bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transgenically Enhanced Sorbitol Synthesis Facilitates Phloem Boron Transport and Increases Tolerance of Tobacco to Boron Deficiency1
Authors: Brown Patrick H. , Bellaloui Nacer , Hu Hening , Dandekar Abhaya 
Published: July 2002

Abstract
The mobility of elements within plants contributes to a plant species' tolerance of nutrient deficiencies in the soil. The genetic manipulation of within-plant nutrient movement may therefore provide a means to enhance plant growth under conditions of variable soil nutrient availability. In these experiments tobacco (Nicotiana tabacum) was engineered to synthesize sorbitol, and the resultant effect on phloem mobility of boron (B) was determined. In contrast to wild-type tobacco, transgenic tobacco plants containing sorbitol exhibit a marked increase in within-plant B mobility and a resultant increase in plant growth and yield when grown with limited or interrupted soil B supply. Growth of transgenic tobacco could be maintained by reutilization of B present in mature tissues or from B supplied as a foliar application to mature leaves. In contrast, B present in mature leaves of control tobacco lines could not be used to provide the B requirements for new plant growth. 10B-labeling experiments verified that B is phloem mobile in transgenic tobacco but is immobile in control lines. These results demonstrate that the transgenic enhancement of within-plant nutrient mobility is a viable approach to improve plant tolerance of nutrient stress.
Regulation and Functional Expression of Cinnamate 4-Hydroxylase from Parsley
Authors: Koopmann Edda , Logemann Elke , Hahlbrock Klaus 
Published: July 2002

Abstract
A previously isolated parsley (Petroselinum crispum) cDNA with high sequence similarity to cinnamate 4-hydroxylase (C4H) cDNAs from several plant sources was expressed in yeast (Saccharomyces cerevisiae) containing a plant NADPH:cytochrome P450 oxidoreductase and verified as encoding a functional C4H (CYP73A10). Low genomic complexity and the occurrence of a single type of cDNA suggest the existence of only oneC4H gene in parsley. The encoded mRNA and protein, in contrast to those of a functionally related NADPH:cytochrome P450 oxidoreductase, were strictly coregulated with phenylalanine ammonia-lyase mRNA and protein, respectively, as demonstrated by coinduction under various conditions and colocalization in situ in cross-sections from several different parsley tissues. These results support the hypothesis that the genes encoding the core reactions of phenylpropanoid metabolism form a tight regulatory unit.
Overexpression of a Novel Arabidopsis Gene Related to Putative Zinc-Transporter Genes from Animals Can Lead to Enhanced Zinc Resistance and Accumulation
Authors: van der Zaal Bert J. , Neuteboom Leon W. , Pinas Johan E. , Chardonnens Agnes N. , Schat Henk , Verkleij Jos A.C. , Hooykaas Paul J.J. 
Published: July 2002

Abstract
We describe the isolation of an Arabidopsis gene that is closely related to the animalZnT genes (Zntransporter). The protein encoded by the ZAT (Zn transporter ofArabidopsisthaliana) gene has 398 amino acid residues and is predicted to have six membrane-spanning domains. To obtain evidence for the postulated function of the Arabidopsis gene, transgenic plants with the ZAT coding sequence under control of the cauliflower mosaic virus 35S promoter were analyzed. Plants obtained with ZAT in the sense orientation exhibited enhanced Zn resistance and strongly increased Zn content in the roots under high Zn exposure. Antisense mRNA-producing plants were viable, with a wild-type level of Zn resistance and content, like plants expressing a truncated coding sequence lacking the C-terminal cytoplasmic domain of the protein. The availability of ZAT can lead to a better understanding of the mechanism of Zn homeostasis and resistance in plants.
A Single Limit Dextrinase Gene Is Expressed Both in the Developing Endosperm and in Germinated Grains of Barley1
Authors: Burton Rachel A. , Zhang Xiao-Qi , Hrmova Maria , Fincher Geoffrey B. 
Published: July 2002

