bluuebunny/crossref_metadata_2025 huggingface dataset:
Inhibition of Cdh1–APC by the MAD2-related protein MAD2L2: a novel mechanism for regulating Cdh1
Authors: Pfleger Cathie M. , Salic Adrian , Lee Ethan , Kirschner Marc W.
Published: July 2002

Exit from mitosis requires the degradation of regulatory proteins including the mitotic cyclins and securin through ubiquitination by the anaphase promoting complex (APC) bound to Cdc20 or Cdh1. Cdc20–APC is regulated through inhibition by the spindle assembly checkpoint protein MAD2. Knowledge of Cdh1–APC regulation is limited to the phosphorylation-dependent dissociation of Cdh1 from APC. We report a novel means of regulating Cdh1 by the MAD2-related gene, MAD2L2. MAD2L2 specifically binds and inhibits Cdh1–APC, paralleling the effect of MAD2 on Cdc20. We suggest that MAD2L2 and MAD2 inhibit the release of substrates from APC and propose a mechanism of inhibition.
A SNP Resource for Human Chromosome 22: Extracting Dense Clusters of SNPs From the Genomic Sequence
Authors: Dawson Elisabeth , Chen Yuan , Hunt Sarah , Smink Luc J. , Hunt Adrienne , Rice Kate , Livingston Simon , Bumpstead Suzannah , Bruskiewich Richard , Sham Pak , Ganske Rocky , Adams Mark , Kawasaki Kazuhiko , Shimizu Nobuyoshi , Minoshima Shinsei , Roe Bruce , Bentley David , Dunham Ian
Published: July 2002

The recent publication of the complete sequence of human chromosome 22 provides a platform from which to investigate genomic sequence variation. We report the identification and characterization of 12,267 potential variants (SNPs and other small insertions/deletions) of human chromosome 22, discovered in the overlaps of 460 clones used for the chromosome sequencing. We found, on average, 1 potential variant every 1.07 kb and approximately 18% of the potential variants involve insertions/deletions. The SNPs have been positioned both relative to each other, and to genes, predicted genes, repeat sequences, other genetic markers, and the 2730 SNPs previously identified on the chromosome. A subset of the SNPs were verified experimentally using either PCR–RFLP or genomic Invader assays. These experiments confirmed 92% of the potential variants in a panel of 92 individuals. [Details of the SNPs and RFLP assays can be found at http://www.sanger.ac.uk and in dbSNP.]
Analyses of Habituation in Caenorhabditis elegans
Authors: Rose Jacqueline K. , Rankin Catharine H.
Published: July 2002

Although the nonassociative form of learning, habituation, is often described as the simplest form of learning, remarkably little is known about the cellular processes underlying its behavioral expression. Here, we review research on habituation in the nematodeCaenorhabditis elegans that addresses habituation at behavioral, neural circuit, and genetic levels. This work highlights the need to understand the dynamics of a behavior before attempting to determine its underlying mechanism. In many cases knowing the characteristics of a behavior can direct or guide a search for underlying cellular mechanisms. We have highlighted the importance of interstimulus interval (ISI) in both short- and long-term habituation and suggested that different cellular mechanisms might underlie habituation at different ISIs. Like other organisms, C. elegans shows both accumulation of habituation with repeated training blocks and long-term retention of spaced or distributed training, but not for massed training. Exposure to heat shock during the interblock intervals eliminates the long-term memory for habituation but not the accumulation of short-term habituation over blocks of training. Analyses using laser ablation of identified neurons, and of identified mutants have shown that there are multiple sites of plasticity for the response and that glutamate plays a role in long-term retention of habituation training.
Molecular and Genetic Characterization of a Non-Climacteric Phenotype in Melon Reveals Two Loci Conferring Altered Ethylene Response in Fruit
Authors: Périn Christophe , Gomez-Jimenez MariCarmen , Hagen Lynda , Dogimont Catherine , Pech Jean-Claude , Latché Alain , Pitrat Michel , Lelièvre Jean-Marc
Published: July 2002

Fruit ripening and abscission are associated with an ethylene burst in several melon (Cucumis melo) genotypes. In cantaloupe as in other climacteric fruit, exogenous ethylene can prematurely induce abscission, ethylene production, and ripening. Melon genotypes without fruit abscission or without ethylene burst also exist and are, therefore, non-climacteric. In the nonabscising melon fruit PI 161375, exogenous ethylene failed to stimulate abscission, loss of firmness, ethylene production, and expression of all target genes tested. However, the PI 161375 etiolated seedlings displayed the usual ethylene-induced triple response. Genetic analysis on a population of recombinant cantaloupe Charentais × PI 161375 inbred lines in segregation for fruit abscission and ethylene production indicated that both characters are controlled by two independent loci, abscission layer(Al)-3 and Al-4. The non-climacteric phenotype in fruit tissues is attributable to ethylene insensitivity conferred by the recessive allelic forms from PI 161375. Five candidate genes (two ACO, two ACS, and ERS) that were localized on the melon genetic map did not exhibit colocalization with Al-3 orAl-4.
Multiple Forms of ADP-Glucose Pyrophosphorylase from Tomato Fruit
Authors: Chen B. Y. , Janes H. W.
Published: July 2002

