bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of Solar Ultraviolet Radiation on the Potential Efficiency of Photosystem II in Leaves of Tropical Plants
Authors: Krause G. Heinrich , Schmude Claudia , Garden Hermann , Koroleva Olga Y. , Winter Klaus 
Published: July 2002

Abstract
The effects of solar ultraviolet (UV)-B and UV-A radiation on the potential efficiency of photosystem II (PSII) in leaves of tropical plants were investigated in Panama (9°N). Shade-grown tree seedlings or detached sun leaves from the outer crown of mature trees were exposed for short periods (up to 75 min) to direct sunlight filtered through plastic or glass filters that absorbed either UV-B or UV-A+B radiation, or transmitted the complete solar spectrum. Persistent changes in potential PSII efficiency were monitored by means of the dark-adapted ratio of variable to maximum chlorophyll a fluorescence. In leaves of shade-grown tree seedlings, exposure to the complete solar spectrum resulted in a strong decrease in potential PSII efficiency, probably involving protein damage. A substantially smaller decline in the dark-adapted ratio of variable to maximum chlorophylla fluorescence was observed when UV-B irradiation was excluded. The loss in PSII efficiency was further reduced by excluding both UV-B and UV-A light. The photoinactivation of PSII was reversible under shade conditions, but restoration of nearly full activity required at least 10 d. Repeated exposure to direct sunlight induced an increase in the pool size of xanthophyll cycle pigments and in the content of UV-absorbing vacuolar compounds. In sun leaves of mature trees, which contained high levels of UV-absorbing compounds, effects of UV-B on PSII efficiency were observed in several cases and varied with developmental age and acclimation state of the leaves. The results show that natural UV-B and UV-A radiation in the tropics may significantly contribute to photoinhibition of PSII during sun exposure in situ, particularly in shade leaves exposed to full sunlight.
A Weakly Voltage-Dependent, Nonselective Cation Channel Mediates Toxic Sodium Influx in Wheat
Authors: Davenport Romola Jane , Tester Mark 
Published: July 2002

Abstract
To determine the transporters responsible for toxic Na+ influx in wheat (Triticum aestivum), root plasma membrane preparations were screened using the planar lipid bilayer technique as an assay for Na+-permeable ion channel activity. The predominant channel in the bilayer was a 44-pS channel that we called the nonselective cation (NSC) channel, which was nonselective for monovalent cations and weakly voltage dependent. Single channel characteristics of the NSC channel were compared with 22Na+ influx into excised root segments. Na+ influx through the NSC channel resembled 22Na+ influx in its partial sensitivity to inhibition by Ca2+, Mg2+, and Gd3+, and its insensitivity to all other inhibitors tested (tetraethylammonium, quinine, Cs+, tetrodotoxin, verapamil, amiloride, and flufenamate). Na+ influx through the NSC channel also closely resembled an instantaneous current in wheat root protoplasts (S.D. Tyerman, M. Skerrett, A. Garill, G.P. Findlay, R. Leigh [1997] J Exp Bot 48: 459–480) in its permeability sequence, selectivity for K+ over Na+(approximately 1.25), insensitivity to tetraethylammonium, voltage independence, and partial sensitivity to Ca2+. Comparison of tissue, protoplast (S.D. Tyerman, M. Skerrett, A. Garill, G.P. Findlay, R. Leigh [1997] J Exp Bot 48: 459–480), and single- channel data indicate that toxic Na+ influx is catalyzed by a single transporter, and this is likely to be the NSC channel identified in planar lipid bilayers.
Hormonal Interactions in the Control of Arabidopsis Hypocotyl Elongation
Authors: Collett Clare E. , Harberd Nicholas P. , Leyser Ottoline 
Published: July 2002

