bluuebunny/crossref_metadata_2025_split huggingface dataset:
Probing in Vivo Metabolism by Stable Isotope Labeling of Storage Lipids and Proteins in Developing Brassica napusEmbryos
Authors: Schwender Jörg , Ohlrogge John B. 
Published: September 2002

Abstract
Developing embryos of Brassica napusaccumulate both triacylglycerols and proteins as major storage reserves. To evaluate metabolic fluxes during embryo development, we have established conditions for stable isotope labeling of cultured embryos under steady-state conditions. Sucrose supplied via the endosperm is considered to be the main carbon and energy source for seed metabolism. However, in addition to 220 to 270 mmcarbohydrates (sucrose, glucose, and fructose), analysis of endosperm liquid revealed up to 70 mm amino acids as well as 6 to 15 mm malic acid. Therefore, a labeling approach with multiple carbon sources is a precondition to quantitatively reflect fluxes of central carbon metabolism in developing embryos. Mid-cotyledon stageB. napus embryos were dissected from plants and cultured for 15 d on a complex liquid medium containing13C-labeled carbohydrates. The 13C enrichment of fatty acids and amino acids (after hydrolysis of the seed proteins) was determined by gas chromatography/mass spectrometry. Analysis of 13C isotope isomers of labeled fatty acids and plastid-derived amino acids indicated that direct glycolysis provides at least 90% of precursors of plastid acetyl-coenzyme A (CoA). Unlabeled amino acids, when added to the growth medium, did not reduce incorporation of 13C label into plastid-formed fatty acids, but substantially diluted 13C label in seed protein. Approximately 30% of carbon in seed protein was derived from exogenous amino acids and as a consequence, the use of amino acids as a carbon source may have significant influence on the total carbon and energy balance in seed metabolism. 13C label in the terminal acetate units of C20 and C22 fatty acids that derive from cytosolic acetyl-CoA was also significantly diluted by unlabeled amino acids. We conclude that cytosolic acetyl-CoA has a more complex biogenetic origin than plastidic acetyl-CoA. Malic acid in the growth medium did not dilute 13C label incorporation into fatty acids or proteins and can be ruled out as a source of carbon for the major storage components of B. napusembryos.
Two New Loci, PLEIADE and HYADE, Implicate Organ-Specific Regulation of Cytokinesis in Arabidopsis
Authors: Müller Sabine , Fuchs Esther , Ovecka Miroslav , Wysocka-Diller Joanna , Benfey Philip N. , Hauser Marie-Theres 
Published: September 2002

Abstract
In screens for regulators of root morphogenesis in Arabidopsis we isolated six new recessive mutants with irregular cell expansion. Complementation analyses placed the mutations in two loci, PLEIADE (PLE) andHYADE (HYA). Phenotypic analyses revealed multinucleated cells, cell wall stubs, and synchronized cell divisions in incompletely separated cells that are all characteristics of defective cytokinesis. These defects were pronounced in roots and undetectable in aerial organs. In addition, fertility and germination were not affected by the mutations. Thus, the alleles that we have isolated of PLE and HYA suggest that the genes may encode organ-specific components needed primarily during root development. Analysis of microtubule arrays during cell cycle inple and hya roots indicates that the presence of several synchronized nuclei influences the position of preprophase band, mitotic spindles, and phragmoplasts. The enhanced and synergistic phenotype ofPLE/ple.hya/hyaseedlings and double mutants point to a role of PLE andHYA in the same process. These mutants provide tools to elucidate the regulation of nuclear cytoskeletal interactions during cell division and cytokinesis.
A Strobilurin Fungicide Enhances the Resistance of Tobacco against Tobacco Mosaic Virus and Pseudomonas syringae pvtabaci
Authors: Herms Stefan , Seehaus Kai , Koehle Harald , Conrath Uwe 
Published: September 2002

