Mass Ejections ◽  
X Rays ◽  
Solar Cycles ◽  
Temperature Function ◽  
X Ray ◽  
Eclipse Observations ◽  
Coronal Structures

AbstractOver the last twenty years, orbiting coronagraphs have vastly increased the amount of observational material for the whitelight corona. Spanning almost two solar cycles, and augmented by ground-based K-coronameter, emission-line, and eclipse observations, these data allow us to assess,inter alia: the typical and atypical behavior of the corona; how the corona evolves on time scales from minutes to a decade; and (in some respects) the relation between photospheric, coronal, and interplanetary features. This talk will review recent results on these three topics. A remark or two will attempt to relate the whitelight corona between 1.5 and 6 R⊙to the corona seen at lower altitudes in soft X-rays (e.g., with Yohkoh). The whitelight emission depends only on integrated electron density independent of temperature, whereas the soft X-ray emission depends upon the integral of electron density squared times a temperature function. The properties of coronal mass ejections (CMEs) will be reviewed briefly and their relationships to other solar and interplanetary phenomena will be noted.

Chemical Species Identification in an SEM by Changes in Emitted X-Ray Energies

1974 ◽  
Vol 32 ◽  
pp. 570-571
Author(s):  
R. H. Duff
Keyword(s):  
Species Identification ◽  
Valence Electron ◽  
Chemical Species ◽  
X Rays ◽  
Chemical Bonds ◽  
Small Shift ◽  
X Ray ◽  
Electron Transitions ◽  
Peak Energy ◽  
Chemical Combination

A material irradiated with electrons emits x-rays having energies characteristic of the elements present. Chemical combination between elements results in a small shift of the peak energies of these characteristic x-rays because chemical bonds between different elements have different energies. The energy differences of the characteristic x-rays resulting from valence electron transitions can be used to identify the chemical species present and to obtain information about the chemical bond itself. Although these peak-energy shifts have been well known for a number of years, their use for chemical-species identification in small volumes of material was not realized until the development of the electron microprobe.

Influence of X-Ray Induced Fluorescence on Energy Dispersive X-Ray Analysis of Thin Foils

1977 ◽  
Vol 35 ◽  
pp. 328-329
Author(s):  
E. A. Kenik ◽  
J. Bentley
Keyword(s):  
Thin Foil ◽  
Electron Excitation ◽  
Simple Approach ◽  
Foil Thickness ◽  
X Rays ◽  
X Ray ◽  
Hole Spectrum ◽  
Illumination System ◽  
Thin Foils ◽  
Intensity Ratios

Cliff and Lorimer (1) have proposed a simple approach to thin foil x-ray analy sis based on the ratio of x-ray peak intensities. However, there are several experimental pitfalls which must be recognized in obtaining the desired x-ray intensities. Undesirable x-ray induced fluorescence of the specimen can result from various mechanisms and leads to x-ray intensities not characteristic of electron excitation and further results in incorrect intensity ratios.In measuring the x-ray intensity ratio for NiAl as a function of foil thickness, Zaluzec and Fraser (2) found the ratio was not constant for thicknesses where absorption could be neglected. They demonstrated that this effect originated from x-ray induced fluorescence by blocking the beam with lead foil. The primary x-rays arise in the illumination system and result in varying intensity ratios and a finite x-ray spectrum even when the specimen is not intercepting the electron beam, an ‘in-hole’ spectrum. We have developed a second technique for detecting x-ray induced fluorescence based on the magnitude of the ‘in-hole’ spectrum with different filament emission currents and condenser apertures.

X-ray micro tomography in the scanning electron microscope

1978 ◽  
Vol 36 (1) ◽  
pp. 106-107 ◽  
Author(s):  
W. Brünger
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Target Surface ◽  
The Body ◽  
X Rays ◽  
Cross Sectional ◽  
X Ray ◽  
Micro Tomography ◽  
Scanning Electron

Reconstructive tomography is a new technique in diagnostic radiology for imaging cross-sectional planes of the human body /1/. A collimated beam of X-rays is scanned through a thin slice of the body and the transmitted intensity is recorded by a detector giving a linear shadow graph or projection (see fig. 1). Many of these projections at different angles are used to reconstruct the body-layer, usually with the aid of a computer. The picture element size of present tomographic scanners is approximately 1.1 mm2.Micro tomography can be realized using the very fine X-ray source generated by the focused electron beam of a scanning electron microscope (see fig. 2). The translation of the X-ray source is done by a line scan of the electron beam on a polished target surface /2/. Projections at different angles are produced by rotating the object.During the registration of a single scan the electron beam is deflected in one direction only, while both deflections are operating in the display tube.

Digital x-ray mapping of nanometer-size supported bimetallic catalysts

1988 ◽  
Vol 46 ◽  
pp. 530-531
Author(s):  
L. T. Germinario
Keyword(s):  
Background Radiation ◽  
Metal Cluster ◽  
Single Element ◽  
Beam Diameter ◽  
X Rays ◽  
X Ray ◽  
Major Interest ◽  
Induced Changes

Understanding the role of metal cluster composition in determining catalytic selectivity and activity is of major interest in heterogeneous catalysis. The electron microscope is well established as a powerful tool for ultrastructural and compositional characterization of support and catalyst. Because the spatial resolution of x-ray microanalysis is defined by the smallest beam diameter into which the required number of electrons can be focused, the dedicated STEM with FEG is the instrument of choice. The main sources of errors in energy dispersive x-ray analysis (EDS) are: (1) beam-induced changes in specimen composition, (2) specimen drift, (3) instrumental factors which produce background radiation, and (4) basic statistical limitations which result in the detection of a finite number of x-ray photons. Digital beam techniques have been described for supported single-element metal clusters with spatial resolutions of about 10 nm. However, the detection of spurious characteristic x-rays away from catalyst particles produced images requiring several image processing steps.

X-ray diffraction properties of curved crystal diffractors

1992 ◽  
Vol 50 (2) ◽  
pp. 1734-1735
Author(s):  
W. Z. Chang ◽  
D. B. Wittry
Keyword(s):  
Diffraction Theory ◽  
X Rays ◽  
Diffraction Image ◽  
X Ray Diffraction ◽  
Rocking Curve ◽  
X Ray ◽  
Bent Crystal ◽  
Diffraction Geometry ◽  
Crystal Parameter ◽  
Quantitative Procedure

Since Du Mond and Kirkpatrick first discussed the principle of a bent crystal spectrograph in 1930, curved single crystals have been widely utilized as spectrometric monochromators as well as diffractors for focusing x rays diverging from a point. Curved crystal diffraction theory predicts that the diffraction parameters - the rocking curve width w, and the peak reflection coefficient r of curved crystals will certainly deviate from those of their flat form. Due to a lack of curved crystal parameter data in current literature and the need for optimizing the choice of diffraction geometry and crystal materials for various applications, we have continued the investigation of our technique presented at the last conference. In the present abstract, we describe a more rigorous and quantitative procedure for measuring the parameters of curved crystals.The diffraction image of a singly bent crystal under study can be obtained by using the Johann geometry with an x-ray point source.

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