Abstract
The Arabidopsis hypocotyl, together with hormone mutants and chemical inhibitors, was used to study the role of auxin in cell elongation and its possible interactions with ethylene and gibberellin. When wild-type Arabidopsis seedlings were grown on media containing a range of auxin concentrations, hypocotyl growth was inhibited. However, when axr1-12 and 35S-iaaL(which have reduced auxin response and levels, respectively) were grown in the same conditions, auxin was able to promote hypocotyl growth. In contrast, auxin does not promote hypocotyl growth ofaxr3-1, which has phenotypes that suggest an enhanced auxin response. These results are consistent with the hypothesis that auxin levels in the wild-type hypocotyl are optimal for elongation and that additional auxin is inhibitory. When ethylene responses were reduced using either the ethylene-resistant mutantetr1 or aminoethoxyvinylglycine, an inhibitor of ethylene synthesis, auxin responses were unchanged, indicating that auxin does not inhibit hypocotyl elongation through ethylene. To test for interactions between auxin and gibberellin, auxin mutants were grown on media containing gibberellin and gibberellin mutants were grown on media containing auxin. The responses were found to be the same as wild-type Arabidopsis seedlings in all cases. In addition, 1 μm of the auxin transport inhibitor 1-naphthylphthalmic acid does not alter the response of wild-type seedlings to gibberellin. Double mutants were made between gibberellin and auxin mutants and the phenotypes of these appear additive. These results indicate that auxin and gibberellin are acting independently in hypocotyl elongation. Thus auxin, ethylene, and gibberellin each regulate hypocotyl elongation independently.
Identification of Rice Varieties with High Tolerance or Sensitivity to Lead and Characterization of the Mechanism of Tolerance
Authors: Yang Young-Yell , Jung Ji-Young , Song Won-Yong , Suh Hak-Soo , Lee Youngsook 
Published: July 2002

Abstract
Pb inhibits plant growth. To study Pb tolerance in rice (Oryza sativa), we screened 229 varieties for Pb tolerance or sensitivity. Three-day-old seedlings were treated for 12 d with 20 μm Pb solution. Based on the dry weight of the root, three Pb-tolerant (var CH-55, var KH-2J, var Kumnung) and three Pb-sensitive (var Aixueru, var C-9491, var Milyang23) rice varieties were selected. The root biomasses of the tolerant varieties were approximately 10-fold higher than those of the sensitive ones. The greatest morphological difference between the two groups was in the growth of the adventitious roots, as tolerant lines were able to develop adventitious roots after 6 d of Pb treatment, whereas sensitive ones did not develop any even after 15 d. The growth of adventitious roots in the tolerant varieties was dependent on a mechanism, whereby Pb was altered to a form that cannot be taken up by the tissue, because (a) the solution in which the tolerant varieties of rice had grown still contained Pb but nevertheless did not affect the root growth of new rice seedlings, and (b) the adventitious roots of tolerant seedlings developed in Pb solution contained little Pb. The oxalate content in the root and root exudate increased upon Pb treatment in the tolerant varieties, whereas the opposite was observed for the sensitive ones. Oxalate added to the growth solution ameliorated the inhibition of root growth by Pb. These results suggest that compounds such as oxalate secreted from the root may reduce the bio-availability of Pb, and that this may constitute an important Pb tolerance mechanism in the tolerant rice varieties studied here.
The Arabidopsis eer1 Mutant Has Enhanced Ethylene Responses in the Hypocotyl and Stem
Authors: Larsen Paul B. , Chang Caren 
Published: July 2002

