bluuebunny/crossref_metadata_2025_split huggingface dataset:
Immobilization of Flax Protoplasts in Agarose and Alginate Beads (Correlation between Ionically Bound Cell-Wall Proteins and Morphogenetic Response)
Authors: Roger D. , David A. , David H. 
Published: July 2002

Abstract
Linum usitatissimum protoplast-derived colonies that are cultured in auxin-supplemented medium and immobilized in Ca2+-alginate matrix form round colonies that develop into polarized, embryo-like structures. On the other hand, protoplast-derived colonies that are immobilized in agarose do not show an organized morphogenetic response, and unique, ionically bound cell-wall protein patterns match this response. Although only slight differences in neosynthesized or total constitutive polypeptides are observed, dramatic changes in ionically bound cell-wall proteins are seen. In protoplasts grown on Ca2+-alginate-solidified, auxin-containing medium. several basic polypeptides were strongly induced and were found tightly bound to the cell wall. In contrast, these basic proteins were found only weakly bound to the walls of protoplasts grown on agarose-solidified, auxin-containing medium or on Ca2+-alginate-solidified, auxin-free medium, in which they were released into the medium. Our results suggest that plant cells can perceive and respond to the adjacent extracellular matrix, since we show that the growth of flax cells on Ca2+-alginate in the presence of auxin-containing medium may promote the binding of specific proteins to the walls. This establishes a direct correlation of an embryo-like morphogenesis with ionically bound cell-wall basic proteins in flax protoplasts grown on Ca2+-alginate-solidified, auxin-containing medium.
Tomato Phosphate Transporter Genes Are Differentially Regulated in Plant Tissues by Phosphorus1
Authors: Liu Chunming , Muchhal Umesh S. , Uthappa Mukatira , Kononowicz Andrzej K. , Raghothama Kaschandra G. 
Published: July 2002

Abstract
Phosphorus is a major nutrient acquired by roots via high-affinity inorganic phosphate (Pi) transporters. In this paper, we describe the tissue-specific regulation of tomato (Lycopersicon esculentum L.) Pi-transporter genes by Pi. The encoded peptides of the LePT1 and LePT2genes belong to a family of 12 membrane-spanning domain proteins and show a high degree of sequence identity to known high-affinity Pi transporters. Both genes are highly expressed in roots, although there is some expression of LePT1 in leaves. Their expression is markedly induced by Pi starvation but not by starvation of nitrogen, potassium, or iron. The transcripts are primarily localized in root epidermis under Pi starvation. Accumulation of LePT1 message was also observed in palisade parenchyma cells of Pi-starved leaves. Our data suggest that the epidermally localized Pi transporters may play a significant role in acquiring the nutrient under natural conditions. Divided root-system studies support the hypothesis that signal(s) for the Pi-starvation response may arise internally because of the changes in cellular concentration of phosphorus.
Respiratory Elicitors from Rhizobium melilotiAffect Intact Alfalfa Roots1
Authors: Volpin Hanne , Phillips Donald A. 
Published: July 2002

Abstract
Molecules produced byRhizobium meliloti increase respiration of alfalfa (Medicago sativa L.) roots. Maximum respiratory increases, measured either as CO2 evolution or as O2 uptake, were elicited in roots of 3-d-old seedlings by 16 h of exposure to living or deadR. meliloti cells at densities of 107bacteria/mL. Excising roots after exposure to bacteria and separating them into root-tip- and root-hair-containing segments showed that respiratory increases occurred only in the root-hair region. In such assays, CO2 production by segments with root hairs increased by as much as 100% in the presence of bacteria. Two partially purified compounds from R. meliloti 1021 increased root respiration at very low, possibly picomolar, concentrations. One factor, peak B, resembled known pathogenic elicitors because it produced a rapid (15-min), transitory increase in respiration. A second factor, peak D, was quite different because root respiration increased slowly for 8 h and was maintained at the higher level. These molecules differ from lipo-chitin oligosaccharides active in root nodulation for the following reasons: (a) they do not curl alfalfa root hairs, (b) they are synthesized by bacteria in the absence of known plant inducer molecules, and (c) they are produced by a mutant R. meliloti that does not synthesize known lipo-chitin oligosaccharides. The peak-D compound(s) may benefit both symbionts by increasing CO2, which is required for growth of R. meliloti, and possibly by increasing the energy that is available in the plant to form root nodules.
Differential Expression of Two Novel Members of the Tomato Ethylene-Receptor Family
Authors: Tieman Denise M. , Klee Harry J. 
Published: July 2002