ADP-glucose pyrophosphorylase (AGP) was purified from tomato (Lycopersicon esculentum Mill.) fruit to apparent homogeneity. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis the enzyme migrated as two close bands with molecular weights of 50,000 and 51,000. Two-dimensional polyacrylamide gel electrophoresis analysis of the purified enzyme, however, revealed at least five major protein spots that could be distinguished by their slight differences in net charge and molecular weight. Whereas all of the spots were recognized by the antiserum raised against tomato fruit AGP holoenzyme, only three of them reacted strongly with the antiserum raised against the potato tuber AGP large subunit, and the other two spots (with lower molecular weights) reacted specifically with antisera raised against spinach leaf AGP holoenzyme and the potato tuber AGP small subunit. The results suggest the existence of at least three isoforms of the AGP large subunit and two isoforms of the small subunit in tomato fruit in vivo. The native molecular mass of the enzyme determined by gel filtration was 220 [plus or minus] 10 kD, indicating a tetrameric structure for AGP from tomato fruit. The purified enzyme is very sensitive to 3-phosphoglycerate/inorganic phosphate regulation.
Co-Permeability of 3H-Labeled Water and14C-Labeled Organic Acids across Isolated Plant Cuticles1
Authors: Niederl Sabine , Kirsch Thomas , Riederer Markus , Schreiber Lukas
Published: July 2002

Penetration of 3H-labeled water (3H2O) and the 14C-labeled organic acids benzoic acid ([14C]BA), salicylic acid ([14C]SA), and 2,4-dichlorophenoxyacetic acid ([14C]2,4-D) were measured simultaneously in isolated cuticular membranes of Prunus laurocerasus L.,Ginkgo biloba L., and Juglans regia L. For each of the three pairs of compounds (3H2O/[14C]BA,3H2O/[14C]SA, and3H2O/[14C]2,4-D) rates of cuticular water penetration were highly correlated with the rates of penetration of the organic acids. Therefore, water and organic acids penetrated the cuticles by the same routes. With the combination3H2O/[14C]BA, co-permeability was measured with isolated cuticles of nine other plant species. Permeances of 3H2O of all 12 investigated species were highly correlated with the permeances of [14C]BA (r2 = 0.95). Thus, cuticular transpiration can be predicted from BA permeance. The application of this experimental method, together with the established prediction equation, offers the opportunity to answer several important questions about cuticular transport physiology in future investigations.
Structure and Expression of a Dhurrinase (β-Glucosidase) from Sorghum1
Authors: Cicek Muzaffer , Esen Asim
Published: July 2002

Sorghum (Sorghum bicolor L. Moench) has two isozymes of the cyanogenic β-glucosidase dhurrinase: dhurrinase-1 (Dhr1) and dhurrinase-2 (Dhr2). A nearly full-length cDNA encoding dhurrinase was isolated from 4-d-old etiolated seedlings and sequenced. The cDNA has a 1695-nucleotide-long open reading frame, which codes for a 565-amino acid-long precursor and a 514-amino acid-long mature protein, respectively. Deduced amino acid sequence of the sorghumDhr showed 70% identity with two maize (Zea mays) β-glucosidase isozymes. Southern-blot data suggested that β-glu-cosidase is encoded by a small multigene family in sorghum. Northern-blot data indicated that the mRNA corresponding to the cloned Dhr cDNA is present at high levels in the node and upper half of the mesocotyl in etiolated seedlings but at low levels in the root—only in the zone of elongation and the tip region. Light-grown seedling parts had lower levels of Dhr mRNA than those of etiolated seedlings. Immunoblot analysis performed using maize-anti-β-glucosidase sera detected two distinct dhurrinases (57 and 62 kD) in sorghum. The distribution of Dhr activity in different plant parts supports the mRNA and immunoreactive protein data, suggesting that the cloned cDNA corresponds to theDhr1 (57 kD) isozyme and that the dhr1gene shows organ-specific expression.
Increase in the Quantum Yield of Photoinhibition Contributes to Copper Toxicity in Vivo1
Authors: Pätsikkä Eija , Aro Eva-Mari , Tyystjärvi Esa
Published: July 2002

The effect of copper on photoinhibition of photosystem II in vivo was studied in bean (Phaseolus vulgaris L. cv Dufrix). The plants were grown hydroponically in the presence of various concentrations of Cu2+ ranging from the optimum 0.3 μm(control) to 15 μm. The copper concentration of leaves varied according to the nutrient medium from a control value of 13 mg kg−1 dry weight to 76 mg kg−1 dry weight. Leaf samples were illuminated in the presence and absence of lincomycin at different light intensities (500–1500 μmol photons m−2 s−1). Lincomycin prevents the concurrent repair of photoinhibitory damage by blocking chloroplast protein synthesis. The photoinhibitory decrease in the light-saturated rate of O2 evolution measured from thylakoids isolated from treated leaves correlated well with the decrease in the ratio of variable to maximum fluorescence measured from the leaf discs; therefore, the fluorescence ratio was used as a routine measurement of photoinhibition in vivo. Excess copper was found to affect the equilibrium between photoinhibition and repair, resulting in a decrease in the steady-state concentration of active photosystem II centers of illuminated leaves. This shift in equilibrium apparently resulted from an increase in the quantum yield of photoinhibition (ΦPI) induced by excess copper. The kinetic pattern of photoinhibition and the independence of ΦPI on photon flux density were not affected by excess copper. An increase in ΦPI may contribute substantially to Cu2+ toxicity in certain plant species.
Induction of Defense-Related Responses in Cf9 Tomato Cells by the AVR9 Elicitor Peptide of Cladosporium fulvum Is Developmentally Regulated1
Authors: Honée Guy , Buitink Julia , Jabs Thorsten , De Kloe José , Sijbolts Fred , Apotheker Marion , Weide Rob , Sijen Titia , Stuiver Maarten , De Wit Pierre J.G.M.
Published: July 2002