Abstract
By screening for enhanced ethylene-response(eer) mutants in Arabidopsis, we isolated a novel recessive mutant, eer1, which displays increased ethylene sensitivity in the hypocotyl and stem. Dark-growneer1 seedlings have short and thick hypocotyls even in the absence of added ethylene. This phenotype is suppressed, however, by the ethylene biosynthesis inhibitor 1-aminoethoxyvinyl-glycine. Following ethylene treatment, the dark-grown eer1hypocotyl response is greatly exaggerated in comparison with the wild type, indicating that the eer1 phenotype is not simply due to ethylene overproduction. eer1 seedlings have significantly elevated levels of basic-chitinaseexpression, suggesting that eer1 may be highly sensitive to low levels of endogenous ethylene. Adult eer1 plants display exaggerated ethylene-dependent stem thickening, which is an ethylene response previously unreported in Arabidopsis.eer1 also has enhanced responsiveness to the ethylene agonists propylene and 2,5-norbornadiene. The eer1phenotype is completely suppressed by the ethylene-insensitive mutationetr1-1, and is additive with the constitutive ethylene-response mutation ctr1-3. Our findings suggest that the wild-type EER1 product acts to oppose ethylene responses in the hypocotyl and stem.
Rietveld refinement of site-occupancy parameters of Mg2−xMnxSiO4using a new weight function in least-squares fitting
Authors: Yamazaki S. , Toraya H. 
Published: July 2002

The crystal structures of olivine-type Mg_{2-x}MnxSiO4(x = 0, 1, 1.4 and 2) were refined using high-resolution synchrotron radiation data and the Rietveld method, adopting the new weight function with the form 1/Y_o^e\;(e\simeq 2) (Yois the observed profile intensity) [Toraya (1998).J. Appl. Cryst.31, 333–343]. Positional parameters were accurately determined by optimizingein 1/Y_o^e. Derived structures were in accordance with observations on olivine structures, having a constant tetrahedral Si–O distance and octahedral metal–oxygen distances which increase linearly on substitution of octahedral atoms with those having larger atomic radii. Site-occupancy parameters of octahedral atoms were refined under various refinement conditions and could be determined within ±1.2% under the constraint of chemical composition. Deviations ofxfrom assumed chemical compositions, when the site-occupancy parameters were refined without the constraint, were 1.0–3.5% using the new weight function; they are comparable with values obtained in single-crystal studies on Mg–Fe olivine (0.5–2.7%). The use of atomic scattering factors for fully ionized atoms gave better site-occupancy parameters, by 0.1–2.5%, than those for neutral atoms in the present analysis.
Structures and phase transitions of B-Ta2O5 and Z-Ta2O5: two high-pressure forms of Ta2O5
Authors: Zibrov I. P. , Filonenko V. P. , Sundberg M. , Werner P.-E. 
Published: July 2002

A sample of Ta2O5, ditantalum pentaoxide, heat-treated in a `toroid'-type high-pressure chamber at P = 8 GPa and T = 1470 K, was studied by X-ray powder diffraction and high-resolution transmission electron microscopy (HRTEM). Two high-pressure modifications of Ta2O5, isostructural with B-Nb2O5 and Z-Nb2O5, were identified from the X-ray powder pattern. Both structures were refined by the Rietveld method from the X-ray diffraction data: B-Ta2O5, a = 12.7853 (4), b = 4.8537 (1), c = 5.5276 (2) Å, β = 104.264 (2)°, V = 332.45 Å3, Z = 4, space group C2/c; Z-Ta2O5, a = 5.2252 (1), b = 4.6991 (1), c = 5.8534 (1) Å, β = 108.200 (2)°, V = 136.53 Å3, Z = 2, space group C2. The Z-Ta2O5 modification is new. The Ta atoms are six-coordinated in B-Ta2O5 and seven-coordinated in Z-Ta2O5. The two structures are closely related, which makes an intergrowth and a transformation between them possible. An idealized model of the intergrowth structure has been given. The HRTEM study showed defect-rich B-Ta2O5 crystals, which could be interpreted as an intergrowth between the B-Ta2O5 and Z-Ta2O5 phases.
Structure, phase transitions and ionic conductivity of K3NdSi6O15·xH2O. II. Structure of β-K3NdSi6O15
Authors: Haile S. M. , Wuensch B. J. 
Published: July 2002

