bluuebunny/crossref_metadata_2025 huggingface dataset:
Neuroanatomic substrates of semantic memory impairment in
Alzheimer's disease: Patterns of functional MRI activation
Authors: SAYKIN ANDREW J. , FLASHMAN LAURA A. , FRUTIGER SALLY A. , JOHNSON STERLING C. , MAMOURIAN ALEXANDER C. , MORITZ CHAD H. , O'JILE JUDITH R. , RIORDAN HENRY J. , SANTULLI ROBERT B. , SMITH CYNTHIA A. , WEAVER JOHN B.
Published: July 2002

Impairment in semantic processing occurs early
in Alzheimer's disease (AD) and differential impact
on subtypes of semantic relations have been reported, yet
there is little data on the neuroanatomic basis of these
deficits. Patients with mild AD and healthy controls underwent
3 functional MRI auditory stimulation tasks requiring semantic
or phonological decisions (match–mismatch) about
word pairs (category–exemplar, category–function,
pseudoword). Patients showed a significant performance
deficit only on the exemplar task. On voxel-based fMRI
activation analyses, controls showed a clear activation
focus in the left superior temporal gyrus for the phonological
task; patients showed additional foci in the left dorsolateral
prefrontal and bilateral cingulate areas. On the semantic
tasks, predominant activation foci were seen in the inferior
and middle frontal gyrus (left greater than right) in both
groups but patients showed additional activation suggesting
compensatory recruitment of locally expanded foci and remote
regions, for example, right frontal activation during the
exemplar task. Covariance analyses indicated that exemplar
task performance was strongly related to signal increase
in bilateral medial prefrontal cortex. The authors conclude
that fMRI can reveal similarities and differences in functional
neuroanatomical processing of semantic and phonological
information in mild AD compared to healthy elderly, and
can help to bridge cognitive and neural investigations
of the integrity of semantic networks in AD. (JINS,
1999, 5, 377–392.)
The linearised Hamiltonian as comprehensive NDP
Authors: WEITZMAN MARTIN L.
Published: July 2002

For guidance in determining which items should be included in comprehensive NDP (net domestic product) and how they should be included, reference is often made to the linearised Hamiltonian from an optimal growth problem. The paper gives a rigorous interpretation of this procedure in terms of a money-metric utility function linked to familiar elements of standard welfare theory. A key insight is that the Hamiltonian itself is a quasilinear utility function, so imposing the money-metric normalisation is simply equivalent to using Marshallian consumer surplus as the appropriate measure of welfare when there are no income effects. The twin concepts of the ‘sustainability-equivalence principle’ and the ‘dynamic welfare-comparison principle’ are explained, and it is indicated why these two principles are important for the theory of national income accounting.
Neuropsychological Advances
in Child and Adolescent Mental
Health: The Decade of the
Brain
Authors: Cody Heather , Hynd George W.
Published: July 2002

As the ‘decade of the brain’ comes to a close, it is clear that the field of
neuropsychology has made many vital contributions to evaluation,
treatment, and research issues in child and adolescent health care. In the
study of brain-behaviour relationships, the neuropsychologist plays a
unique role. The practice of child neuropsychology is differentiated from
adult work because developmental and environmental influences have a
significant impact on practice. The various goals of the child neuropsychologist
may include psychoeducational and neuropsychological
assessment, the exploration of brain-behaviour relationships, consultation
with a variety of professionals ranging from teachers to neurologists, and
rehabilitation training. Advances in medical treatment have contributed
to an expanding population of children and adolescents with neurological
and/or neuropsychiatric concerns. New research in this field has also
provided evidence of disordered or dysfunctional neurological systems
in a number of childhood disorders and psychiatric conditions. This paper
reviews some contributions that neuropsychology has made to the health
care of children and adolescents in the past decade.
Remarks on Salkie and Reed's (1997) ‘pragmatic hypothesis’ of tense in reported speech
Authors: Declerck Renaat
Published: July 2002

Salkie & Reed (1997) offer a ‘pragmatic hypothesis’ of tense in reported speech which runs counter to Jespersen's & Comrie's quotative or ‘sequence of tenses’ analysis as well as to the more semantically based analysis proposed by Declerck (1990b, 1991a). In doing so they also cast doubt on the model of the English tense system which was proposed by Declerck (1991a) and has since been further refined and elaborated in a number of articles and in Declerck (1997).

The present article goes into the many arguments that S&R advance, refutes them, and adduces additional evidence for D's theory and against S&R's ‘pragmatic hypothesis’.
Mitogen-activated protein kinase phosphatase is required for genotoxic stress relief inArabidopsis
Authors: Ulm Roman , Revenkova Ekaterina , di Sansebastiano Gian-Pietro , Bechtold Nicole , Paszkowski Jerzy
Published: July 2002

Genotoxic stress activates complex cellular responses allowing for the repair of DNA damage and proper cell recovery. Although plants are exposed constantly to increasing solar UV irradiation, the signaling cascades activated by genotoxic environments are largely unknown. We have identified anArabidopsismutant (mkp1) hypersensitive to genotoxic stress treatments (UV-C and methyl methanesulphonate) due to disruption of a gene that encodes anArabidopsishomolog ofmitogen-activated proteinkinasephosphatase (AtMKP1). Growth of themkp1mutant under standard conditions is indistinguishable from wild type, indicating a stress-specific function of AtMKP1. MAP kinase phosphatases (MKPs), the potent inactivators of MAP kinases, are considered important regulators of MAP kinase signaling. Although biochemical data from mammalian cell cultures suggests an involvement of MKPs in cellular stress responses, there is no in vivo genetic support for this view in any multicellular organism. The genetic and biochemical data presented here imply a central role for a MAP kinase cascade in genotoxic stress signaling in plants and indicate AtMKP1 to be a crucial regulator of the MAP kinase activity in vivo, determining the outcome of the cellular reaction and the level of genotoxic resistance.
Division site selection protein DivIVA of Bacillus subtilis has a second distinct function in chromosome segregation during sporulation
Authors: Thomaides Helena B. , Freeman Marcelle , Karoui Meriem El , Errington Jeffery
Published: July 2002

