bluuebunny/crossref_metadata_2025_split huggingface dataset:
Glucosinolate and Amino Acid Biosynthesis in Arabidopsis
Authors: Field Ben , Cardon Guillermo , Traka Maria , Botterman Johan , Vancanneyt Guy , Mithen Richard 
Published: June 2004

AbstractEnzymes that catalyze the condensation of acetyl coenzyme A and 2-oxo acids are likely to be important in two distinct metabolic pathways in Arabidopsis. These are the synthesis of isopropylmalate, an intermediate of Leu biosynthesis in primary metabolism, and the synthesis of methylthioalkylmalates, intermediates of Met elongation in the synthesis of aliphatic glucosinolates (GSLs), in secondary metabolism. Four Arabidopsis genes in the ecotype Columbia potentially encode proteins that could catalyze these reactions. MAM1 and MAML are adjacent genes on chromosome 5 at the Gsl-elong locus, while MAML-3 and MAML-4 are at opposite ends of chr 1. The isopropylmalate synthase activity of each member of the MAM-like gene family was investigated by heterologous expression in an isopropylmalate synthase-null Escherichia coli mutant. Only the expression of MAML-3 restored the ability of the mutant to grow in the absence of Leu. A MAML knockout line (KO) lacked long-chain aliphatic GSLs, which were restored when the KO was transformed with a functional MAML gene. Variation in expression of MAML did not alter the total levels of Met-derived GSLs, but just the ratio of chain lengths. MAML overexpression in Columbia led to an increase in long-chain GSLs, and an increase in 3C GSLs. Moreover, plants overexpressing MAML contained at least two novel amino acids. One of these was positively identified via MS/MS as homo-Leu, while the other, with identical mass and fragmentation patterns, was likely to be homo-Ile. A MAML-4 KO did not exhibit any changes in GSL profile, but had perturbed soluble amino acid content.
Trehalose Mediated Growth Inhibition of Arabidopsis Seedlings Is Due to Trehalose-6-Phosphate Accumulation
Authors: Schluepmann Henriette , van Dijken Anja , Aghdasi Mahnaz , Wobbes Barry , Paul Matthew , Smeekens Sjef 
Published: June 2004

Abstract
Trehalose-6-phosphate (T6P) is required for carbon utilization during Arabidopsis development, and its absence is embryo lethal. Here we show that T6P accumulation inhibits seedling growth. Wild-type seedlings grown on 100 mm trehalose rapidly accumulate T6P and stop growing, but seedlings expressing Escherichia coli trehalose phosphate hydrolase develop normally on such medium. T6P accumulation likely results from much-reduced T6P dephosphorylation when trehalose levels are high. Metabolizable sugars added to trehalose medium rescue T6P inhibition of growth. In addition, Suc feeding leads to a progressive increase in T6P concentrations, suggesting that T6P control over carbon utilization is related to available carbon for growth. Expression analysis of genes from the Arabidopsis trehalose metabolism further supports this: Suc rapidly induces expression of trehalose phosphate synthase homolog AtTPS5 to high levels. In contrast, T6P accumulation after feeding trehalose in the absence of available carbon induces repression of genes encoding T6P synthases and expression of T6P phosphatases. To identify processes controlled by T6P, we clustered expression profile data from seedlings with altered T6P content. T6P levels correlate with expression of a specific set of genes, including the S6 ribosomal kinase ATPK19, independently of carbon status. Interestingly, Suc addition represses 15 of these genes, one of which is AtKIN11, encoding a Sucrose Non Fermenting 1 (SNF1)-related kinase known to play a role in Suc utilization.
A Family of Auxin-Conjugate Hydrolases That Contributes to Free Indole-3-Acetic Acid Levels during Arabidopsis Germination
Authors: Rampey Rebekah A. , LeClere Sherry , Kowalczyk Mariusz , Ljung Karin , Sandberg Göran , Bartel Bonnie 
Published: June 2004

