bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural cell‐wall proteins in protoxylem development: evidence for a repair process mediated by a glycine‐rich protein
Authors: Ryser Ulrich , Schorderet Martine , Zhao Gui‐Fang , Studer Daniel , Ruel Katia , Haul Gunter , Keller Beat 
Published: March 2003

SummaryPolyclonal antibodies were used to localize structural cell‐wall proteins in differentiating protoxylem elements in etiolated bean and soybean hypocotyls at the light‐ and electron‐microscopic level. A proline‐rich protein was localized in the lignified secondary walls, but not in the primary walls of protoxylem elements, which remain unlignified, as shown with lignin‐specific antibodies. Secretion of the proline‐rich protein was observed during lignification in different cell types. A glycine‐rich protein (GRP1.8) was specifically localized in the modified primary walls of mature protoxylem elements and in cell corners between xylem elements and xylem parenchyma cells. The protein was secreted by Golgi bodies both in protoxylem cells after the lignification of their secondary walls and in the surrounding xylem parenchyma cells. The modified primary walls of protoxylem elements were visualized under the light microscope as filaments or sheets staining distinctly with the protein stain Coomassie blue. Electron micrographs of these walls show that they are composed of an amorphous material of moderate electron‐density and of polysaccharide microfibrils. These materials form a three‐dimensional network, interconnecting the ring‐ or spiral‐shaped secondary wall thickenings of protoxylem elements and xylem parenchyma cells. The results demonstrate that the modified primary walls of protoxylem cells are not simply breakdown products due to partial hydrolysis and passive elongation, as believed until now. Extensive repair processes produce cell walls with unique staining properties. It is concluded that these walls are unusually rich in protein and therefore have special chemical and physical properties.
High‐affinity binding site for ethylene‐inducing xylanase elicitor on Nicotiana tabacum membranes
Authors: Hanania Uri , Avni Adi 
Published: March 2003

SummaryChallenge of Nicotiana tabacum cv Xanthi with the ethylene‐inducing xylanase (EIX) from Trichoderma viride causes rapid induction of plant defense responses leading to hypersensitive necrosis. This phenomenon is cultivar‐specific; no response is detected when N. tabacum cv Hicks is similarly treated. The responsiveness is determined in tobacco and tomato by a single dominant gene. EIX was labeled with fluorescein‐isothiocyanate and incubated with cell suspension cultures, protoplasts or microsomal membranes. Binding of EIX to the microsomal membranes was found to be specific and saturable, with a dissociation constant of 6.2 nM. Using confocal laser microscopy, the EIX binding site was localized to the plasma membrane. Binding of EIX to its high‐affinity site occurred in responsive species. These results demonstrate the existence of a high‐affinity binding site for EIX on the plasma membrane of responsive cultivars. Chemical cross‐linking of EIX to microsomal membranes from responding plants revealed a 66 kDa protein complex. This protein may function as the receptor that mediates the hypersensitive response induced by EIX binding.
A pectate lyase from Zinnia elegans is auxin inducible
Authors: Domingo Concha , Roberts Keith , Stacey Nicola J. , Connerton Ian , Ruíz‐teran Francisco , McCann Maureen C. 
Published: March 2003

SummaryThe Zinnia mesophyll cell system consists of isolated leaf mesophyll cells in culture that can be induced, by auxin and cytokinin, to reproducibly trans‐differentiate into tracheary elements (TE) after 96 h, while in the presence of auxin alone the cells simply elongate. In a search for genes involved in modifications to cell‐wall architecture before any overt signs of cell differentiation, a differential hybridization of a 72‐h cDNA library with probes from mRNA at time‐points of 24 h and 72 h was done revealing a number of transcripts up‐regulated between these times. One of these cDNAs shows homology to pectate lyase, a pectin‐degrading enzyme. The complete cDNA sequence (ZePel) corresponds to a translated protein of 44 kDa with an N‐terminal signal peptide of about 2 kDa, and one potential N‐glycosylation site. Northern analysis confirms that the strong expression of this gene during TE induction occurs at a very early stage of the process and is due solely to the presence of auxin in the induction medium. In situ hybridization studies in young Zinnia stems show that ZePel expression is associated with vascular bundles and shoot primordia. Recombinant protein made in Escherichia coli possesses calcium‐dependent pectate lyase activity. Pectate lyase activity is detected in elongating and differentiating in vitro cell populations. The role of this enzyme in remodelling the cell wall during cell elongation and differentiation is discussed.
Reversible protein phosphorylation regulates jasmonic acid‐dependent and ‐independent wound signal transduction pathways in Arabidopsis thaliana
Authors: Rojo Enrique , Titarenko Elena , León José , Berger Susanne , Vancanneyt Guy , Sánchez‐Serrano José J. 
Published: March 2003