DivIVA is a coiled-coil, tropomyosin-like protein of Gram-positive bacteria. Previous work showed that this protein is targeted to division sites and retained at the cell poles after division. In vegetative cells, DivIVA sequesters the MinCD division inhibitor to the cell poles, thereby helping to direct cell division to the correct midcell site. We now show that DivIVA has a second, quite separate role in sporulating cells of Bacillus subtilis. It again acts at the cell pole but in this case interacts with the chromosome segregation machinery to help position the oriC region of the chromosome at the cell pole, in preparation for polar division. We isolated mutations in divIVA that separate the protein's role in sporulation from its vegetative function in cell division. DivIVA therefore appears to be a bifunctional protein with distinct roles in division-site selection and chromosome segregation.
Cooperative action of Tbx2 and Nkx2.5 inhibits ANF expression in the atrioventricular canal: implications for cardiac chamber formation
Authors: Habets Petra E.M.H. , Moorman Antoon F.M. , Clout Danielle E.W. , van Roon Marian A. , Lingbeek Merel , van Lohuizen Maarten , Campione Marina , Christoffels Vincent M.
Published: July 2002

During heart development, chamber myocardium forms locally from the embryonic myocardium of the tubular heart. The atrial natriuretic factor (ANF) gene is specifically expressed in this developing chamber myocardium and is one of the first hallmarks of chamber formation. We investigated the regulatory mechanism underlying this selective expression. Transgenic analysis shows that a small fragment of the ANF gene is responsible for the developmental pattern of endogenous ANF gene expression. Furthermore, this fragment is able to repress cardiac troponin I (cTnI) promoter activity selectively in the embryonic myocardium of the atrioventricular canal (AVC). In vivo inactivation of a T-box factor (TBE)- or NK2-homeobox factor binding element (NKE) within theANF fragment removed the repression in the AVC without affecting its chamber activity. The T-box family member Tbx2, encoding a transcriptional repressor, is expressed in the embryonic myocardium in a pattern mutually exclusive to ANF, thus suggesting a role in the suppression of ANF. Tbx2 formed a complex with Nkx2.5 on the ANF TBE–NKE, and was able to repress ANF promoter activity. Our data provide a potential mechanism for chamber-restricted gene activity in which the cooperative action of Tbx2 and Nkx2.5 inhibits expression in the AVC.
p21 is a transcriptional target of HOXA10 in differentiating myelomonocytic cells
Authors: Bromleigh V. Carrie , Freedman Leonard P.
Published: July 2002

The myeolomonocytic cell line U937 differentiates into macrophages in response to a variety of agents. Several genes including the cyclin-dependent kinase inhibitor p21waf1/cip1 and the homeobox gene transcription factor HOXA10 are induced at the onset of differentiation. Ectopic expression of either gene results in U937 differentiation. In this paper, we describe a mechanism by which p21 and HOXA10 may act in concert, where HOXA10 can bind directly to the p21 promoter and, together with its trimeric partners PBX1 and MEIS1, activate p21 transcription, resulting in cell cycle arrest and differentiation. These experiments for the first time identify p21 as a selective target for a HOX protein and link the differentiative properties of a transcription factor and a cell cycle inhibitor.
Ventral neural patterning by Nkx homeobox genes: Nkx6.1 controls somatic motor neuron and ventral interneuron fates
Authors: Sander Maike , Paydar Sussan , Ericson Johan , Briscoe James , Berber Elizabeth , German Michael , Jessell Thomas M. , Rubenstein John L.R.
Published: July 2002

There is growing evidence that sonic hedgehog (Shh) signaling regulates ventral neuronal fate in the vertebrate central nervous system through Nkx-class homeodomain proteins. We have examined the patterns of neurogenesis in mice carrying a targeted mutation in Nkx6.1. These mutants show a dorsal-to-ventral switch in the identity of progenitors and in the fate of postmitotic neurons. At many axial levels there is a complete block in the generation of V2 interneurons and motor neurons and a compensatory ventral expansion in the domain of generation of V1 neurons, demonstrating the essential functions of Nkx6.1 in regional patterning and neuronal fate determination.
Spt5 and Spt6 are associated with active transcription and have characteristics of general elongation factors in D. melanogaster
Authors: Kaplan Craig D. , Morris James R. , Wu C.-ting , Winston Fred
Published: July 2002