Abstract
The strobilurin class of fungicides comprises a variety of synthetic plant-protecting compounds with broad-spectrum antifungal activity. In the present study, we demonstrate that a strobilurin fungicide, F 500 (Pyraclostrobin), enhances the resistance of tobacco (Nicotiana tabacum cv Xanthi nc) against infection by either tobacco mosaic virus (TMV) or the wildfire pathogenPseudomonas syringae pv tabaci. F 500 was also active at enhancing TMV resistance in NahGtransgenic tobacco plants unable to accumulate significant amounts of the endogenous inducer of enhanced disease resistance, salicylic acid (SA). This finding suggests that F 500 enhances TMV resistance in tobacco either by acting downstream of SA in the SA signaling mechanism or by functioning independently of SA. The latter assumption is the more likely because in infiltrated leaves, F 500 did not cause the accumulation of SA-inducible pathogenesis-related (PR)-1 proteins that often are used as conventional molecular markers for SA-induced disease resistance. However, accumulation of PR-1 proteins and the associated activation of the PR-1 genes were elicited upon TMV infection of tobacco leaves and both these responses were induced more rapidly in F 500-pretreated plants than in the water-pretreated controls. Taken together, our results suggest that F 500, in addition to exerting direct antifungal activity, may also protect plants by priming them for potentiated activation of subsequently pathogen-induced cellular defense responses.
An Endoplasmic Reticulum-Bound Ca2+/Mn2+Pump, ECA1, Supports Plant Growth and Confers Tolerance to Mn2+ Stress
Authors: Wu Zhongyi , Liang Feng , Hong Bimei , Young Jeff C. , Sussman Michael R. , Harper Jeffrey F. , Sze Heven 
Published: September 2002

Abstract
Plants can grow in soils containing highly variable amounts of mineral nutrients, like Ca2+ and Mn2+, though the mechanisms of adaptation are poorly understood. Here, we report the first genetic study to determine in vivo functions of a Ca2+ pump in plants. Homozygous mutants of Arabidopsis harboring a T-DNA disruption in ECA1 showed a 4-fold reduction in endoplasmic reticulum-type calcium pump activity. Surprisingly, the phenotype of mutant plants was indistinguishable from wild type when grown on standard nutrient medium containing 1.5 mmCa2+ and 50 μm Mn2+. However, mutants grew poorly on medium with low Ca2+ (0.2 mm) or high Mn2+ (0.5 mm). On high Mn2+, the mutants failed to elongate their root hairs, suggesting impairment in tip growth processes. Expression of the wild-type gene (CAMV35S::ECA1) reversed these conditional phenotypes. The activity of ECA1 was examined by expression in a yeast (Saccharomyces cerevisiae) mutant, K616, which harbors a deletion of its endogenous calcium pumps. In vitro assays demonstrated that Ca2+, Mn2+, and Zn2+stimulated formation of a phosphoenzyme intermediate, consistent with the translocation of these ions by the pump. ECA1 provided increased tolerance of yeast mutant to toxic levels of Mn2+ (1 mm) and Zn2+(3 mm), consistent with removal of these ions from the cytoplasm. These results show that despite the potential redundancy of multiple Ca2+ pumps and Ca2+/H+ antiporters in Arabidopsis, pumping of Ca2+ and Mn2+ by ECA1 into the endoplasmic reticulum is required to support plant growth under conditions of Ca2+ deficiency or Mn2+ toxicity.
Mitochondrial-Driven Bicarbonate Transport Supports Photosynthesis in a Marine Microalga
Authors: Huertas I. Emma , Colman Brian , Espie George S. 
Published: September 2002

Abstract
The CO2-concentrating mechanism (CCM) of the marine eustigmatophycean microalga Nannochloropsis gaditana consists of an active HCO3 −transport system and an internal carbonic anhydrase to facilitate accumulation and conversion of HCO3 − to CO2 for photosynthetic fixation. Aqueous inlet mass spectrometry revealed that a portion of the CO2 generated within the cells leaked to the medium, resulting in a significant rise in the extracellular CO2 concentration to a level above its chemical equilibrium that was diagnostic for active HCO3 − transport. The transient rise in extracellular CO2 occurred in the light and the dark and was resolved from concurrent respiratory CO2efflux using H13CO3 − stable isotope techniques. H13CO3 −pump-13CO2 leak activity of the CCM was unaffected by 10 μm3(3,4-dichlorophenyl)-1,1-dimethylurea, an inhibitor of chloroplast linear electron transport, although photosynthetic O2evolution was reduced by 90%. However, low concentrations of cyanide, azide, and rotenone along with anoxia significantly reduced or abolished 13CO2 efflux in the dark and light. These results indicate that H13CO3 − transport was supported by mitochondrial energy production in contrast to other algae and cyanobacteria in which it is supported by photosynthetic electron transport. This is the first report of a direct role for mitochondria in the energization and functioning of the CCM in a photosynthetic organism.
Effect of Regulated Overexpression of the MADS Domain Factor AGL15 on Flower Senescence and Fruit Maturation
Authors: Fang Su-Chiung , Fernandez Donna E. 
Published: September 2002