SummaryPlants responses to mechanical injury are complex and include the induced expression of defence‐related genes. The phytohormone JA has been reported to mediate some of these responses. To elucidate further the signal transduction processes involved, the action of specific agonists and antagonists of known signalling effectors on the response of Arabidopsis thaliana plantlets to JA and wounding was investigated. The identification and characterization of a reversible protein phosphorylation step in a transduction pathway leading to JA‐induced gene transcription is reported. This phosphorylation event involved the opposing activities of a staurosporine‐sensitive protein kinase, negatively regulating the pathway, and a protein phosphatase, most probably of type 2 A, which activated JA‐responsive gene expression. JA activation via this pathway was blocked in the A. thaliana JA‐insensitive mutants jin1, jin4 and coi1, and by exogenous application of cycloheximide or auxins. Wound‐induced activation of JA‐responsive genes was also regulated by this protein phosphorylation step. An alternative wound signalling pathway, independent of JA, was also identified, leading to the transcriptional activation of a different set of genes. This JA‐independent pathway was also regulated by a protein phosphorylation switch, in which the protein kinase positively regulated the pathway while the protein phosphatase negatively regulated it. Moreover, a labile protein apparently repressed the expression of these genes. One of the genes analysed, JR3, had a complex pattern of expression, possibly because it was regulated via both of the wound signalling pathways identified. According to the function of an homologous gene, JR3 may be involved in feedback inhibition of the JA response.
Isolation of an Arabidopsis thaliana mutant in which accumulation of cucumber mosaic virus coat protein is delayed
Authors: Yoshii Motoyasu , Yoshioka Norimichi , Ishikawa Masayuki , Naito Satoshi 
Published: March 2003

SummaryCucumber mosaic virus (CMV) is known to systemically infect Arabidopsis thaliana ecotype Columbia plants. In order to identify the host factors involved in the multiplication of CMV, we isolated an A. thaliana mutant in which the accumulation of the coat protein (CP) of CMV in upper uninoculated leaves was delayed. Genetic analyses suggested that the phenotype of delayed accumulation of CMV CP in the mutant plants was caused by a single, nuclear and recessive mutation designated cum1‐1, which was located on chromosome IV. The cum1‐1 mutation did not affect the multiplication of tobacco mosaic virus, turnip crinkle virus or turnip yellow mosaic virus, which belong to different taxonomic groups from CMV. Accumulation of CMV CP in the inoculated leaves of cum1‐1 plants was also delayed either when CMV virion or CMV virion RNA was inoculated. On the other hand, when cum1‐1 and the wild‐type Col‐0 protoplasts were inoculated with CMV virion RNA by electroporation, the accumulations of CMV‐related RNAs and the coat protein were similar. These results suggest that the cum1‐1 mutation did not affect the uncoating of CMV virion and subsequent replication in an initially infected cell but affected the spreading of CMV within an infected leaf, possibly the cell‐to‐cell movement of CMV in a virus‐specific manner.
Production of yellow colour in flowers: redirection of flavonoid biosynthesis in Petunia
Authors: Davies Kevin M. , Bloor Stephen J. , Spiller Gayle B. , Deroles Simon C. 
Published: March 2003