The Spt4, Spt5, and Spt6 proteins are conserved throughout eukaryotes and are believed to play critical and related roles in transcription. They have a positive role in transcription elongation inSaccharomyces cerevisiae and in the activation of transcription by the HIV Tat protein in human cells. In contrast, a complex of Spt4 and Spt5 is required in vitro for the inhibition of RNA polymerase II (Pol II) elongation by the drug DRB, suggesting also a negative role in vivo. To learn more about the function of the Spt4/Spt5 complex and Spt6 in vivo, we have identified Drosophila homologs of Spt5 and Spt6 and characterized their localization onDrosophila polytene chromosomes. We find that Spt5 and Spt6 localize extensively with the phosphorylated, actively elongating form of Pol II, to transcriptionally active sites during salivary gland development and upon heat shock. Furthermore, Spt5 and Spt6 do not colocalize widely with the unphosphorylated, nonelongating form of Pol II. These results strongly suggest that Spt5 and Spt6 play closely related roles associated with active transcription in vivo.
ArabidopsisNAC1 transduces auxin signal downstream of TIR1 to promote lateral root development
Authors: Xie Qi , Frugis Giovanna , Colgan Diana , Chua Nam-Hai
Published: July 2002

Auxin plays a key role in lateral root formation, but the signaling pathway for this process is poorly understood. We show here thatNAC1, a new member of theNACfamily, is induced by auxin and mediates auxin signaling to promote lateral root development. NAC1 is a transcription activator consisting of an N-terminal conserved NAC-domain that binds to DNA and a C-terminal activation domain. This factor activates the expression of two downstream auxin-responsive genes,DBPandAIR3. Transgenic plants expressing sense or antisenseNAC1cDNA show an increase or reduction of lateral roots, respectively. Finally, TIR1-induced lateral root development is blocked by expression of antisenseNAC1cDNA, and NAC1 overexpression can restore lateral root formation in the auxin-response mutanttir1, indicating that NAC1 acts downstream of TIR1.
Conversion of a gene-specific repressor to a regional silencer
Authors: Rine Laura N. Rusché and Jasper
Published: July 2002

In Saccharomyces cerevisiae, gene silencing at theHMR and HML loci is normally dependent on Sir2p, Sir3p, and Sir4p, which are structural components of silenced chromatin. Sir2p is a NAD+-dependent histone deacetylase required for silencing. Silencing can be restored in cells lacking Sir proteins by a dominant mutation in SUM1, which normally acts as a mitotic repressor of meiotic genes. This study found that mutant Sum1-1p, but not wild-type Sum1p, associated directly with HM loci. The origin recognition complex (ORC) was required for Sum1-1p-mediated silencing, and mutations in ORC genes reduced association of Sum1-1p with theHM loci. Sum1-1p-mediated silencing also depended onHST1, a paralog of SIR2. Both Sum1-1p and wild-type Sum1p interacted with Hst1p in coimmunoprecipitation experiments. Therefore, the SUM1-1 mutation did not change the affinity of Sum1p for Hst1p, but rather relocalized Sum1p to the HM loci. Sum1-1–Hst1p action led to hypoacetylation of the nucleosomes atHM loci. Thus, Sum1-1p and Hst1p could substitute for Sir proteins to achieve silencing through formation of a compositionally distinct type of heterochromatin.
Phosphorylation of three regulatory serines of Tob by Erk1 and Erk2 is required for Ras-mediated cell proliferation and transformation
Authors: Suzuki Toru , K-Tsuzuku Junko , Ajima Rieko , Nakamura Takahisa , Yoshida Yutaka , Yamamoto Tadashi
Published: July 2002

tob is a member of an emerging family of genes with antiproliferative function. Tob is rapidly phosphorylated at Ser 152, Ser 154, and Ser 164 by Erk1 and Erk2 upon growth-factor stimulation. Oncogenic Ras-induced transformation and growth-factor-induced cell proliferation are efficiently suppressed by mutant Tob that carries alanines but not glutamates, mimicking phosphoserines, at these sites. Wild-type Tob inhibits cell growth when the three serine residues are not phosphorylated but is less inhibitory when the serines are phosphorylated. Because growth of Rb-deficient cells was not affected by Tob, Tob appears to function upstream of Rb. Intriguingly, cyclin D1 expression is elevated in serum-starved tob−/−cells. Reintroduction of wild-type Tob and mutant Tob with serine-to-alanine but not to glutamate mutations on the Erk phosphorylation sites in these cells restores the suppression of cyclin D1 expression. Finally, the S-phase population was significantly increased in serum-starved tob−/− cells as compared with that in wild-type cells. Thus, Tob inhibits cell growth by suppressing cyclin D1 expression, which is canceled by Erk1- and Erk2-mediated Tob phosphorylation. We propose that Tob is critically involved in the control of early G1 progression.
Control of neuronal subtype identity by the C. elegans ARID protein CFI-1
Authors: Shaham Shai , Bargmann Cornelia I.
Published: July 2002

The Caenorhabditis elegans hermaphrodite nervous system is composed of 302 neurons that fall into at least 118 diverse classes. Here we describe cfi-1, a gene that contributes to the development of neuronal diversity. cfi-1 promotes appropriate differentiation of the URA sensory neurons and inhibits URA from expressing the male-specific CEM neuronal fate. The UNC-86 POU homeodomain protein is present in CEM and URA neurons, and can promote expression of CEM-specific genes in both CEM and URA, but CFI-1 inhibits expression of these genes in the URA cells. cfi-1 also promotes appropriate differentiation and glutamate receptor expression in the AVD and PVC interneurons. cfi-1 encodes a conserved neuron- and muscle-restricted DNA-binding protein containing an A/T rich interaction domain (ARID). ARID proteins regulate early patterning and muscle fate in Drosophila, but they have not previously been implicated in the control of neuronal subtype identity.
Genome-wide Detection of Allelic Imbalance Using Human SNPs and High-density DNA Arrays
Authors: Mei Rui , Galipeau Patricia C. , Prass Cynthia , Berno Anthony , Ghandour Ghassan , Patil Nila , Wolff Roger K. , Chee Mark S. , Reid Brian J. , Lockhart David J.
Published: July 2002

