bluuebunny/crossref_metadata_2025_split huggingface dataset:
Direct Interference with Rhamnogalacturonan I Biosynthesis in Golgi Vesicles
Authors: Skjøt Michael , Pauly Markus , Bush Maxwell S. , Borkhardt Bernhard , McCann Maureen C. , Ulvskov Peter 
Published: July 2002

Abstract
Pectin is a class of complex cell wall polysaccharides with multiple roles during cell development. Assigning specific functions to particular polysaccharides is in its infancy, in part, because of the limited number of mutants and transformants available with modified pectic polymers in their walls. Pectins are also important polymers with diverse applications in the food and pharmaceutical industries, which would benefit from technology for producing pectins with specific functional properties. In this report, we describe the generation of potato (Solanum tuberosum L. cv Posmo) tuber transformants producing pectic rhamnogalacturonan I (RGI) with a low level of arabinosylation. This was achieved by the expression of a Golgi membrane-anchored endo-α-1,5-arabinanase. Sugar composition analysis of RGI isolated from transformed and wild-type tubers showed that the arabinose content was decreased by approximately 70% in transformed cell walls compared with wild type. The modification of the RGI was confirmed by immunolabeling with an antibody recognizing α-1,5-arabinan. This is the first time, to our knowledge, that the biosynthesis of a plant cell wall polysaccharide has been manipulated through the action of a glycosyl hydrolase targeted to the Golgi compartment.
Nearest-Neighbor Analysis of Higher-Plant Photosystem I Holocomplex
Authors: Jansson S. , Andersen B. , Scheller H. V. 
Published: July 2002

Abstract
Photosystem I (PSI) preparations from barley (Hordeum vulgare) and spinach (Spinacia oleracea) were subjected to chemical cross-linking using the cleavable homobifunctional cross-linkers dithiobis(succinimidylpropionate) and 3,3[prime]-dithiobis(sulfosuccinimidyl-propionate). The overall pattern of cross-linked products was analyzed by the simple but powerful technique of diagonal electrophoresis, in which the disulfide bond in the cross-linker was cleaved between the first and second dimensions of the gel, and immunoblotting. A large number of cross-linked products were identified. Together with preexisting data on the structure of PSI, it was deduced that the subunits PSI-D, PSI-H, PSI-I, and PSI-L occupy one side of the complex, whereas PSI-E, PSI-F, and PSI-J occupy the other. PSI-K and PSI-G appear to be adjacent to Lhca3 and Lhca2, respectively, and not close to the other small subunits. Experiments with isolated light-harvesting complex I preparations indicate that the subunits are organized as dimers, which seem to associate to the PSI-A/PSI-B proteins independent of each other. We suggest which PSI subunit corresponds to each membrane-spanning helix in the cyanobacterial PSI structure, and present a model for higher-plant PSI.
Ethylene-Mediated Phospholipid Catabolic Pathway in Glucose-Starved Carrot Suspension Cells1
Authors: Hyun Lee Soo , Sook Chae Hyun , Kyun Lee Taek , Hee Kim Se , Ho Shin Sung , Huey Cho Bong , Ho Cho Sung , Kang Bin G. , Sung Lee Woo 
Published: July 2002

Abstract
Glucose (Glc) starvation of suspension-cultured carrot (Daucus carotaL.) cells resulted in sequential activation of phospholipid catabolic enzymes. Among the assayed enzymes involved in the degradation, phospholipase D (PLD) and lipolytic acyl hydrolase were activated at the early part of starvation, and these activities were followed by β-oxidation and the glyoxylate cycle enzymes in order. The activity of PLD and lipolytic acyl hydrolase was further confirmed by in vivo-labeling experiments. It was demonstrated that Glc added to a medium containing starving cells inhibited the phospholipid catabolic activities, indicating that phospholipid catabolism is negatively regulated by Glc. There was a burst of ethylene production 6 h after starvation. Ethylene added exogeneously to a Glc-sufficient medium activated PLD, indicating that ethylene acts as an element in the signal transduction pathway leading from Glc depletion to PLD activation. Activation of lipid peroxidation, suggestive of cell death, occurred immediately after the decrease of the phospholipid degradation, suggesting that the observed phospholipid catabolic pathway is part of the metabolic strategies by which cells effectively survive under Glc starvation.
Differential Expression of the Arabidopsis Nia1 andNia2 Genes1
Authors: Yu Xiaodan , Sukumaran Sujatha , Márton László 
Published: July 2002