Abstract
Auxins are hormones important for numerous processes throughout plant growth and development. Plants use several mechanisms to regulate levels of the auxin indole-3-acetic acid (IAA), including the formation and hydrolysis of amide-linked conjugates that act as storage or inactivation forms of the hormone. Certain members of an Arabidopsis amidohydrolase family hydrolyze these conjugates to free IAA in vitro. We examined amidohydrolase gene expression using northern and promoter-β-glucuronidase analyses and found overlapping but distinct patterns of expression. To examine the in vivo importance of auxin-conjugate hydrolysis, we generated a triple hydrolase mutant, ilr1 iar3 ill2, which is deficient in three of these hydrolases. We compared root and hypocotyl growth of the single, double, and triple hydrolase mutants on IAA-Ala, IAA-Leu, and IAA-Phe. The hydrolase mutant phenotypic profiles on different conjugates reveal the in vivo activities and relative importance of ILR1, IAR3, and ILL2 in IAA-conjugate hydrolysis. In addition to defective responses to exogenous conjugates, ilr1 iar3 ill2 roots are slightly less responsive to exogenous IAA. The triple mutant also has a shorter hypocotyl and fewer lateral roots than wild type on unsupplemented medium. As suggested by the mutant phenotypes, ilr1 iar3 ill2 imbibed seeds and seedlings have lower IAA levels than wild type and accumulate IAA-Ala and IAA-Leu, conjugates that are substrates of the absent hydrolases. These results indicate that amidohydrolases contribute free IAA to the auxin pool during germination in Arabidopsis.
Intracellular Localization of Arabidopsis Sulfurtransferases
Authors: Bauer Michael , Dietrich Christof , Nowak Katharina , Sierralta Walter D. , Papenbrock Jutta 
Published: June 2004

Abstract
Sulfurtransferases (Str) comprise a group of enzymes widely distributed in archaea, eubacteria, and eukaryota which catalyze the transfer of a sulfur atom from suitable sulfur donors to nucleophilic sulfur acceptors. In all organisms analyzed to date, small gene families encoding Str proteins have been identified. The gene products were localized to different compartments of the cells. Our interest concerns the localization of Str proteins encoded in the nuclear genome of Arabidopsis. Computer-based prediction methods revealed localization in different compartments of the cell for six putative AtStrs. Several methods were used to determine the localization of the AtStr proteins experimentally. For AtStr1, a mitochondrial localization was demonstrated by immunodetection in the proteome of isolated mitochondria resolved by one- and two-dimensional gel electrophoresis and subsequent blotting. The respective mature AtStr1 protein was identified by mass spectrometry sequencing. The same result was obtained by transient expression of fusion constructs with the green fluorescent protein in Arabidopsis protoplasts, whereas AtStr2 was exclusively localized to the cytoplasm by this method. Three members of the single-domain AtStr were localized in the chloroplasts as demonstrated by transient expression of green fluorescent protein fusions in protoplasts and stomata, whereas the single-domain AtStr18 was shown to be cytoplasmic. The remarkable subcellular distribution of AtStr15 was additionally analyzed by transmission electron immunomicroscopy using a monospecific antibody against green fluorescent protein, indicating an attachment to the thylakoid membrane. The knowledge of the intracellular localization of the members of this multiprotein family will help elucidate their specific functions in the organism.
IAR4, a Gene Required for Auxin Conjugate Sensitivity in Arabidopsis, Encodes a Pyruvate Dehydrogenase E1α Homolog
Authors: LeClere Sherry , Rampey Rebekah A. , Bartel Bonnie 
Published: June 2004

Abstract
The formation and hydrolysis of indole-3-acetic acid (IAA) conjugates represent a potentially important means for plants to regulate IAA levels and thereby auxin responses. The identification and characterization of mutants defective in these processes is advancing the understanding of auxin regulation and response. Here we report the isolation and characterization of the Arabidopsis iar4 mutant, which has reduced sensitivity to several IAA-amino acid conjugates. iar4 is less sensitive to a synthetic auxin and low concentrations of an ethylene precursor but responds to free IAA and other hormones tested similarly to wild type. The gene defective in iar4 encodes a homolog of the E1α-subunit of mitochondrial pyruvate dehydrogenase, which converts pyruvate to acetyl-coenzyme A. We did not detect glycolysis or Krebs-cycle-related defects in the iar4 mutant, and a T-DNA insertion in the IAR4 coding sequence conferred similar phenotypes as the originally identified missense allele. In contrast, we found that disruption of the previously described mitochondrial pyruvate dehydrogenase E1α-subunit does not alter IAA-Ala responsiveness or confer any obvious phenotypes. It is possible that IAR4 acts in the conversion of indole-3-pyruvate to indole-3-acetyl-coenzyme A, which is a potential precursor of IAA and IAA conjugates.
Fluorescent Screening of Transgenic Arabidopsis Seeds without Germination
Authors: Wei Shu , Bravdo Ben-Ami , Shoseyov Oded 
Published: June 2004