Most human cancers are characterized by genomic instability, the accumulation of multiple genetic alterations and allelic imbalance throughout the genome. Loss of heterozygosity (LOH) is a common form of allelic imbalance and the detection of LOH has been used to identify genomic regions that harbor tumor suppressor genes and to characterize tumor stages and progression. Here we describe the use of high-density oligonucleotide arrays for genome-wide scans for LOH and allelic imbalance in human tumors. The arrays contain redundant sets of probes for 600 genetic loci that are distributed across all human chromosomes. The arrays were used to detect allelic imbalance in two types of human tumors, and a subset of the results was confirmed using conventional gel-based methods. We also tested the ability to study heterogeneous cell populations and found that allelic imbalance can be detected in the presence of a substantial background of normal cells. The detection of LOH and other chromosomal changes using large numbers of single nucleotide polymorphism (SNP) markers should enable identification of patterns of allelic imbalance with potential prognostic and diagnostic utility.
First Pass Annotation of Promoters on Human Chromosome 22
Authors: Scherf Matthias , Klingenhoff Andreas , Frech Kornelie , Quandt Kerstin , Schneider Ralf , Grote Korbinian , Frisch Matthias , Gailus-Durner Valérie , Seidel Alexander , Brack-Werner Ruth , Werner Thomas
Published: July 2002

The publication of the first almost complete sequence of a human chromosome (chromosome 22) is a major milestone in human genomics. Together with the sequence, an excellent annotation of genes was published which certainly will serve as an information resource for numerous future projects. We noted that the annotation did not cover regulatory regions; in particular, no promoter annotation has been provided. Here we present an analysis of the complete published chromosome 22 sequence for promoters. A recent breakthrough in specific in silico prediction of promoter regions enabled us to attempt large-scale prediction of promoter regions on chromosome 22. Scanning of sequence databases revealed only 20 experimentally verified promoters, of which 10 were correctly predicted by our approach. Nearly 40% of our 465 predicted promoter regions are supported by the currently available gene annotation. Promoter finding also provides a biologically meaningful method for “chromosomal scaffolding”, by which long genomic sequences can be divided into segments starting with a gene. As one example, the combination of promoter region prediction with exon/intron structure predictions greatly enhances the specificity of de novo gene finding. The present study demonstrates that it is possible to identify promoters in silico on the chromosomal level with sufficient reliability for experimental planning and indicates that a wealth of information about regulatory regions can be extracted from current large-scale (megabase) sequencing projects. Results are available on-line at http://genomatix.gsf.de/chr22/.
Fluorescence Polarization in Homogeneous Nucleic Acid Analysis II: 5′-Nuclease Assay
Authors: Latif Sherif , Bauer-Sardina Irma , Ranade Kostubh , Livak Kenneth J. , Kwok Pui-Yan
Published: July 2002

When the temperature and viscosity of the solvent is held constant, the degree of fluorescence polarization (FP) detected when a fluorescent dye is excited by plane polarized light depends mostly on the molecular weight of the dye molecule. By monitoring the FP of a fluorescent dye molecule, one can detect significant changes in the molecular weight of a fluorescent molecule without separation or purification. The 5′-nuclease (TaqMan) assay is a robust single nucleotide polymorphism genotyping method where an allele-specific probe that binds to a perfectly complementary target is cleaved by the 5′-nuclease activity of Taq DNA polymerase. Because the TaqMan probe is labeled with a fluorescent dye, it has high FP value when intact but a low FP value after cleavage. In this study, we compared the results of the 5′-nuclease assay based on standard fluorescence intensity readings and FP readings when genotyping 90 individuals with 20 single nucleotide polymorphisms. Our results show that FP is just as robust and reliable as the standard fluorescence detection method. Use of FP detection makes it possible to reduce the cost of TaqMan probes by abrogating the need for a fluorescence quencher.
SGP-1: Prediction and Validation of Homologous Genes Based on Sequence Alignments
Authors: Wiehe Thomas , Gebauer-Jung Steffi , Mitchell-Olds Thomas , Guigó Roderic
Published: July 2002

Conventional methods of gene prediction rely on the recognition of DNA-sequence signals, the coding potential or the comparison of a genomic sequence with a cDNA, EST, or protein database. Reasons for limited accuracy in many circumstances are species-specific training and the incompleteness of reference databases. Lately, comparative genome analysis has attracted increasing attention. Several analysis tools that are based on human/mouse comparisons are already available. Here, we present a program for the prediction of protein-coding genes, termed SGP-1 (Syntenic Gene Prediction), which is based on the similarity of homologous genomic sequences. In contrast to most existing tools, the accuracy of SGP-1 depends little on species-specific properties such as codon usage or the nucleotide distribution. SGP-1 may therefore be applied to nonstandard model organisms in vertebrates as well as in plants, without the need for extensive parameter training. In addition to predicting genes in large-scale genomic sequences, the program may be useful to validate gene structure annotations from databases. To this end, SGP-1 output also contains comparisons between predicted and annotated gene structures in HTML format. The program can be accessed via a Web server at http://soft.ice.mpg.de/sgp-1. The source code, written in ANSI C, is available on request from the authors.
Context Learning and the Effect of Context on Memory Retrieval in Lymnaea
Authors: Haney James , Lukowiak Ken
Published: July 2002

