bluuebunny/crossref_metadata_2025_split huggingface dataset:
Glycolytic Flux Is Adjusted to Nitrogenase Activity in Nodules of Detopped and Argon-Treated Alfalfa Plants1
Authors: Curioni Paola M.G. , Hartwig Ueli A. , Nösberger Josef , Schuller Kathryn A. 
Published: July 2002

Abstract
To investigate the short-term (30–240 min) interactions among nitrogenase activity, NH4+ assimilation, and plant glycolysis, we measured the concentrations of selected C and N metabolites in alfalfa (Medicago sativa L.) root nodules after detopping and during continuous exposure of the nodulated roots to Ar:O2 (80:20, v/v). Both treatments caused an increase in the ratios of glucose-6-phosphate to fructose-1,6-bisphosphate, fructose-6-phosphate to fructose-1,6-bisphosphate, phosphoenolpyruvate (PEP) to pyruvate, and PEP to malate. This suggested that glycolytic flux was inhibited at the steps catalyzed by phosphofructokinase, pyruvate kinase, and PEP carboxylase. In the Ar:O2-treated plants the apparent inhibition of glycolytic flux was reversible, whereas in the detopped plants it was not. In both groups of plants the apparent inhibition of glycolytic flux was delayed relative to the decline in nitrogenase activity. The decline in nitrogenase activity was followed by a dramatic increase in the nodular glutamate to glutamine ratio. In the detopped plants this was coincident with the apparent inhibition of glycolytic flux, whereas in the Ar:O2-treated plants it preceded the apparent inhibition of glycolytic flux. We propose that the increase in the nodular glutamate to glutamine ratio, which occurs as a result of the decline in nitrogenase activity, may act as a signal to decrease plant glycolytic flux in legume root nodules.
Complementary DNA Cloning and Characterization of Ferredoxin Localized in Bundle-Sheath Cells of Maize Leaves1
Authors: Matsumura Tomohiro , Kimata-Ariga Yoko , Sakakibara Hitoshi , Sugiyama Tatsuo , Murata Hiroshi , Takao Toshifumi , Shimonishi Yasutsugu , Hase Toshiharu 
Published: July 2002

AbstractIn maize (Zea mays L.) two leaf-specific ferredoxin (Fd) isoproteins, Fd I and Fd II, are distributed differentially in mesophyll and bundle-sheath cells. A novel cDNA encoding the precursor of Fd II (pFD2) was isolated by heterologous hybridization using a cDNA for Fd I (pFD1) as a probe. The assignment of the cDNAs to the Fds was verified by capillary liquid-chromatography/electrospray ionization-mass spectrometry. RNA-blot analysis demonstrated that transcripts for Fd I and Fd II accumulated specifically in mesophyll and bundle-sheath cells, respectively. The mature regions of pFD1 and pFD2 were expressed in Escherichia coli as functional Fds. Fd I and Fd II had similar redox potentials of −423 and −406 mV, respectively, but the Km value of Fd-NADP+ reductase for Fd II was about 3-fold larger than that for Fd I. Asparagine at position 65 of Fd II is a unique residue compared with Fd I and other Fds from various plants, which have aspartic acid or glutamic acid at the corresponding position as an electrostatic interaction site with Fd-NADP+ reductase. Substitution of asparagine-65 with aspartic acid increased the affinity of Fd II with Fd-NADP+ reductase to a level comparable to that of Fd I. These structural and functional differences of Fd I and Fd II may be related to their cell-specific expression in the leaves of a C4 plant.
Changes of Mitochondrial Properties in Maize Seedlings Associated with Selection for Germination at Low Temperature. Fatty Acid Composition, CytochromecOxidase, and Adenine Nucleotide Translocase Activities1
Authors: De Santis Aurelio , Landi Pierangelo , Genchi Giuseppe 
Published: July 2002

