bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mollusc-Algal Chloroplast Endosymbiosis. Photosynthesis, Thylakoid Protein Maintenance, and Chloroplast Gene Expression Continue for Many Months in the Absence of the Algal Nucleus
Authors: Green Brian J. , Li Wei-Ye , Manhart James R. , Fox Theodore C. , Summer Elizabeth J. , Kennedy Robert A. , Pierce Sidney K. , Rumpho Mary E. 
Published: July 2002

AbstractEarly in its life cycle, the marine mollusc Elysia chlorotica Gould forms an intracellular endosymbiotic association with chloroplasts of the chromophytic alga Vaucheria litorea C. Agardh. As a result, the dark green sea slug can be sustained in culture solely by photoautotrophic CO2fixation for at least 9 months if provided with only light and a source of CO2. Here we demonstrate that the sea slug symbiont chloroplasts maintain photosynthetic oxygen evolution and electron transport activity through photosystems I and II for several months in the absence of any external algal food supply. This activity is correlated to the maintenance of functional levels of chloroplast-encoded photosystem proteins, due in part at least to de novo protein synthesis of chloroplast proteins in the sea slug. Levels of at least one putative algal nuclear encoded protein, a light-harvesting complex protein homolog, were also maintained throughout the 9-month culture period. The chloroplast genome ofV. litorea was found to be 119.1 kb, similar to that of other chromophytic algae. Southern analysis and polymerase chain reaction did not detect an algal nuclear genome in the slug, in agreement with earlier microscopic observations. Therefore, the maintenance of photosynthetic activity in the captured chloroplasts is regulated solely by the algal chloroplast and animal nuclear genomes.
Gibberellin-Induced Changes in Growth Anisotropy Precede Gibberellin-Dependent Changes in Cortical Microtubule Orientation in Developing Epidermal Cells of Barley Leaves. Kinematic and Cytological Studies on a Gibberellin-Responsive Dwarf Mutant, M489
Authors: Wenzel Carol L. , Williamson Richard E. , Wasteneys Geoffrey O. 
Published: July 2002

Abstract
We conducted kinematic and cytological studies on “between vein” epidermal cells of the gibberellin (GA)-deficient M489 dwarf mutant of barley (Hordeum vulgare L. Himalaya). GAs affect radial and axial components of cell expansion and cortical microtubule orientation. Adaxial cells in particular expand radially after leaving the elongation zone (EZ), probably as part of leaf unrolling. Exogenous gibberellic acid corrects the mutant's short, wide blades, short EZ, and slow elongation rate. Cell production rates increase more on the adaxial than on the abaxial surface. Cells spend equal periods of time elongating in dwarf and tall plants, but relative elemental growth rates start to decline sooner in the dwarf. GA increased the rate at which longitudinal wall area increased because the increased axial growth more than compensated for reduced radial growth. In dwarf leaves, increased radial expansion was detected in basal parts of the EZ before cortical microtubules lost transverse orientation in the distal elongation zone. We conclude that loss of microtubule orientation is not required for low GA levels to reduce growth anisotropy.
Genetic Analysis of Seed-Soluble Oligosaccharides in Relation to Seed Storability of Arabidopsis
Authors: Bentsink Leónie , Alonso-Blanco Carlos , Vreugdenhil Dick , Tesnier Karine , Groot Steven P.C. , Koornneef Maarten 
Published: July 2002

Abstract
Seed oligosaccharides (OSs) and especially raffinose series OSs (RSOs) are hypothesized to play an important role in the acquisition of desiccation tolerance and consequently in seed storability. In the present work we analyzed the seed-soluble OS (sucrose, raffinose, and stachyose) content of several Arabidopsis accessions and thus identified the genotype Cape Verde Islands having a very low RSO content. By performing quantitative trait loci (QTL) mapping in a recombinant inbred line population, we found one major QTL responsible for the practically monogenic segregation of seed stachyose content. This locus also affected the content of the two other OSs, sucrose, and raffinose. Two candidate genes encoding respectively for galactinol synthase and raffinose synthase were located within the genomic region around this major QTL. In addition, three smaller-effect QTL were identified, each one specifically affecting the content of an individual OS. Seed storability was analyzed in the same recombinant inbred line population by measuring viability (germination) under two different seed aging assays: after natural aging during 4 years of dry storage at room temperature and after artificial aging induced by a controlled deterioration test. Thus, four QTL responsible for the variation of this trait were mapped. Comparison of the QTL genetic positions showed that the genomic region containing the major OS locus did not significantly affect the seed storability. We concluded that in the studied material neither RSOs nor sucrose content had a specific effect on seed storability.
Subcellular Compartmentation of the Diterpene Carnosic Acid and Its Derivatives in the Leaves of Rosemary
Authors: Munné-Bosch Sergi , Alegre Leonor 
Published: July 2002

