bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation of Ethylene Biosynthesis in Response to Pollination in Tomato Flowers
Authors: Llop-Tous Immaculada , Barry Cornelius S. , Grierson Donald
Published: July 2002

Pollination of many flowers leads to an increase in ethylene synthesis and flower senescence. We have investigated the regulation of pollination-induced ethylene synthesis in tomato (Lycopersicon esculentum) using flowers of the dialytic(dl) mutant, in which pollination can be manipulated experimentally, with the aim of developing a model system to study tomato flower senescence. Ethylene synthesis increased rapidly indl pistils following pollination, leading to accelerated petal senescence, and was delayed in ethylene-insensitiveNever-ripe (Nr) pistils. However,Nr pistils eventually produced more ethylene thandl pistils, suggesting the presence of negative feedback regulation of ethylene synthesis following pollination.LEACS1A expression correlated well with increased ethylene production in pollinated dl pistils, and expression in Nr revealed that regulation is via an ethylene-independent mechanism. In contrast, the induction of the 1-aminocyclopropane-1-carboxylic acid oxidases, LEACO1and LEACO3, following pollination is ethylene dependent. In addition, the expression profiles of ACS andACO genes were determined during petal senescence and a hypothesis proposed that translocated 1-aminocyclopropane-1-carboxylic acid from the pistil may be important for regulating the initial burst of ethylene production during petal senescence. These results are discussed and differences between tomato and the ornamental species previously studied are highlighted.
Identification and Characterization of Three Orchid MADS-Box Genes of the AP1/AGL9 Subfamily during Floral Transition
Authors: Yu Hao , Goh Chong Jin
Published: July 2002

Gene expressions associated with in vitro floral transition in an orchid hybrid (Dendrobium grex Madame Thong-In) were investigated by differential display. One clone, orchid transitional growth related gene 7 (otg7), encoding a new MADS-box gene, was identified to be specifically expressed in the transitional shoot apical meristem (TSAM). Using this clone as a probe, three orchid MADS-box genes, DOMADS1, DOMADS2, andDOMADS3, were subsequently isolated from the TSAM cDNA library. Phylogenetic analyses show that DOMADS1 andDOMADS2 are new members of the AGL2 subfamily and SQUA subfamily, respectively. DOMADS3 contains the signature amino acids as with the members in the independent OSMADS1 subfamily separated from the AGL2 subfamily. All three of theDOMADS genes were expressed in the TSAM during floral transition and later in mature flowers. DOMADS1 RNA was uniformly expressed in both of the inflorescence meristem and the floral primordium and later localized in all of the floral organs.DOMADS2 showed a novel expression pattern that has not been previously characterized for any other MADS-box genes.DOMADS2 transcript was expressed early in the 6-week-old vegetative shoot apical meristem in which the obvious morphological change to floral development had yet to occur. It was expressed throughout the process of floral transition and later in the columns of mature flowers. The onset of DOMADS3 transcription was in the early TSAM at the stage before the differentiation of the first flower primordium. Later, DOMADS3 transcript was only detectable in the pedicel tissues. Our results suggest that theDOMADS genes play important roles in the process of floral transition.
Protein Dynamics in Thylakoids of the Desiccation-Tolerant PlantBoea hygroscopica during Dehydration and Rehydration
Authors: Navari-Izzo Flavia , Quartacci Mike F. , Pinzino Calogero , Rascio Nicoletta , Vazzana Concetta , Sgherri Cristina L.M.
Published: July 2002

Plants of Boea hygroscopica F. Muell were dehydrated to 9% relative water content (RWC) by withholding water for 26 d, and afterward the plants were rehydrated. Leaves were taken from control plants after 7, 12, and 26 d from the beginning of dehydration, and after 6 and 48 h from rehydration. The RWC decreased by 80% during dehydration, but the leaves regained RWC with rehydration. Dehydrated plants showed lesser amounts of proteins, lipids, and chlorophyll, all of which increased following rewatering. The lipid-to-protein ratio, which decreased during dehydration, returned to control level after 48 h of rehydration. Thylakoid lipids were more unsaturated when RWC reached the value of 9%. EPR measurements of spin-labeled proteins showed the presence of three different groups of proteins with different mobility in thylakoid membranes. The rotational correlation time of groups 1 and 2 increased with dehydration and decreased upon rehydration, whereas group 3 showed little changes. Desiccation did not cause thylakoid swelling or breakage, but the membrane system assemblage showed changes in thylakoid stacking. After 48 h of rehydration the membrane system recovered completely the organization of the fully hydrated state, showing several well-defined and regularly distributed grana.
The Isolation and Characterization in Yeast of a Gene for ArabidopsisS-Adenosylmethionine:Phospho-EthanolamineN-Methyltransferase
Authors: Bolognese Cynthia P. , McGraw Patricia
Published: July 2002

Saccharomyces cerevisiae opi3 mutant strains do not have the phospholipid N-methyltransferase that catalyzes the two terminal methylations in the phosphatidylcholine (PC) biosynthetic pathway. This results in a build up of the intermediate phosphatidylmonomethylethanolamine, causing a temperature-sensitive growth phenotype. An Arabidopsis cDNA library was used to isolate three overlapping plasmids that complemented the temperature-sensitive phenotype. Phospholipid analysis showed that the presence of the cloned cDNA caused a 65-fold reduction in the level of phosphatidylmonomethylethanolamine and a significant, though not equivalent, increase in the production of PC. Sequence analysis established that the cDNA was not homologous to OPI3 or to CHO2, the only other yeast phospholipidN-methyltransferase, but was similar to several other classes of methyltransferases.S-adenosyl-Met:phospho-baseN-methyltransferase assays revealed that the cDNA catalyzed the three sequential methylations of phospho-ethanolamine to form phospho-choline. Phospho-choline is converted to PC by the CDP-choline pathway, explaining the phenotype conferred upon the yeast mutant strain by the cDNA. In accordance with this the gene has been named AtNMT1. The identification of this enzyme and the failure to isolate a plant phospholipidN-methyltransferase suggests that there are fundamental differences between the pathways utilized by yeast and by some plants for synthesis of PC.
Primary Structure and Expression of a 24-kD Vacuolar Protein (VP24) Precursor in Anthocyanin-Producing Cells of Sweet Potato in Suspension Culture
Authors: Xu Wenxin , Shioiri Hidenari , Kojima Mineo , Nozue Masayuki
Published: July 2002