AbstractMitochondria are affected by low temperature during seedling establishment in maize (Zea mays L.). We evaluated the associated changes in the mitochondrial properties of populations selected for high (C4-H) and low (C4-L) germination levels at 9.5°C. When seedlings of the two populations were grown at 14°C (near the lower growth limit), the mitochondrial inner membranes of C4-H showed a higher percentage of 18-carbon unsaturated fatty acids, a higher fluidity, and a higher activity of cytochrome c oxidase. We found a positive relationship between these properties and the activity of a mitochondrial peroxidase, allowing C4-H to reduce lipid peroxidation relative to C4-L. The specific activity of reconstituted ATP/ADP translocase was positively associated with this peroxidase activity, suggesting that translocase activity is also affected by chilling. The level of oxidative stress and defense mechanisms are differently expressed in tolerant and susceptible populations when seedlings are grown at a temperature near the lower growth limit. Thus, the interaction between membrane lipids and cytochrome coxidase seems to play a key role in maize chilling tolerance. Furthermore, the divergent-recurrent selection procedure apparently affects the allelic frequencies of genes controlling such an interaction.
Phytochrome D Acts in the Shade-Avoidance Syndrome in Arabidopsis by Controlling Elongation Growth and Flowering Time1
Authors: Devlin Paul F. , Robson Paul R.H. , Patel Samita R. , Goosey Lynn , Sharrock Robert A. , Whitelam Garry C. 
Published: July 2002

Abstract
Shade avoidance in higher plants is regulated by the action of multiple phytochrome (phy) species that detect changes in the red/far-red ratio (R/FR) of incident light and initiate a redirection of growth and an acceleration of flowering. The phyB mutant of Arabidopsis is constitutively elongated and early flowering and displays attenuated responses to both reduced R/FR and end-of-day far-red light, conditions that induce strong shade-avoidance reactions in wild-type plants. This indicates that phyB plays an important role in the control of shade avoidance. In Arabidopsis phyB and phyD are the products of a recently duplicated gene and share approximately 80% identity. We investigated the role played by phyD in shade avoidance by analyzing the responses of phyD-deficient mutants. Compared with the monogenic phyB mutant, the phyB-phyDdouble mutant flowers early and has a smaller leaf area, phenotypes that are characteristic of shade avoidance. Furthermore, compared with the monogenic phyB mutant, the phyB-phyDdouble mutant shows a more attenuated response to a reduced R/FR for these responses. Compared with the phyA-phyB double mutant, the phyA-phyB-phyD triple mutant has elongated petioles and displays an enhanced elongation of internodes in response to end-of-day far-red light. These characteristics indicate that phyD acts in the shade-avoidance syndrome by controlling flowering time and leaf area and that phyC and/or phyE also play a role.
Isolation of Ethylene-Insensitive Soybean Mutants That Are Altered in Pathogen Susceptibility and Gene-for-Gene Disease Resistance1
Authors: Hoffman Thomas , Schmidt J. Scott , Zheng Xiangyang , Bent Andrew F. 
Published: July 2002

Abstract
Plants commonly respond to pathogen infection by increasing ethylene production, but it is not clear if this ethylene does more to promote disease susceptibility or disease resistance. Ethylene production and/or responsiveness can be altered by genetic manipulation. The present study used mutagenesis to identify soybean (Glycine max L. Merr.) lines with reduced sensitivity to ethylene. Two new genetic loci were identified,Etr1 and Etr2. Mutants were compared with isogenic wild-type parents for their response to different soybean pathogens. Plant lines with reduced ethylene sensitivity developed similar or less-severe disease symptoms in response to virulentPseudomonas syringae pv glycinea andPhytophthora sojae, but some of the mutants developed similar or more-severe symptoms in response to Septoria glycines and Rhizoctonia solani. Gene-for-gene resistance against P. syringae expressingavrRpt2 remained effective, butRps1-k-mediated resistance against P. sojae races 4 and 7 was disrupted in the strong ethylene-insensitive etr1-1 mutant.Rps1-k-mediated resistance against P. sojae race 1 remained effective, suggesting that theRps1-k locus may encode more than one gene for disease resistance. Overall, our results suggest that reduced ethylene sensitivity can be beneficial against some pathogens but deleterious to resistance against other pathogens.
Inhibition of Nitrate Uptake by Ammonium in Barley. Analysis of Component Fluxes1
Authors: Kronzucker Herbert J. , Glass Anthony D.M. , Siddiqi M. Yaeesh 
Published: July 2002