The AVR9 elicitor from the fungal pathogen Cladosporium fulvum induces defense-related responses, including cell death, specifically in tomato (Lycopersicon esculentum Mill.) plants that carry the Cf-9 resistance gene. To study biochemical mechanisms of resistance in detail, suspension cultures of tomato cells that carry the Cf-9 resistance gene were initiated. Treatment of cells with various elicitors, except AVR9, induced an oxidative burst, ion fluxes, and expression of defense-related genes. Agrobacterium tumefaciens-mediated transformation of Cf9 tomato leaf discs with Avr9-containing constructs resulted efficiently in transgenic callus formation. Although transgenic callus tissue showed normal regeneration capacity, transgenic plants expressing both theCf-9 and the Avr9 genes were never obtained. Transgenic F1 seedlings that were generated from crosses between tomato plants expressing the Avr9 gene and wild-type Cf9 plants died within a few weeks. However, callus cultures that were initiated on cotyledons from these seedlings could be maintained for at least 3 months and developed similarly to callus cultures that contained only the Cf-9 or theAvr9 gene. It is concluded, therefore, that induction of defense responses in Cf9 tomato cells by the AVR9 elicitor is developmentally regulated and is absent in callus tissue and cell-suspension cultures, which consists of undifferentiated cells. These results are significant for the use of suspension-cultured cells to investigate signal transduction cascades.
(+)-Abscisic Acid Metabolism, 3-Ketoacyl-Coenzyme A Synthase Gene Expression, and Very-Long-Chain Monounsaturated Fatty Acid Biosynthesis inBrassica napus Embryos1
Authors: Qi Qungang , Rose Patricia A. , Abrams Garth D. , Taylor David C. , Abrams Suzanne R. , Cutler Adrian J.
Published: July 2002

Microspore-derived embryos ofBrassica napus cv Reston were used to examine the effects of exogenous (+)-abscisic acid (ABA) and related compounds on the accumulation of very-long-chain monounsaturated fatty acids (VLCMFAs), VLCMFA elongase complex activity, and induction of the 3-ketoacyl-coenzyme A synthase (KCS) gene encoding the condensing enzyme of the VLCMFA elongation system. Of the concentrations tested, (+)-ABA at 10 μm showed the strongest effect. Maximum activity of the elongase complex, observed 6 h after 10 μm (+)-ABA treatment, was 60% higher than that of the untreated embryos at 24 h. The transcript of the KCS gene was induced by 10 μm (+)-ABA within 1 h and further increased up to 6 h. The VLCMFAs eicosenoic acid (20:1) and erucoic acid (22:1) increased by 1.5- to 2-fold in embryos treated with (+)-ABA for 72 h. Also, (+)-8′-methylene ABA, which is metabolized more slowly than ABA, had a stronger ABA-like effect on the KCS gene transcription, elongase complex activity (28% higher), and level of VLCMFAs (25–30% higher) than ABA. After 24 h approximately 60% of the added (+)-[3H]ABA (10 μm) was metabolized, yielding labeled phaseic and dihydrophaseic acid. This study demonstrates that (+)-ABA promotes VLCMFA biosynthesis via increased expression of the KCS gene and that reducing ABA catabolism would increase VLCMFAs in microspore-derived embryos.
Overexpression of 20-Oxidase Confers a Gibberellin-Overproduction Phenotype in Arabidopsis
Authors: Huang Shihshieh , Raman Anuradha S. , Ream Joel E. , Fujiwara Hideji , Cerny R. Eric , Brown Sherri M.
Published: July 2002

In the gibberellin (GA) biosynthesis pathway, 20-oxidase catalyzes the oxidation and elimination of carbon-20 to give rise to C19-GAs. All bioactive GAs are C19-GAs. We have overexpressed a cDNA encoding 20-oxidase isolated from Arabidopsis seedlings in transgenic Arabidopsis plants. These transgenic plants display a phenotype that may be attributed to the overproduction of GA. The phenotype includes a longer hypocotyl, lighter-green leaves, increased stem elongation, earlier flowering, and decreased seed dormancy. However, the fertility of the transgenic plants is not affected. Increased levels of endogenous GA1, GA9, and GA20 were detected in seedlings of the transgenic line examined. GA4, which is thought to be the predominantly active GA in Arabidopsis, was not present at increased levels in this line. These results suggest that the overexpression of this 20-oxidase increases the levels of some endogenous GAs in transgenic seedlings, which causes the GA-overproduction phenotype.
Cellular Compartmentation of Zinc in Leaves of the Hyperaccumulator Thlaspi caerulescens1
Authors: Küpper Hendrik , Jie Zhao Fang , McGrath Steve P.
Published: July 2002

Cellular compartmentation of Zn in the leaves of the hyperaccumulator Thlaspi caerulescens was investigated using energy-dispersive x-ray microanalysis and single-cell sap extraction. Energy-dispersive x-ray microanalysis of frozen, hydrated leaf tissues showed greatly enhanced Zn accumulation in the epidermis compared with the mesophyll cells. The relative Zn concentration in the epidermal cells correlated linearly with cell length in both young and mature leaves, suggesting that vacuolation of epidermal cells may promote the preferential Zn accumulation. The results from single-cell sap sampling showed that the Zn concentrations in the epidermal vacuolar sap were 5 to 6.5 times higher than those in the mesophyll sap and reached an average of 385 mm in plants with 20,000 μg Zn g−1 dry weight of shoots. Even when the growth medium contained no elevated Zn, preferential Zn accumulation in the epidermal vacuoles was still evident. The concentrations of K, Cl, P, and Ca in the epidermal sap generally decreased with increasing Zn. There was no evidence of association of Zn with either P or S. The present study demonstrates that Zn is sequestered in a soluble form predominantly in the epidermal vacuoles in T. caerulescens leaves and that mesophyll cells are able to tolerate up to at least 60 mm Zn in their sap.
Evidence for a Slow-Turnover Form of the Ca2+-Independent Phosphoenolpyruvate Carboxylase Kinase in the Aleurone-Endosperm Tissue of Germinating Barley Seeds1
Authors: Osuna Lidia , Pierre Jean-Nöel , González Marı́a-Cruz , Alvarez Rosario , Cejudo Francisco J. , Echevarrı́a Cristina , Vidal Jean
Published: July 2002