Abstract
The phytohormone ethylene regulates many aspects of plant growth, development, and environmental responses. Much of the developmental regulation of ethylene responses in tomato (Lycopersicon esculentum) occurs at the level of hormone sensitivity. In an effort to understand the regulation of ethylene responses, we isolated and characterized tomato genes with sequence similarity to the Arabidopsis ETR1 (ethyleneresponse 1) ethylene receptor. Previously, we isolated three genes that exhibit high similarity to ETR1 and to each other. Here we report the isolation of two additional genes,LeETR4 and LeETR5, that are only 42% and 40% identical to ETR1, respectively. Although the amino acids known to be involved in ethylene binding are conserved, LeETR5 lacks the histidine within the kinase domain that is predicted to be phosphorylated. This suggests that histidine kinase activity is not necessary for an ethylene response, because mutated forms of both LeETR4 and LeETR5 confer dominant ethylene insensitivity in transgenic Arabidopsis plants. Expression analysis indicates thatLeETR4 accounts for most of the putative ethylene-receptor mRNA present in reproductive tissues, but, likeLeETR5, it is less abundant in vegetative tissues. Taken together, ethylene perception in tomato is potentially quite complex, with at least five structurally divergent, putative receptor family members exhibiting significant variation in expression levels throughout development.
Molecular and Biochemical Characterization of the Involvement of Cyclin-Dependent Kinase A during the Early Development of Tomato Fruit
Authors: Joubès Jérôme , Phan Thi-Hai , Just Daniel , Rothan Christophe , Bergounioux Catherine , Raymond Philippe , Chevalier Christian 
Published: July 2002

AbstractFollowing fruit set, the early development of tomato (Lycopersicon esculentum Mill.) fruit comprises two distinct phases: a cell division phase and a consecutive phase of cell expansion until the onset of ripening. In this study, we analyzed cytological and molecular changes characterizing these early phases of tomato fruit development. First we investigated the spatial and temporal regulation of the mitotic activity during fruit development. The DNA content of isolated nuclei from the different fruit tissues was determined by flow cytometry analysis. The results confirm the data of mitotic activity measurements and show that cell differentiation, leading to expanded cells, is characterized by endoreduplication. Second, we isolated two cDNAs, named Lyces;CDKA1 (accession no. Y17225) and Lyces;CDKA2 (accession no. Y17226), encoding tomato homologs of the cyclin-dependent kinase (CDK) p34cdc2. Tomato CDKA gene expression was followed at both the transcriptional and translational levels during fruit development. The transcripts for Lyces;CDKA1 and Lyces;CDKA2 and the corresponding CDKA proteins are predominantly accumulated during the phase of cell division between anthesis and 5 d post anthesis (DPA). In whole fruits, the maximum CDK activity was obtained between 5 and 10 DPA. The determination of the kinase activity using protein extracts from the different fruit tissues was in agreement with mitotic activity analysis. It showed the particular disappearance of the activity in the gel tissue as early as 15 DPA. The overall data of CDK activity measurements suggest a strong post-translational regulation of CDK at the temporal and spatial levels during early tomato fruit development.
A Possible Role for Pyrophosphate in the Coordination of Cytosolic and Plastidial Carbon Metabolism within the Potato Tuber
Authors: Farré Eva M. , Geigenberger Peter , Willmitzer Lothar , Trethewey Richard N. 
Published: July 2002

AbstractThe early stages of tuber development are characterized by cell division, high metabolic activity, and the predominance of invertase as the sucrose (Suc) cleaving activity. However, during the subsequent phase of starch accumulation the cleavage of Suc occurs primarily by the action of Suc synthase. The mechanism that is responsible for this switch in Suc cleaving activities is currently unknown. One striking difference between the invertase and Suc synthase mediated cleavage of Suc is the direct involvement of inorganic pyrophosphate (PPi) in the latter case. There is presently no convincing explanation of how the PPi required to support this process is generated in potato (Solanum tuberosum) tubers. The major site of PPi production in a maturing potato tubers is likely to be the reaction catalyzed by ADP-glucose pyrophosphorylase, the first committed step of starch biosynthesis in amyloplasts. We present data based on the analysis of the PPi levels in various transgenic plants altered in starch and Suc metabolism that support the hypothesis that PPi produced in the plastid is used to support cytosolic Suc breakdown and that PPi is an important coordinator of cytosolic and plastidial metabolism in potato tubers.
Antisense Inhibition of the Nr Gene Restores Normal Ripening to the Tomato Never-ripe Mutant, Consistent with the Ethylene Receptor- Inhibition Model
Authors: Hackett Rachel M. , Ho Chin-Wen , Lin Zhefeng , Foote Humphrey C.C. , Fray Rupert G. , Grierson Don 
Published: July 2002