Abstract
In this paper, we describe a reliable method for the screening and selection of Arabidopsis transgenic seeds within minutes without germination. Expression of the Aspergillus niger β-glucosidase gene BGL1 in the plant's endoplasmic reticulum was used as a visual marker, together with 4-methylumbelliferyl-β-d-glucopyranoside (MUGluc) as a substrate. Subsequent to incubation in a solution of MUGluc at room temperature for 2 to 15 min, transgenic seeds expressing BGL1 demonstrated a distinct fluorescent signal under UV light. Optimal screening conditions at room temperature were achieved between 75 and 450 μ m MUGluc, at a pH of 2.5 to 5.0 and 2 to 5 min of incubation. No significant loss of viability was detected in transgenic seeds that were redried and stored for 45 d after incubation in MUGluc solution for 2 to 150 min. Transgenic plants expressing BGL1 displayed normal phenotypes relative to the wild type. Selection frequency was 3.1% ± 0.34% for the fluorescence selection method, while kanamycin resistant selection resulted in only 0.56% ± 0.13% using the same seed batch. This novel selection method is nondestructive, practical, and efficient, and eliminates the use of antibiotic genes. In addition, the procedure shortens the selection time from weeks to minutes.
Salicylate Accumulation Inhibits Growth at Chilling Temperature in Arabidopsis
Authors: Scott Ian M. , Clarke Shannon M. , Wood Jacqueline E. , Mur Luis A.J. 
Published: June 2004

Abstract
The growth of Arabidopsis plants in chilling conditions could be related to their levels of salicylic acid (SA). Plants with the SA hydroxylase NahG transgene grew at similar rates to Col-0 wild types at 23°C, and growth of both genotypes was slowed by transfer to 5°C. However, at 5°C, NahG plants displayed relative growth rates about one-third greater than Col-0, so that by 2 months NahG plants were typically 2.7-fold larger. This resulted primarily from greater cell expansion in NahG rosette leaves. Specific leaf areas and leaf area ratios remained similar in both genotypes. Net assimilation rates were similar in both genotypes at 23°C, but higher in NahG at 5°C. Chlorophyll fluorescence measurements revealed no PSII photodamage in chilled leaves of either genotype. Col-0 shoots at 5°C accumulated SA, particularly in glucosylated form. SA in NahG shoots showed similar tendencies at 5°C, but at greatly depleted levels. Catechol was not detected as a metabolite of the NahG transgene product. We also examined growth and SA levels in SA signaling and metabolism mutants at 5°C. The partially SA-insensitive npr1 mutant displayed growth intermediate between NahG and Col-0, while the SA-deficient eds5 mutant behaved like NahG. In contrast, the cpr1 mutant at 5°C accumulated very high levels of SA and its growth was much more inhibited than wild type. At both temperatures, cpr1 was the only SA-responsive genotype in which oxidative damage (measured as thiobarbituric acid-reactive substances) was significantly different from wild type.
Chlamydomonas and Arabidopsis. A Dynamic Duo
Authors: Gutman Benjamin L. , Niyogi Krishna K. 
Published: June 2004

Abstract
A translational biology perspective on Chlamydomonas and Arabidopsis might be expected to focus on those genes, cellular components, or biological processes found first in Chlamydomonas and subsequently studied in Arabidopsis. There are indeed many such examples. There are also examples that flow from Arabidopsis to Chlamydomonas in terms of initial discovery and subsequent study. However, the differences can also be illuminating. In this brief essay, we make a case for the pairing of Chlamydomonas and Arabidopsis as model organisms that bracket a major subset of photosynthetic eukaryotes, the green plants (Mishler, 2000). By analogy with the yeast-mouse dyad, this green pair has tremendous potential as we enter an era of renewed interest in comparative biology.
AtCAND1, A HEAT-Repeat Protein That Participates in Auxin Signaling in Arabidopsis
Authors: Cheng Youfa , Dai Xinhua , Zhao Yunde 
Published: June 2004

Abstract
Auxin affects many aspects of plant growth and development. We previously used chemical genetics to dissect auxin-signaling mechanisms and identified a small molecule, sirtinol, that constitutively activated auxin signaling (Y. Zhao et al. [2003], Science 301: 1107–1110). Here we describe the isolation, characterization, and cloning of an Arabidopsis mutant Atcand1-1 that emerged from a genetic screen for mutants insensitive to sirtinol. Loss-of-function mutants of AtCAND1 were resistant to sirtinol and auxin, but not to gibberellins or brassinolide. Atcand1 displayed developmental phenotypes similar to those of axr1, namely, short petioles, downwardly curling leaves, short inflorescence, and reduced fertility. AtCAND1 is homologous to human CAND1, a protein that is composed almost entirely of HEAT-repeat units and has been implicated in regulating the assembly and disassembly of the SCF protein degradation machinery. Taken together with previous biochemical studies, this work helps to elucidate the roles of AtCAND1 in protein degradation and auxin signaling.
Acute desensitization of presynaptic GABAB‐mediated inhibition and induction of epileptiform discharges in the neonatal rat hippocampus
Authors: Tosetti P. , Bakels R. , Colin‐Le Brun I. , Ferrand N. , Gaiarsa J. L. , Caillard O. 
Published: June 2004