Hydrothermally grown crystals of β-K3NdSi6O15, potassium neodymium silicate, have been studied by single-crystal X-ray methods. Under appropriate conditions, the compound crystallizes in space group Bb21
m and has lattice constants a = 14.370 (2), b = 15.518 (2) and c = 14.265 (2) Å. There are 30 atom sites in the asymmetric unit of the basic structure. With eight formula units per unit cell, the calculated density is 2.798 Mg m−3. Refinement was carried out to a residual, wR(F
2), of 0.1177 [R(F) = 0.0416] using anisotropic temperature factors for all atoms. The structure is based on (Si2O5
2−)∞ layers, connected by Nd polyhedra to form a three-dimensional framework. Potassium ion sites, some of which are only partially occupied, are located within channels that run between the silicate layers. The silica–neodymia framework of β-K3NdSi6O15, in particular the linkages formed between the silicate layers and Nd polyhedra, bears some similarities to that of the essentially isocompositional phase α-K3NdSi6O15·2H2O. In both, the silicate layers are corrugated so as to accommodate a simple cubic array of NdO6 octahedra with lattice constant ∼ 7.5 Å. Furthermore, the Si2O5 layers in β-K3NdSi6O15 are topologically identical to those of the mineral sazhinite, Na2HCeSi6O15. Although β-K3NdSi6O15 and sazhinite are not isostructural, the structures of each can be described as slight distortions of a high-symmetry parent structure with space group Pbmm.
Purification, crystallization and preliminary X-ray crystallographic analysis of recombinant murine Golgi mannosidase IA, a class I α-mannosidase involved in Asn-linked oligosaccharide maturation
Authors: Vallée Francois , Lal Anita , Moremen Kelley W. , Howell P. Lynne 
Published: July 2002

Golgi mannosidase IA is a class I α-mannosidase which catalyzes the conversion of Man9GlcNAc2 or Man8GlcNAc2 oligosaccharide substrates to Man5GlcNAc2 during the maturation of Asn-linked oligosaccharides. The enzyme is a type II membrane protein, and a recombinant form of mannosidase IA from mouse, lacking the transmembrane domain, has been expressed in Pichia pastoris, purified to homogeneity and crystallized by the hanging-drop vapor-diffusion method. The crystals grow as thin rods, with unit-cell dimensions a = 54.9, b = 135.01, c = 69.9 Å. The crystals exhibit the symmetry of space group P2221 and diffract to 2.8 Å resolution. The asymmetric unit contains one monomer (∼53 kDa) and has a solvent content of 59%.
Purification, characterization, crystallization and preliminary X-ray diffraction of acuthrombin-B, a thrombin-like enzyme from Agkistrodon acutus venom
Authors: Liu Si-jiu , Huang Qing-qiu , Zhu Xue-yong , Teng Mai-kun , Niu Li-wen 
Published: July 2002

Acuthrombin-B, a thrombin-like enzyme from Agkistrodon acutus venom, has been isolated and purified to homogeneity by ion-exchange chromatography on DEAE-Sepharose, gel filtration on Sephacryl S-100 and fast performance liquid chromatography on DEAE-8HR. The protease is an acid protein (pI 6.0) consisting of two non-identical polypeptide chains (14.4 and 16 kDa) and there is no disulfide bond between the subunits. Its molecular weight is 27 kDa as estimated by gel filtration on Sephacryl S-100. The protease has arginine-esterase activity and hydrolyzes synthetic substrates such as p-toluenesulfonyl arginine methyl ester and α-N-benzoyl-L-arginine amide ethyl ester, and shows clotting activity with human fibrinogen, rabbit citrated plasma and human citrated plasma in vitro. The specific activity with human fibrinogen was estimated to be 230 NIH units mg−1. The protease is considered as a serine-type protease and contains metal ion(s) to some extent, as indicated by the fact that its clotting and arginine-esterase activities could be completely inhibited by PMSF and partially inhibited by the chelating agent EDTA, while the thrombin inhibitor heparin had no effect on its clotting activity towards rabbit citrated plasma. Acuthrombin-B crystals with a resolution limit of 2.06 Å were obtained by conventional hanging-drop vapour diffusion. The crystals belong to space group P21 with unit-cell parameters a = 34.97, b = 53.58, c = 67.88 Å, β = 98.89° and contain one molecule per asymmetric unit.
Crystallization and preliminary X-ray crystallographic analysis of a periplasmic tetrahaem flavocytochrome c
3 from Shewanella frigidimarina NCIMB400 which has fumarate reductase activity
Authors: Bamford Vicki , Dobbin Paul S. , Lee Sor-cheng , Reilly Ann , Powell Anne K. , Richardson David J. , Hemmings Andrew M. 
Published: July 2002