Abstract
The single gene encoding limit dextrinase (pullulan 6-glucanohydrolase; EC 3.2.1.41) in barley (Hordeum vulgare) has 26 introns that range in size from 93 to 822 base pairs. The mature polypeptide encoded by the gene has 884 amino acid residues and a calculated molecular mass of 97,417 D. Limit dextrinase mRNA is abundant in gibberellic acid-treated aleurone layers and in germinated grain. Gibberellic acid response elements were found in the promoter region of the gene. These observations suggest that the enzyme participates in starch hydrolysis during endosperm mobilization in germinated grain. The mRNA encoding the enzyme is present at lower levels in the developing endosperm of immature grain, a location consistent with a role for limit dextrinase in starch synthesis. Enzyme activity was also detected in developing grain. The limit dextrinase has a presequence typical of transit peptides that target nascent polypeptides to amyloplasts, but this would not be expected to direct secretion of the mature enzyme from aleurone cells in germinated grain. It remains to be discovered how the enzyme is released from the aleurone and whether another enzyme, possibly of the isoamylase group, might be equally important for starch hydrolysis in germinated grain.
Characterization of Mutants with Alterations of the Phosphorylation Site in the D2 Photosystem II Polypeptide ofChlamydomonas reinhardtii1
Authors: Fleischmann Mark M. , Rochaix Jean-David 
Published: July 2002

AbstractWe have changed the potential phosphorylation site, a threonine residue at position 2 of the D2 polypeptide of the photosystem II complex of Chlamydomonas reinhardtii, to alanine, valine, aspartate, proline, glycine, or glutamate. Mutants with neutral amino acid changes did not display any phenotype with regard to photoautotrophic growth, light sensitivity, fluorescence transients, or photoinhibition. Pulse labeling of these mutants with 32P indicated that a phosphorylated protein of the same size as D2 is absent in these mutants, suggesting that threonine-2 is indeed the unique phosphorylation site of D2. In contrast, mutants in which threonine-2 has been replaced with acidic residues are deficient in photosystem II. Use of chimeric genes containing the psbD5′-untranslated region revealed that the initiation of translation was not affected in these mutants, but the mutations interfered with a later step of D2 synthesis and accumulation.
Arabidopsis Contains at Least Four Independent Blue-Light-Activated Signal Transduction Pathways1
Authors: Lascève Gérard , Leymarie Juliette , Olney Margaret A. , Liscum Emmanuel , Christie John M. , Vavasseur Alain , Briggs Winslow R. 
Published: July 2002

Abstract
We have investigated the stomatal and phototropic responses to blue light of a number of single and double mutants at various loci that encode proteins involved in blue-light responses in Arabidopsis. The stomatal responses of light-grown mutant plants (cry1, cry2, nph1, nph3, nph4, cry1cry2, andnph1cry1) did not differ significantly from those of their wild-type counterparts. Second positive phototropic responses of etiolated mutant seedlings, cry1, cry2, cry1cry2, andnpq1-2, were also similar to those of their wild-type counterparts. Although npq1 and single and double cry1cry2 mutants showed somewhat reduced amplitude for first positive phototropism, threshold, peak, and saturation fluence values for first positive phototropic responses of etiolated seedlings did not differ from those of wild-type seedlings. Similar to the cry1cry2 double mutants and tonpq1-2, a phyAphyB mutant showed reduced curvature but no change in the position or shape of the fluence-response curve. By contrast, the phototropism mutantnph1-5 failed to show phototropic curvature under any of the irradiation conditions used in the present study. We conclude that the chromoproteins cry1, cry2, nph1, and the blue-light photoreceptor for the stomatal response are genetically separable. Moreover, these photoreceptors appear to activate separate signal transduction pathways.
Identification of a Promoter Sequence from theBETL1Gene Cluster Able to Confer Transfer-Cell-Specific Expression in Transgenic Maize
Authors: Hueros Gregorio , Gomez Elisa , Cheikh Nordine , Edwards Janice , Weldon Marcia , Salamini Francesco , Thompson Richard D. 
Published: July 2002

AbstractThe maize (Zea maysL.) betl1 locus, encoding a basal endosperm transfer layer-specific protein, has been mapped and molecularly cloned in its entirety. The locus is shown to consist of three gene copies in the maize inbred line A69Y. To distinguish the three transcription units from the locus name, we have termed them BETL1a, BETL1b,and BETL1c. Two of the copies are expressed, whereas one is inactive and contains retrotransposon-like insertions in both promoter and intron regions. Based on this information, and a restriction site map covering 17 kb around the BETL1locus, a DNA fragment putatively containing an active promoter sequence was identified. This fragment was tested for its ability to confer transfer-cell-specific expression in transient and stably transformed maize tissues. The transgenic maize plants obtained showed the predicted cell-type specificity of expression restricted to the basal endosperm transfer cells, although there were minor deviations in promoter strength and timing and accumulation of the transgene product from the corresponding BETL-1 endogene expression pattern.
Both phyA and phyB Mediate Light-Imposed Repression ofPHYA Gene Expression in Arabidopsis
Authors: Cantón Francisco R. , Quail Peter H. 
Published: July 2002