Abstract
Nitrate reductase (NR) activity increased up to 14-fold in response to treatment of Arabidopsis thaliana seedlings with the cytokinin benzyladenine. NR induction was observed in seedlings germinated directly on cytokinin-containing medium, seedlings transferred to cytokinin medium, and seedlings grown in soil in which cytokinin was applied directly to the leaves. About the same level of induction was seen in both wild-type and Nia2-deletion mutants, indicating that increased NR activity is related to the expression of the minor NR gene, Nia1. The steady-stateNia1 mRNA level was increased severalfold in both wild-type and mutant seedlings after benzyladenine treatment. Transcript levels of the Nia2 gene, which is responsible for 90% of the NR activity in developing wild-type seedlings, did not show any changes upon cytokinin treatment. Nuclear run-on assays demonstrated that Nia1 gene transcription increased dramatically after cytokinin treatment.
Quantitative Intercellular Localization of NADH-Dependent Glutamate Synthase Protein in Different Types of Root Cells in Rice Plants1
Authors: Hayakawa Toshihiko , Hopkins Laura , Peat Lucy J. , Yamaya Tomoyuki , Tobin Alyson K. 
Published: July 2002

AbstractThe quantitative analysis with immunogold-electron microscopy using a single-affinity-purified anti-NADH-glutamate synthase (GOGAT) immunoglobulin G (IgG) as the primary antibody showed that the NADH-GOGAT protein was present in various forms of plastids in the cells of the epidermis and exodermis, in the cortex parenchyma, and in the vascular parenchyma of root tips (&lt;10 mm) of rice (Oryza sativa) seedlings supplied with 1 mm NH4+ for 24 h. The values of the mean immunolabeling density of plastids were almost equal among these different cell types in the roots. However, the number of plastids per individual cell type was not identical, and some parts of the cells in the epidermis and exodermis contained large numbers of plastids that were heavily immunolabeled. Although there was an indication of labeling in the mitochondria using the single-affinity-purified anti-NADH-GOGAT IgG, this was not confirmed when a twice-affinity-purified IgG was used, indicating an exclusively plastidial location of the NADH-GOGAT protein in rice roots. These results, together with previous work from our laboratory (K. Ishiyama, T. Hayakawa, and T. Yamaya [1998] Planta 204: 288–294), suggest that the assimilation of exogeneously supplied NH4+ions is primarily via the cytosolic glutamine synthetase/plastidial NADH-GOGAT cycle in specific regions of the epidermis and exodermis in rice roots. We also discuss the role of the NADH-GOGAT protein in vascular parenchyma cells.
Iron Superoxide Dismutase Protects against Chilling Damage in the Cyanobacterium Synechococcus species PCC79421
Authors: Thomas David J. , Thomas Jannette B. , Prier Shane D. , Nasso Nicole E. , Herbert Stephen K. 
Published: July 2002

Abstract
A strain ofSynechococcus sp. PCC7942 lacking functional Fe superoxide dismutase (SOD), designatedsodB−, was characterized by its growth rate, photosynthetic pigments, inhibition of photosynthetic electron transport activity, and total SOD activity at 0°C, 10°C, 17°C, and 27°C in moderate light. At 27°C, thesodB− and wild-type strains had similar growth rates, chlorophyll and carotenoid contents, and cyclic photosynthetic electron transport activity. ThesodB− strain was more sensitive to chilling stress at 17°C than the wild type, indicating a role for FeSOD in protection against photooxidative damage during moderate chilling in light. However, both the wild-type andsodB− strains exhibited similar chilling damage at 0°C and 10°C, indicating that the FeSOD does not provide protection against severe chilling stress in light. Total SOD activity was lower in the sodB− strain than in the wild type at 17°C and 27°C. Total SOD activity decreased with decreasing temperature in both strains but more so in the wild type. Total SOD activity was equal in the two strains when assayed at 0°C.
The Delivery of Salts to the Xylem. Three Types of Anion Conductance in the Plasmalemma of the Xylem Parenchyma of Roots of Barley
Authors: Köhler Barbara , Raschke Klaus 
Published: July 2002