Abstract
The potent antioxidant properties of rosemary (Rosmarinus officinalis) extracts have been attributed to its major diterpene, carnosic acid. Carnosic acid has received considerable attention in food science and biomedicine, but little is known about its function in the plant in vivo. We recently found that highly oxidized diterpenes increase in rosemary plants exposed to drought and high light stress as a result of the antioxidant activity of carnosic acid (S. Munné-Bosch, K. Schwarz, L. Alegre [1999] Plant Physiol 121: 1047–1052). To elucidate the significance of the antioxidant function of carnosic acid in vivo we measured the relative amounts of carnosic acid and its metabolites in different compartments of rosemary leaves. Subcellular localization studies show that carnosic acid protects chloroplasts from oxidative stress in vivo by following a highly regulated compartmentation of oxidation products. Carnosic acid scavenges free radicals within the chloroplasts, giving rise to diterpene alcohols, mainly isorosmanol. This oxidation product isO-methylated within the chloroplasts, and the resulting form, 11,12-di-O-methylisorosmanol, is transferred to the plasma membrane. This appears to represent a mechanism of a way out for free radicals from chloroplasts. Carnosic acid also undergoes direct O-methylation within the chloroplasts, and its derived product, 12-O-methylcarnosic acid, accumulates in the plasma membrane. O-methylated diterpenes do not display antioxidant activity, but they may influence the stability of the plasma membrane. This study shows the relevance of the compartmentation of carnosic acid metabolism to the protection of rosemary plants from oxidative stress in vivo.
Effect of Solar Ultraviolet-B Radiation during Springtime Ozone Depletion on Photosynthesis and Biomass Production of Antarctic Vascular Plants
Authors: Xiong Fusheng S. , Day Thomas A. 
Published: July 2002

Abstract
We assessed the influence of springtime solar UV-B radiation that was naturally enhanced during several days due to ozone depletion on biomass production and photosynthesis of vascular plants along the Antarctic Peninsula. Naturally growing plants of Colobanthus quitensis (Kunth) Bartl. and Deschampsia antarctica Desv. were potted and grown under filters that absorbed or transmitted most solar UV-B. Plants exposed to solar UV-B from mid-October to early January produced 11% to 22% less total, as well as above ground biomass, and 24% to 31% less total leaf area. These growth reductions did not appear to be associated with reductions in photosynthesis per se: Although rates of photosynthetic O2 evolution were reduced on a chlorophyll and a dry-mass basis, on a leaf area basis they were not affected by UV-B exposure. Leaves on plants exposed to UV-B were denser, probably thicker, and had higher concentrations of photosynthetic and UV-B absorbing pigments. We suspect that the development of thicker leaves containing more photosynthetic and screening pigments allowed these plants to maintain their photosynthetic rates per unit leaf area. Exposure to UV-B led to reductions in quantum yield of photosystem II, based on fluorescence measurements of adaxial leaf surfaces, and we suspect that UV-B impaired photosynthesis in the upper mesophyll of leaves. Because the ratio of variable to maximal fluorescence, as well as the initial slope of the photosynthetic light response, were unaffected by UV-B exposure, we suggest that impairments in photosynthesis in the upper mesophyll were associated with light-independent enzymatic, rather than photosystem II, limitations.
The Salt Stress-Inducible Protein Kinase Gene, Esi47, from the Salt-Tolerant WheatgrassLophopyrum elongatum Is Involved in Plant Hormone Signaling
Authors: Shen Wei , Gómez-Cadenas Aurelio , Routly Elizabeth L. , Ho Tuan-Hua David , Simmonds John A. , Gulick Patrick J. 
Published: July 2002