AbstractNO3− uptake by plant roots is rapidly inhibited by exposure to NH4+. The rapidity of the effect has led to the presumption that the inhibition results from the direct effects of NH4+ at the plasma membrane. The mechanism of this inhibition, however, has been in contention. In the present study we used the radiotracer 13N to determine the relative effects of short-term exposures to NH4+ on the13NO3− influx, efflux, and partitioning of absorbed 13N in barley (Hordeum vulgare) roots. Plants were grown without NO3− or NO2−(uninduced for NO3− uptake), or with 0.1, 1.0, 10 mm NO3−, or 0.1 mmNO2− (to generate plant roots induced for NO3− uptake). Exposure to 1 mmNH4+ strongly reduced influx; the effect was most pronounced in plants induced for NO3−uptake when NO3− absorption was measured at low external NO3−. At higher [NO3−] and in uninduced plants the inhibitory effect was much diminished, indicating that NH4+ inhibition of influx was mediated via effects on the inducible high-affinity transport system rather than on the constitutive high-affinity transport system or the low-affinity transport system. Exposure to NH4+ also caused increased NO3− efflux; the largest effect was at low external [NO3−] in uninduced plants. In absolute terms, the reduction of influx made the dominant contribution to the observed reduction of net uptake of NO3−. Differences in response between plants induced with NO3− and those induced with NO2− indicate that NO2− may not be an appropriate analog for NO3− under all conditions.
PsbU, a Protein Associated with Photosystem II, Is Required for the Acquisition of Cellular Thermotolerance inSynechococcus species PCC 70021
Authors: Nishiyama Yoshitaka , Los Dmitry A. , Murata Norio 
Published: July 2002

Abstract
PsbU is an extrinsic protein of the photosystem II complex of cyanobacteria and red algae. Our previous in vitro studies (Y. Nishiyama, D.A. Los, H. Hayashi, N. Murata [1997] Plant Physiol 115: 1473–1480) revealed that PsbU stabilizes the oxygen-evolving machinery of the photosystem II complex against heat-induced inactivation in the cyanobacteriumSynechococcus sp. PCC 7002. To elucidate the role of PsbU in vivo, we inactivated the psbU gene inSynechococcus sp. PCC 7002 by targeted mutagenesis. Inactivation of the psbU gene resulted in marked changes in the acclimative responses of cells to high temperature: Mutated cells were unable to increase the thermal stability of their oxygen-evolving machinery when grown at moderately high temperatures. Moreover, the cellular thermotolerance of the mutated cells failed to increase upon acclimation of cells to high temperature. The heat-shock response, as assessed in terms of the levels of homologs of the heat-shock proteins Hsp60, Hsp70, and Hsp17, was unaffected by the mutation in psbU, suggesting that heat-shock proteins were not involved in the changes in the acclimative responses. Our observations indicate that PsbU is involved in the mechanism that underlies the enhancement of the thermal stability of the oxygen-evolving machinery and that the stabilization of the oxygen-evolving machinery is crucial for the acquisition of cellular thermotolerance.
Hydrogen Peroxide from the Oxidative Burst Is Neither Necessary Nor Sufficient for Hypersensitive Cell Death Induction, Phenylalanine Ammonia Lyase Stimulation, Salicylic Acid Accumulation, or Scopoletin Consumption in Cultured Tobacco Cells Treated with Elicitin
Authors: Dorey Stéphan , Kopp Marguerite , Geoffroy Pierrette , Fritig Bernard , Kauffmann Serge 
Published: July 2002

Abstract
H2O2 from the oxidative burst, cell death, and defense responses such as the production of phenylalanine ammonia lyase (PAL), salicylic acid (SA), and scopoletin were analyzed in cultured tobacco (Nicotiana tabacum) cells treated with three proteinaceous elicitors: two elicitins (α-megaspermin and β-megaspermin) and one glycoprotein. These three proteins have been isolated from Phytophthora megasperma H20 and have been previously shown to be equally efficient in inducing a hypersensitive response (HR) upon infiltration into tobacco leaves. However, in cultured tobacco cells these elicitors exhibited strikingly different biological activities. β-Megaspermin was the only elicitor that caused cell death and induced a strong, biphasic H2O2 burst. Both elicitins stimulated PAL activity similarly and strongly, while the glycoprotein caused only a slight increase. Only elicitins induced SA accumulation and scopoletin consumption, and β-megaspermin was more efficient. To assess the role of H2O2 in HR cell death and defense response expression in elicitin-treated cells, a gain and loss of function strategy was used. Our results indicated that H2O2 was neither necessary nor sufficient for HR cell death, PAL activation, or SA accumulation, and that extracellular H2O2 was not a direct cause of intracellular scopoletin consumption.
Arabidopsis Mutants Lacking the 43- and 54-Kilodalton Subunits of the Chloroplast Signal Recognition Particle Have Distinct Phenotypes
Authors: Amin Pinky , Sy Donna A.C. , Pilgrim Marsha L. , Parry Devin H. , Nussaume Laurent , Hoffman Neil E. 
Published: July 2002

