bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photosystem II Peripheral Accessory Chlorophyll Mutants inChlamydomonas reinhardtii. Biochemical Characterization and Sensitivity to Photo-Inhibition,
Authors: Ruffle Stuart V. , Wang Jun , Johnston Heather G. , Gustafson Terry L. , Hutchison Ronald S. , Minagawa Jun , Crofts Anthony , Sayre Richard T. 
Published: November 2008

AbstractIn addition to the four chlorophylls (Chls) involved in primary charge separation, the photosystem II (PSII) reaction center polypeptides, D1 and D2, coordinate a pair of symmetry-related, peripheral accessory Chls. These Chls are axially coordinated by the D1-H118 and D2-H117 residues and are in close association with the proximal Chl antennae proteins, CP43 and CP47. To gain insight into the function(s) of each of the peripheral Chls, we generated site-specific mutations of the amino acid residues that coordinate these Chls and characterized their energy and electron transfer properties. Our results demonstrate that D1-H118 and D2-H117 mutants differ with respect to: (a) their relative numbers of functional PSII complexes, (b) their relative ability to stabilize charge-separated states, (c) light-harvesting efficiency, and (d) their sensitivity to photo-inhibition. The D2-H117N and D2-H117Q mutants had reduced levels of functional PSII complexes and oxygen evolution capacity as well as reduced light-harvesting efficiencies relative to wild-type cells. In contrast, the D1-H118Q mutant was capable of near wild-type rates of oxygen evolution at saturating light intensities. The D1-H118Q mutant also was substantially more resistant to photo-inhibition than wild type. This reduced sensitivity to photo-inhibition is presumably associated with a reduced light-harvesting efficiency in this mutant. Finally, it is noted that the PSII peripheral accessory Chls have similarities to a to a pair of Chls also present in the PSI reaction center complex.
Dissection of the Light Signal Transduction Pathways Regulating the TwoEarly Light-Induced ProteinGenes in Arabidopsis
Authors: Harari-Steinberg Orit , Ohad Itzhak , Chamovitz Daniel A. 
Published: November 2008

AbstractThe expression of light-regulated genes in plants is controlled by different classes of photoreceptors that act through a variety of signaling molecules. During photomorphogenesis, the early light-induced protein (Elip) genes are among the first to be induced. To understand the light signal transduction pathways that regulate Elip expression, the twoElip genes, Elip1 andElip2, in Arabidopsis were studied, taking advantage of the genetic tools available for studying light signaling in Arabidopsis. Using two independent quantitative reverse transcriptase-PCR techniques, we found that red, far-red, and blue lights positively regulate expression of the Elip genes. Phytochrome A and phytochrome B are involved in this signaling. The cryptochrome or phototropin photoreceptors are not required for blue-light induction of either Elip gene, suggesting the involvement of an additional, unidentified, blue-light receptor. Although the COP9 signalosome, a downstream regulator, is involved in dark repression of both Elips, Elip1 andElip2 show different expression patterns in the dark. The transcription factor HY5 promotes the light induction ofElip1, but not Elip2. A defect in photosystem II activity in greening of hy5 seedlings may result from the loss of Elip1. Heat shock positively controlled Elip1 and Elip2 in a light-independent fashion. This induction is independent of HY5, indicating that heat shock and light activate transcription of the Elip genes through independent pathways.
Root Hair Initiation Is Coupled to a Highly Localized Increase of Xyloglucan Endotransglycosylase Action in Arabidopsis Roots
Authors: Vissenberg Kris , Fry Stephen C. , Verbelen Jean-Pierre 
Published: November 2008

Abstract
Root hairs are formed by two separate processes: initiation and subsequent tip growth. Root hair initiation is always accompanied by a highly localized increase in xyloglucan endotransglycosylase (XET) action at the site of future bulge formation, where the trichoblast locally loosens its cell wall. This suggests an important role of XET in the first stages of root hair initiation. The tip of growing root hairs is not marked by localized high XET action. Experiments in which root hair initiation was modulated and observations on root hair mutants support this view. The ethylene precursor 1-aminocyclopropane-1-carboxylic acid shifts both root hair initiation and the local increase in XET action toward the root tip. On the other hand, roots treated with the ethylene inhibitor aminoethoxyvinyl-glycine, as well as roots of mutants affected in root hair initiation (rhl1, rhd6-1, andaxr2-1) revealed no localized increases of XET action at all and consequently did not initiate root hairs. Disruption of actin and microtubules did not prevent the localized increase in XET action. Also, the temporal and spatial pattern of action as the specific pH dependence suggest that different isoforms of XET act in different processes of root development.
Senescence Is Induced in Individually Darkened Arabidopsis Leaves, but Inhibited in Whole Darkened Plants
Authors: Weaver L. Michael , Amasino Richard M. 
Published: November 2008