Abstract
To explore possible pathways for anions to enter the xylem in the root during the transport of salts to the shoot, we used the patch-clamp method on protoplasts prepared from the xylem parenchyma of barley (Hordeum vulgare L.) plants. K+ currents were suppressed by tetraethylammonium orN-methylglucamine in the solutions in the pipette and the bath, and the permeating anions were Cl− or NO3 −. We recorded the activities of three distinct anion conductances: (a) an inwardly rectifying anion channel (X-IRAC), characterized by activation at hyperpolarization and open times of up to several seconds; (b) a quickly activating anion conductance (X-QUAC), important for anion efflux at voltages between −50 mV and the equilibrium potential of the prevailing anion; and (c) a slowly activating anion conductance (X-SLAC), activating above −100 mV. Both X-IRAC and X-QUAC were permeable for Cl− and NO3 −; X-QUAC was also permeable for malate. The occurrence of X-IRAC became more frequent with an increase in cytoplasmic Ca2+, while the occurrence of X-QUAC decreased. Anion currents through X-SLAC, and particularly through X-QUAC, were estimated to be large enough to account for reported rates of xylem loading, which is in accordance with the notion that xylem loading is a passive process.
Calcium-Independent Activation of Salicylic Acid-Induced Protein Kinase and a 40-Kilodalton Protein Kinase by Hyperosmotic Stress
Authors: Hoyos Mary Elizabeth , Zhang Shuqun 
Published: July 2002

AbstractReversible protein phosphorylation/dephosphorylation plays important roles in signaling the plant adaptive responses to salinity/drought stresses. Two protein kinases with molecular masses of 48 and 40 kD are activated in tobacco cells exposed to NaCl. The 48-kD protein kinase was identified as SIPK (salicylic acid-induced protein kinase), a member of the tobacco MAPK (mitogen-activated protein kinase) family that is activated by various other stress stimuli. The activation of the 40-kD protein kinase is rapid and dose-dependent. Other osmolytes such as Pro and sorbitol activate these two kinases with similar kinetics. The activation of 40-kD protein kinase is specific for hyperosmotic stress, as hypotonic stress does not activate it. Therefore, this 40-kD kinase was named HOSAK (high osmotic stress-activated kinase). HOSAK is a Ca2+-independent kinase and uses myelin basic protein (MBP) and histone equally well as substrates. The kinase inhibitor K252a rapidly activates HOSAK in tobacco cells, implicating a dephosphorylation mechanism for HOSAK activation. Activation of both SIPK and HOSAK by high osmotic stress is Ca2+ and abscisic acid (ABA) independent. Furthermore, mutation in SOS3locus does not affect the activation of either kinase in Arabidopsis seedlings. These results suggest that SIPK and 40-kD HOSAK are two new components in a Ca2+- and ABA-independent pathway that may lead to plant adaptation to hyperosmotic stress.
fhy3-1 Retains Inductive Responses of Phytochrome A
Authors: Yanovsky Marcelo J. , Whitelam Garry C. , Casal Jorge J. 
Published: July 2002

Abstract
The fhy3 mutation of Arabidopsis impairs phytochrome A (phyA)-mediated inhibition of hypocotyl growth without affecting the levels of phyA measured spectrophotometrically or immunochemically. We investigated whether the fhy3-1 mutation has similar effects on very low fluence responses (VLFR) and high irradiance responses (HIR) of phyA. When exposed to hourly pulses of far-red light, etiolated seedlings of the wild type or of thefhy3-1 mutant showed similar inhibition of hypocotyl growth, unfolding of the cotyledons, anthocyanin synthesis, and greening upon transfer to white light. In the wild type, continuous far-red light was significantly more effective than hourly far-red pulses (at equal total fluence). In the fhy3-1 mutant, hourly pulses were as effective as continuous far-red light, i.e. the failure of reciprocity typical of HIR was not observed. Germination was similarly promoted by continuous or pulsed far-red in wild-type andfhy3-1 seeds. Thus, for hypocotyl growth, cotyledon unfolding, greening, and seed germination, the fhy3-1mutant retains VLFR but is severely impaired in HIR. These data are consistent with the idea that VLFR and HIR involve divergent signaling pathways of phyA.
Induction of a C4-Like Mechanism of CO2Fixation in Egeria densa, a Submersed Aquatic Species
Authors: Casati Paula , Lara Marı́a V. , Andreo Carlos S. 
Published: July 2002

Abstract
The expression of phosphoenolpyruvate carboxylase (PEPC) and NADP-malic enzyme (NADP-ME) in Egeria densaleaves was studied under low temperature and light (LTL) following incubation under high temperature and light (HTL), conditions previously shown to induce high and low CO2 compensation points, respectively. Transfer from LTL to HTL conditions induced increases in the activities and amounts of both enzymes. One NADP-ME isoform was observed in induced and uninduced samples. Two isoforms of PEPC were expressed, with the lower M risoform being induced by HTL. NADP-ME showed properties similar to those of the isoform in C3 species. The inducible PEPC isoform has a low K m for both substrates. PEPC kinetic and regulatory properties (V maxand K m for phosphoenolpyruvate, and I 50for l-malate) are different in samples taken in the dark from those in the light, indicating that some modification of PEPC may be occurring during the day. Finally, abscisic acid induced the expression of PEPC and NADP-ME in a manner similar to temperature induction, except that the activities of both PEPC isoforms were increased. A different signaling system may exist in this species in response to high temperature or abscisic acid, both of which induce changes in photosynthetic metabolism.
Phosphate Availability Regulates Root System Architecture in Arabidopsis
Authors: Williamson Lisa C. , Ribrioux Sebastien P.C.P. , Fitter Alastair H. , Leyser H.M. Ottoline 
Published: July 2002