The fumarate reductase of Escherichia coli and other bacteria is a membrane-bound enzyme consisting of four subunits. A soluble periplasmic 64 kDa tetrahaem flavocytochrome c
3 from Shewanella frigidimarina NCIMB400 which possesses a catalytic fumarate reductase activity has been crystallized. The crystals belong to space group P212121 with unit-cell parameters a = 72.4, b = 110.1, c = 230.2 Å. Assuming a molecular dimer in the asymmetric unit, the crystals contain 65% solvent and, when cryocooled to 100 K, the crystals diffract to at least 3.0 Å resolution. The crystals, however, display an inherent lack of isomorphism and the plausibility of a MAD phasing experiment has therefore been investigated by measuring the iron K absorption edge from a single crystal.
Crystallization and preliminary diffraction studies of the RNA polymerase subunit RPB5 from Saccharomyces cerevisiae
Authors: Hodach Meredith , Todone Flavia , Eloranta Jyrki J. , Onesti Silvia , Weinzierl Robert O. J. 
Published: July 2002

Crystals of the RNA polymerase subunit RPB5 from Saccharomyces cerevisiae have been obtained by vapour-diffusion techniques. The protein has been overexpressed in bacterial cells as a fusion with glutathione S-transferase. Two monoclinic crystal forms can be grown under different sets of conditions. In both cases, the diffraction is consistent with space group P21, with unit-cell parameters a = 45.3, b = 135.3, c = 47.3 Å, β = 118.6° for crystal form I and a = 48.4, b = 137.1, c = 47.1 Å, β = 118.6° for crystal form II.
Crystallization of Helix pomatia agglutinin (HPA), a protein from the edible snail
Authors: Lisgarten John N. , Pitts James E. , Palmer Rex A. , Reynolds Colin D. , Dao-Thi Minh Hoa , Van Driessche Edilbert , Beeckmans Sonia 
Published: July 2002

Crystals of Helix pomatia agglutinin (HPA) have been grown by the hanging-drop technique using polyethylene glycol as the precipitant at 293 K. Over a period of one to two weeks the crystals grew to maximum dimensions of 0.10 × 0.05 × 0.02 mm. The crystals belong to space group P6322, with unit-cell dimensions a = b = 63.3, c = 105.2 Å and Z = 12 identical monomers of Mr
= 13 kDa, aggregating into two 78 kDa hexameric protein molecules per unit cell, each with symmetry 32 (D
3). The diffraction pattern extends to 3.6 Å at 293 K.
Purification, crystallization and preliminary crystallographic study of a Kunitz-type trypsin inhibitor from Delonix regia seeds
Authors: Polikarpov I. , Golubev A. M. , Perles L. A. , Pando S. C. , Novello J. C. , Marangoni S. 
Published: July 2002