AbstractThe consequences of sustained activation of GABAB receptors on GABAB‐mediated inhibition and network activity were investigated in the neonatal rat hippocampus using whole‐cell and extracellular field recordings. GABAB‐mediated presynaptic control of γ‐aminobutyric acid (GABA) release progressively diminished with time in spite of the continued presence of the agonist (100 µm baclofen, 15 min), indicating acute desensitization of presynaptic GABAB‐mediated inhibition on GABAergic terminals. By contrast, neither GABAB‐mediated inhibition of glutamate release nor postsynaptic GABAB‐mediated inhibition seemed to produce this desensitization. Efficacy of presynaptic GABAB receptors was still reduced by 49% 30 min after baclofen washout, suggesting a long timeframe for recovery from desensitization. The 15‐min baclofen application was followed by a dramatic modification of the spontaneous network activity, with the occurrence of epileptiform events called ictal‐like discharges (ILDs). Extracellular field recordings confirmed the epileptic nature of the discharges that could be recorded up to 4 h after baclofen washout. ILDs did not occur when the GABAB receptor antagonist CGP35348 was coapplied with baclofen. This indicates that ILD induction is a consequence of the sustained activation of GABAB receptors and the correlated changes in GABAB‐mediated inhibition. Furthermore, ILDs were also induced when blocking with CGP35348 an amount of GABAB receptors that exactly mimicked the loss of inhibition obtained with desensitization. These results show that presynaptic GABAB‐mediated inhibition of GABA release acutely and specifically desensitizes following a sustained application of the GABAB receptor agonist baclofen. Conditions that induce desensitization of the GABAB‐mediated responses also trigger persistent epileptiform discharges in the neonatal rat hippocampus.
Anterior thalamic lesions stop immediate early gene activation in selective laminae of the retrosplenial cortex: evidence of covert pathology in rats?
Authors: Jenkins Trisha A. , Vann Seralynne D. , Amin Eman , Aggleton John P. 
Published: June 2004

AbstractLesions involving the anterior thalamic nuclei stopped immediate early gene (IEG) activity in specific regions of the rat retrosplenial cortex, even though there were no apparent cytoarchitectonic changes. Discrete anterior thalamic lesions were made either by excitotoxin (Experiment 1) or radiofrequency (Experiment 2) and, following recovery, the rats foraged in a radial‐arm maze in a novel room. Measurements made 6–12 weeks postsurgery showed that, in comparison with surgical controls, the thalamic lesions produced the same, selective patterns of Fos changes irrespective of method. Granular (caudal granular cortex and rostral granular cortex), but not dysgranular (dysgranular cortex), retrosplenial cortex showed a striking loss of Fos‐positive cells. While a loss of between 79 and 89% of Fos‐positive cells was found in the superficial laminae, the deeper layers appeared normal. In Experiments 3 and 4, rats 9–10 months postsurgery were placed in an activity box for 30 min. Anterior thalamic lesions (Experiment 3) led to a pronounced IEG decrease of both Fos and zif268 throughout the retrosplenial cortex that now included the dysgranular area. These IEG losses were found even though the same regions appeared normal using standard histological techniques. Lesions of the postrhinal cortex (Experiment 4) did not bring about a loss of retrosplenial IEG activity even though this region is also reciprocally connected with the retrosplenial cortex. This selective effect of anterior thalamic damage upon retrosplenial activity may both amplify the disruptive effects of anterior thalamic lesions and help to explain the posterior cingulate hypoactivity found in Alzheimer's disease.
Neonatal medial prefrontal cortex lesion enhances the sensitivity of the mesoaccumbal dopamine system
Authors: Bennay Mustapha , Gernert Manuela , Schwabe Kerstin , Enkel Thomas , Koch Michael 
Published: June 2004