Aerial respiratory behavior in Lymnaea was operantly conditioned so that the animals perform aerial respiration significantly less often. Using the standard training procedure (pond water made hypoxic by bubbling N2 through it) both food-deprived and fed animals learned and exhibited long-term memory (LTM). However, food-deprived animals exhibited neither learning nor memory when trained under a condition in which the hypoxic pond water also contained a food odorant (carrot, the food-odorant procedure). Fed animals, however, learned and exhibited LTM with the food-odorant procedure. Thus, the presence of the food odorant per se did not prevent learning or the establishment of LTM. Further experimentation, however, revealed that the ability of the snails to have recall (i.e., memory) for the learned behavior was dependent on the context in which memory was tested. That is, if animals were trained with the food-odorant procedure they could only exhibit recall if tested in the food-odorant context and vice versa with the standard training procedure. Thus, although fed animals could learn and show LTM with either training and testing procedure, LTM could only be seen when they were tested in the context in which they were trained.
Role of a Striatal Slowly Inactivating Potassium Current in Short-Term Facilitation of Corticostriatal Inputs: A Computer Simulation Study
Authors: Mahon Séverine , Deniau Jean-Michel , Charpier Stéphane , Delord Bruno
Published: July 2002

Striatal output neurons (SONs) integrate glutamatergic synaptic inputs originating from the cerebral cortex. In vivo electrophysiological data have shown that a prior depolarization of SONs induced a short-term (≤1 sec) increase in their membrane excitability, which facilitated the ability of corticostriatal synaptic potentials to induce firing. Here we propose, using a computational model of SONs, that the use-dependent, short-term increase in the responsiveness of SONs mainly results from the slow kinetics of a voltage-dependent, slowly inactivating potassium A-current. This mechanism confers on SONs a form of intrinsic short-term memory that optimizes the synaptic input–output relationship as a function of their past activation.
Environmental Enrichment Modifies the PKA-Dependence of Hippocampal LTP and Improves Hippocampus-Dependent Memory
Authors: Duffy Steven N. , Craddock Kenneth J. , Abel Ted , Nguyen Peter V.
Published: July 2002

cAMP-dependent protein kinase (PKA) is critical for the expression of some forms of long-term potentiation (LTP) in area CA1 of the mouse hippocampus and for hippocampus-dependent memory. Exposure to spatially enriched environments can modify LTP and improve behavioral memory in rodents, but the molecular bases for the enhanced memory performance seen in enriched animals are undefined. We tested the hypothesis that exposure to a spatially enriched environment may alter the PKA dependence of hippocampal LTP. Hippocampal slices from enriched mice showed enhanced LTP following a single burst of 100-Hz stimulation in the Schaffer collateral pathway of area CA1. In slices from nonenriched mice, this single-burst form of LTP was less robust and was unaffected by Rp-cAMPS, an inhibitor of PKA. In contrast, the enhanced LTP in enriched mice was attenuated by Rp-cAMPS. Enriched slices expressed greater forskolin-induced, cAMP-dependent synaptic facilitation than did slices from nonenriched mice. Enriched mice showed improved memory for contextual fear conditioning, whereas memory for cued fear conditioning was unaffected following enrichment. Our data indicate that exposure of mice to spatial enrichment alters the PKA dependence of LTP and enhances one type of hippocampus-dependent memory. Environmental enrichment can transform the pharmacological profile of hippocampal LTP, possibly by altering the threshold for activity-dependent recruitment of the cAMP-PKA signaling pathway following electrical and chemical stimulation. We suggest that experience-dependent plasticity of the PKA dependence of hippocampal LTP may be important for regulating the efficacy of hippocampus-based memory.
Leaf Urea Metabolism in Potato. Urease Activity Profile and Patterns of Recovery and Distribution of 15N after Foliar Urea Application in Wild-Type and Urease-Antisense Transgenics
Authors: Witte Claus-Peter , Tiller Sarah A. , Taylor Mark A. , Davies Howard V.
Published: July 2002

The influence of urease activity on N distribution and losses after foliar urea application was investigated using wild-type and transgenic potato (Solanum tuberosum cv Désirée) plants in which urease activity was down-regulated. A good correlation between urease activity and 15N urea metabolism (NH3accumulation) was found. The general accumulation of ammonium in leaves treated with urea indicated that urease activity is not rate limiting, at least initially, for the assimilation of urea N by the plant. It is surprising that there was no effect of urease activity on either N losses or 15N distribution in the plants after foliar urea application. Experiments with wild-type plants in the field using foliar-applied 15N urea demonstrated an initial rapid export of N from urea-treated leaves to the tubers within 48 h, followed by a more gradual redistribution during the subsequent days. Only 10% to 18% of urea N applied was lost (presumably because of NH3 volatilization) in contrast to far greater losses reported in several other studies. The pattern of urease activity in the canopy was investigated during plant development. The activity per unit protein increased up to 10-fold with leaf and plant age, suggesting a correlation with increased N recycling in senescing tissues. Whereas several reports have claimed that plant urease is inducible by urea, no evidence for urease induction could be found in potato.
Snakin-2, an Antimicrobial Peptide from Potato Whose Gene Is Locally Induced by Wounding and Responds to Pathogen Infection
Authors: Berrocal-Lobo Marta , Segura Ana , Moreno Manuel , López Gemma , Garcı́a-Olmedo Francisco , Molina Antonio
Published: July 2002