Abstract
The negatively photoregulatedPHYA gene has a complex promoter structure in Arabidopsis, with three active transcription start sites. To identify the photoreceptors responsible for regulation of this gene, and to assess the relative roles of the three transcription start sites, we analyzed the changes in PHYA transcript levels in wild-type and photoreceptor mutant seedlings under various irradiation conditions. Continuous far-red or red light exposures each induced a significant decline in transcript levels in wild-type etiolated seedlings. Analysis of mutants specifically lacking either phyA or phyB protein demonstrated that these phytochromes are required for the negative regulation induced by far-red and red light, respectively. Ribonuclease protection experiments showed further that this negative regulation is confined almost exclusively to the shortest, most abundant PHYA transcript, and occurs predominantly in shoots. By contrast, both of the other minor transcripts in shoots, and all three transcripts in roots, exhibit near constitutive expression. This complex expression pattern indicates that the PHYAgene is subject to regulation by multiple signals, including environmental, developmental, and organ-specific signals.
ATMPK4, an Arabidopsis Homolog of Mitogen-Activated Protein Kinase, Is Activated in Vitro by AtMEK1 through Threonine Phosphorylation
Authors: Huang Yafan , Li Hui , Gupta Rajeev , Morris Peter C. , Luan Sheng , Kieber Joseph J. 
Published: July 2002

Abstract
The modulation of mitogen-activated protein kinase (MAPK) activity regulates many intracellular signaling processes. In animal and yeast cells, MAP kinases are activated via phosphorylation by the dual-specificity kinase MEK (MAP kinase kinase). Several plant homologs of MEK and MAPK have been identified, but the biochemical events underlying the activation of plant MAPKs remain unknown. We describe the in vitro activation of an Arabidopsis homolog of MAP kinase, ATMPK4. ATMPK4 was phosphorylated in vitro by an Arabidopsis MEK homolog, AtMEK1. This phosphorylation occurred principally on threonine (Thr) residues and resulted in elevated ATMPK4 kinase activity. A second Arabidopsis MEK isoform, ATMAP2Kα, failed to phosphorylate ATMPK4 in vitro. Tyr dephosphorylation by the Arabidopsis Tyr-specific phosphatase AtPTP1 resulted in an almost complete loss of ATMPK4 activity. Immunoprecipitates of Arabidopsis extracts with anti-ATMPK4 antibodies displayed myelin basic protein kinase activity that was sensitive to treatment with AtPTP1. These results demonstrate that a plant MEK can phosphorylate and activate MAPK, and that Tyr phosphorylation is critical for the catalytic activity of MAPK in plants. Surprisingly, in contrast to the animal enzymes, AtMEK1 may not be a dual-specificity kinase but, rather, the required Tyr phosphorylation on ATMPK4 may result from autophosphorylation.
The Forms and Sources of Cytokinins in Developing White Lupine Seeds and Fruits
Authors: Emery R.J. Neil , Ma Qifu , Atkins Craig A. 
Published: July 2002

Abstract
A comprehensive range of cytokinins (CK) was identified and quantified by gas chromatography-mass spectrometry in tissues of and in xylem and phloem serving developing white lupine (Lupinus albus) fruits. Analyses were initiated at anthesis and included stages of podset, embryogenesis, and seed filling up to physiological maturation 77 d post anthesis (DPA). In the first 10 DPA, fertilized ovaries destined to set pods accumulated CK. The proportion of cis-CK:trans-CK isomers was initially 10:1 but declined to less than 1:1. In ovaries destined to abort, the ratio of cis-isomers to trans-isomers remained high. During early podset, accumulation of CK (30–40 pmol ovary−1) was accounted for by xylem and phloem translocation, both containing more than 90% cis-isomers. During embryogenesis and early seed filling (40–46 DPA), translocation accounted for 1% to 14% of the increases of CK in endosperm (20 nmol fruit−1) and seed coat (15 nmol fruit−1), indicating synthesis in situ. High CK concentrations in seeds (0.6 μmol g−1 fresh weight) were transient, declining rapidly to less than 1% of maximum levels by physiological maturity. These data pose new questions about the localization and timing of CK synthesis, the significance of translocation, and the role(s) of CK forms in reproductive development.
Adenosine Kinase of Arabidopsis. Kinetic Properties and Gene Expression
Authors: Moffatt Barbara A. , Wang Li , Allen Mike S. , Stevens Yvonne Y. , Qin Wensheng , Snider Jamie , von Schwartzenberg Klaus 
Published: July 2002