A 24-kD vacuolar protein (VP24) accumulates abundantly in intravacuolar pigmented globules in anthocyanin-containing sweet potato (Ipomoea batatas) cells in suspension culture. A cDNA clone encoding VP24 was isolated from a cDNA library constructed from light-irradiated suspension-cultured cells. Sequence analysis revealed that a 2.9-kbp VP24 cDNA encodes a protein of 893 amino acid residues with a molecular mass of 96.3 kD. According to the deduced amino acid sequence of VP24 cDNA, VP24 is probably synthesized as a large precursor protein with an N-terminal extension composed of a signal peptide and a propeptide, plus the polypeptide of the mature VP24 and its C-terminal propeptide, which contains the multiple transmembrane domains. A search in the ProDom database revealed the mature VP24 domain belongs to the zinc metalloprotease family. Northern analysis revealed that the single 2.9-kb VP24 mRNA increases rapidly after light irradiation, whereas VP24 mRNA was undetectable in the dark-cultured cells or in the presence of a high concentration of 2,4-dichlorophenoxyacetic acid. Light-induced VP24 gene expression closely correlated with the accumulation of anthocyanin in the vacuoles. These results suggested that proteins derived from the VP24 precursor protein may be involved in vacuolar transport and/or accumulation of anthocyanin synthesized in the cytosol.
Evidence That Intragenic Recombination Contributes to Allelic Diversity of the S-RNase Gene at the Self-Incompatibility (S) Locus in Petunia inflata
Authors: Wang Xi , Hughes Austin L. , Tsukamoto Tatsuya , Ando Toshio , Kao Teh-Hui
Published: July 2002

For Solanaceae type self-incompatibility, discrimination between self and nonself pollen by the pistil is controlled by the highly polymorphic S-RNase gene. To date, the mechanism generating the allelic diversity of this gene is largely unknown. Natural populations offer a good opportunity to address this question because they likely contain different alleles that share recent common progenitors. We identified 19 S haplotypes from a natural population ofPetunia inflata in Argentina, used reverse transcriptase-polymerase chain reaction to obtain cDNAs for 15 alleles of the S-RNase gene, and sequenced all the cDNAs. Phylogenetic studies revealed that five of these alleles and two previously identified alleles form a major clade, and that the 5′ region ofS  19 allele was derived from an ancestor allele closely related to S  2, whereas its 3′ region was derived from an ancestor allele closely related to S  8. A similar evolutionary relationship was found among S  3,S  12, andS  15 alleles. These findings suggest that intragenic recombination contributed to the generation of the allelic diversity of the S-RNase gene. Two additional findings emerged from the sequence comparisons. First, the nucleotide sequence of theS  1 allele identified in this work is completely identical to that of the previously identifiedS  1 allele of a different origin. Second, in the two hypervariable regions HVa and HVb, thought to be involved in determining S allele specificity,S  6 andS  9 alleles differ only by four nucleotides, all in HVb, resulting in two amino acid differences. The implications of these findings are discussed.
Hydrophobic Interactions of the Structural Protein GRP1.8 in the Cell Wall of Protoxylem Elements
Authors: Ringli Christoph , Hauf Gunter , Keller Beat
Published: July 2002

The glycine-rich structural protein GRP1.8 of French bean (Phaseolus vulgaris) is specifically localized in the modified primary cell walls of protoxylem elements. Continuous deposition of GRP1.8 into the cell walls during elongation growth of the plant suggests that GRP1.8 is part of a repair mechanism to strengthen the protoxylem. In this work, a reporter-protein system was developed to study the interaction of GRP1.8 with the extracellular matrix. Fusion proteins of a highly soluble chitinase with different domains of GRP1.8 were expressed in the vascular tissue of tobacco (Nicotiana tabacum), and the chemical nature of the interaction of these fusion proteins in the cell wall compartment was analyzed. In contrast with chitinase that required only low-salt conditions for complete extraction, the different chitinase/GRP1.8 fusion proteins were completely extracted only by a nonionic or ionic detergent, indicating hydrophobic interactions of GRP1.8. The same interactions were found with the endogenous GRP1.8 in bean hypocotyls. In addition, in vitro experiments indicate that oxidative cross-linking of tyrosines might account for the insolubilization of GRP1.8 observed in later stages of protoxylem development. Our data suggest that GRP1.8 forms a hydrophobic protein-layer in the cell wall of protoxylem vessels.
Mutator Transposase Is Widespread in the Grasses
Authors: Lisch Damon R. , Freeling Michael , Langham Richard J. , Choy Ming Y.
Published: July 2002

Although the Mutator (Mu) system is well characterized in maize (Zea mays), very little is known about this highly mutagenic system of transposons in other grasses. Mutator is regulated by the MuDRclass of elements, which encodes two genes, one of which,mudrA, has similarity to a number of bacterial transposases. Experiments in our laboratory, as well as database searches, demonstrate that mudrA sequences are ubiquitous and diverse in the grasses. In several species it is clear that multiple paralogous elements can be present in a single genome. In some species such as wheat (Triticum aestivum) and rice (Oryza sativa), mudrA-similar sequences are represented in cDNA databases, suggesting the presence of activeMu transposon systems in these species. Further, in rice and in sorghum, mudrA-like genes are flanked by long terminal inverted repeats, as well as the short host sequence direct repeats diagnostic of insertion. Thus, there is ample evidence that systems related to Mu in maize are at least potentially active in a wide variety of grasses. However, the mudrBgene, though important for Mu activity in maize, is not necessarily a component of Mu elements in other grasses.
Chloroplast and Mitochondrial Proteases in Arabidopsis. A Proposed Nomenclature
Authors: Adam Zach , Adamska Iwona , Nakabayashi Kazumi , Ostersetzer Oren , Haussuhl Kirsten , Manuell Andrea , Zheng Bo , Vallon Olivier , Rodermel Steven R. , Shinozaki Kazuo , Clarke Adrian K.
Published: July 2002