The peptide snakin-2 (StSN2) has been isolated from potato (Solanum tuberosum cv Jaerla) tubers and found to be active (EC50 = 1–20 μm) against fungal and bacterial plant pathogens. It causes a rapid aggregation of both Gram-positive and Gram-negative bacteria. The correspondingStSN2 cDNA encodes a signal sequence followed by a 15-residue acidic sequence that precedes the mature StSN2 peptide, which is basic (isoelectric point = 9.16) and 66 amino acid residues long (molecular weight of 7,025). The StSN2gene is developmentally expressed in tubers, stems, flowers, shoot apex, and leaves, but not in roots, or stolons, and is locally up-regulated by wounding and by abscisic acid treatment. Expression of this gene is also up-regulated after infection of potato tubers with the compatible fungus Botritys cinerea and down-regulated by the virulent bacteria Ralstonia solanacearum and Erwinia chrysanthemi. These observations are congruent with the hypothesis that the StSN2 is a component of both constitutive and inducible defense barriers.
Castor Bean Isocitrate Lyase Lacking the Putative Peroxisomal Targeting Signal 1 ARM Is Imported into Plant Peroxisomes Both in Vitro and in Vivo
Authors: Gao X. , Marrison J. L. , Pool M. R. , Leech R. M. , Baker A.
Published: July 2002

To understand and manipulate plant peroxisomal protein targeting, it is important to establish the universality or otherwise of targeting signals. Contradictory results have been published concerning the nature and location of the glyoxysomal/peroxisomal targeting signal of isocitrate lyase (ICL). L.J. Olsen, W.F. Ettinger, B. Damsz, K. Matsudaira, A. Webb, and J.J. Harada ([1993] Plant Cell 5: 941–952) concluded that the last 5 amino acids (AKSRM) of Brassica napus ICL were sufficient and the last 37 amino acids were necessary for targeting to Arabidopsis leaf peroxisomes. In contrast, R. Behari and A. Baker ([1993] J Biol Chem 268: 7315–7322) could find no requirement for the almost identical carboxy-terminal sequence AKARM for import of Ricinus communis ICL into isolated sunflower cotyledon glyoxysomes. To resolve this discrepancy, the import characteristics of a mutant R. communis ICL lacking the last 19 amino acids of the carboxy terminus was studied. ICL[delta]19 was able to be imported by isolated sunflower glyoxysomes and by tobacco leaf peroxisomes when expressed transgenically. These results demonstrate that the in vitro import system faithfully reflects targeting in vivo, and that the source of the organelles (Arabidopsis versus sunflower, leaf peroxisomes versus seed glyoxysomes) is not responsible for observed differences between B. napus and R. communis ICL. The R. communis enzyme would therefore appear to possess an additional glyoxysome/peroxisome targeting signal that is lacking in the B. napus protein.
Origin of the Thiazole Ring of Camalexin, a Phytoalexin from Arabidopsis thaliana
Authors: Zook M. , Hammerschmidt R.
Published: July 2002

The principal phytoalexin that accumulates in Arabidopsis thaliana after infection by fungi or bacteria is 3-thiazol-2[prime]-yl-indole (camalexin). Detached noninoculated leaves of Arabidopsis and leaves inoculated with the fungus Cochliobolus carbonum were fed [35S]cysteine (Cys) and [35S]methionine. Inoculated leaves incorporated more than a 200-fold greater amount of radioactivity from [35S]Cys into camalexin, as compared with noninoculated leaves. The amount of radioactivity from [35S]Cys that was incorporated into camalexin from inoculated Arabidopsis leaves was 10-fold greater than the amount of radioactivity that was incorporated into camalexin from [35S]methionine. Additional labeling experiments were performed to determine whether other atoms of Cys are incorporated into camalexin. [14C]Cys and [35S]Cys were incorporated into camalexin with approximately the same efficiency. Cys labeled either with deuterium (D3-Cys[2,3,3]) or 13C and 15N ([U-13C,15N]Cys) was also fed to inoculated leaves of Arabidopsis; camalexin was analyzed by mass spectroscopic analysis. The average ratio of molecular ion intensities of 203/200 for [U-13C,15N]Cys-labeled camalexin was 4.22, as compared with 0.607 for the average 203/200 ratio for unlabeled camalexin. The mass fragment-ion intensity ratios of 60/58 (thiazole ring ion fragment) and 143/142 were also higher for [U-13C,15N]Cys-labeled camalexin, as compared with unlabeled camalexin. The 59/58 and 201/200 ratios were higher for D3-Cys-labeled camalexin as compared with unlabeled camalexin. These data are consistent with the predicted formation of the thiazole ring of camalexin from Cys.
hcf5, a Nuclear Photosynthetic Electron Transport Mutant of Arabidopsis thaliana with a Pleiotropic Effect on Chloroplast Gene Expression
Authors: Dinkins R. D. , Bandaranayake H. , Baeza L. , Griffiths AJF. , Green B. R.
Published: July 2002

A photosynthetic mutant of Arabidopsis thaliana, hcf5, was isolated by screening M2 seedlings for high chlorophyll fluorescence. Thylakoid morphology was strikingly abnormal, with large grana stacks and almost no stroma lamellae. Fluorescence induction kinetics, activity assays, and immunoblotting showed that photosystem II was absent. Polypeptides of the photosystem I complex, the Cyt b6/f complex, coupling factor, and the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase were also severely depleted. However, the nuclear-encoded chlorophyll a/b light-harvesting complex polypeptides were unaffected. The rbcL transcript was present at very low levels, the pattern of transcripts from the polycistronic psbB-psbH-petB-petD operon was abnormal, and the mature psbH message was almost completely lacking. This suggests that the hcf5 locus may encode a product required for the correct expression of several chloroplast genes.
A Gene Encoding a Chloroplast-Targeted Lipoxygenase in Tomato Leaves Is Transiently Induced by Wounding, Systemin, and Methyl Jasmonate
Authors: Heitz T. , Bergey D. R. , Ryan C. A.
Published: July 2002