Abstract
Plant root systems are highly plastic in their development and can adapt their architecture in response to the prevailing environmental conditions. One important parameter is the availability of phosphate, which is highly immobile in soil such that the arrangement of roots within the soil will profoundly affect the ability of the plant to acquire this essential nutrient. Consistent with this, the availability of phosphate was found to have a marked effect on the root system architecture of Arabidopsis. Low phosphate availability favored lateral root growth over primary root growth, through increased lateral root density and length, and reduced primary root growth mediated by reduced cell elongation. The ability of the root system to respond to phosphate availability was found to be independent of sucrose supply and auxin signaling. In contrast, shoot phosphate status was found to influence the root system architecture response to phosphate availability.
Structural features of a zinc binding site in the superantigen strepococcal pyrogenic exotoxin A (SpeA1): Implications for MHC class II recognition
Authors: Baker Matthew , Gutman Delia M. , Papageorgiou Anastassios C. , Collins Carleen M. , Acharya K. Ravi 
Published: July 2002

AbstractStreptococcal pyrogenic exotoxin A (SpeA) is produced by Streptococcus pyogenes, and has been associated with severe infections such as scarlet fever and Streptococcal Toxic Shock Syndrome (STSS). In this study, the crystal structure of SpeA1 (the product of speA allele 1) in the presence of 2.5 mM zinc was determined at 2.8 Å resolution. The protein crystallizes in the orthorhombic space group P21212, with four molecules in the crystallographic asymmetric unit. The final structure has a crystallographic R‐factor of 21.4% for 7,031 protein atoms, 143 water molecules, and 4 zinc atoms (one zinc atom per molecule). Four protein ligands—Glu 33, Asp 77, His 106, and His 110—form a zinc binding site that is similar to the one observed in a related superantigen, staphylococcoal enterotoxin C2. Mutant toxin forms substituting Ala for each of the zinc binding residues were generated. The affinity of these mutants for zinc ion confirms the composition of this metal binding site. The implications of zinc binding to SpeA1 for MHC class II recognition are explored using a molecular modeling approach. The results indicate that, despite their common overall architecture, superantigens appear to have multiple ways of complex formation with MHC class II molecules.
Abstract: Interaction of ion beams with solids
Authors: Davies J. A. 
Published: July 2002

Ion implantation is now a widely used technique for modifying the chemical and physical properties of a shallow surface region of a solid. In principle, almost any combination of ion (Z1) and target (Z2) can be used over a wide concentration range, and with independent and precise control of the number and the depth distribution of the implanted ions. Furthermore, with modern vacuum techniques, ion implantation is an ideal ’’clean room’’ process, an advantage which has not yet been fully exploited. We will review briefly the major physical processes involved in implantation: viz., (i) the number and depth distribution (range) of the implanted ions, with particular emphasis on some of the complicating factors, such as ion reflection, charge exchange (in the beam), channeling, enhanced diffusion effects, and trapping at interfaces, which must be either eliminated or taken into account; (ii) the depth and nature of the radiation damage produced by the implantation; and (iii) the ultimate lattice location of the implanted ions within the crystal structure of the host lattice.
The radiation damage problem will then be considered in more detail, as this is generally the most important and also the most complicated aspect of ion bombardment. In particular, some recent work on the role of molecular ion beams will be presented in which equal atom−dose implants of various diatomic and monatomic ions were injected into Si and Ge at room temperature. In each case, the molecular ion implant had the same energy per atom and the same atomic flux and fluence as the corresponding monatomic implant. Yet, the molecular beam (As+2, Sb+2, Bi+2) produced ∠50% more damage than the monatomic beam, indicating that damage production depends not only on the total amount but also on the localized concentration of deposited energy. For the highest density cascades studied, the observed amount (Nd) of damage per ion corresponds to almost 100% of the predicted cascade volume; furthermore, there is no evidence of the molecular effect levelling off as the damage approaches this 100% limit. Also, the Nd values in semiconductor crystals are all considerably greater than the upper limit of 0.8 ν (E)/2Ed predicted by the Kinchin−Pease equation, 1 and the discrepancy becomes even worse for similar implants at low (30 K) temperature. These results provide strong experimental evidence for a breakdown of the generally accepted linear−cascade model, and suggest that at fairly low energies some sort of energy−spike model (as recently proposed by Sigmund 2) may indeed be more appropriate.
In Vitro Selection of Resistance to Clinafloxacin, Ciprofloxacin, and Trovafloxacin in
Streptococcus pneumoniae
Authors: Nagai Kensuke , Davies Todd A. , Pankuch Glenn A. , Dewasse Bonifacio E. , Jacobs Michael R. , Appelbaum Peter C. 
Published: July 2002