AbstractThe chloroplast signal recognition particle (cpSRP) is a protein complex consisting of 54- and 43-kD subunits encoded by the fifty-four chloroplast, which encodes cpSRP54 (ffc), and chaos (cao) loci, respectively. Two new null alleles in the ffc locus have been identified.ffc1-1 is caused by a stop codon in exon 10, whileffc1-2 has a large DNA insertion in intron 8.ffc mutants have yellow first true leaves that subsequently become green. The reaction center proteins D1, D2, and psaA/B, as well as seven different light-harvesting chlorophyll proteins (LHCPs), were found at reduced levels in the youngffc leaves but at wild-type levels in the older leaves. The abundance of the two types of LHCP was unaffected by the mutation, while two others were increased in the absence of cpSRP54. Null mutants in the cao locus contain reduced levels of the same subset of LHCP proteins as ffc mutants, but are distinguishable in four ways: young leaves are greener, the chlorophylla/b ratio is elevated, levels of reaction center proteins are normal, and there is no recovery in the level of LHCPs in the adult plant. The data suggest that cpSRP54 and cpSRP43 have some nonoverlapping roles and that alternative transport pathways can compensate for the absence of a functional cpSRP.
Analysis of the Relative Increase in Photosynthetic O2 Uptake When Photosynthesis in Grapevine Leaves Is Inhibited following Low Night Temperatures and/or Water Stress
Authors: Flexas Jaume , Badger Murray , Chow Wah Soon , Medrano Hipólito , Osmond Charles Barry 
Published: July 2002

AbstractWe found similarities between the effects of low night temperatures (5°C–10°C) and slowly imposed water stress on photosynthesis in grapevine (Vitis vinifera L.) leaves. Exposure of plants growing outdoors to successive chilling nights caused light- and CO2-saturated photosynthetic O2 evolution to decline to zero within 5 d. Plants recovered after four warm nights. These photosynthetic responses were confirmed in potted plants, even when roots were heated. The inhibitory effects of chilling were greater after a period of illumination, probably because transpiration induced higher water deficit. Stomatal closure only accounted for part of the inhibition of photosynthesis. Fluorescence measurements showed no evidence of photoinhibition, but nonphotochemical quenching increased in stressed plants. The most characteristic response to both stresses was an increase in the ratio of electron transport to net O2evolution, even at high external CO2 concentrations. Oxygen isotope exchange revealed that this imbalance was due to increased O2 uptake, which probably has two components: photorespiration and the Mehler reaction. Chilling- and drought-induced water stress enhanced both O2 uptake processes, and both processes maintained relatively high rates of electron flow as CO2 exchange approached zero in stressed leaves. Presumably, high electron transport associated with O2uptake processes also maintained a high ΔpH, thus affording photoprotection.
Molecular Dissection of the Role of Histidine in Nickel Hyperaccumulation in Thlaspi goesingense(Hálácsy)
Authors: Persans Michael W. , Yan Xiange , Patnoe Jean-Marc M.L. , Krämer Ute , Salt David E. 
Published: July 2002

Abstract
To understand the role of free histidine (His) in Ni hyperaccumulation in Thlaspi goesingense, we investigated the regulation of His biosynthesis at both the molecular and biochemical levels. Three T. goesingense cDNAs encoding the following His biosynthetic enzymes, ATP phosphoribosyltransferase (THG1, GenBank accession no. AF003347), imidazoleglycerol phosphate dehydratase (THB1, GenBank accession no. AF023140), and histidinol dehydrogenase (THD1, GenBank accession no. AF023141) were isolated by functional complementation of Escherichia coli His auxotrophs. Northern analysis of THG1,THD1, and THB1 gene expression revealed that each gene is expressed in both roots and shoots, but at the concentrations and dosage times of Ni treatment used in this study, these genes failed to show any regulation by Ni. We were also unable to observe any increases in the concentration of free His in root, shoot, or xylem sap of T. goesingense in response to Ni exposure. X-ray absorption spectroscopy of root and shoot tissue fromT. goesingense and the non-accumulator speciesThlaspi arvense revealed no major differences in the coordination of Ni by His in these tissues. We therefore conclude that the Ni hyperaccumulation phenotype in T. goesingense is not determined by the overproduction of His in response to Ni.
Sustained Photobiological Hydrogen Gas Production upon Reversible Inactivation of Oxygen Evolution in the Green AlgaChlamydomonas reinhardtii
Authors: Melis Anastasios , Zhang Liping , Forestier Marc , Ghirardi Maria L. , Seibert Michael 
Published: July 2002