Abstract
Protein kinases play a central role in signal transduction in all organisms and to study signal transduction in response to salt stress we have identified and characterized a gene encoding a protein kinase that is induced by salt stress and abscisic acid (ABA) in the salt-tolerant wild wheatgrass Lophopyrum elongatum(Host) A. Love. The product of the early salt stress-induced gene,Esi47, was found to belong to the “novel Arabidopsis protein kinase” group of plant serine/threonine protein kinases. Transient gene expression assays in barley aleurone tissue showedEsi47 to suppress the gibberellin induction of the barley low-pI α-amylase gene promoter, thus providing evidence for the role of this protein kinase gene in plant hormone signaling.Esi47 contains a small upstream open reading frame in the 5′-untranslated region of its transcript that is implicated in mediating the repression of the basal level of the gene expression and in regulating the ABA inducibility of the gene, as shown in the transient gene expression assay in maize callus. Three Arabidopsis homologs of Esi47 were identified, and different members of this clade of genes showed differential patterns of regulation by salt stress and ABA in Arabidopsis roots and leaves. At least one of the Arabidopsis homologs contains a small open reading frame in its 5′-untranslated region, indicating that the unusual regulatory mechanism identified in Esi47 may be widely conserved.
Cooperative Action of SLR1 and SLR2 Is Required for Lateral Root-Specific Cell Elongation in Maize
Authors: Hochholdinger Frank , Park Woong June , Feix Günter H. 
Published: July 2002

Abstract
Lateral roots play an important role in water and nutrient uptake largely by increasing the root surface area. In an effort to characterize lateral root development in maize (Zea mays), we have isolated from Mutator(Mu) transposon stocks and characterized two nonallelic monogenic recessive mutants: slr1 andslr2 (short lateral roots1 and2), which display short lateral roots as a result of impaired root cell elongation. The defects in both mutants act specifically during early postembryonic root development, affecting only the lateral roots emerging from the embryonic primary and seminal roots but not from the postembryonic nodal roots. These mutations have no major influence on the aboveground performance of the affected plants. The double mutant slr1; slr2 displays a strikingly different phenotype than the single mutants. The defect inslr1; slr2 does not only influence lateral root specific cell elongation, but also leads to disarranged cellular patterns in the primary and seminal roots. However, the phase-specific nature of the single mutants is retained in the double mutant, indicating that the two loci cooperate in the wild type to maintain the lateral root specificity during a short time of early root development.
Carrier-Mediated Uptake and Phloem Systemy of a 350-Dalton Chlorinated Xenobiotic with an α-Amino Acid Function
Authors: Delétage-Grandon Céline , Chollet Jean-François , Faucher Mireille , Rocher Francoise , Komor Ewald , Bonnemain Jean-Louis 
Published: July 2002

Abstract
In a previous paper we have shown that ε-(phenoxyalkanecarboxylyl)-l-Lys conjugates are potent inhibitors of amino acid transport systems and that it is possible to modulate the uptake inhibition by hydrophobic or hydrophilic additions in the 4-position of the aromatic ring (J.F. Chollet, C. Delétage, M. Faucher, L. Miginiac, J.L. Bonnemain [1997] Biochem Biophys Acta 1336: 331–341). In this report we demonstrate that ε-(2,4-dichlorophenoxyacetyl)-l-Lys (2,4D-Lys), one of the largest molecules of the series and one of the most potent inhibitors, is a highly permeant conjugate. Uptake of 2,4D-Lys by broad bean (Vicia faba) leaf discs is mediated by an active carrier system (K m1 = 0.2 mm;V max1 = 2.4 nmol cm−2h−1 at pH 5.0) complemented by an important diffusive component. Among the compounds tested (neutral, basic, and acidic amino acids, auxin, glutathione, and sugars), only the aromatic amino acids clearly compete with 2,4D-Lys. The conjugate accumulates in the vein network, is exported toward the growing organs, and exhibits a distribution pattern different from that of the herbicide moiety. However, over time 2,4D-Lys progressively splits into 2,4D and lysine. Analyses by high-performance liquid chromatography and liquid scintillation spectrometry of the phloem sap collected from the castor bean system, used as a systemy test, indicate decreasing capacities of 2,4D, 2,4D-Lys, and glyphosate, respectively, to move from the epidermis cell wall to the sieve element. Our results show that it is possible to design synthesis of large-size xenobiotics (approximately 350 D) with a lipophilic pole, exhibiting high mobility within the vascular system.
A New Approach to Measure Gross CO2 Fluxes in Leaves. Gross CO2 Assimilation, Photorespiration, and Mitochondrial Respiration in the Light in Tomato under Drought Stress
Authors: Haupt-Herting Silke , Klug Klaus , Fock Heinrich P. 
Published: July 2002