Abstract
The hormone ethylene regulates many aspects of plant growth and development, including fruit ripening. In transgenic tomato (Lycopersicon esculentum) plants, antisense inhibition of ethylene biosynthetic genes results in inhibited or delayed ripening. The dominant tomato mutant, Never-ripe(Nr), is insensitive to ethylene and fruit fail to ripen. The Nr phenotype results from mutation of the ethylene receptor encoded by the NR gene, such that it can no longer bind the hormone. NR has homology to the Arabidopsis ethylene receptors. Studies on ethylene perception in Arabidopsis have demonstrated that receptors operate by a “receptor inhibition” mode of action, in which they actively repress ethylene responses in the absence of the hormone, and are inactive when bound to ethylene. In ripening tomato fruit, expression of NR is highly regulated, increasing in expression at the onset of ripening, coincident with increased ethylene production. This expression suggests a requirement for the NR gene product during the ripening process, and implies that ethylene signaling via the tomato NR receptor might not operate by receptor inhibition. We used antisense inhibition to investigate the role of NR in ripening tomato fruit and determine its mode of action. We demonstrate restoration of normal ripening in Nr fruit by inhibition of the mutantNr gene, indicating that this receptor is not required for normal ripening, and confirming receptor inhibition as the mode of action of the NR protein.
Regulation of a Wheat Actin-Depolymerizing Factor during Cold Acclimation
Authors: Ouellet François , Carpentier Éric , Cope M. Jamie T.V. , Monroy Antonio F. , Sarhan Fathey 
Published: July 2002

Abstract
We have previously shown that the wheat (Triticum aestivum) TaADF gene expression level is correlated with the plants capacity to tolerate freezing. Sequence analysis revealed that this gene encodes a protein homologous to members of the actin-depolymerizing factor (ADF)/cofilin family. We report here on the characterization of the recombinant TaADF protein. Assays for ADF activity showed that TaADF is capable of sequestering actin, preventing nucleotide exchange, and inducing actin depolymerization. In vitro phosphorylation studies showed that TaADF is a substrate for a wheat 52-kD kinase. The activity of this kinase is modulated by low temperature during the acclimation period. Western-blot analyses revealed that TaADF is expressed only in cold-acclimated Gramineae species and that the accumulation level is much higher in the freezing-tolerant wheat cultivars compared with the less tolerant ones. This accumulation was found to be regulated by a factor(s) encoded by a gene(s) located on chromosome 5A, the chromosome most often found to be associated with cold hardiness. The induction of an active ADF during cold acclimation and the correlation with an increased freezing tolerance suggest that the protein may be required for the cytoskeletal rearrangements that may occur upon low temperature exposure. These remodelings might be important for the enhancement of freezing tolerance.
Urea Is a Product of Ureidoglycolate Degradation in Chickpea. Purification and Characterization of the Ureidoglycolate Urea-Lyase
Authors: Muñoz Alfonso , Piedras Pedro , Aguilar Miguel , Pineda Manuel 
Published: July 2002

AbstractA ureidoglycolate-degrading activity was analyzed in different organs of chickpea (Cicer arietinum). Activity was detected in all the tissues analyzed, but highest levels of specific activity were found in pods, from which it has been purified and characterized. This is the first ureidoglycolate-degrading activity that has been purified to homogeneity from any photosynthetic organism. Only one ureidoglycolate-degrading activity was found during the purification. The enzyme was purified 1,500-fold, and specific activity for the pure enzyme was 8.6 units mg−1, which corresponds with a turnover number of 1,600 min−1. The native enzyme has a molecular mass of 180 kD and consists of six identical or similar-sized subunits of 31 kD each. The enzyme exhibited hyperbolic, Michaelian kinetics for (−) ureidoglycolate withK m values of 6 and 10 μm in the presence or absence of Mn2+, respectively. Optimum pH was between 7 and 8 and maximum activity was found at temperatures above 70°C, the enzyme being extremely stable and resistant to heat denaturation. The activity was inhibited by EDTA and enhanced by several bivalent cations, thus suggesting that the enzyme is a metalloprotein. This enzyme has been characterized as a ureidoglycolate urea-lyase (EC 4.3.2.3), which catalyzes the degradation of (−) ureidoglycolate to glyoxylate and urea. This is the first time that such an activity is detected in plant tissues. A possible function for this activity and its implications in the context of nitrogen mobilization in legume plants is also discussed.
Purification and Characterization of the Preprotein Translocase of the Outer Mitochondrial Membrane from Arabidopsis. Identification of Multiple Forms of TOM20
Authors: Werhahn Wolf , Niemeyer Astrid , Jänsch Lothar , Kruft Volker , Schmitz Udo K. , Braun Hans-Peter 
Published: July 2002