Abstract
We have examined the effect of regulated overexpression of AGL15, a member of the MADS domain family of regulatory factors, on reproductive tissues. Using molecular and physiological markers, we show that constitutive overexpression of AGL15 in Arabidopsis leads to delay and down-regulation of senescence programs in perianth organs and developing fruits and alters the process of seed desiccation. Through genetic crosses, we show that the rate of water loss in the maturing seeds is dictated by the genetic composition and physiological state of the maternal tissue, rather than the embryo. To define the developmental time and/or place when senescence programs are most affected by elevated AGL15 levels, we expressed AGL15 under the control of various promoters. Expression during senescence or in abscission zone cells did not produce delays in floral organ senescence or abscission. Using a glucocorticoid-inducible expression system, we show that an increase in AGL15 levels around the time of flower opening is necessary to delay senescence and increase floral organ longevity.
Early Embryo Development in Fucus distichusIs Auxin Sensitive
Authors: Basu Swati , Sun Haiguo , Brian Leigh , Quatrano Ralph L. , Muday Gloria K. 
Published: September 2002

Abstract
Auxin and polar auxin transport have been implicated in controlling embryo development in land plants. The goal of these studies was to determine if auxin and auxin transport are also important during the earliest stages of development in embryos of the brown alga Fucus distichus. Indole-3-acetic acid (IAA) was identified in F. distichus embryos and mature tissues by gas chromatography-mass spectroscopy. F. distichus embryos accumulate [3H]IAA and an inhibitor of IAA efflux, naphthylphthalamic acid (NPA), elevates IAA accumulation, suggesting the presence of an auxin efflux protein complex similar to that found in land plants. F. distichus embryos normally develop with a single unbranched rhizoid, but growth on IAA leads to formation of multiple rhizoids and growth on NPA leads to formation of embryos with branched rhizoids, at concentrations that are active in auxin accumulation assays. The effects of IAA and NPA are complete before 6 h after fertilization (AF), which is before rhizoid germination and cell division. The maximal effects of IAA and NPA are between 3.5 and 5 h AF and 4 and 5.5 h AF, respectively. Although, the location of the planes of cell division was significantly altered in NPA- and IAA-treated embryos, these abnormal divisions occurred after abnormal rhizoid initiation and branching was observed. The results of this study suggest that auxin acts in the formation of apical basal patterns inF. distichus embryo development.
Developmentally Regulated Dual-Specificity Kinase from Peanut That Is Induced by Abiotic Stresses
Authors: Rudrabhatla Parvathi , Rajasekharan Ram 
Published: September 2002

Abstract
Tyrosine (Tyr) phosphorylation represents an important biochemical mechanism to regulate many cellular processes. No Tyr kinase has been cloned so far in plants. Dual-specificity kinases are reported in plants and the function of these kinases remains unknown. A 1.7-kb cDNA that encodes serine/threonine/Tyr (STY) kinase was isolated by screening peanut (Arachis hypogaea) expression library using the anti-phospho-Tyr antibody. The histidine-tagged recombinant kinase histidine-6-STY predominantly autophosphorylated on Tyr and phosphorylated the histone primarily on threonine. Genomic DNA gel-blot analysis revealed that STY kinase is a member of a small multigene family. The transcript of STY kinase is accumulated in the mid-maturation stage of seed development, suggesting a role in the signaling of storage of seed reserves. The STY kinase mRNA expression, as well as kinase activity, markedly increased in response to cold and salt treatments; however, no change in the protein level was observed, suggesting a posttranslational activation mechanism. The activation of the STY kinase is detected after 12 to 48 h of cold and salt treatments, which indicates that the kinase may not participate in the initial response to abiotic stresses, but may play a possible role in the adaptive process to adverse conditions. The transcript levels and kinase activity were unaltered with abscisic acid treatment, suggesting an abscisic acid-independent cold and salt signaling pathway. Here, we report the first identification of a non-MAP kinase cascade dual-specificity kinase involved in abiotic stress and seed development.
Resistance of Cultivated Tomato to Cell Content-Feeding Herbivores Is Regulated by the Octadecanoid-Signaling Pathway
Authors: Li Chuanyou , Williams Mark M. , Loh Ying-Tsu , Lee Gyu In , Howe Gregg A. 
Published: September 2002