Phosphoenolpyruvate carboxylase (PEPC) activity was detected in aleurone-endosperm extracts of barley (Hordeum vulgare) seeds during germination, and specific anti-sorghum (Sorghum bicolor) C4 PEPC polyclonal antibodies immunodecorated constitutive 103-kD and inducible 108-kD PEPC polypeptides in western analysis. The 103- and 108-kD polypeptides were radiolabeled in situ after imbibition for up to 1.5 d in 32P-labeled inorganic phosphate. In vitro phosphorylation by a Ca2+-independent PEPC protein kinase (PK) in crude extracts enhanced the enzyme's velocity and decreased its sensitivity to l-malate at suboptimal pH and [PEP]. Isolated aleurone cell protoplasts contained both phosphorylated PEPC and a Ca2+-independent PEPC-PK that was partially purified by affinity chromatography on blue dextran-agarose. This PK activity was present in dry seeds, and PEPC phosphorylation in situ during imbibition was not affected by the cytosolic protein-synthesis inhibitor cycloheximide, by weak acids, or by various pharmacological reagents that had proven to be effective blockers of the light signal transduction chain and PEPC phosphorylation in C4 mesophyll protoplasts. These collective data support the hypothesis that this Ca2+-independent PEPC-PK was formed during maturation of barley seeds and that its presumed underlying signaling elements were no longer operative during germination.
Refilling of Embolized Vessels in Young Stems of Laurel. Do We Need a New Paradigm?1
Authors: Tyree Melvin Thomas , Salleo Sebastiano , Nardini Andrea , Assunta Lo Gullo Maria , Mosca Roberto
Published: July 2002

Recovery of hydraulic conductivity after the induction of embolisms was studied in woody stems of laurel (Laurus nobilis). Previous experiments confirming the recovery of hydraulic conductivity when xylem pressure potential was less than −1 MPa were repeated, and new experiments were done to investigate the changes in solute composition in xylem vessels during refilling. Xylem sap collected by perfusion of excised stem segments showed elevated levels of several ions during refilling. Stem segments were frozen in liquid N2 to view refilling vessels using cryoscanning electron microscopy. Vessels could be found in all three states of presumed refilling: (a) mostly water with a little air, (b) mostly air with a little water, or (c) water droplets extruding from vessel pits adjacent to living cells. Radiographic probe microanalysis of refilling vessels revealed nondetectable levels of dissolved solutes. Results are discussed in terms of proposed mechanisms of refilling in vessels while surrounding vessels were at a xylem pressure potential of less than −1 MPa. We have concluded that none of the existing paradigms explains the results.
Histidine-41 of the Cytochrome b
5Domain of the Borage Δ6 Fatty Acid Desaturase Is Essential for Enzyme Activity
Authors: Sayanova Olga , Shewry Peter R. , Napier Johnathan A.
Published: July 2002

Unlike most other plant microsomal desaturases, the Δ6-fatty acid desaturase from borage (Borago officinalis) contains an N-terminal extension that shows homology to the small hemoprotein cytochrome (Cyt)b  5. To determine if this domain serves as a functional electron donor for the Δ6-fatty acid desaturase, mutagenesis and functional analysis by expression in transgenic Arabidopsis was carried out. Although expression of the wild-type borage Δ6-fatty acid desaturase resulted in the synthesis and accumulation of Δ6-unsaturated fatty acids, this was not observed in plants transformed with N-terminally deleted forms of the desaturase. Site-directed mutagenesis was used to disrupt one of the axial heme-binding residues (histidine-41) of the Cytb  5 domain; expression of this mutant form of the Δ6-desaturase in transgenic plants failed to produce Δ6-unsaturated fatty acids. These data indicate that the Cyt b  5 domain of the borage Δ6-fatty acid desaturase is essential for enzymatic activity.
Bordered Pit Structure and Vessel Wall Surface Properties. Implications for Embolism Repair
Authors: Zwieniecki Maciej Andrzej , Holbrook Noel Michele
Published: July 2002

The idea that embolized xylem vessels can be refilled while adjacent vessels remain under tension is difficult to accept if the cavitated vessels remain hydraulically connected to vessels under tension. A mechanism by which embolized conduits could be hydraulically isolated from adjacent conduits requires the existence of a non-zero contact angle and a flared opening into the bordered pit chamber such that a convex air-water interface forms at the entrance into the pit chamber. We measured the contact angle and pit chamber geometry for six species. The contact angle measured in the vessel lumen ranged between 42° to 55°, whereas the opening into the pit chamber ranged between 144° and 157°. If the surface properties within the pit chamber are similar to those in the lumen, a convex meniscus will form at the flared opening into the pit chamber. The maximum pressure difference between water in the lumen and gas in the pit chamber that could be stabilized by this interface was calculated to be within the range of 0.07 to 0.30 MPa.
Ethylene Induces Epidermal Cell Death at the Site of Adventitious Root Emergence in Rice
Authors: Mergemann Heidi , Sauter Margret
Published: July 2002