Abstract
The translocase of the outer mitochondrial membrane (TOM) complex is a preprotein translocase that mediates transport of nuclear-encoded mitochondrial proteins across the outer mitochondrial membrane. Here we report the purification of this protein complex from Arabidopsis. On blue-native gels the Arabidopsis TOM complex runs at 230 kD and can be dissected into subunits of 34, 23, 21, 8, 7, and 6 kD. The identity of four subunits could be determined by immunoblotting and/or direct protein sequencing. The 21- and the 23-kD subunits exhibit significant sequence homology to the TOM20 preprotein receptor from other organisms. Analysis by two-dimensional isoelectric focusing/Tricine sodium dodecyl sulfide-polyacrylamide gel electrophoresis revealed the presence of further forms for Arabidopsis TOM20. All TOM20 proteins comprise a large cytoplasmically exposed hydrophilic domain, which is degraded upon trypsination of intact mitochondria. Clones encoding four different forms of Arabidopsis TOM20 were identified and sequenced. The deduced amino acid sequences are rather conserved in the N-terminal half and in the very C-terminal part, but include a highly variable glycine-rich region close to the C terminus. Implications on the function of plant TOM complexes are discussed. Based on peptide and nucleic acid sequence data, the primary structure for Arabidopsis TOM40 is presented.
Flavonoid Accumulation Patterns of Transparent Testa Mutants of Arabidopsis
Authors: Peer Wendy Ann , Brown Dana E. , Tague Brian W. , Muday Gloria K. , Taiz Lincoln , Murphy Angus S. 
Published: July 2002

Abstract
Flavonoids have been implicated in the regulation of auxin movements in Arabidopsis. To understand when and where flavonoids may be acting to control auxin movement, the flavonoid accumulation pattern was examined in young seedlings and mature tissues of wild-type Arabidopsis. Using a variety of biochemical and visualization techniques, flavonoid accumulation in mature plants was localized in cauline leaves, pollen, stigmata, and floral primordia, and in the stems of young, actively growing inflorescences. In young Landsbergerecta seedlings, aglycone flavonols accumulated developmentally in three regions, the cotyledonary node, the hypocotyl-root transition zone, and the root tip. Aglycone flavonols accumulated at the hypocotyl-root transition zone in a developmental and tissue-specific manner with kaempferol in the epidermis and quercetin in the cortex. Quercetin localized subcellularly in the nuclear region, plasma membrane, and endomembrane system, whereas kaempferol localized in the nuclear region and plasma membrane. The flavonoid accumulation pattern was also examined in transparent testa mutants blocked at different steps in the flavonoid biosynthesis pathway. The transparent testa mutants were shown to have precursor accumulation patterns similar to those of end product flavonoids in wild-type Landsberg erecta, suggesting that synthesis and end product accumulation occur in the same cells.
Intersubsystem chemical bonds in the misfit layer compounds (LaS)1.13TaS2 and (LaS)1.14NbS2
Authors: Jobst Andreas , van Smaalen Sander 
Published: July 2002