The identity and scope of chloroplast and mitochondrial proteases in higher plants has only started to become apparent in recent years. Biochemical and molecular studies suggested the existence of Clp, FtsH, and DegP proteases in chloroplasts, and a Lon protease in mitochondria, although currently the full extent of their role in organellar biogenesis and function remains poorly understood. Rapidly accumulating DNA sequence data, especially from Arabidopsis, has revealed that these proteolytic enzymes are found in plant cells in multiple isomeric forms. As a consequence, a systematic approach was taken to catalog all these isomers, to predict their intracellular location and putative processing sites, and to propose a standard nomenclature to avoid confusion and facilitate scientific communication. For the Clp protease most of the ClpP isomers are found in chloroplasts, whereas one is mitochondrial. Of the ATPase subunits, the one ClpD and two ClpC isomers are located in chloroplasts, whereas both ClpX isomers are present in mitochondria. Isomers of the Lon protease are predicted in both compartments, as are the different forms of FtsH protease. DegP, the least characterized protease in plant cells, has the most number of isomers and they are predicted to localize in several cell compartments. These predictions, along with the proposed nomenclature, will serve as a framework for future studies of all four families of proteases and their individual isomers.
Increased Cysteine Biosynthesis Capacity of Transgenic Tobacco Overexpressing an O-Acetylserine(thiol) Lyase Modifies Plant Responses to Oxidative Stress
Authors: Youssefian Shohab , Nakamura Michimi , Orudgev Emin , Kondo Noriaki
Published: July 2002

O-Acetylserine(thiol) lyase (OASTL), a key enzyme of plant sulfur metabolism, catalyzes the formation of Cys from sulfide and O-acetylserine. The biosynthesis of Cys is regarded as the exclusive function of sulfur reduction in plants, and a key limiting step in the production of glutathione (GSH), a thiol implicated in various cellular functions, including sulfur transport, gene expression, scavenging of reactive oxygen species (ROS), and resistance to biotic and abiotic stresses. To examine whether an increased capacity for cysteine (Cys) biosynthesis alters cellular responses to such stresses, we studied the differential changes in thiol levels and ROS scavenging of transgenic tobacco (Nicotiana tabacum) plants expressing the wheat (Triticum aestivum) OASTL gene, cys1, to SO2 and to the ROS generator, methyl viologen. Intracellular Cys and GSH contents were generally higher incys1 transgenics than in controls under normal growth conditions, but became especially elevated in transgenic plants after SO2 exposure. An examination of differences in the ROS scavenging system of the transgenic plants also demonstrated the specific accumulation of Cu/Zn superoxide dismutase transcripts, known to be induced by Cys or GSH, and elevated cellular superoxide dismutase activities. The transgenic plants accordingly showed dramatic reductions in the extent of both foliar and photooxidative damage in response to acute SO2, as well as reduced levels of chlorosis and membrane damage following methyl viologen treatment. Overall, our results imply that OASTL plays a pivotal role in the synthesis of Cys and GSH that are required for regulation of plant responses to oxidative stress.
Mitochondrial Adaptations to NaCl. Complex I Is Protected by Anti-Oxidants and Small Heat Shock Proteins, Whereas Complex II Is Protected by Proline and Betaine
Authors: Hamilton E. William , Heckathorn Scott A.
Published: July 2002

High soil sodium (Na) is a common stress in natural and agricultural systems. Roots are usually the first tissues exposed to Na stress and Na stress-related impairment of mitochondrial function is likely to be particularly important in roots. However, neither the effects of NaCl on mitochondrial function, nor its protection by several potential adaptive mechanisms, have been well studied. This study investigated the effects of NaCl stress on maize (Zea mays) mitochondrial electron transport and its relative protection by osmoprotectants (proline, betaine, and sucrose), antioxidants (ascorbate, glutathione, and α-tocopherol), antioxidant enzymes (catalase and Cu/Zn-superoxide dismutase), and mitochondrial small heat shock proteins (sHsps). We demonstrate that Complex I electron transport is protected by antioxidants and sHsps, but not osmoprotectants, whereas Complex II is protected only by low concentrations of proline and betaine. These results indicate that NaCl stress damaged Complex I via oxidative stress and suggests that sHsps may protect Complex I as antioxidants, but NaCl damaged Complex II directly. This is the first study to demonstrate that NaCl stress differentially affects Complex I and II in plants and that protection of Complex I and II during NaCl stress is achieved by different mechanisms.
The Catalytic Site of the Pectin Biosynthetic Enzyme α-1,4-Galacturonosyltransferase Is Located in the Lumen of the Golgi
Authors: Sterling Jason D. , Quigley Heather F. , Orellana Ariel , Mohnen Debra
Published: July 2002