In deepwater rice (Oryza sativa), adventitious root primordia initiate at the nodes as part of normal development. Emergence of the roots is dependent on flooding of the plant and is mediated by ethylene action. Root growth was preceded by the induced death of epidermal cells of the node external to the tip of the root primordium. Cell death proceeded until the epidermis split open. Through this crack the root eventually emerged. Induced death was confined to nodal epidermal cells covering the tip of the primordia. Our results suggest that this process facilitates adventitious root emergence and prevents injury to the growing root. Cell death was inducible not only by submergence but also by application of 1-aminocyclopropane-1-carboxylic acid, the natural precursor of ethylene and it was suppressed in the presence of 2,5-norbornadiene (bicyclo[2.2.1]hepta-2,5-diene), an inhibitor of ethylene action. Adventitious root growth and epidermal cell death are therefore linked to the ethylene signaling pathway, which is activated in response to low oxygen stress.
Hydroxylated Phytosiderophore Species Possess an Enhanced Chelate Stability and Affinity for Iron(III)
Authors: von Wirén Nicolaus , Khodr Hicham , Hider Robert C.
Published: July 2002

Graminaceous plant species acquire soil iron by the release of phytosiderophores and subsequent uptake of iron(III)-phytosiderophore complexes. As plant species differ in their ability for phytosiderophore hydroxylation prior to release, an electrophoretic method was set up to determine whether hydroxylation affects the net charge of iron(III)-phytosiderophore complexes, and thus chelate stability. At pH 7.0, non-hydroxylated (deoxymugineic acid) and hydroxylated (mugineic acid; epi-hydroxymugineic acid) phytosiderophores form single negatively charged iron(III) complexes, in contrast to iron(III)-nicotianamine. As the degree of phytosiderophore hydroxylation increases, the corresponding iron(III) complex was found to be less readily protonated. Measured pKa values of the amino groups and calculated free iron(III) concentrations in presence of a 10-fold chelator excess were also found to decrease with increasing degree of hydroxylation, confirming that phytosiderophore hydroxylation protects against acid-induced protonation of the iron(III)-phytosiderophore complex. These effects are almost certainly associated with intramolecular hydrogen bonding between the hydroxyl and amino functions. We conclude that introduction of hydroxyl groups into the phytosiderophore skeleton increases iron(III)-chelate stability in acid environments such as those found in the rhizosphere or the root apoplasm and may contribute to an enhanced iron acquisition.
Isoprene Increases Thermotolerance of Fosmidomycin-Fed Leaves
Authors: Sharkey Thomas D. , Chen Xiuyin , Yeh Sansun
Published: July 2002

Isoprene is synthesized and emitted in large amounts by a number of plant species, especially oak (Quercus sp.) and aspen (Populussp.) trees. It has been suggested that isoprene improves thermotolerance by helping photosynthesis cope with high temperature. However, the evidence for the thermotolerance hypothesis is indirect and one of three methods used to support this hypothesis has recently been called into question. More direct evidence required new methods of controlling endogenous isoprene. An inhibitor of the deoxyxylulose 5-phosphate pathway, the alternative pathway to the mevalonic acid pathway and the pathway by which isoprene is made, is now available. Fosmidomycin eliminates isoprene emission without affecting photosynthesis for several hours after feeding to detached leaves. Photosynthesis of fosmidomycin-fed leaves recovered less following a 2-min high-temperature treatment at 46°C than did photosynthesis of leaves fed water or fosmidomycin-fed leaves in air supplemented with isoprene. Photosynthesis of Phaseolus vulgaris leaves, which do not make isoprene, exhibited increased thermotolerance when isoprene was supplied in the airstream flowing over the leaf. Other short-chain alkenes also improved thermotolerance, whereas alkanes reduced thermotolerance. It is concluded that thermotolerance of photosynthesis is a substantial benefit to plants that make isoprene and that this benefit explains why plants make isoprene. The effect may be a general hydrocarbon effect and related to the double bonds in the isoprene molecule.
New methods for diffraction stress measurement: a critical evaluation of new and existing methods
Authors: Kamminga J.-D. , de Keijser Th. H. , Mittemeijer E. J. , Delhez R.
Published: July 2002

New methods of diffraction stress analysis of polycrystalline materials, consisting of cubic elastically anisotropic crystallites, are proposed and compared with existing methods. Whereas for the existing methods knowledge of the diffraction elastic constants is presupposed, three new methods are presented that require only knowledge of the (macroscopic) mechanical elastic constants. The stress values obtained with these new methods on the basis of the mechanical elastic constants are more reliable than those obtained with the methods on the basis of the diffraction elastic constants. New and existing methods are illustrated by means of measurements of X-ray diffraction from a magnetron-sputtered TiN layer.
Novel image analysis of two-dimensional X-ray fiber diffraction patterns: example of a polypropylene fiber drawing study
Authors: Ran Shaofeng , Zong Xinhua , Fang Dufei , Hsiao Benjamin S. , Chu Benjamin , Ross Roger
Published: July 2002

On-line studies of the structural development during continuous drawing of a polypropylene fiber were carried out using synchrotron wide-angle X-ray diffraction. A unique image analysis method was introduced to extract quantitative information on the crystal, amorphous and mesomorphic fractions. In addition, the unit-cell parameters and the crystal orientation were obtained under various draw conditions. It was found that the mesophase remained about constant during drawing. At draw ratios less than 6.0, the crystallinity increased and the crystal density decreased as a result of the stress-induced crystallization of crystals with a large degree of disordering. At draw ratios above 6.0, the crystallinity increased slowly and the decrease in crystal density was also retarded because of the draw-induced melting. The crystal orientation increased with increasing draw ratio up to a ratio of 6.0 and then decreased, probably because of chain breakage.
Study of disorder in a tetragonal tungsten bronze ferroelectric relaxor: a structural approach
Authors: Hornebecq V. , Elissalde C. , Weill F. , Villesuzanne A. , Menetrier M. , Ravez J.
Published: July 2002