Abstract
The octadecanoid signaling pathway has been shown to play an important role in plant defense against various chewing insects and some pathogenic fungi. Here, we examined the interaction of a cell-content feeding arachnid herbivore, the two-spotted spider mite (Tetranychus urticae Koch), with cultivated tomato (Lycopersicon esculentum) and an isogenic mutant line (defenseless-1 [def-1]) that is deficient in the biosynthesis of the octadecanoid pathway-derived signal, jasmonic acid (JA). Spider mite feeding and fecundity ondef-1 plants was significantly greater than on wild-type plants. Decreased resistance of def-1 plants was correlated with reduced JA accumulation and expression of defensive proteinase inhibitor (PI) genes, which were induced in mite-damaged wild-type leaves. Treatment of def-1 plants with methyl-JA restored resistance to spider mite feeding and reduced the fecundity of female mites. Plants expressing a35S::prosystemin transgene that constitutively activates the octadecanoid pathway in a Def-1-dependent manner were highly resistant to attack by spider mites and western flower thrips (Frankliniella occidentalis), another cell-content feeder of economic importance. These findings indicate that activation of the octadecanoid signaling pathway promotes resistance of tomato to a broad spectrum of herbivores. The techniques of amplified fragment length polymorphism (AFLP) and bulk segregant analysis were used to map the Def-1 gene to a region on the long arm of chromosome 3 that is genetically separable from the map position of known JA biosynthetic genes. Tight linkage ofDef-1 to a T-DNA insertion harboring the maize (Zea mays) Dissociation transposable element suggests a strategy for directed transposon tagging of the gene.
Patterns of Expression and Normalized Levels of the Five Arabidopsis Phytochromes
Authors: Sharrock Robert A. , Clack Ted 
Published: September 2002

Abstract
Using monoclonal antibodies specific for each apoprotein and full-length purified apoprotein standards, the levels of the five Arabidopsis phytochromes and their patterns of expression in seedlings and mature plants and under different light conditions have been characterized. Phytochrome levels are normalized to the DNA content of the various tissue extracts to approximate normalization to the number of cells in the tissue. One phytochrome, phytochrome A, is highly light labile. The other four phytochromes are much more light stable, although among these, phytochromes B and C are reduced 4- to 5-fold in red- or white-light-grown seedlings compared with dark-grown seedlings. The total amount of extractable phytochrome is 23-fold lower in light-grown than dark-grown tissues, and the percent ratios of the five phytochromes, A:B:C:D:E, are measured as 85:10:2:1.5:1.5 in etiolated seedlings and 5:40:15:15:25 in seedlings grown in continuous white light. The four light-stable phytochromes are present at nearly unchanging levels throughout the course of development of mature rosette and reproductive-stage plants and are present in leaves, stems, roots, and flowers. Phytochrome protein expression patterns over the course of seed germination and under diurnal and circadian light cycles are also characterized. Little cycling in response to photoperiod is observed, and this very low amplitude cycling of some phytochrome proteins is out of phase with previously reported cycling ofPHY mRNA levels. These studies indicate that, with the exception of phytochrome A, the family of phytochrome photoreceptors in Arabidopsis constitutes a quite stable and very broadly distributed array of sensory molecules.
A Role for the DOF Transcription Factor BPBF in the Regulation of Gibberellin-Responsive Genes in Barley Aleurone
Authors: Mena Montaña , Cejudo Francisco Javier , Isabel-Lamoneda Ines , Carbonero Pilar 
Published: September 2002