SummaryChalcones are intermediates in the biosynthesis of all flavonoids. In addition, in some species they constitute the major yellow flower pigments. There are two types of chalcones, distinguished by the presence (6′‐hydroxychalcones) or absence (6′‐deoxychalcones) of a hydroxyl group at the 6′ position of the A‐ring. The 6′‐deoxychalcones are formed when the enzyme chalcone reductase (CHR) is active in conjunction with chalcone synthase (CHS). In Petunia, only 6′‐hydroxychalcones are synthesized, and except in the pollen of some genotypes, they are ephemeral intermediates in flavonoid metabolism. By introducing a CHR cDNA from Medicago sativa under the control of the 35S CaMV promoter into acyanic‐ or cyanic‐flowered lines of Petunia, flower colour was changed from either white to pale yellow or deep purple to pale purple, respectively. Lines were generated that accumulated up to 60% of their petal flavonoids as 6′‐deoxychalcones. Several different 6′‐deoxychalcones accumulated in the petals of the CHR transgenics. The structures of three of these were determined: one, butein 4‐O‐glucoside, is a novel plant chalcone. Another chalcone compound was identified in the pollen of the transgenics. The results show that the Petunia chalcone isomerase is unable to use 6′‐deoxychalcones as substrates so that 6′‐deoxychalcones are stable in Petunia petals, leaves and pollen, but some Petunia flavonoid enzymes can use 6′‐deoxychalcones as substrates to modify their structures. The introduction of CHR provides a method to redirect the flavonoid pathway into chalcone production, in order to modify flower colour or to reduce the biosynthesis of other flavonoid types.
Repair of genomic double‐strand breaks in somatic plant cells by one‐sided invasion of homologous sequences
Authors: Puchta Holger 
Published: March 2003

SummaryDouble‐strand breaks (DSB) strongly enhance homologous recombination in the genome of somatic plant cells. To characterize the mechanism of homologous DSB repair in detail, Agrobacterium‐mediated targeting experiments were performed in tobacco, with repair constructs being homologous to either one or both ends of a transiently induced DSB. The recombination frequencies obtained were at least two orders of magnitude higher than without DSB induction and differed between the two T‐DNA by only one‐third. Thus, occurrence of homologies at both ends of the break is no prerequisite for recombination. The results demonstrate that most, if not all, reactions are initiated by one‐sided invasion of a homologous sequence. This indicates that the classical double‐strand break repair (DSBR) model originally proposed for meiotic recombination might be less appropriate for the description of homologous DSB repair in somatic plant cells than an integrative model based on a combination of the synthesis‐dependent strand annealing (SDSA) model and of a modified version of the one‐sided invasion (OSI) model of recombination. Direct consequences of this finding for the performance of gene targeting experiments, as well as possible implications for the stability of highly repetitive plant genomes, are discussed.
Lipochito‐oligosaccharides re‐initiate root hair tip growth in Vicia sativa with high calcium and spectrin‐like antigen at the tip
Authors: D Norbert C. A. , Ruijter  , Rook Martin B. , Bisseling Ton , Emons Anne Mie C. 
Published: March 2003

SummaryLipochito‐oligosaccharides, Nod factors secreted by Rhizobium bacteria, are signal molecules that induce deformation of root hairs of their host plant. A bioassay was used for deformation, and the cytological changes induced by specific lipochito‐oligosaccharides in root hairs of Vicia sativa L. (vetch), grown between glass slides, were examined. In the assay, root hairs of a particular developmental stage, those that were terminating growth, were susceptible to deformation. These hairs obtained characteristics of tip‐growing cells again: (i) a polar cytoplasmic organization and reverse fountain streaming, (ii) an accumulation of a spectrin‐like antigen at the tip, and (iii) a tip‐focused calcium gradient. Calcium gradients were visualized in Indo‐1 loaded root hairs with UV confocal microscopy and ratio‐imaging. The results show that hairs respond to the bacterial signal by recovering cytoplasmic polarity and exocytosis.
The Arabidopsis thaliana cDNAs coding for eIF4E and eIF(iso)4E are not functionally equivalent for yeast complementation and are differentially expressed during plant development
Authors: Rodriguez Cecilia Monica , Freire Miguel Angel , Camilleri Christine , Robaglia Christophe 
Published: March 2003

SummaryTwo cDNAs (At.EIF4E1 and At.EIF4E2) encoding, respectively, the eukaryotic initiation factors eIF4E and eIF(iso)4E of Arabidopsis thaliana were isolated by complementation of a Saccharomyces cerevisiae conditional mutant. The deduced amino acid sequences of the proteins are homologous to those from monocotyledonous plants, yeast and mammals. The corresponding genes were identified in YAC clones mapping to chromosome IV (At.EIF4E1) and to chromosome V (At.EIF4E2). The yeast strain complemented by At.EIF4E2 grew poorly compared with an isogenic strain expressing At.EIF4E1. Northern and in situ hybridization analysis show that both Arabidopsis At.EIF4E1 and At.EIF4E2 mRNAs are differentially accumulated in plant tissues. The At.EIF4E1 mRNA is expressed in all tissues except in the cells of the specialization zone of the roots; the At.EIF4E2 mRNA is particularly abundant in floral organs and in young developing tissues. This work further demonstrates an association between a high level of EIF4E mRNAs and cell proliferation and suggests that the plant eIF4E isoforms may have distinct functions in cell development and metabolism.
Identification of cDNAS encoding plastid‐targeted glutathione peroxidase
Authors: Mullineaux Philip M. , Karpinski Stanislaw , Jiménez Ana , Cleary Suzanne P. , Robinson Colin , Creissen Gary P. 
Published: March 2003