AbstractWe developed a new method using 13CO2 and mass spectrometry to elucidate the role of photorespiration as an alternative electron dissipating pathway under drought stress. This was achieved by experimentally distinguishing between the CO2fluxes into and out of the leaf. The method allows us to determine the rates of gross CO2 assimilation and gross CO2evolution in addition to net CO2 uptake by attached leaves during steady-state photosynthesis. Furthermore, a comparison between measurements under photorespiratory and non-photorespiratory conditions may give information about the contribution of photorespiration and mitochondrial respiration to the rate of gross CO2evolution at photosynthetic steady state. In tomato (Lycopersicon esculentum Mill. cv Moneymaker) leaves, drought stress decreases the rates of net and gross CO2uptake as well as CO2 release from photorespiration and mitochondrial respiration in the light. However, the ratio of photorespiratory CO2 evolution to gross CO2assimilation rises with water deficit. Also the contribution of re-assimilation of (photo) respiratory CO2 to gross CO2 assimilation increases under drought.
Role of Auxin-Induced Reactive Oxygen Species in Root Gravitropism
Authors: Joo Jung Hee , Bae Yun Soo , Lee June Seung 
Published: July 2002

Abstract
We report our studies on root gravitropism indicating that reactive oxygen species (ROS) may function as a downstream component in auxin-mediated signal transduction. A transient increase in the intracellular concentration of ROS in the convex endodermis resulted from either gravistimulation or unilateral application of auxin to vertical roots. Root bending was also brought about by unilateral application of ROS to vertical roots pretreated with the auxin transport inhibitor N-1-naphthylphthalamic acid. Furthermore, the scavenging of ROS by antioxidants (N-acetylcysteine, ascorbic acid, and Trolox) inhibited root gravitropism. These results indicate that the generation of ROS plays a role in root gravitropism.
A noncanonical WD‐repeat protein from the cyanobacterium Synechocystis PCC6803: Structural and functional study
Authors: Hisbergues Michael , Gaitatzes Chrysanthe G. , Joset Françoise , Bedu Sylvie , Smith Temple F. 
Published: July 2002

AbstractSynechocystis PCC6803 possesses several open reading frames encoding putative WD‐repeat proteins. One, the Hat protein, is involved in the control of a high‐affinity transport system for inorganic carbon that is active when the cells are grown under a limiting concentration of this carbon substrate. The protein is composed of two major domains separated by a hydrophobic linker region of 20 amino acid residues. The N‐terminal domain of Hat has no homolog in standard databases and does not display any particular structural features. Eleven WD repeats have been identified in the C‐terminal moiety. The region encompassing the four terminal WD repeats is essential for growth under a limiting inorganic carbon regime. The region encompassing the two most terminal WD repeats is required for the activity of the high‐affinity transport system. However, because the Hat protein is located in the thylakoids, it should not be itself an element of the transport system. The structural organization of the WD‐containing domain of Hat was modeled from the crystal structure of the G protein β subunit (with seven WD repeats) and of hemopexin (a structural analog with four blades). Functional and structural data argue in favor of an organization of the Hat WD moiety in two subdomains of seven and four WD repeats. The C‐terminal 4‐mer subdomain might interact with another, yet unknown, protein/peptide. This interaction could be essential in modulating the stability of the 4‐mer structure and, thus, the accessibility of this subdomain, or at least of the region encompassing the last two WD repeats.
TM Finder: A prediction program for transmembrane protein segments using a combination of hydrophobicity and nonpolar phase helicity scales
Authors: Deber Charles M. , Wang Chen , Liu Li‐Ping , Prior Andrew S. , Agrawal Shuchi , Muskat Brenda L. , Cuticchia A. Jamie 
Published: July 2002