Abstract
To assess the functional significance of adenosine salvage in plants, the cDNAs and genes encoding two isoforms of adenosine kinase (ADK) were isolated from Arabidopsis. TheADK1- and ADK2-coding sequences are very similar, sharing 92% and 89% amino acid and nucleotide identity, respectively. Each cDNA was overexpressed in Escherichia coli, and the catalytic activity of each isoform was determined. Both ADKs had similar catalytic properties with aK m andV max/K m for adenosine of 0.3 to 0.5 μm and 5.4 to 22 L min−1 mg−1 protein, respectively. TheK m andV max/K m for the cytokinin ribosideN 6(isopentenyl) adenosine are 3 to 5 μm and 0.021 to 0.14 L min−1mg−1 protein, respectively, suggesting that adenosine is the preferred substrate for both ADK isoforms. In Arabidopsis plants, both ADK genes are expressed constitutively, with the highest steady-state mRNA levels being found in stem and root.ADK1 transcript levels were generally higher than those of ADK2. ADK enzyme activity reflected relative ADK protein levels seen in immunoblots for leaves, flowers, and stems but only poorly so for roots, siliques, and dry seeds. The catalytic properties, tissue accumulation, and expression levels of these ADKs suggest that they play a key metabolic role in the salvage synthesis of adenylates and methyl recycling in Arabidopsis. They may also contribute to cytokinin interconversion.
Free and Conjugated Benzoic Acid in Tobacco Plants and Cell Cultures. Induced Accumulation upon Elicitation of Defense Responses and Role as Salicylic Acid Precursors
Authors: Chong Julie , Pierrel Marie-Agnès , Atanassova Rossitza , Werck-Reichhart Danièle , Fritig Bernard , Saindrenan Patrick 
Published: July 2002

Abstract
Salicylic acid (SA) is a key endogenous component of local and systemic disease resistance in plants. In this study, we investigated the role of benzoic acid (BA) as precursor of SA biosynthesis in tobacco (Nicotiana tabacum cv Samsun NN) plants undergoing a hypersensitive response following infection with tobacco mosaic virus or in tobacco cell suspensions elicited with β-megaspermin, an elicitor from Phytophthora megasperma. We found a small pool of conjugated BA in healthy leaves and untreated cell suspensions of tobacco, whereas free BA levels were barely detectable. Infection of plants with tobacco mosaic virus or elicitation of cells led to a rapid de novo synthesis and accumulation of conjugated BA, whereas free BA was weakly induced. In presence of diphenylene iodonium, an inhibitor of superoxide anion formation, SA accumulation was abolished in elicited cells and much higher BA levels were concomitantly induced, mainly as a conjugated form. Furthermore, piperonylic acid, an inhibitor of cinnamate-4-hydroxylase was used as a powerful tool to redirect the metabolic flow from the main phenylpropanoid pathway into the SA biosynthetic branch. Under these conditions, in vivo labeling and radioisotope dilution experiments with [14C]trans-cinnamic acid as precursor clearly indicated that the free form of BA produced in elicited tobacco cells is not the major precursor of SA biosynthesis. The main conjugated form of BA accumulating after elicitation of tobacco cells was identified for the first time as benzoyl-glucose. Our data point to the likely role of conjugated forms of BA in SA biosynthesis.
The 5′ End of the Pea Ferredoxin-1 mRNA Mediates Rapid and Reversible Light-Directed Changes in Translation in Tobacco
Authors: Hansen Eric R. , Petracek Marie E. , Dickey Lynn F. , Thompson William F. 
Published: July 2002