AbstractNeurodevelopmental models of schizophrenia posit that early brain damage leads to dys‐ or misconnection effects possibly altering synaptic transmission in brain sites distal of the lesion. We tested the hypothesis that neonatal medial prefrontal cortex (mPFC) lesions affect the sensitivity of the mesoaccumbal dopamine (DA) system. Using extracellular single‐unit recordings combined with systemic application of the DA agonist apomorphine, followed by the D2 receptor antagonist haloperidol or the D1 receptor antagonist SCH23390, we compared electrophysiological properties of nucleus accumbens core and shell neurons after bilateral excitotoxic lesions of mPFC induced at postnatal day 7 or in adult rats. Whereas animals with adult mPFC lesions showed an altered discharge pattern within the core region, neonatal mPFC lesions altered the discharge pattern within the shell region. Subcutaneous administration of apomorphine (4 mg/kg) reduced accumbal firing rate in 77% of all neurons. Onset and magnitude of apomorphine‐induced inhibition of neuronal activity was faster and stronger in rats with neonatal but not adult mPFC lesions in both core and shell regions. Apomorphine‐induced inhibition was partially reversed by 0.1 mg/kg haloperidol only in core region of neonatal lesioned rats. Apomorphine‐induced excitation of neuronal activity (in 21% of all neurons) was reversed by the D1 receptor antagonist SCH23390 (0.1 mg/kg) in all excited neurons. These data support the hypothesis that neonatal but not adult lesions of mPFC alter cortico‐striatal networks and suggest that disturbance of mPFC development leads to neurodevelopmental changes in mesoaccumbal DA system during adulthood.
Exposure to interferon‐γ during synaptogenesis increases inhibitory activity after a latent period in cultured rat hippocampal neurons
Authors: Brask Johan , Kristensson Krister , Hill Russell H. 
Published: June 2004

AbstractCertain disorders of the nervous system may have their origin in disturbances in the development of synaptic connections and network structure that may not become overt until later in life. As inflammatory cytokines can influence synaptic activity in neuronal cultures, we analysed whether cytokine exposure during synaptogenesis can lead to imbalances in a neuronal network. Short‐term application of interferon‐γ (IFN‐γ), but not tumour necrosis factor‐α, during peak synaptogenesis (but not before or after) in Sprague–Dawley rat hippocampal cultures, caused both a decrease in the frequency of spontaneous excitatory postsynaptic currents (EPSCs) and an increase in the frequency of spontaneous inhibitory postsynaptic currents (IPSCs). These effects were only detected in recordings made weeks later. This was not due to a depression of glutamatergic synapses or to a change in the relative number of neurons containing glutamic acid decarboxylase (GAD). There was an increase in the average amplitude of miniature IPSCs, and in GAD‐expressing neurons the amplitude of miniature EPSCs were larger as well as the responses to glutamate. This indicates that IFN‐γ‐treatment induced increased inhibition via postsynaptic changes. These effects of IFN‐γ treatment were not observed when neuronal nitric oxide synthase was inhibited. Our study therefore shows that exposure to IFN‐γ during a restricted period of development, which coincides with the peak of excitatory synaptogenesis, can cause progressive changes in synaptic activity in the network. Thus, cytokine exposure at a critical period of development may constitute a ‘hit‐and‐run’ mechanism for certain nervous system disorders that become manifest after a latency period.
Preferential vulnerability of astroglia and glial precursors to combined opioid and HIV‐1 Tat exposure in vitro
Authors: Khurdayan Valeriya K. , Buch Shreya , El‐Hage Nazira , Lutz Sarah E. , Goebel Susan M. , Singh Indrapal N. , Knapp Pamela E. , Turchan‐Cholewo Jadwiga , Nath Avindra , Hauser Kurt F. 
Published: June 2004

AbstractHuman immunodeficiency virus (HIV)‐1 infection can cause characteristic neural defects such as progressive motor dysfunction, striatal pathology and gliosis. Recent evidence suggests that HIV‐induced pathogenesis is exacerbated by heroin abuse and that the synergistic neurotoxicity is a direct effect of heroin on the CNS, an alarming observation considering the high incidence of HIV infection with injection drug abuse. Although HIV infection results in neurodegeneration, neurons themselves are not directly infected. Instead, HIV affects microglia and astroglia, which subsequently contributes to the neurodegenerative changes. Opioid receptors are widely expressed by macroglia and macroglial precursors, and the activation of µ‐opioid receptors can modulate programmed cell death, as well as the response of neural cells to cytotoxic insults. For this reason, we questioned whether opioid drugs might modify the vulnerability of macroglia and macroglial precursors to HIV‐1 Tat protein. To address this problem, the effects of morphine and/or HIV Tat1−72 on the viability of macroglia and macroglial precursors were assessed in mixed‐glial cultures derived from mouse striatum. Our findings indicate that sustained exposure to morphine and Tat1−72 viral protein induces the preferential death of glial precursors and some astrocytes. Moreover, the increased cell death is mediated by µ‐opioid receptors and accompanied by the activation of caspase‐3. Our results imply that opiates can enhance the cytotoxicity of HIV‐1 Tat through direct actions on glial precursors and/or astroglia, suggesting novel cellular targets for HIV–opiate interactions.