AbstractBased on the principle of dual prediction by segment hydrophobicity and nonpolar phase helicity, in concert with imposed threshold values of these two parameters, we developed the automated prediction program TM Finder that can successfully locate most transmembrane (TM) segments in proteins. The program uses the results of experiments on a series of host‐guest TM segment mimic peptides of prototypic sequence KK AAAXAAAAAXAAWAAXAAAKKKK‐amide (where X = each of the 20 commonly occurring amino acids) through which an HPLC‐derived hydropathy scale, a hydrophobicity threshold for spontaneous membrane insertion, and a nonpolar phase helical propensity scale were determined. Using these scales, the optimized prediction algorithm of TM Finder defines TM segments by first searching for competent core segments using the combination of hydrophobicity and helicity scales, and then performs a gap‐joining operation, which minimizes prediction bias caused by local hydrophilic residues and/or the choice of window size. In addition, the hydrophobicity threshold requirement enables TM Finder to distinguish reliably between membrane proteins and globular proteins, thereby adding an important dimension to the program. A full web version of the TM Finder program can be accessed at http://www.bioinformatics‐canada.org/TM/.
Coupling of antibodies via protein Z on modified polyoma virus‐like particles
Authors: Gleiter Stefan , Lilie Hauke 
Published: July 2002

AbstractTherapeutic application of virus‐based delivery systems often implies a change of the tropism of these vectors. This can be achieved by insertion of polypeptides (e.g., antibody fragments) in viral coat proteins. Such fusion proteins have only been used in viral vectors so far and, as part of a virus, they have not been available for a detailed biophysical characterization. We analyzed a fusion protein called VP1‐Z, which is based on the polyoma virus coat protein VP1 and protein Z. Protein Z is an engineered antibody‐binding domain derived from protein A fromStaphylococcus aureus. The fusion VP1‐Z was constructed by insertion of protein Z in the HI‐loop of VP1. As wild‐type VP1, VP1‐Z formed pentameric capsomers and assembled to VLPs in vitro. The stability of these particles was very similar compared to that of VLPs of wild‐type VP1. Protein Z was fully structured in the fusion protein and was still capable of binding antibodies on the surface of VLPs of VP1‐Z. Using this fusion protein, we could change the tropism of polyoma VLPs toward cells presenting on their surface the antigen of the coupled antibody.
Sialidase‐like Asp‐boxes: Sequence‐similar structures within different protein folds
Authors: Copley Richard R. , Russell Robert B. , Ponting Chris P. 
Published: July 2002

AbstractSequence similarity is the most common measure currently used to infer homology between proteins. Typically, homologous protein domains show sequence similarity over their entire lengths. Here we identify Asp box motifs, initially found as repeats in sialidases and neuraminidases, in new structural and sequence contexts. These motifs represent significantly similar sequences, localized to β hairpins within proteins that are otherwise different in sequence and three‐dimensional structure. By performing a combined sequence‐ and structure‐based analysis we detect Asp boxes in more than nine protein families, including bacterial ribonucleases, sulfite oxidases, reelin, netrins, some lipoprotein receptors, and a variety of glycosyl hydrolases. Although the function common to each of these proteins, if any, remains unclear, we discuss possible functions of Asp boxes on the basis of previously determined experimental results and discuss different evolutionary scenarios for the origin of Asp‐box containing proteins.
Prediction of the transmembrane regions of β‐barrel membrane proteins with a neural network‐based predictor
Authors: Jacoboni Irene , Martelli Pier Luigi , Fariselli Piero , De Pinto Vito , Casadio Rita 
Published: July 2002

AbstractA method based on neural networks is trained and tested on a nonredundant set of β‐barrel membrane proteins known at atomic resolution with a jackknife procedure. The method predicts the topography of transmembrane β strands with residue accuracy as high as 78% when evolutionary information is used as input to the network. Of the transmembrane β‐strands included in the training set, 93% are correctly assigned. The predictor includes an algorithm of model optimization, based on dynamic programming, that correctly models eight out of the 11 proteins present in the training/testing set. In addition, protein topology is assigned on the basis of the location of the longest loops in the models. We propose this as a general method to fill the gap of the prediction of β‐barrel membrane proteins.
Stabilization of hen egg white lysozyme by a cavity‐filling mutation
Authors: Ohmura Tadahiro , Ueda Tadashi , Ootsuka Keiichi , Saito Minoru , Imoto Taiji 
Published: July 2002

AbstractStabilization of a protein using cavity‐filling strategy has hardly been successful because of unfavorable van der Waals contacts. We succeeded in stabilizing lysozymes by cavity‐filling mutations. The mutations were checked by a simple energy minimization in advance. It was shown clearly that the sum of free energy change caused by the hydrophobicity and the cavity size was correlated very well with protein stability. We also considered the aromatic–aromatic interaction. It is reconfirmed that the cavity‐filling mutation in a hydrophobic core is a very useful method to stabilize a protein when the mutation candidate is selected carefully.