SummaryA cDNA was isolated from pea leaf RNA which encodes a phospholipid hydroperoxide glutathione peroxidase (PHGPX; E.C. 1.1.1.1.9). The N‐terminal section of this PHGPX encodes a recognisable chloroplast transit peptide. Efficient import in vitro of the pre‐PHGPX protein into the stroma of isolated pea chloroplasts confirmed that the PHGPX is a chloroplast‐located enzyme. The pea PHGPX has highly conserved homologues in Arabidopsis, citrus and Nicotiana sylvestris and the authors suggest that these proteins are also localised in the chloroplast and not in the cytosol as previously supposed.
The role of UDP‐glucose epimerase in carbohydrate metabolism of Arabidopsis
Authors: Dörmann Peter , Benning Christoph 
Published: March 2003

SummaryUridine 5′‐diphospho‐glucose‐4‐epimerase (UDP‐Glc epimerase) catalyses the reversible epimerization of UDP‐galactose and UDP‐glucose. In contrast to bacteria and yeast, expression of the UDP‐Glc epimerase gene in Arabidopsis was found not to be induced by galactose. To elucidate the metabolic role of this enzyme, transgenic Arabidopsis plants expressing the respective cDNA in sense or antisense orientation were constructed, leading to a range of plant lines with different UDP‐Glc epimerase activities. No alterations in morphology were observed and the relative amounts of different galactose‐containing compounds were not affected if the plants were raised on soil. However, on agar plates in the presence of galactose, the growth of different lines was increasingly repressed with decreasing enzyme activity, and an increase in the UDP‐Gal content was observed in parallel, whereas the UDP‐Glc content was nearly constant. The amount of galactose in the cell wall was increased in plants with low UDP‐Glc epimerase activity grown on galactose, whereas the cellulose content in the leaves was not altered. Furthermore, starch determined at different times of the day was highly abundant in plants with low UDP‐Glc epimerase activity in the presence of galactose. It is proposed that low endogenous UDP‐Glc epimerase activity is responsible for the galactose toxicity of the wild‐type. Possible mechanisms by which the starch content might be modulated are discussed.
Disease resistance gene homologs correlate with disease resistance loci of Arabidopsis thaliana
Authors: Speulman Elly , Bouchez David , Holub Eric B. , Beynon Jim L. 
Published: March 2003

SummaryThe disease resistance genes RPS2 of Arabidopsis and N of tobacco, among other recently cloned resistance genes, share several conserved sequences. Degenerate oligonucleotide primers, based on conserved sequences in the nucleotide binding site (NBS) and a weak hydrophobic domain of RPS2 and N, were used to amplify homologous sequences from Arabidopsis thaliana. Amplification products were obtained that were similar in sequence to the disease resistance genes RPS2, RPM1, N and L6. The Arabidopsis CIC‐YAC library was used to identify the position of the disease resistance homologs on the Arabidopsis genome. Their map positions could be correlated with the disease resistance loci RPS5, RAC1, RPP9, CAR1, RPP7, RPW2, RPP1, RPP10, RPP14, RPP5, RPP4, RPS2, RPW6, HRT, RPS4, RPP8, RPP21, RPP22, RPP23, RPP24 and TTR1. This method was therefore not only successful in the identification of sequences located within gene clusters that are involved in disease resistance, but could also contribute to the cloning of disease resistance genes from Arabidopsis.
Molecular analysis of a second functional A1 gene (dihydroflavonol 4‐reductase) in Zea mays
Authors: Bernhardt Jürgen , Stich Karl , Schwarz‐Sommer Zsuzsanna , Saedler Heinz , Wienand Udo 
Published: March 2003