AbstractFunctional analyses of a number of hydrolase gene promoters, induced by gibberellin (GA) in aleurone cells following germination, have identified a GA-responsive complex as a tripartite element containing a pyrimidine box motif 5′-CCTTTT-3′. We describe here that BPBF, a barley (Hordeum vulgare) transcription factor of the DOF (DNA-Binding with One Finger) class, previously shown to be an activator of reserve protein encoding genes during development, also has a role in the control of hydrolase genes following seed germination. Northern-blot, reverse transcriptase-polymerase chain reaction, and in situ hybridization analyses evidenced that the transcripts of the BPBF-encoding gene (Pbf), besides being present during endosperm development, are also expressed in aleurone cells of germinated seeds where they are induced by GA, an effect counteracted by abscisic acid. Electrophoretic mobility shift assays have shown that the BPBF protein binds specifically to the pyrimidine box motif in vitro within the different sequence contexts that naturally occur in the promoters of genes encoding a cathepsin B-like protease (Al21) and a low-isoelectric point α-amylase (Amy2/32b), both induced in the aleurone layers in response to GA. In transient expression experiments, BPBF repressed transcription of theAl21 promoter in GA-treated barley aleurone layers and reverted the GAMYB-mediated activation of this protease promoter.
The Bifunctional LKR/SDH Locus of Plants Also Encodes a Highly Active Monofunctional Lysine-Ketoglutarate Reductase Using a Polyadenylation Signal Located within an Intron,
Authors: Tang Guiliang , Zhu Xiaohong , Gakiere Bertrand , Levanony Hanna , Kahana Anat , Galili Gad 
Published: September 2002

Abstract
Both plants and animals catabolize lysine (Lys) via two consecutive enzymes, Lys-ketoglutarate reductase (LKR) and saccharopine dehydrogenase (SDH), which are linked on a single polypeptide encoded by a single LKR/SDHgene. We have previously shown that the ArabidopsisLKR/SDH gene also encodes a monofunctional SDH that is transcribed from an internal promoter. In the present report, we have identified two cDNAs derived from cotton (Gossypium hirsutum) boll abscission zone that encode a novel enzymatic form of Lys catabolism, i.e. a catabolic monofunctional LKR. The monofunctional LKR mRNA is also encoded by theLKR/SDH gene, using two weak polyadenylation sites located within an intron. In situ mRNA hybridization and quantitative reverse transcriptase-polymerase chain reaction analyses also suggest that the cotton monofunctional LKR is relatively abundantly expressed in parenchyma cells of the abscission zone. DNA sequence analysis of theLKR/SDH genes of Arabidopsis, maize (Zea mays), and tomato (Lycopersicon esculentum) suggests that these genes can also encode a monofunctional LKR mRNA by a similar mechanism. To test whether the LKR/SDH and monofunctional LKR enzymes possess different biochemical properties, we used recombinant Arabidopsis LKR/SDH and monofunctional LKR enzymes expressed in yeast (Saccharomyces cerevisiae) cells. The K m of the monofunctional LKR to Lys was nearly 10-fold lower than its counterpart that is linked to SDH. Taken together, our results suggest that theLKR/SDH locus of plants is a super-composite locus that can encode three related but distinct enzymes of Lys catabolism. These three enzymes apparently operate in concert to finely regulate Lys catabolism during plant development.
Engineering Herbicide Metabolism in Tobacco and Arabidopsis with CYP76B1, a Cytochrome P450 Enzyme from Jerusalem Artichoke
Authors: Didierjean Luc , Gondet Laurence , Perkins Roberta , Lau Sze-Mei Cindy , Schaller Hubert , O'Keefe Daniel P. , Werck-Reichhart Danièle 
Published: September 2002

Abstract
The Jerusalem artichoke (Helianthus tuberosus) xenobiotic inducible cytochrome P450, CYP76B1, catalyzes rapid oxidative dealkylation of various phenylurea herbicides to yield nonphytotoxic metabolites. We have found that increased herbicide metabolism and tolerance can be achieved by ectopic constitutive expression of CYP76B1 in tobacco (Nicotiana tabacum) and Arabidopsis. Transformation with CYP76B1 conferred on tobacco and Arabidopsis a 20-fold increase in tolerance to linuron, a compound detoxified by a single dealkylation, and a 10-fold increase in tolerance to isoproturon or chlortoluron, which need successive catalytic steps for detoxification. Two constructs for expression of translational fusions of CYP76B1 with P450 reductase were prepared to test if they would yield even greater herbicide tolerance. Plants expressing these constructs had lower herbicide tolerance than CYP76B1 alone, which is apparently a consequence of reduced stability of the fusion proteins. In all cases, increased herbicide tolerance results from more extensive metabolism, as demonstrated with exogenously fed phenylurea. Beside increased herbicide tolerance, expression of CYP76B1 has no other visible phenotype in the transgenic plants. Our data indicate that CYP76B1 can function as a selectable marker for plant transformation, allowing efficient selection in vitro and in soil-grown plants. Plants expressing CYP76B1 may also be a potential tool for phytoremediation of contaminated sites.