We investigated the relationship between the expression of lipoxygenase (LOX) genes and the systemin-dependent wound response in tomato (Lycopersicon esculentum) leaves. A polymerase chain reaction-based approach was used to isolate two tomato Lox cDNAs, called TomLoxC and TomLoxD. Both TomLOXC and TomLOXD amino acid sequences possess an N-terminal extension of about 60 residues that were shown by in vitro uptake to function as transit peptides, targeting these proteins into the chloroplast. Within 30 to 50 min following wounding or systemin or methyl jasmonate treatments, the TomLoxD mRNA level increased and reached a maximum between 1 and 2 h. TomLoxC mRNA was not detectable in leaves and was not found following wounding, but it was found in ripening fruits, indicating that the two tomato Lox genes are regulated in different tissues by different processes. The results suggest that the TomLoxD gene is up-regulated in leaves in response to wounding and encodes a chloroplast LOX that may play a role as a component of the octadecanoid defense-signaling pathway.
A G-Box-Binding Protein from Soybean Binds to the E1 Auxin-Response Element in the Soybean GH3 Promoter and Contains a Proline-Rich Repression Domain
Authors: Liu Z. B. , Hagen G. , Guilfoyle T. J.
Published: July 2002

The E1 promoter fragment (-249 to -203) is one of three auxin-response elements (AuxREs) in the soybean (Glycine max L.) GH3 promoter (Z.-B. Liu, T. Ulmasov, X. Shi, G. Hagen, T.J. Guilfoyle [1994] Plant Cell 6: 645–657). Results presented here further characterize and delimit the AuxRE within the E1 fragment. The E1 fragment functioned as an AuxRE in transgenic tobacco (Nicotiana tabacum L.) plants, as well as in transfected protoplasts. The AuxRE within E1 contains a G-box, and this G-box was used to clone a G-box-binding factor (GBF) from soybean (SGBF-2). This 45-kD GBF contains an N-terminal proline-rich domain and a C-terminal basic/leucine zipper DNA-binding domain. Gel-mobility shift assays were used to characterize the binding specificity of SGBF-2. Antiserum raised against recombinant SGBF-2 was used to further characterize SGBF-2 and antigenically related GBFs in soybean nuclear extracts. Co-transfection assays with effector and reporter plasmids in carrot (Daucus carota L.) protoplasts indicated that the N-terminal proline-rich domain of SGBF-2 functioned as a repression domain in both basal and auxin-inducible transcription.
Jasmonic Acid-Dependent and -Independent Signaling Pathways Control Wound-Induced Gene Activation in Arabidopsis thaliana
Authors: Titarenko E. , Rojo E. , Leon J. , Sanchez-Serrano J. J.
Published: July 2002

Plant response to mechanical injury includes gene activation both at the wound site and systemically in nondamaged tissues. The model developed for the wound-induced activation of the proteinase inhibitor II (Pin2) gene in potato (Solanum tuberosum) and tomato (Lycopersicon esculentum) establishes the involvement of the plant hormones abscisic acid and jasmonic acid (JA) as key components of the wound signal transduction pathway. To assess in Arabidopsis thaliana the role of these plant hormones in regulating wound-induced gene expression, we isolated wound- and JA-inducible genes by the differential mRNA display technique. Their patterns of expression upon mechanical wounding and hormonal treatments revealed differences in the spatial distribution of the transcripts and in the responsiveness of the analyzed genes to abscisic acid and JA. A correlation can be established between sensitivity to JA and the accumulation of the transcripts in systemic tissues upon wounding. A comparative study of the wound response in wild-type and JA-insensitive coi1 mutant plants indicated that in A. thaliana wound signals are transmitted via at least two different pathways. One of them does not involve JA as a mediator and is preferentially responsible for gene activation in the vicinity of the wound site, whereas the other requires JA perception and activates gene expression throughout the aerial part of the plant.
Rice Hemoglobins (Gene Cloning, Analysis, and O2-Binding Kinetics of a Recombinant Protein Synthesized in Escherichia coli)
Authors: Arredondo-Peter R. , Hargrove M. S. , Sarath G. , Moran J. F. , Lohrman J. , Olson J. S. , Klucas R. V.
Published: July 2002

Although nonsymbiotic hemoglobins (Hbs) are found in different tissues of dicots and monocots, very little is known about hb genes in monocots and the function of Hbs in nonsymbiotic tissues. We report the cloning and analysis of two rice (Oryza sativa L.) hb genes, hb1 and hb2, that code for plant Hbs. Rice hb1 and hb2 genes contain four exons and three introns, as with all of the known plant hb genes. At least three copies of the hb gene were detected in rice DNA, and analysis of gene expression shows that hb1 and hb2 are expressed in leaves but only hb1 is expressed in roots. A cDNA for rice Hb1 was expressed in Escherichia coli, and the recombinant Hb (rHb1) shows an unusually high affinity for O2 because of a very low dissociation constant. The absorbance spectra of the ferric and deoxyferrous rHb1 indicate that, in contrast to symbiotic Hbs, a distal ligand is coordinated to the ligand-binding site. Mutation of the distal His demonstrates that this residue coordinates the heme Fe of ferric and deoxyferrous rHb1 and stabilizes O2 in oxy-rHb1. The biochemical properties of rice rHb1 suggest that this protein probably does not function to facilitate the diffusion of O2.
Signal Transduction in the Carnivorous Plant Sarracenia purpurea (Regulation of Secretory Hydrolase Expression during Development and in Response to Resources)
Authors: Gallie D. R. , Chang S. C.
Published: July 2002