α-1,4-Galacturonosyltransferase (GalAT) is an enzyme required for the biosynthesis of the plant cell wall pectic polysaccharide homogalacturonan (HGA). GalAT activity in homogenates from pea (Pisum sativum L. var. Alaska) stem internodes co-localized in linear and discontinuous sucrose gradients with latent UDPase activity, an enzyme marker specific for Golgi membranes. GalAT activity was separated from antimycin A-insensitive NADH:cytochromec reductase and cytochrome c oxidase activities, enzyme markers for the endoplasmic reticulum and the mitochondria, respectively. GalAT and latent UDPase activities were separated from the majority (80%) of callose synthase activity, a marker for the plasma membrane, suggesting that little or no GalAT is present in the plasma membrane. GalAT activities in proteinase K-treated and untreated Golgi vesicles were similar, whereas no GalAT activity was detected after treating Golgi vesicles with proteinase K in the presence of Triton X-100. These results demonstrate that the catalytic site of GalAT resides within the lumen of the Golgi. The products generated by Golgi-localized GalAT were converted by endopolygalacturonase treatment to mono- and di-galacturonic acid, thereby showing that GalAT synthesizes 1→4-linked α-d-galacturonan. Our data provide the first enzymatic evidence that a glycosyltransferase involved in HGA synthesis is present in the Golgi apparatus. Together with prior results of in vivo labeling and immunocytochemical studies, these results show that pectin biosynthesis occurs in the Golgi. A model for the biosynthesis of the pectic polysaccharide HGA is proposed.
Data smoothing and distortion of X-ray diffraction peaks. I. Theory
Authors: Wang Hejing , Zhou Jian
Published: July 2002

A general model of smoothing-induced distortions of an X-ray diffraction (XRD) peak is derived from theoretical analyses by convoluting a Savitzky–Golay (S.–G.) polynomial filter with the Gaussian, Lorentzian and pseudo-Voigt curves. This is based on the assumption that an XRD peak consists of five basic parameters and two additional parameters. Flattening and broadening are the general effects of smoothing. No change in peak area after smoothing is a new feature revealed by this analysis. An unusual change (sharpening with narrowing first, then flattening with broadening as usual) of the peak in a short smoothing range is found for an asymmetric peak. This phenomenon is variable, being governed mainly by the degree of asymmetry of the peak and factors such as peak shifting, curve type, state of the peak top and smoothing range. Formulae describing the smoothing changes of all parameters of a peak are derived. Constants used to link these formulae are set and their properties are analysed with different functions, different states of the peak top, coefficients of shape perfection (`shape-perfect coefficients'), degrees of asymmetry and smoothing ranges.
Recording of electron-diffraction patterns of radiation-sensitive materials in the high-voltage electron microscope with luminescent radiographic screens
Authors: King M. V. , Parsons D. F.
Published: July 2002

An effective method for greatly reducing the electron exposure of radiation-sensitive organic or biological specimens while recording their diffraction patterns in a high-voltage (MeV range) electron microscope is described. It involves recording on double-coated screen-type medical X-ray film and backing it with a luminescent radiographic screen which intercepts the transmitted electrons and emits visible light that exposes the bottom emulsion of the film. Values of sensitivity, resolution, and enhancement ratio are tabulated: the latter values range up to 41. Typical patterns taken with l-valine are shown.
Crystal data for zinc oxysulphate [Zn3O(SO4)2]
Authors: Erdös E.
Published: July 2002

Zinc oxysulphate [Zn3O(SO4)2] crystallizes with a monoclinic unit cell, a = 7.867 (7), b= 6.700 (7), c = 7.374 (7) Å, β = 117.3 (1)°, Z = 2, space group P21 or P21/m, Dm
3.89, Dx
= 3.887 g cm−3. An indexed powder pattern is given.
Background evaluation and spot recognition on crystallographic diffraction photographs
Authors: Taupin D. , Nogues J.
Published: July 2002

A computer method is described which provides a means for determination of both background and spot characteristics without the knowledge a priori of the positions of those spots in a crystallographic diffraction photograph. The background is first determined in any arbitrary region by means of a histogram technique. Then the sets of points emerging from the background's statistical tolerances are collected together with simple neighbouring rules. The problem of large areas which do not fit in a computer memory is discussed and solved with an overlapping window technique. The accuracy of the method is checked by means of a simulation (characteristic retrieval of computer generated spots); the precision appears to be better than the classical rectangular box method except for weak spots.
An N-pattern display for an SSD X-ray diffractometer
Authors: Hosoya S. , Sakamaki T. , Nakano Y. , Fukamachi T.
Published: July 2002

The present paper describes a new type of display for X-ray diffraction patterns which corresponds to the N pattern well known in electron diffraction. This has been realized by an ω-circle SSD (solid-state detector) diffractometer equipped with a CRT display all operated by a small computer. The merits are described of its possible applications.
The information available from anomalous scattering on fibres at different wavelengths
Authors: Nave C.
Published: July 2002

The contribution of a particular atom in a molecule to the total X-ray scattering can be altered by varying the wavelength in the region of the absorption edge of the atom. It is shown that only the changes in the real part of the anomalous scattering of the atom provide significant changes in a pattern from a fibre containing molecules with helical symmetry. Changes due to the imaginary component are small and Friedel differences cannot be observed, owing to the fibre disorder. The information which can be obtained is equivalent to that given by a truly isomorphous heavy-atom derivative. For the general case this is not sufficient to provide unambiguous phase information. If a twofold axis is present at right angles to the fibre axis then the amplitudes are real and the phase problem can, in favourable cases, be solved.
Addition of symmetry-related contact restraints to PROTIN and PROLSQ
Authors: Sheriff S.
Published: July 2002

Symmetry-related van der Waals contacts and hydrogen bonds are stereochemical restraints which are often ignored in macromolecular structure refinement programs. PROTIN and PROLSQ have been modified to account for symmetry-related contacts. The derivatives calculated for an atom in its symmetry-transformed position need only be multiplied by the appropriate rotation matrix to be applied to the atom in its untransformed position. Therefore the code already present in PROLSQ for van der Waals contacts is readily adapted to account for symmetry-related contacts. The `cubing' algorithm, shown to be much faster than residue-by-residue center and radius methods for generating potential contacts, has been incorporated in PROTIN.
The effect of crystallographic orientation on the optical anisotropy of graphite layers on diamond surfaces
Authors: van Enckevort W. J. P.
Published: July 2002