SummarySome genes involved in anthocyanin biosynthesis in Zea mays are duplicated and differentially expressed. From the analysis of the A1 gene (dihydroflavonol 4‐reductase), which is involved in this pathway, no molecular evidence for gene duplication was known to date. Isolation and analysis of A1 homologous genomic clones revealed the presence of a second A1 gene in maize and also two copies of the gene in Teosinte guerrero. The duplicated genes are structurally very similar and, at least in maize, the second gene is expressed.
The use of vibratome sections of cereal spikelets to study anther development and meiosis
Authors: Aragon‐Alcaide Luis , Beven Alison , Moore Graham , Shaw Peter 
Published: March 2003

SummaryWe have developed a method using vibratome sectioning coupled with confocal microscopy to analyse pre‐meiotic and meiotic events in developing wheat anthers. This report describes the application of fluorescence in situ hybridization to three‐dimensionally preserved tissue sections from intact florets. We show that excellent imaging of all the stages of meiosis up to telophase I can be achieved, and show centromere positions and pre‐meiotic homologous pairing both in meiocytes and tapetum cells. These clear results using intact tissue sections are contrasted with conventional spreading methods for analysis of meiosis in plants, which we show can produce artefactual or uninterpretable results.
Phosphatidate phosphatase from avocado (Persea americana) – purification, substrate specificity and possible metabolic implications for the Kennedy pathway and cell signalling in plants
Authors: Pearce Matthew L. , Slabas Antoni R. 
Published: March 2003

SummaryPhosphatidate phosphatase (PAP; EC 3.1.3.4) is a pivotal enzyme in plant lipid metabolism positioned at a major branchpoint between the biosyntheses of phospholipids and triacylglycerols. The enzyme has been purified 7000‐fold from the microsomes of maturing Avocado fruit. The enzyme has a subunit molecular mass, as determined on SDS‐PAGE, of 49 kDa, and gel filtration studies revealed that it is monomeric. The enzyme was examined for the ability to hydrolyse sn‐1,2‐dioleoylglycerol‐3‐phosphate (PA), sn‐1‐oleoylglycerol‐3‐phosphate (LPA), sn‐2‐oleoylglycerol‐3‐phosphate (sn‐2‐LPA), and ceramide‐1‐phosphate. All substrates were used, but the apparent Vmax values for ceramide‐1‐phosphate and sn‐2‐LPA were considerably lower than for PA or LPA. A kinetic analysis of the purified enzyme was conducted using PA and LPA in Triton X‐100 mixed micelles according to the surface dilution kinetic model. The Vmax and interfacial Michaelis constant (KmB) were calculated for PA as 47 μmol min–1 mg–1 and 1.49 mol%, respectively. LPA was found to be a better substrate with a Vmax and KmB of 100 μmol min–1 mg–1 and 1.06 mol%, respectively. A detailed kinetic analysis of the effect of LPA on PA hydrolysis revealed LPA to be a potent competitive inhibitor of the reaction, with a Ki of 1.4 mol%. This possibly indicates that strict metabolic channelling is in operation in the Kennedy Pathway, with very low steady state concentrations of lyso‐phosphatidate with respect to phosphatidate in vivo.
Cloning and functional characterisation of a peptide transporter expressed in the scutellum of barley grain during the early stages of germination
Authors: West Christopher E. , Waterworth Wanda M. , Stephens Susan M. , Smith Craig P. , Bray Clifford M. 
Published: March 2003

SummaryA peptide transport gene (HvPTR1) expressed in the scutella of germinating barley grain has been cloned by an RT–PCR approach. Sequence analysis of the full length cDNA (2260 bp) revealed an open reading frame encoding a 579 amino acid protein of predicted molecular mass 63 kDa, which displayed 58% identity to the Arabidopsis thaliana peptide transporter AtPTR2‐B. Expression of HvPTR1 in Xenopus laevis oocytes conferred a 48‐fold increase in alanyl‐[14C]phenylalanine uptake relative to water injected oocytes, confirming the function of HvPTR1 as a peptide transporter. HvPTR1 expression was detectable only in the scutellum of the germinating barley grain, with no transcript found in roots, shoots or the embryo axis. Transcript levels increased rapidly from 6 to 24 h imbibition, correlating with the development of peptide transport activity in the barley scutellum. Peptide transport provides a significant source of organic nitrogen to the barley embryo for use in germination and growth processes associated with the early stages of seedling development. The temporal and spatial pattern of HvPTR1 expression is consistent with a central role for HvPTR1 in the transport of peptides in the germinating barley grain.