The modulated structures of incommensurate composite crystals (La0.912S)1.13TaS2 at room temperature and of (La0.949S)1.14NbS2 at T = 115 K are refined against high-resolution X-ray data. The compounds are isostructural with superspace group F′m2m(α,0,0)00s. For (LaS)1.13TaS2, lattice parameters of the first subsystem TaS2 were obtained as a = 3.2922 (1), b = 5.7776 (2) and c = 23.013 (2) Å. For the second subsystem LaS, the same b and c parameters were found, but a = 5.8090 (8) Å. Refinements led to a final structure model with R = 0.036 for 4767 observed unique reflections (R = 0.023 for 2147 main reflections, R = 0.099 for 1554 first-order satellites and R = 0.112 for 1042 second-order satellites). The final model includes modulation parameters up to the second-order harmonics for the displacements of the atoms, for the occupational parameters and for the temperature parameters. A clear correlation is found between the relative positions of the subsystems, the displacement modulation, the occupational modulation and the modulation of the temperature parameters. The analysis shows that the variations in environments are resolved by correlated variations in the temperature factors. For (LaS)1.14NbS2, lattice parameters at T = 115 K of the NbS2 subsystem were obtained as a = 3.3065 (4), b = 5.7960 (5) and c = 22.956 (3) Å. For the LaS subsystem, the same values for b and c were obtained, but a = 5.7983 (7) Å. Refinements led to a final structure model with R = 0.048 for 5909 observed unique reflections (R = 0.034 for 2528 main reflections, R = 0.092 for 2171 first-order satellites and R = 0.113 for 1103 second-order satellites). The final structure model is similar to that of (LaS)1.13TaS2. In particular, it is found that the values of the modulation parameters are almost equal and it is concluded that the modulations are independent of the temperature and the replacement of Ta with Nb, and thus represent a general mechanism of resolving the strain between the mutually incommensurate layers.
Crystallization and preliminary X-ray diffraction studies of the carboxylesterase EST2 from Alicyclobacillus acidocaldarius
Authors: De Simone Giuseppina , Manco Giuseppe , Galdiero Stefania , Lombardi Angela , Rossi Mosè , Pavone Vincenzo 
Published: July 2002

EST2, a thermophilic carboxylesterase from Alicyclobacillus acidocaldarius, belonging to the HSL group of the esterase/lipase superfamily, has been crystallized for the first time. Ammonium sulfate was used as a precipitant and the crystallization proceeded at pH 7.8. The crystals belong to space group P41212 or its enantiomorph P43212, with unit-cell parameters a = b = 78.8, c = 106.4 Å. A complete data set has been collected at the synchrotron source Elettra in Trieste to 2.4 Å resolution, using a single frozen crystal.
Co-crystallization and preliminary crystallographic analysis of the high mobility group domain of HMG-D bound to DNA
Authors: Murphy Frank V. , Sehy Jonathan V. , Dow Linda K. , Gao Yi-Gui , Churchill Mair E. A. 
Published: July 2002

Structural studies are essential to understand mechanisms of non-sequence-specific DNA binding used by chromosomal proteins. A non-histone high-mobility group (HMG) chromosomal protein from Drosophila melanogaster, HMG-D, binds duplex DNA in a non-sequence-specific fashion. The DNA-binding domain of HMG-D has been co-crystallized with a duplex DNA fragment in the primitive orthorhombic space group P212121, with unit-cell dimensions a = 43.74, b = 53.80, c = 86.84 Å. Data have been collected to 2.20 Å at 99 K, with diffraction observed to at least 2.0 Å. Heavy-atom derivative crystals have been obtained by co-crystallization with oligonucleotides halogenated at major-groove positions near the end of the DNA.
Novel α7‐like nicotinic acetylcholine receptor subunits in the nematode Caenorhabditis elegans
Authors: Mongan Nigel P. , Jones Andrew K. , Smith Graham R. , Sansom Mark S.P. , Sattelle David B. 
Published: July 2002

AbstractWe have used reverse‐transcription‐polymerase chain reaction (RT‐PCR) and DNA sequencing techniques to confirm the transcription of seven (six α and one non‐α) novel candidate nicotinic acetylcholine receptor (nAChR) subunit‐encoding genes identified in the genome sequence of the nematode Caenorhabditis elegans. Compared to vertebrate nAChR subunits, they most closely resemble the homomer‐forming, neuronal α7 subunit. Comparison of the predicted amino acid sequences of the new nAChR subunits with those described previously in C. elegans reveals five subunits (four α and one non‐α) which resemble the DEG‐3‐like group of subunits. To date, this highly divergent nAChR subunit group is unique to C. elegans. ACR‐22 is the first non‐α member of the DEG‐3‐like group of subunits to be identified. Two new members of the related ACR‐16‐like nAChR group of subunits have also been shown to be transcribed, making the ACR‐16‐like subunit group the largest in C. elegans. Residues in the α subunit second transmembrane region (M2) which contribute to the channel lining show variations with implications for channel function. For example, in ACR‐22, the highly conserved 0′ lysine of M2 is replaced by histidine. Restrained molecular dynamics simulations have been used to generate molecular models of homo‐pentameric M2 helix bundles for the novel subunits, enabling identification and display of pore‐lining and protein interface residues. The number and diversity of genes encoding C. elegans nAChR subunits with similarities to the homomer‐forming vertebrate α7 subunits and the identification of related non‐α subunits, only found in C. elegans to date, suggest that at least some of these subunits may contribute to heteromers in vivo.