Abstract
Ferredoxin-1 (Fed-1) mRNA contains an internal light response element (iLRE) that destabilizes mRNA when light-grown plants are placed in darkness. mRNAs containing this element dissociate from polyribosomes in the leaves of transgenic tobacco (Nicotiana tabacum) plants transferred to the dark for 2 d. Here, we report in vivo labeling experiments with a chloramphenicol acetyl transferase mRNA fused to theFed-1 iLRE. Our data indicate that theFed-1 iLRE mediates a rapid decline in translational efficiency and that iLRE-containing mRNAs dissociate from polyribosomes within 20 min after plants are transferred to darkness. Both events occur before the decline in mRNA abundance, and polyribosome association is rapidly reversible if plants are re-illuminated. These observations support a model in which Fed-1 mRNA in illuminated leaves is stabilized by its association with polyribosomes, and/or by translation. In darkness a large portion of the mRNA dissociates from polyribosomes and is subsequently degraded. We also show that a significant portion of total tobacco leaf mRNA is shifted from polyribosomal to non-polyribosomal fractions after 20 min in the dark, indicating that translation of other mRNAs is also rapidly down-regulated in response to darkness. This class includes some, but not all, cytoplasmic mRNAs encoding proteins involved in photosynthesis.
Asymmetric Subcellular mRNA Distribution Correlates with Carbonic Anhydrase Activity in Acetabularia acetabulum
Authors: Serikawa Kyle A. , Porterfield D. Marshall , Mandoli Dina F. 
Published: July 2002

Abstract
The unicellular green macroalga Acetabularia acetabulum L. Silva is an excellent system for studying regional differentiation within a single cell. In late adults, physiologically mediated extracellular alkalinity varies along the long axis of the alga with extracellular pH more alkaline along the apical and middle regions of the stalk than at and near the rhizoid. Respiration also varies with greater respiration at and near the rhizoid than along the stalk. We hypothesized that the apical and middle regions of the stalk require greater carbonic anhydrase (CA) activity to facilitate inorganic carbon uptake for photosynthesis. Treatment of algae with the CA inhibitors acetazolamide and ethoxyzolamide decreased photosynthetic oxygen evolution along the stalk but not at the rhizoid, indicating that CA facilitates inorganic carbon uptake in the apical portions of the alga. To examine the distribution of enzymatic activity within the alga, individuals were dissected into apical, middle, and basal tissue pools and assayed for both total and external CA activity. CA activity was greatest in the apical portions. We cloned two CA genes (AaCA1 andAaCA2). Northern analysis demonstrated that both genes are expressed throughout much of the life cycle of A. acetabulum. AaCA1 mRNA first appears in early adults.AaCA2 mRNA appears in juveniles. TheAaCA1 and AaCA2 mRNAs are distributed asymmetrically in late adults with highest levels of each in the apical portion of the alga. mRNA localization and enzyme activity patterns correlate for AaCA1 and AaCA2, indicating that mRNA localization is one mechanism underlying regional differentiation in A. acetabulum.
Constitutive Overexpression of Cytosolic Glutamine Synthetase (GS1) Gene in Transgenic Alfalfa Demonstrates That GS1 May Be Regulated at the Level of RNA Stability and Protein Turnover
Authors: Ortega Jose Luis , Temple Stephen J. , Sengupta-Gopalan Champa 
Published: July 2002

Abstract
Glutamine synthetase (GS) catalyzes the ATP-dependent condensation of NH4 + with glutanate to yield glutamine. Gene constructs consisting of the cauliflower mosaic virus (CaMV) 35S promoter driving a cytosolic isoform of GS (GS1) gene have been introduced into alfalfa (Medicago sativa). Although transcripts for the transgene were shown to accumulate to high levels in the leaves, they were undetectable in the nodules. However, significant amounts of β-glucuronidase activity could be detected in nodules of plants containing the CaMV 35S promoter-β-glucuronidase gene construct, suggesting that the transcript for the GS1transgene is not stable in the root nodules. Leaves of alfalfa plants with the CaMV 35S promoter-GS1 gene showed high levels of accumulation of the transcript for the transgene when grown under low-nitrogen conditions and showed a significant drop in the level of GS1 transcripts when fed with high levels of NO3 −. However, no increase in GS activity or polypeptide level was detected in the leaves of transgenic plants. The results suggest that GS1 is regulated at the level of RNA stability and protein turnover.