The optical anisotropy of polycrystalline graphite layers formed after catalytic graphitization of single-crystal diamond surfaces has been studied as a function of crystallographic substrate orientation. It was found that the shapes and orientations of the two-dimensional indicatrices of the graphite coatings were in complete agreement with the two-dimensional point-group symmetry of the underlying diamond surfaces. This means the graphite crystallites have one or more preferential orientations imposed by the substrate.
Crystal setting by Bairsto's method
Authors: Jeffreys J. A. D.
Published: July 2002

The graphical method described by Bairsto [J. Sci. Instrum. (1948). 25, 215–216] can be replaced by an analytical solution.
The half-widths of Bragg intensity profiles measured with a triple-crystal diffractometer at a synchrotron-radiation source. I. Derivation of a simple expression for the full width at half-maximum
Authors: Rossmanith E.
Published: July 2002

On the basis of the expressions given by Rossmanith [Acta Cryst. (1992), A48, 596–610; (1993), A49, 80–91], a simple approximation is derived for the half-widths of Bragg intensity profiles measured with a triple-crystal diffractometer at a synchrotron-radiation source. This new formula facilitates insight into the effects of four parameters – divergence, wavelength spread, mosaic spread and mosaic block size – on the widths of the profiles.
Towards Automatic Indexing of the Laue Diffraction Pattern
Authors: Ravelli R. B. G. , Hezemans A. M. F. , Krabbendam H. , Kroon J.
Published: July 2002

A method is presented for the semi-automatic indexing of the Laue diffraction pattern. The method is based on the recognition of conics in the Laue pattern by a plane-search algorithm in reciprocal space, after which possible cells are constructed in direct space and relative cell parameters and crystal orientation are obtained. These cells, scaled to an arbitrary volume, are refined, reduced and grouped in order of frequency of occurrence. Usually, the cell that occurs most frequently is the correct one. Other cells found have one or more axes doubled. Such cells are easily discriminated by comparison of the corresponding simulated Laue pattern with the measured one. The method is tested with different data sets of an organic and an organometallic compound collected with an image plate using white radiation of a molybdenum sealed tube. For each pattern, the correct cell was found. Further refinement of the relative cell parameters by matching of the calculated and observed positions of the Lane spots showed good agreement with the relative cell parameters obtained from monochromatic data. To scale the cells, additional information is needed. This paper demonstrates the use of the Mo emission line Kβ
1 to determine the cell volume within 1.2%.
Help for checking space-group symmetry
Authors: Nardelli M.
Published: July 2002

Ten examples of crystal structures, taken from a paper by Marsh & Bernal [Acta Cryst. (1995), B51, 300–307], are considered to show how the PARST program works when it compares atomic sets in the search for lost symmetries.
A computer program to derive (3+1)-dimensional symmetry operations from two-line symbols
Authors: Fu Z.-Q. , Fan H.-F.
Published: July 2002

A computer program has been written for the derivation of (3 + 1)-dimensional symmetry operations from the two-line symbols. The derivation is based on the concept of generators {[Γ(Rv
E
), ∊v
, s

v
, τv
, q)|v = 1, NG}, in which {[Γ(Rv
E
), s

v
)|v = 1, NG} denotes the set of generators of the basic space group represented by the upper line. The program, called SPGR4D, is written in Fortran77 and based on the program by Burzlaff & Hountas (1982). [J. Appl. Cryst. (1982), 15, 464–467] for the derivation of symmetry operations in three-dimensional space. SPGR4D has been incorporated into a new version of the direct-methods program DIMS for solving incommensurate modulated crystal structures.
Simple device for mounting crystals for single-crystal diffractometry
Authors: Vochten R. , Huysmans R. , Blaton N. , Peeters O. M.
Published: July 2002

This work describes a micrometfic manipulating device for easy mounting of small crystals on a needle along a preferred orientation.
The location of p-dichlorobenzene in a single crystal of zeolite H-ZSM-5 at high sorbate loading
Authors: van Koningsveld H. , Jansen J. C. , van Bekkum H.
Published: July 2002

The crystal structure of a high-loaded complex of H-ZSM-5 with eight molecules of p-dichlorobenzene per unit cell has been solved by single-crystal X-ray diffraction. The orthorhombic space group P212121 with a = 20.102 (6), b = 19.797 (9), c = 13.436 (3) Å and V = 5347 (3) Å3 has four Si23.92Al0.08O48.2C6H4Cl2 units per unit cell. Dx
= 2.164 Mg m−3, λ(MoKα) = 0.71073 Å and μ(Mo Kα) = 0.876 mm−1. The final R(wR) = 0.046 (0.039), w = 1/σ
2(F), for 6090 observed reflections with I > 1.0σ(I) measured at 293 K. The straight channel parallel to [010] is slightly corrugated. The elliptical cross sections have limiting apertures of 6.0 × 4.9 Å (r
oxygen = 1.35 Å). The sinusoidal channel parallel to [100] is elliptical with major and minor axes of 6.1 × 4.8 Å, respectively. One of the two independent p-dichlorobenzene molecule lies at the intersection of the straight and sinusoidal channels with its long molecular axis almost parallel to (100) and deviating ~8° from [010]. The second p-dichlorobenzene molecule is in the sinusoidal channel. Its long molecular axis deviates almost 7° from [100] and is practically parallel to (010). The structural aspects are in all details comparable to those in the high-loaded H-ZSM-5/p-xylene complex [van Koningsveld, Tuinstra, van Bekkum & Jansen (1989). Acta Cryst. B45, 423–431] , except for the main interaction forces between the p-dichlorobenzene molecules at the channel intersection.
Structures of four o-nitrobenzonitriles
Authors: Britton D. , Cramer C. J.
Published: July 2002