ABSTRACT

Ability of daily sequential subcultures in subinhibitory concentrations of clinafloxacin, ciprofloxacin, and trovafloxacin to select resistant mutants was studied in 10 pneumococci (ciprofloxacin MICs, 1 to 4 μg/ml, and clinafloxacin and trovafloxacin MICs, 0.06 to 0.125 μg/ml [
n
= 9]; ciprofloxacin, clinafloxacin, and trovafloxacin MICs, 32, 0.5, and 2 μg/ml, respectively [
n
= 1]). Subculturing was done 50 times, or until MICs increased fourfold or more. Mutants for which MICs were fourfold (or more) higher than those for parent strains were selected in five strains by clinafloxacin, in six strains by trovafloxacin, and nine strains by ciprofloxacin. Sequence analysis of type II topoisomerase showed that most mutants had mutations in ParC at Ser79 or Asp83 and in GyrA at Ser81, while a few mutants had mutations in ParE or GyrB. In the presence of reserpine, the MICs of ciprofloxacin and clinafloxacin for most mutants were lower (four to eight times lower), but for none of the mutants were trovafloxacin MICs lower, suggesting an efflux mechanism affecting the first two agents but not trovafloxacin. Single-step mutation rates were also determined for eight strains for which the MICs were as follows: 0.06 μg/ml (clinafloxacin), 0.06 to 0.125 μg/ml (trovafloxacin), and 1 μg/ml (ciprofloxacin). Single-step mutation rates with drugs at the MIC were 2.0×10
−9
to <1.1×10
−11
, 5.0×10
−4
to 3.6×10
−9
, and 4.8×10
−4
to 6.7×10
−9
, respectively. For two strains with clinafloxacin MICs of 0.125 to 0.5 μg/ml trovafloxacin MICs of 0.125 to 2 μg/ml, ciprofloxacin MICs of 4 to 32 μg/ml mutation rates with drugs at the MIC were 1.1×10
−8
−9.6×10
−8
, 3.3×10
−6
−6.7×10
−8
, and 2.3×10
−5
−2.4×10
−7
, respectively. Clinafloxacin was bactericidal at four times the MIC after 24 h against three parent and nine mutant strains by time-kill study. This study showed that single and multistep clinafloxacin exposure selected for resistant mutants less frequently than similar exposures to other drugs studied.
Efficacy of a New Cream Formulation of Mupirocin: Comparison with Oral and Topical Agents in Experimental Skin Infections
Authors: Gisby John , Bryant Joanna 
Published: July 2002

ABSTRACTA new cream formulation of mupirocin developed to improve patient compliance was compared with systemic and topical antibiotics commonly used to treat primary and secondary skin infections. A mouse surgical wound model infected withStaphylococcus aureusorStreptococcus pyogeneswas used. Topical treatment was applied at 4 and 10 h postinfection or oral treatment at a clinically relevant dose was administered 4, 8, and 12 h postinfection; treatments were continued three times daily for a further 3 days. Mupirocin cream was significantly more effective than (P< 0.01; two of eight studies) or not significantly different from (six of eight studies) mupirocin ointment in reducing bacterial numbers. Mupirocin cream was similar in efficacy to oral flucloxacillin but significantly more effective (P< 0.001) than oral erythromycin. It was also similar in efficacy to cephalexin againstS. pyogenesbut superior againstS. aureus(P< 0.01). Mupirocin cream had a similar efficacy to fusidic acid cream againstS. aureusbut was significantly superior againstS. pyogenes(P< 0.01). A hamster impetigo model infected withS. aureuswas also used. Topical or oral treatment was administered at 24 and 30 h postinfection (also 36 h postinfection for oral therapy) and then three times daily for a further 2 days. On day 5, mupirocin cream was significantly more effective than mupirocin ointment in one study (P< 0.01) and of similar efficacy in the other two studies. Mupirocin cream was not significantly different from fusidic acid cream or neomycin-bacitracin cream, but it was significantly superior (P< 0.01) to oral erythromycin and cephalexin. Mupirocin cream was as effective as, or superior to, oral and other topical agents commonly used for skin infections.