Abstract
The work describes a novel approach for sustained photobiological production of H2 gas via the reversible hydrogenase pathway in the green alga Chlamydomonas reinhardtii. This single-organism, two-stage H2 production method circumvents the severe O2 sensitivity of the reversible hydrogenase by temporally separating photosynthetic O2 evolution and carbon accumulation (stage 1) from the consumption of cellular metabolites and concomitant H2 production (stage 2). A transition from stage 1 to stage 2 was effected upon S deprivation of the culture, which reversibly inactivated photosystem II (PSII) and O2 evolution. Under these conditions, oxidative respiration by the cells in the light depleted O2 and caused anaerobiosis in the culture, which was necessary and sufficient for the induction of the reversible hydrogenase. Subsequently, sustained cellular H2 gas production was observed in the light but not in the dark. The mechanism of H2 production entailed protein consumption and electron transport from endogenous substrate to the cytochromeb 6-f and PSI complexes in the chloroplast thylakoids. Light absorption by PSI was required for H2 evolution, suggesting that photoreduction of ferredoxin is followed by electron donation to the reversible hydrogenase. The latter catalyzes the reduction of protons to molecular H2in the chloroplast stroma.
Lignification in Transgenic Poplars with Extremely Reduced Caffeic Acid O-Methyltransferase Activity
Authors: Jouanin Lise , Goujon Thomas , de Nadaı̈ Véronique , Martin Marie-Thérèse , Mila Isabelle , Vallet Christelle , Pollet Brigitte , Yoshinaga Arata , Chabbert Brigitte , Petit-Conil Michel , Lapierre Catherine 
Published: July 2002

Abstract
Transgenic poplars (Populus tremula ×Populus alba) were obtained by introduction of a sense homologous transgene encoding caffeic acidO-methyltransferase (COMT) under the control either of the cauliflower mosaic virus double 35S promoter or of the eucalyptus cinnamyl alcohol dehydrogenase promoter. Although these constructs conferred a moderate overexpression of COMT in some lines, a transgenic line with the double 35S promoter was found where COMT activity in woody tissues was close to zero due to a gene-silencing phenomenon. For the first time in COMT down-regulated trees, this alteration substantially reduced lignin level in 6-month-old trees (17% decrease). Lignin structure was found to be strongly altered, with a two times higher content in condensed bonds, an almost complete lack of syringyl units, and the incorporation of 5-hydroxyguaiacyl units to the most remarkable extent reported so far. Consistent with the higher cellulose content and with the higher condensation degree of the lignin, the impact of the transformation on the kraft-pulping performances of the poplar trees positively affected the pulp yield (10% relative increase), but made lignins less amenable to industrial degradations.
Production and Characterization of Diverse Developmental Mutants of Medicago truncatula
Authors: Penmetsa R. Varma , Cook Douglas R. 
Published: July 2002

Abstract
The diploid annual legume Medicago truncatula has been developed as a tractable genetic system for studying biological questions that are unique to, or well suited for study in legume species. An efficient mutagenesis protocol using ethyl-methyl sulfonate and a polymorphic ecotype with properties appropriate for use as a mapping parent are described. Isolation and characterization of three developmental mutants are described. The mtapetalamutation results in homeotic conversions of floral organ whorls 2 and 3 into sepals and carpelloid structures, respectively, similar to mutations in the apetala3/pistillata genes of Arabidopsis. The palmyra mutation primarily affects seedling shoot meristem initiation, and thus phenocopies meristem function mutations identified in Arabidopsis such as thezwille locus. The phenotype of thepalmyra and mtapetala double mutant is additive, with seedling shoot meristems and floral organs indistinguishable from those of the single palmyra andmtapetala mutants, respectively. These results are consistent with a lack of genetic interaction between these loci. A third mutant, speckle, is characterized by spontaneous necrotic lesion formation on leaves, root, and stems, similar to necrosis mutants identified in other plant species. In addition to documenting the efficient mutagenesis of M. truncatula, the availability of developmental mutants that phenocopy characterized Arabidopsis mutants will provide a basis for establishing orthologous gene function between M. truncatula and Arabidopsis, once the genes responsible are cloned. Moreover, the male-sterile, female-fertile nature of the mtapetala mutant provides a convenient tool for genetic analyses in M. truncatula.