The crystal structures of 6-methyl- (I), 6-chloro- (II) and 5-chloro-2-nitrobenzonitrile (III), as well as 2,6-dinitrobenzonitrile (IV), have been determined. (I), orthorhombic, Pbca, a = 9.969 (2), b = 14.728 (4), c = 10.179 (3) Å, T = 180 K; (II), orthorhombic, Pbca, a = 9.469 (5), b = 14.752 (7), c = 10.859 (5) Å, T = 297 K; (III), monoclinic, P21/n, a = 7.889 (2), b = 15.064 (12), c = 7.311 (4) Å, β = 118.22 (3)°, T = 189 K; (IV), orthorhombic, Pbcn, a = 13.081 (6), b = 9.027 (4), c = 6.545 (3) Å, T = 297 K. In (I)–(III) there is a short intramolecular distance [I 2.552 (4), II 2.579 (3), III 2.599 (2) Å] between one of the nitro O atoms and the adjacent nitrile C atom. These short distances plus the accompanying molecular distortions are taken as indications of incipient nucleophilic attack of the O atoms on the electrophilic nitrile C atom. Molecular orbital calculations at the Hartree–Fock level using the 6-31G* basis set support this interpretation; natural bond-orbital analysis indicates an n
O1 → π*CN delocalization energy of 10–15 kJ mol−1 for (I), (II) and (III). In (III) and (IV) the molecules pack in sheets, apparently driven by two C—H...O hydrogen bonds and a CN...Cl interaction in (III) and two C—H...O and one C—H...N hydrogen bonds in (IV).
Vacancies and electron localization in the incommensurate intergrowth compound (La0.95Se)1.21VSe2
Authors: Ren Y. , Baas J. , Meetsma A. , de Boer J. L. , Wiegers G. A.
Published: July 2002

The structure of the inorganic misfit layer compound (La0.95Se)1.21VSe2 has been determined on the basis of a four-dimensional superspace group. The crystal is composed of an alternate stacking of VSe2 sandwiches and two-atom-thick LaSe layers. The first subsystem VSe2 has a distorted CdI2-type structure with V atoms in trigonal antiprisms of Se atoms. It has space-group symmetry C{\bar 1} and its basic structure unit-cell dimensions are a
11 = 3.576 (3), a
12 = 6.100 (2), a13 = 11.690 (2) Å, α
1 = 95.12 (2), β
1 = 85.96 (2) and γ = 89.91 (2)°. The second subsystem LaSe has a distorted rock-salt structure with space-group symmetry C{\bar 1} and a basic structure unit cell given by a
21 = 5.911 (2), a
22 = 6.101 (2), a
23 = 11.684 (2) Å, α
2 = 95.07 (2), β
2 = 85.76 (2), γ
2 = 90.02 (2)°. The two subsystems have the common (a*
ν2, a*
ν3) plane and have a displacive modulation according to the two mutually incommensurate periodicities along the
v1 axes. The symmetry of the complete system is described by the superspace group Gs
= C{\bar 1} [0.6050 (7), 0.0020 (7), −0.007 (1)] with C-centring (½,½, 0, ½). Reciprocal lattice parameters for this superstructure embedding are (a
*
1, a
*
2, a
*
3, a
*
4) = (a
*
11, a
*
12, a
*
13, a
*
21). For 2125 unique reflections with I> 2.5σ(I), measured using Mo Kα1 radiation, refinement smoothly converged to wR = 0.055 (R = 0.045) on a modulated structure model with 77 parameters including La vacancies. The presence of ~ 5% of La vacancies in the LaSe subsystem leads to an exact charge balance between La3+, V3+ and Se2−. The largest modulation occurs on the V atoms, which results in strong variation in the V—V distances. Thus, the semiconducting behaviour of this compound is interpreted in terms of La vacancies in LaSe and modulation-induced Mott localization in VSe2.
The rare trans-syn thymine photodimers: structures of polyoxyethylene-linked bisthymines and the derived trans-syn thymine photodimers. Comparison of the stereochemistry before and after photodimerization
Authors: Suresh C. G. , Gangamani B. P. , Ganesh K. N.
Published: July 2002

trans-syn Photodimer of polyoxyethylene bisthymine (1) [1,1′-(ethylenedioxydiethylene)dithymine], trans-syn-1,8-(ethylenedioxyethylene)hexahydro-4a,4b-dimethylcyclobuta[1,2-d:4,3-d′]dipyrimidine-2,4,5,7(3H,6H)-tetrone (2), C16H22N4O6, Mr
= 366.4, triclinic P{\bar 1}, a = 7.900 (4), b = 10.061 (8), c = 12.048 (4) Å, α = 71.37 (5), β = 78.13 (13), γ = 72.17 (5)°, V = 857.7 (9) Å3, Z = 2, Dx
= 1.418 g cm−3, μ = 0.103 mm−1, F(000) = 388, R = 0.0953 for 1482 observed reflections; 1,1′-(1,2-phenylenedioxydiethylene)dithymine (3), C20H22N4O6, Mr
= 414.4, triclinic, P{\bar 1}, a = 8.558 (2), b = 11.077 (2), c = 11.437 (3) Å, α = 108.57 (2), β = 94.37 (2), γ = 99.77 (2)°, V = 1003.1 (4) Å3, Z = 2, Dx
= 1.377 g cm−3, μ = 0.096 mm−1, F(000) = 436, R = 0.0443 for all reflections; trans-syn photodimer of (3), 1,8-(1,2-phenylenedioxydiethylene)hexahydro-4a,4b-dimethylcyclobuta[1,2-d:4,3-d′]dipyrimidine-2,4,5,7(3H,6H)-tetrone (4), C20H22N4O6, Mr
= 414.4, monoclinic, P21/n, a = 10.357 (4), b = 14.578 (5), c = 12.676 (2) Å, β = 97.99 (3)°, V = 1895 (1) Å3, Z = 4, Dx
= 1.453 g cm−3, μ = 0.102 mm−1, F(000) = 872, R = 0.0628 for 1077 observed reflections. The bisthymines (1) and (3) on photodimerization produce cyclobutane-linked trans-syn thymine dimers as the exclusive products. The planar thymines stack one above the other in (1), while they are approximately perpendicular in (3). Planarities of the thymines are altered on photodimerization. The stereochemistry around the cyclobutane ring in photoproducts (2) and (4) is highly strained. The distortions in the bond lengths and angles due to this strain are concentrated mainly on the C5 and C6 atoms, which form the interpyramidal bonds. This strain is comparatively less in the rigid catechol-linked dimer (4). The N3 atom of thymines forms hydrogen bonds in all structures. Photoproducts show closer packing compared with the parent compounds.
Villamaninite, a case of noncubic pyrite-type structure
Authors: Marcos C. , Paniagua A. , Moreiras D. B. , García-Granda S. , Díaz M. R.
Published: July 2002