Abstract
It has long been known that leaf senescence can be induced in many plant species by detaching leaves and placing them in the darkness. It recently has been shown that entire Arabidopsis plants placed in the darkness are not induced to senesce, as judged by visible yellowing and certain molecular markers. Here, we show that when individual Arabidopsis leaves are darkened, but not when entire plants are darkened, senescence is induced in the covered leaves. This induction of senescence is highly localized. The phenomenon is leaf age dependent in that it occurs more rapidly and strongly in older leaves than in younger ones, as is the case with many forms of induced senescence. Whole adult plants placed in darkness, in contrast, show delayed senescence, although seedlings lacking primary leaves do not. These observations imply that the light status of the entire plant affects the senescence of individual leaves. A model summarizing the results is presented.
Cadmium-Induced Changes in Antioxidative Systems, Hydrogen Peroxide Content, and Differentiation in Scots Pine Roots
Authors: Schützendübel Andres , Schwanz Peter , Teichmann Thomas , Gross Kristina , Langenfeld-Heyser Rosemarie , Godbold Douglas L. , Polle Andrea 
Published: November 2008

Abstract
To investigate whether Cd induces common plant defense pathways or unspecific necrosis, the temporal sequence of physiological reactions, including hydrogen peroxide (H2O2) production, changes in ascorbate-glutathione-related antioxidant systems, secondary metabolism (peroxidases, phenolics, and lignification), and developmental changes, was characterized in roots of hydroponically grown Scots pine (Pinus sylvestris) seedlings. Cd (50 μm, 6 h) initially increased superoxide dismutase, inhibited the systems involved in H2O2 removal (glutathione/glutathione reductase, catalase [CAT], and ascorbate peroxidase [APX]), and caused H2O2accumulation. Elongation of the roots was completely inhibited within 12 h. After 24 h, glutathione reductase activities recovered to control levels; APX and CAT were stimulated by factors of 5.5 and 1.5. Cell death was increased. After 48 h, nonspecific peroxidases and lignification were increased, and APX and CAT activities were decreased. Histochemical analysis showed that soluble phenolics accumulated in the cytosol of Cd-treated roots but lignification was confined to newly formed protoxylem elements, which were found in the region of the root tip that normally constitutes the elongation zone. Roots exposed to 5 μm Cd showed less pronounced responses and only a small decrease in the elongation rate. These results suggest that in cells challenged by Cd at concentrations exceeding the detoxification capacity, H2O2 accumulated because of an imbalance of redox systems. This, in turn, may have triggered the developmental program leading to xylogenesis. In conclusion, Cd did not cause necrotic injury in root tips but appeared to expedite differentiation, thus leading to accelerated aging.
Effect of Temperature on Rates of Alternative and Cytochrome Pathway Respiration and Their Relationship with the Redox Poise of the Quinone Pool
Authors: Atkin Owen K. , Zhang Qisen , Wiskich Joe T. 
Published: November 2008

AbstractWe investigated the effect of short-term changes in temperature on alternative (Alt) and cytochrome (Cyt) pathway respiration, both in intact tissues and isolated mitochondria of 14-d-old cotyledons of soybean (Glycine max L. cv Stevens). We also established the extent to which temperature alters the interaction between the oxidizing pathways and the level of ubiquinone (UQ) reduction (UQr/UQt). No difference was found between the temperature coefficient of respiration (Q 10; proportional change per 10°C) of Alt and Cyt pathway respiration in cotyledon slices (Q 10 = 1.92 and 1.86, respectively). In isolated mitochondria, the Q 10 of the fully activated Alt pathway (Q 10 = 2.24–2.61) was always equal to, or higher than, that of Cytc oxidase (COX) alone (Q 10 = 2.08) and the complete Cyt pathway (Q 10 = 2.40–2.55). This was true regardless of substrate or whether ADP was present. There was little difference in the Q 10 of the Cyt pathway with or without ADP; however, theQ 10 of COX was substantially lower in the presence of an uncoupler (Q 10 = 1.61) than its absence (Q 10 = 2.08). The kinetics of Alt and Cyt pathway activity in relation to UQr/UQt were not affected by temperature. For a given UQr/UQt value, the proportion of maximum flux taking place was similar at all temperatures for both pathways (±ADP). However, the Q 10 of the Alt and the Cyt pathways (+ADP) increased with increasing UQr/UQt. We conclude that the Alt pathway is not less temperature sensitive than the Cyt pathway or COX per se and that changes in the degree of control exerted by individual steps in the respiratory apparatus could result in changes in theQ 10 of mitochondrial O2uptake.
An Off-Line Implementation of the Stable Isotope Technique for Measurements of Alternative Respiratory Pathway Activities
Authors: Nagel Oscar W. , Waldron Susan , Jones Hamlyn G. 
Published: November 2008