Electron diffraction analysis, nuclear magnetic resonance measurements, structure determinations and refinements were performed on two ferroelectric lead-containing ceramics (classical and relaxor), with tetragonal tungsten bronze structure, in order to investigate the origin of the relaxor behaviour in such compounds. In both compounds the lead atoms are found to be off-centred in the CN (coordination number) 15 (A2) site. The main difference between the two compositions is the proportion of lead in this site: in the relaxor composition, theA2 site is at least half occupied by lead atoms. Disorder in the repartition of lead and potassium atoms in theA1 (CN 12) andA2 sites was also studiedviacombinatorial calculations to correlate the evolution of the relaxor behaviour in the Pb5Ta10O30–Li10Ta10O30–K10Ta10O30ternary system with composition. The combinatorial study demonstrated that the relaxor behaviour is enhanced by the disorder in cationic repartition.
Crystallization and cryocrystallography inside X-ray capillaries
Authors: López-Jaramillo F. J. , García-Ruiz J. M. , Gavira J. A. , Otálora F.
Published: July 2002

This paper presents a modification of the gel acupuncture method to grow isolated crystals inside X-ray capillaries. Protein crystals are grown from 2–12 µl of gelled agarose–protein solution, cryoprotected and immobilized by the gel matrix. The same X-ray capillary that acts as a crystallization reactor is used to transport the crystals to the X-ray source and to collect data at both room temperature and 100 K, without any post-crystallization manipulation. To enhance the flash-cooling stage, two additional elements are proposed for inclusion in the cryosystems currently in use: a laser pointer to illuminate the crystal to be flash-cooled and a trap to divert the N2flow and switch from room temperature to 100 K without misalignment of the crystal. With the proposed implementation, data can be collected at different temperatures from the same crystal in exactly the same orientation. This permits the study, at lattice level, of changes in unit-cell parameters, mosaic spread and crystal quality induced by cryogenic temperatures and annealing techniques.
Modelling of line profile asymmetry caused by axial divergence in powder diffraction
Authors: Masson O. , Guinebretiere R. , Dauger A.
Published: July 2002

A procedure is presented for modelling the axial divergence aberration profile, taking into account all second-order and end effects of the diffractometer system. It is shown that relatively simple calculations, which could be introduced into Rietveld refinement programs, allow the instrument line profile to be modelled accurately at low and high scattering angles. This model compares well with ray-tracing calculations and can give better results than the usually used model proposed by Van Laar & Yelon [J. Appl. Cryst.(1984),17, 47–54] and Finger, Cox & Jephcoat [J. Appl. Cryst.(1994),27, 892–900].
Diffraction contrast in X-ray radiographic images of octahedrite meteorites
Authors: Weiss W. , Bunge H. J.
Published: July 2002

Slices of ∼12 mm thickness cut out of an octahedritic iron–nickel meteorite of the Gibeon shower were investigated by conventional X-ray transmission radiography. When the direction of the incident X-ray beam is parallel to one or two of the four habit planes of the kamacite lamellae, black–white contrast lines are observed in the radiographs. These lines are attributed to Bragg reflection, at lattice planes parallel to the lamellae planes, of a narrow band of wavelengths filtered out of the incident white spectrum by absorption in the sample.
X-ray study of the orientational order of a concentrated dispersion of kaolinite under flow
Authors: Barè Simona , Cockcroft Jeremy K. , Colston Sally L. , Jupe Andrew C. , Rennie Adrian R.
Published: July 2002

Diffraction with high-energy X-rays is used to determine the orientational alignment of kaolinite particles dispersed in water as they flow down a pipe. Angle-dispersive and energy-dispersive diffraction methods are compared. Detailed studies of samples as thick as 1 cm were possible using energy-dispersive diffraction. A tomographic technique with the sample scanned and rotated in the beam allows maps of the alignment to be determined. The alignment across a pipe of rectangular section was determined. A strong effect caused by the walls was observed, the plate-like particles tending to lie parallel to the wall near the boundary of the pipe.
A double-radius Gandolfi X-ray camera for the generation of powder-like diffractograms of small single crystals, using an imaging plate detector
Authors: Otto H. H. , Hofmann W. , Schröder K.
Published: July 2002

This is a report on the construction and the main features of an X-ray camera following the Debye–Scherrer geometry, combined with a sample mounting and rotation device for single crystals as first suggested by Gandolfi. Doubling of the camera radius and replacing of the wet-film technology by a highly dynamic imaging plate system allows well resolved digital diffraction patterns to be recorded within a short exposure time. Sophisticated calibration, correction and evaluation possibilities are supported by suitable software. Further optional improvements, such as the evacuation of the camera, the adaptation of totally reflecting collimators for an almost parallel primary X-ray beam and a built-in instead of an external imaging plate readout device, will further improve the resolution and peak to background ratio. The simple and versatile apparatus is indispensable for the fast and non-destructive identification of unique mineralogical or technical micro-samples in the form of single-crystal pieces. Initial representative data sets attest to the accuracy, efficiency and sensitivity of the method presented.
X-ray monochromator combining high resolution with high intensity
Authors: Servidori M.
Published: July 2002