This paper reports the results obtained in a study of the crystal structure of two villamaninite samples from Villamanín (León, Spain), labeled (1) and (2). Villamaninite, (Cu,Ni,Co,Fe)(S,Se)2, is a pyrite-type disulfide. Different long-period elements, including Au, in ionic substitution are also observed. Previous authors have assumed a cubic Pa{\bar 3} symmetry for this mineral. The result of our single-crystal study shows a deviation from the cubic symmetry Pa{\bar 3} pyrite-type to a pseudocubic symmetry, which is in agreement with the observed optical anisotropy shown by both samples. The structural refinement process leads to a monoclinic model, space group P1211, with a = 5.709 (2), b = 5.707 (2), c = 5.708 (2) Å, β = 90.01 (1)° for sample (1),° and a = 5.704 (3), b = 5.703 (3), c = 5.704 (3) Å, β = 89.99 (2)° for sample (2), with Z = 4. Previous Mössbauer spectroscopic studies stating two different cation sites for Au support the monoclinic model.
Electron Density in YTiO3
Authors: Hester J. R. , Tomimoto K. , Noma H. , Okamura F. P. , Akimitsu J.
Published: July 2002

Accurate electron density analyses have been performed on the title compound, yttrium titanate, at room and low temperature using W K\alpha radiation. Room- and low temperature \delta\rho maps are generally consistent. Difference electron densities near the two symmetrically independent O atoms differ markedly. These observations may have significance for understanding the role of the O atom in mediating d-electron interactions between neighbouring Ti coordination polyhedra. Features having lower symmetry than that of the approximately octahedral local environment are observed within the Ti coordination octahedron. Crystal data at room temperature: YTiO3, M

r
= 184.79, T = 293 K, Pnma, a = 5.6901 (4), b = 7.6130 (7), c = 5.3381 (6) Å, V = 231.24 (4) Å3, Z = 4, D

x
= 5.308 Mg m-3, \mu(W K\alpha) = 1.02 mm−1, R = 0.024, wR = 0.017, S = 1.64 (2) for 2996 independent reflections. Low temperature: T = 127 K, Pnma, a = 5.690 (4), b = 7.583 (6), c = 5.318 (5) Å, V = 229.5 (3) Å3, D

x
= 5.35 Mg m−3, \mu(W K\alpha) = 1.02 mm−1, R = 0.021, wR = 0.015, S = 1.80 (2) for 2968 independent reflections.
X-ray and Electron Diffraction Study of MgO
Authors: Tsirelson V. G. , Avilov A. S. , Abramov Yu. A. , Belokoneva E. L. , Kitaneh R. , Feil D.
Published: July 2002

Precise X-ray and high-energy transmission electron diffraction methods were used for the study of electron density and electrostatic potential in MgO crystals. The structure amplitudes were determined and their accuracy estimated using ab initio Hartree–Fock structure amplitudes as criteria. The electrostatic potential distributions, reconstructed using Fourier series from both X-ray and electron diffraction data, are in satisfactory mutual agreement and are similar to the theory. They, however, suffer from restricted experimental resolution and, therefore, the reconstruction of the electrostatic potential via an analytical structural model is preferable. The κ model of electron density was adjusted to X-ray experimental structure amplitudes and those calculated by the Hartree–Fock method. The electrostatic potential, deformation electron density and the Laplacian of the electron density were calculated with this model. The critical points in both experimental and theoretical model electron densities were found and compared with those for procrystals from spherical atoms and ions. A disagreement concerning the type of critical point at (1\over 4,1\over 4,0) in the area of low, near-uniform electron density is observed. It is noted that topological analysis of the electron density in crystals can be related with a close-packing concept.
Neutron and X-ray Diffraction Study of the Thermal Motion in K2PtCl6 as a Function of Temperature
Authors: Schefer J. , Schwarzenbach D. , Fischer P. , Koetzle Th. , Larsen F. K. , Haussühl S. , Rüdlinger M. , McIntyre G. , Birkedal H. , Bürgi H.-B.
Published: July 2002

The crystal structure and thermal displacement parameters of potassium hexachloroplatinate, K2PtCl6, have been studied as functions of temperature between 8 and 380 K, using four single crystal neutron diffraction, five single crystal X-ray diffraction and two neutron powder diffraction data sets. Third-order anharmonic Gram–Charlier terms have been determined in all the neutron single crystal and two of the X-ray refinements. Results are consistent with a predominantly ionic compound K^{+}_{2}(PtCl6)2−. The dimensions of the octahedral (PtCl6)2− ion hardly vary with temperature. During thermal expansion, these rigid ions move farther apart. The temperature dependence of the atomic mean-square displacements agrees well with that of ensemble-averaged quantized harmonic oscillators. The thermal motion of (PtCl6)2− is dominated by rigid-body libration and translation, but contributions from internal vibrations are also identified. The anharmonic coefficients of Cl at high temperature agree with curvilinear motion due to the rigid-body libration. The motion of K+ is also anharmonic.
Low-temperature crystallization and structure determination of N-(trifluoromethyl)formamide, N-(2,2,2-trifluoroethyl)formamide and 2,2,2-trifluoroethyl isocyanide
Authors: Perpétuo G. J. , Buschmann J. , Luger P. , Lentz D. , Dreissig D.
Published: July 2002