Carnivory in plants has developed as an evolutionary adaptation to nutrient-poor environments. A significant investment of the resources of a carnivorous plant is committed to producing the traps, attractants, and digestive enzymes needed for the carnivory. The cost:benefit ratio of carnivory can be improved by either maximizing the prey capture rate or by reducing the metabolic commitment toward carnivory. Using the pitcher plant Sarracenia purpurea, we have investigated whether the expression of the hydrolytic enzymes needed for digestion is regulated in response to the presence of prey. Expression of protease, RNase, nuclease, and phosphatase activities could be induced in the fluid of nonactive traps by the addition of nucleic acids, protein, or reduced nitrogen, suggesting that hydrolase expression is induced upon perception of the appropriate chemical signal. Hydrolase expression was also developmentally controlled since expression commenced upon opening of a trap, increased for several days, and in the absence of prey largely ceased within 2 weeks. Nevertheless, the traps remained competent to induce expression in response to the appropriate signals. These data suggest that in young traps hydrolase expression is developmentally regulated, which is later replaced by a signal transduction mechanism, and they demonstrate the ability of a carnivorous species to respond to the availability of resources.
Regulation of Actin Tension in Plant Cells by Kinases and Phosphatases1
Authors: Grabski Sharon , Arnoys Eric , Busch Benjamin , Schindler Melvin
Published: July 2002

Changes in the organization and mechanical properties of the actin network within plant and animal cells are primary responses to cell signaling. These changes are suggested to be mediated through the regulation of G/F-actin equilibria, alterations in the amount and/or type of actin-binding proteins, the binding of myosin to F-actin, and the formation of myosin filaments associated with F-actin. In the present communication, the cell optical displacement assay was used to investigate the role of phosphatases and kinases in modifying the tension and organization within the actin network of soybean cells. The results from these biophysical measurements suggest that: (a) calcium-regulated kinases and phosphatases are involved in the regulation of tension, (b) calcium transients induce changes in the tension and organization of the actin network through the stimulation of proteins containing calmodulin-like domains or calcium/calmodulin-dependent regulatory proteins, (c) myosin and/or actin cross-linking proteins may be the principal regulator(s) of tension within the actin network, and (d) these actin cross-linking proteins may be the principal targets of calcium-regulated kinases and phosphatases.
Chickpea Defensive Proteinase Inhibitors Can Be Inactivated by Podborer Gut Proteinases1
Authors: Giri Ashok P. , Harsulkar Abhay M. , Deshpande Vasanti V. , Sainani Mohini N. , Gupta Vidya S. , Ranjekar Prabhakar K.
Published: July 2002

Developing chickpea (Cicer arietinum L.) seeds 12 to 60 d after flowering (DAF) were analyzed for proteinase inhibitor (Pi) activity. In addition, the electrophoretic profiles of trypsin inhibitor (Ti) accumulation were determined using a gel-radiographic film-contact print method. There was a progressive increase in Pi activity throughout seed development, whereas the synthesis of other proteins was low from 12 to 36 DAF and increased from 36 to 60 DAF. Seven different Ti bands were present in seeds at 36 DAF, the time of maximum podborer (Helicoverpa armigera) attack. Chickpea Pis showed differential inhibitory activity against trypsin, chymotrypsin, H. armigera gut proteinases, and bacterial proteinase(s). In vitro proteolysis of chickpea Ti-1 with various proteinases generated Ti-5 as the major fragment, whereas Ti-6 and -7 were not produced. The amount of Pi activity increased severalfold when seeds were injured by H. armigera feeding. In vitro and in vivo proteolysis of the early- and late-stage-specific Tis indicated that the chickpea Pis were prone to proteolytic digestion by H. armigera gut proteinases. These data suggest that survival of H. armigera on chickpea may result from the production of inhibitor-insensitive proteinases and by secretion of proteinases that digest chickpea Pis.
Guard Cells Possess a Calcium-Dependent Protein Kinase That Phosphorylates the KAT1 Potassium Channel1
Authors: Li Jiaxu , Julie Lee Yuh-Ru , Assmann Sarah M.
Published: July 2002

Increasing evidence suggests that changes in cytosolic Ca2+ levels and phosphorylation play important roles in the regulation of stomatal aperture and as ion transporters of guard cells. However, protein kinases responsible for Ca2+ signaling in guard cells remain to be identified. Using biochemical approaches, we have identified a Ca2+-dependent protein kinase with a calmodulin-like domain (CDPK) in guard cell protoplasts of Vicia faba. Both autophosphorylation and catalytic activity of CDPK are Ca2+dependent. CDPK exhibits a Ca2+-induced electrophoretic mobility shift and its Ca2+-dependent catalytic activity can be inhibited by the calmodulin antagonists trifluoperazine andN-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide. Antibodies to soybean CDPKα cross-react with CDPK. Micromolar Ca2+ concentrations stimulate phosphorylation of several proteins from guard cells; cyclosporin A, a specific inhibitor of the Ca2+-dependent protein phosphatase calcineurin enhances the Ca2+-dependent phosphorylation of several soluble proteins. CDPK from guard cells phosphorylates the K+ channel KAT1 protein in a Ca2+-dependent manner. These results suggest that CDPK may be an important component of Ca2+ signaling in guard cells.