A two-germanium-crystal four-220-reflection (+ - - \,+) monochromator, combining high intensity with high resolution, is proposed in this work. The main characteristic is that only the first reflection is asymmetric. The asymmetry factor was chosen so as to allow mixing of asymmetric and symmetric reflections in a monolithic channel-cut crystal without the need for rotation of the two monolith components to correct for the different refraction-induced angular shifts of the reflection pair. It is demonstrated that the exit-beam divergence in the diffraction plane and the fractional wavelength band-pass are smaller by 40% than those of the widely used germanium 220 Bartels monochromator, while the photon flux collected from the source is larger by a factor of five. The optical features and performance of the monochromator are discussed and compared with those of other (+ - - \,+) monochromators reported in the literature.
On the intrinsic hook effect associated with pseudo-Voigt profiles
Authors: Dasgupta Prabal
Published: July 2002

An intrinsic hook effect was always found to be associated with pseudo-Voigt (p-V) profiles when η was less than 0.328 and the FWHM was small (∼0.02°), where η is the fraction of the Cauchy component and FWHM is the full width at half-maximum. The applicability of the Warren–Averbach (WA) analysis for the case of p-V profiles was thoroughly studied and it was found that a p-V profile with η values ranging from 0 to 1 can be safely subjected to WA analysis, provided that the FWHM of the profile is large enough (2w≃ 0.378°).
Parallel processing for Rietveld refinement
Authors: Zeitler Todd R. , Toby Brian H.
Published: July 2002

A method for speeding Rietveld refinements using parallel computing is presented. The method can be applied to most, if not all, Rietveld refinement programs. An example implementation for the Los AlamosGeneral Structure Analysis System(GSAS) package is described. Using a cluster with seven processors, least-squares refinements are completed 2.5 to 5 times faster than on an equivalent single-processor computer.
High-dynamic range SAXS data acquisition with an X-ray image intensifier
Authors: Pontoni Diego , Narayanan T. , Rennie Adrian R.
Published: July 2002

Data with a wide dynamic range of intensity can be collected with a pinhole high-brilliance small-angle X-ray scattering (SAXS) camera using an image-intensified charge-coupled device (CCD) detector. The point spread function (PSF) of this detector has a narrow peak with a broad low tail such that a high level of scattered intensity at small angles can cause a significant background in the detector elements at higher angles. A correction scheme for the long tail of the PSF of the detector is needed when this integrating area detector is used for measuring intensity that spans a dynamic range of four to five orders of magnitude. A procedure is described for measuring the PSF contribution by masking a small part of the detector from the scattered radiation with an absorbing material. In order to measure the PSF, it is necessary to use a high-intensity spot, which is readily achieved by using a sample that scatters strongly at small angles. Although this intensity is spread over many pixels, the sharp features in the scattering from the silica sample chosen for this study permit one to obtain simultaneously both the narrow and the broad parts of the PSF. The data are compared with the actual scattering function, which has been measured exactly with a point-geometry Bonse–Hart camera. The advantages of this procedure are discussed.
Deconvolution of morphological texture from crystallographic texture data
Authors: Langelaan Gijs , Delannay Laurent , Verpoest Ignaas , Van Houtte Paul
Published: July 2002

The physical properties of composite materials reinforced with fibres usually depend significantly on the orientation distribution of these fibres. The goal of this study is to develop a technique to measure the orientation distribution of second-phase particles which in themselves have a strong crystallographic texture. This permits the well known methods of pole-figure measurements to be used and the deconvolution of the `morphological texture function' from these data. In the current paper, the deconvolution procedure is presented and validated by simulations. Finally, the procedure is applied to an experimental system, which further confirms the validity of the approach. The simulations convoluted a morphological texture function with a crystallographic texture using a discrete representation of the orientation distribution function (ODF). After the convolution, the resulting ODF was converted to a series-expansion representation, which then permitted the deconvolution by an independent method. The results of the deconvolution return the original MTF, hence validating the procedure derived. The experimental system measured the crystallographic texture of 316L stainless-steel yarns woven into a fabric. The crystallographic texture obtained from straight yarns was used as the reference texture. The X-ray diffraction measurements reveal the weave pattern but with some ghosting errors. These are attributed to an insufficient measurement volume, which could be overcome by using radiation with a greater penetration, such as neutrons.
Peak shifts and peak broadening in powder neutron-diffraction patterns due to finite aperture counters
Authors: Thomas M. W.
Published: July 2002

The theoretical expressions of Cooper & Sayer [J. Appl. Cryst. (1975), 8, 615] for the peak shift from the true Bragg angle and for the peak broadening in powder neutron-diffraction patterns are confirmed experimentally for detectors with finite aperture. It is shown that these factors can be important even at relatively large scattering angles.
Calculation of the X-ray powder reflection profiles of very small needle-like crystals. II. Quantitative results on eskisehir sepiolite fibers
Authors: Yücel A. , Rautureau M. , Tchoubar D. , Tchoubar C.
Published: July 2002

A calculation method for the X-ray profiles from small, needle-like crystallites [Yücel, Rautureau, Tchoubar & Tchoubar (1980). J. Appl. Cryst.
13, 370–374] is applied to natural Eskisehir sepiolite mineral. By analysing the hk0 reflections, quantitative results are given on the average cross-sectional dimensions, their distribution, preferred directions of growth, lattice parameters, hydration state, and imperfections. Practical methods for the determination of the zeolitic water content and the importance of boundary effects are proposed.
Oscillation camera data processing. 3. General diffraction spot size, shape and energy profile: formalism for polychromatic diffraction experiments with monochromatized synchrotron X-radiation from a singly bent triangular monochromator
Authors: Greenhough T. J. , Helliwell J. R. , Rule S. A.
Published: July 2002