The Kunitz-type trypsin inhibitor from seeds of Flamboyant (Delonix regia) has been purified to homogeneity and plate-like crystals suitable for X-ray analysis have been grown by the hanging-drop method using PEG 6000 as a precipitant. The crystals belong to space group P212121 with unit-cell parameters a = 32.15, b = 69.39, c = 72.54 Å. X-ray diffraction data have been collected to 2.95 Å resolution. The structure has been solved by molecular replacement using the known structures of trypsin inhibitors from Erythrina caffra seeds (PDB code 1tie) and from soya beans (Glycine max; PDB code 1ba7) as search models.
Purification, solution properties and crystallization of SIV integrase containing a continuous core and C-terminal domain
Authors: Li Ying , Yan Youwei , Zugay-Murphy Joan , Xu Bei , Cole James L. , Witmer Marc , Felock Peter , Wolfe Abigail , Hazuda Daria , Sardana Mohinder K. , Chen Zhongguo , Kuo Lawrence C. , Sardana Vinod V. 
Published: July 2002

The C-terminal two-thirds segment of integrase derived from the simian immunodeficiency virus has been cloned, expressed in Escherichia coli, and purified to greater than 95% homogeneity. The protein encompasses amino-acid residues 50–293 and contains a F185H substitution to enhance solubility. In dilute solutions at concentrations below 1 mg ml−1, the enzyme is predominantly dimeric. At the higher concentrations (>10 mg ml−1) required to enable crystallization, the enzyme self-associates to form species with molecular weights greater than 200 kDa. Despite the apparent high aggregation in solution, the enzyme crystallizes from a 8%(v/v) polyethylene glycol (molecular weight 6000) solution in a form suitable for X-ray diffraction studies. The resulting single crystals belong to the space group P212121, with unit-cell parameters a = 79.76, b = 99.98, c = 150.2 Å, α = β = γ = 90° and Z = 4. Under X-ray irradiation generated with a rotating-anode generator, the crystals diffract to 2.8 Å resolution and allow collection of a native 3 Å resolution diffraction data set.
Crystallization and preliminary X-ray diffraction studies of hyperthermostable glutamate dehydrogenase from Thermococcus profundus
Authors: Higuchi Sadaharu , Nakasako Masayoshi , Kudo Toshiaki 
Published: July 2002

Recombinant glutamate dehydrogenase from a hyperthermophilic archaeon, Thermococcus profundus, was crystallized in the presence of both polyethylene glycol 8000 and lithium sulfate. Four types of crystals having different morphologies appeared in the crystallization trials; however, only one type was suitable for X-ray crystal structure analysis. The crystal belonged to the monoclinic space group P21 and the unit-cell parameters were a = 112.99, b = 163.70, c = 133.07 Å, β = 113.46° at 110 K. The calculated VM
value of 3.42 Å3 Da−1 was acceptable when one hexamer of the enzyme, which was the physiological functional unit, occupied a crystallographic asymmetric unit. X-ray diffraction intensity data were collected to a resolution of 2.25 Å with good statistics at the BL44B2 beamline of SPring-8.
High-resolution hard X-ray phase-contrast microscopy with a large-diameter and high-numerical-aperture zone plate
Authors: Kagoshima Yasushi , Yokoyama Yoshiyuki , Ibuki Takashi , Niimi Toshihiro , Tsusaka Yoshiyuki , Takai Kengo , Matsui Junji 
Published: July 2002

An imaging transmission hard X-ray microscope has been constructed at beamline BL24XU of SPring-8. It makes use of a phase zone plate made of tantalum with a diameter of 1 mm and an outer-most zone width of 50 nm, aiming at a wide field of view and a high spatial resolution. The performance test was carried out at a photon energy of 10 keV. A field of view as wide as ∼200 µm in diameter was achieved. The spatial resolution was measured to be 220 nm by analyzing a knife-edge image. Further, a line-and-space pattern as fine as 100 nm could be imaged. By placing a phase plate made of gold in the back focal plane of the zone plate, phase-contrast microscopy using Zernike's method was also carried out. The feasibility of phase-contrast microscopy for observing transparent samples was successfully demonstrated by imaging small polystyrene particles.