Crystals of N-(trifluoromethyl)formamide, C2H2F3NO, (I), N-(2,2,2-trifluoroethyl)formamide, C3H4F3NO, (II), and 2,2,2-trifluoroethyl isocyanide, C3H2F3N, (III), were grown in situ on an X-ray diffractometer and analysed by single-crystal X-ray diffraction methods at low temperatures. Crystal data: (I) orthorhombic, P212121, a = 4.547 (2) Å, b = 5.947 (3) Å, c = 14.731 (9) Å, V = 398.3 (4) Å3, Z = 4, M

r
= 113.05, T = 143 K, D

x
= 1.885 Mg m−3; (II) monoclinic, P21/n, a = 4.807 (1) Å, b = 16.707 (3) Å, c = 6.708 (1) Å, β = 109.90 (1)°, V = 506.6 (2) Å3, Z = 4, M

r
= 127.07, T = 141 K, D

x
= 1.666 Mg m−3; (III) orthorhombic, P212121, a = 5.668 (2) Å, b = 9.266 (3) Å, c = 8.626 (2) Å, V = 453.0 (2) Å3, Z = 4, M

r
= 109.06, T = 163 K, D

x
= 1.599 Mg m−3. The results showed that in the crystal both formamides (I) and (II) are exclusively present in the form of the Z isomer, although measurements of solutions of (I) have shown that the E isomer prevails [Lentz et al. (1987). Angew. Chem. 99, 951–953]. In addition ab initio calculations for (I) predicted the E isomer to be the more stable one. In compound (III) the isocyanide group is staggered with respect to the trifluoroethyl group. In the crystal packing of (I) and (II) intermolecular N—H\cdotsO hydrogen bonds generate infinite chains. In (I), these chains are linked to form sheets by C—H\cdotsO contacts. In the crystal structure of (III) each isocyanide dipole is surrounded by four electronegative F atoms with intermolecular C\cdotsF contacts between 3.4 and 3.5 Å.
Synchrotron X-ray analysis of the electron density in HoFe2
Authors: Streltsov Victor A. , Ishizawa Nobuo
Published: July 2002

Structure factors for a small holmium diiron HoFe2 Laves crystal were measured with focused λ = 0.75 Å synchrotron X-radiation using a fast avalanche photodiode (APD) counter. The deformation electron density (Δρ) maps are remarkable for significant excess electron density midway between the Ho atoms, which is not dissimilar to the peaks attributed to classic `covalent bonding' in C and Si crystals. These residual electrons accumulate at the centres of the kagomé net hexagons and form, with the Fe atoms, a triangular lattice which is characterized by more stable magnetic order than the kagomé net. Similar peaks occur along the Ho–Fe and Fe–Fe contacts. These results confirm the hypothesis that 5d electrons of the rare-earth atoms are important in the spin-coupling mechanism for HoFe2-type compounds. The 5d electrons are far less localized than the 4f electrons, and considerable 5d–5d and 5d–3d orbital overlap occurs between neighbouring atoms. Aspherical electron density near the Ho nuclei can be associated with the Ho 4f subshell electrons. Strong depletions of the Δρ near the atoms along the Ho–Ho, Ho–Fe and Fe–Fe vectors are indications of exchange repulsion. The effect of anharmonicity on the Δρ is insignificant.
Crystallization and preliminary X-ray analysis of the Tet-repressor/operator complex
Authors: Orth Peter , Alings Claudia , Schnappinger Dirk , Saenger Wolfram , Hinrichs Winfried
Published: July 2002

Three crystal forms of the repressor protein TetR class D in complex with the palindromic 17 bp operator sequence containing T overhangs on both sides were obtained by hanging-drop vapor-diffusion methods using PEG 4000 and PEG monomethylether 5000 as precipitants. Although the crystallization conditions were very similar, up to three different crystal forms were observed in the same drop. The space groups are monoclinic C2, P21 and hexagonal P6122. The asymmetric units of the latter two crystal forms contain one repressor–operator complex. The crystal structures of these forms were solved by molecular replacement using the Tet-repressor molecule of the complex with tetracycline as a search model.
Crystallization and preliminary X-ray studies of sialidase L from the leech Macrobdella decora
Authors: Luo Yu , Chou Min-yuan , Li Su-chen , Li Yu-teh , Luo Ming
Published: July 2002

Functional monomeric 83 kDa sialidase L, a NeuAcα2→3Gal-specific sialidase from Macrobdella leech, was expressed in Escherichia coli and readily crystallized by a macroseeding technique. The crystal belongs to space group P1 with unit-cell parameters a = 46.4, b = 69.3, c = 72.5 Å, α = 113.5, β = 95.4 and γ = 107.3°. There is one molecule per unit cell, giving a Vm
= 2.4 Å3 Da−1 and a solvent content of 40%. Native and mercury-derivative data sets were collected to 2.0 Å resolution. Threading and molecular-replacement calculations confirmed the existence of a bacterial sialidase-like domain.
Crystallization and preliminary X-ray analysis of human platelet profilin complexed with an oligo proline peptide
Authors: Mahoney Nicole M. , Almo Steven C.
Published: July 2002

Profilin is an actin-monomer binding protein that regulates the distribution and dynamics of the actin cytoskeleton. Profilin binds poly-L-proline and proline-rich peptides in vitro and co-localizes with proline-rich proteins in focal adhesions and at the site of actin tail assembly on the surface of intracellular parasites such as Listeria monocytogenes. The crystallization of the complex between human platelet profilin (HPP) and an L-proline decamer [(Pro)10] is reported here. Diffraction from these crystals is consistent with the space group P21212 with unit-cell constants a = 68.25, b = 97.64, c = 39.10 Å. The crystals contain two HPP molecules per asymmetric unit and diffract to 2.2 Å.