The size and shape of diffraction spots produced by monochromated synchrotron X-radiation from a singly bent triangular monochromator are derived following a simpler more comparative treatment given in earlier work on reflecting range and prediction of partiality for oscillation camera data [Greenhough & Helliwell (1982). J. Appl. Cryst.
15, 493–508]. In that treatment the possibility of a polychromatic experiment {[see Arndt Nucl. Instrum. Methods (1978), 152, 307–311] for an earlier suggestion} was identified and here the energy profile within each diffraction spot is derived along with the spectral resolution ∂E/E at any point in the profile due to experimental conditions and sample characteristics. A firm theoretical basis is established so that experimental problems and procedures can be discussed with a view to optimizing the method in the light of the presentation of the first reported polychromatic experiment [Arndt, Greenhough, Helliwell, Howard, Rule & Thompson (1982). Nature (London), 298, 835–838].
Crystal data for p-bromochlorobenzene and p-dichlorobenzene/p-bromochlorobenzene mixed crystals at 293 K
Authors: Labrador M. , Tauler E. , Haget Y. , Calvet T. , Cuevas M. A. , Estop E.
Published: July 2002

The powder data for p-bromochlorobenzene(pBCB) and p-dichlorobenzene/p-bromochlorobenzene mixed crystals [pDCB]
x
[pBCB]1 − x
at 293 K are reported; their thermal stability at 293 K is given. Vertical diffractomer, graphite monochromator, Cu Kα, λ = 1.5405 Å. They are all isomorphous, monoclinic, P21/a with Z = 2. a = 15.134(4), b = 5.843(2), c = 4.073(1) Å, β = 112.53(1)°, V = 332.7 Å3, Dx
= 1.911 Mg m−3 for pBCB. a = 14.890(5), b = 5.848(5), c = 4.046(2) Å, β = 112.53(2)°, V = 325.4 Å3, Dx
= 1.636 Mg m−3 for [pDCB]0.70[pBCB]0.30. a = 15.004(6), b = 5.840(3), c = 4.059(2) Å, β = 112.48(2)°, V = 328.6 Å3, Dx
= 1.755 Mg m−3 for [pDCB]0.40[pBCB]0.60. a = 15.101(4), b = 5.844(2), c = 4.066(2) Å, β = 112.51(2)°, V = 331.5 Å3, Dx
= 1.873 Mg m−3 for [pDCB]0. 10[pBCB]0.90. The JCPDS Nos. are: 36-1995 for pBCB; 36-1994 for [pDCB]0.70[PBCB]0.30; 36-1993 for [pDCB]0.40[pBCB]0.60; 36-1992 for [pDCB]0.10[pBCB]0.90. Data for [pDCB]0.90[pBCB]0.10, [pDCB]0.80 [pBCB]0.20, [pDCB]0.60 [pBCB]0.40, [pDCB]0.50[pBCB]0.50, [pDCB]0.30[pBCB]0.70 and [pDCB]0.20[pBCB]0.80 have also been measured and are available from the authors or as part of the Supplementary Publication.
Asymmetric X-ray line broadening of plastically deformed crystals. I. Theory
Authors: Groma I. , Ungár T. , Wilkens M.
Published: July 2002

X-ray diffraction line profiles of plastically deformed Cu single crystals orientated for ideal multiple slip were recently found to be markedly asymmetric. A theory is developed to interpret this kind of asymmetric line broadening in terms of the average dislocation density, the dipole polarization of the dislocation structure and the mean square fluctuation of the dislocation density.
Changes of pH during biomacromolecule crystallization by vapor diffusion using ammonium sulfate as the precipitant
Authors: Mikol V. , Rodeau J.-L. , Giegé R.
Published: July 2002

Possible pH variations during crystallization of biological macromolecules by the vapor diffusion method have not been taken into account in most experiments so far reported. The present study demonstrates that when ammonium sulfate is used as the precipitant, pH changes occur due to ammonia transfer following ammonium/ammonia equilibrium. The pH in a crystallization droplet is shown to be controlled by that of the reservoir. The theory of the effect is given and the consequences of pH variations during crystallization are discussed in terms of reproducibility of experiments. An application, the crystallization of concanavalin A induced by pH variation, is presented.
Diffractometer alignment and polarization determination of X-ray beams by means of the Borrmann effect
Authors: Staudenmann J.-L. , Chapman L. D.
Published: July 2002

The Borrmann effect, that is, the anomalous transmission of X-ray beams through sufficiently thick perfect crystals in Laue geometry, is a sensitive diffraction tool which has many fundamental and practical applications: the accurate alignment of any full four-circle instrument (equipped with a cradle in asymmetric design) with respect to the incident beam, measurement of the divergence of any X-ray beam, and the precise determination of the beam polarization, incident or diffracted. For these applications, it is shown that no modifications to the diffractometer are required. The measurements simply consist of measuring φ and χ rocking curves of the anomalous transmitted beam where the ω angle is used as a parameter. The analyses require the findings of the peak centroid positions, the full widths at half maximum and the rocking-curve integrated intensities. Some results are presented as illustrations of the method. These Borrmann-effect applications promise to be more helpful for diffractometers installed at synchrotrons than for in-house laboratories.
Automatic evaluation of general spot profiles in oscillation photography
Authors: Chakravarty S. , Kannan K. K.
Published: July 2002

An algorithm to determine the exact profiles of digitized spots having arbitrary shapes and sizes is described. It does not require any prior knowledge of crystallographic parameters and can be applied to the digitized data set of any random distribution of arbitrarily shaped peaks of finite size having an average intensity significantly higher than a nearly constant background. Application to the case of oscillation photography data from protein crystals is described.