Abstract
In situ measurements of alternative respiratory pathway activity are needed to provide insight into the energy efficiency of plant metabolism under various conditions in the field. The only reliable method at present to measure alternative oxidase (AOX) activity is through measurement of changes in δ18O(O2), which to date has only been used in laboratory environments. We have developed a cuvette system to measure partitioning of electrons to AOX that is suitable for off-line use and for field experiments. Plant samples are enclosed in airtight cuvettes and O2 consumption is monitored. Gas samples from the cuvette are stored in evacuated gas containers until measurement of δ18O(O2). We have validated this method using differing plant material to assess AOX activity. Fractionation factors were calculated from δ18O(O2) measurements, which could be measured with an accuracy and precision to 0.1‰ and 0.3‰, respectively. Potential sources of error are discussed and quantified. Our method provides results similar to those obtained with laboratory incubations on-line to a mass spectrometer but greatly increases the potential for adoption of the stable isotope method.
Analysis of the Arabidopsis Mitochondrial Proteome
Authors: Millar A. Harvey , Sweetlove Lee J. , Giegé Philippe , Leaver Christopher J. 
Published: November 2008

Abstract
The complete set of nuclear genes that encode proteins targeted to mitochondria in plants is currently undefined and thus the full range of mitochondrial functions in plants is unknown. Analysis of two-dimensional gel separations of Arabidopsis cell culture mitochondrial protein revealed approximately 100 abundant proteins and 250 low-abundance proteins. Comparison of subfractions of mitochondrial protein on two-dimensional gels provided information on the soluble, membrane, or integral membrane locations of this protein set. A total of 170 protein spots were excised, trypsin-digested, and matrix-assisted laser desorption ionization/time of flight mass spectrometry spectra obtained. Using this dataset, 91 of the proteins were identified by searching translated Arabidopsis genomic databases. Of this set, 81 have defined functions based on sequence comparison. These functions include respiratory electron transport, tricarboxylic acid cycle metabolism, amino acid metabolism, protein import, processing, and assembly, transcription, membrane transport, and antioxidant defense. A total of 10 spectra were matched to Arabidopsis putative open reading frames for which no specific function has been determined. A total of 64 spectra did not match to an identified open reading frame. Analysis of full-length putative protein sequences using bioinformatic tools to predict subcellular targeting (TargetP, Psort, and MitoProt) revealed significant variation in predictions, and also a lack of mitochondrial targeting prediction for several characterized mitochondrial proteins.
A Gene Controlling Variation in Arabidopsis Glucosinolate Composition Is Part of the Methionine Chain Elongation Pathway
Authors: Kroymann Juergen , Textor Susanne , Tokuhisa Jim G. , Falk Kimberly L. , Bartram Stefan , Gershenzon Jonathan , Mitchell-Olds Thomas 
Published: November 2008

Abstract
Arabidopsis and other Brassicaceae produce an enormous diversity of aliphatic glucosinolates, a group of methionine (Met)-derived plant secondary compounds containing a β-thio-glucose moiety, a sulfonated oxime, and a variable side chain. We fine-scale mappedGSL-ELONG, a locus controlling variation in the side-chain length of aliphatic glucosinolates. Within this locus, a polymorphic gene was identified that determines whether Met is extended predominantly by either one or by two methylene groups to produce aliphatic glucosinolates with either three- or four-carbon side chains. Two allelic mutants deficient in four-carbon side-chain glucosinolates were shown to contain independent missense mutations within this gene. In cell-free enzyme assays, a heterologously expressed cDNA from this locus was capable of condensing 2-oxo-4-methylthiobutanoic acid with acetyl-coenzyme A, the initial reaction in Met chain elongation. The gene methylthioalkylmalate synthase1(MAM1) is a member of a gene family sharing approximately 60% amino acid sequence similarity with 2-isopropylmalate synthase, an enzyme of leucine biosynthesis that condenses 2-oxo-3-methylbutanoate with acetyl-coenzyme A.
Dominant Negative Guard Cell K+ Channel Mutants Reduce Inward-Rectifying K+ Currents and Light-Induced Stomatal Opening in Arabidopsis
Authors: Kwak June M. , Murata Yoshiyuki , Baizabal-Aguirre Victor M. , Merrill Jennifer , Wang Michele , Kemper Andrea , Hawke Scott D. , Tallman Gary , Schroeder Julian I. 
Published: November 2008

Abstract
Inward-rectifying potassium (K+ in) channels in guard cells have been suggested to provide a pathway for K+ uptake into guard cells during stomatal opening. To test the proposed role of guard cell K+ in channels in light-induced stomatal opening, transgenic Arabidopsis plants were generated that expressed dominant negative point mutations in the K+ in channel subunit KAT1. Patch-clamp analyses with transgenic guard cells from independent lines showed that K+ in current magnitudes were reduced by approximately 75% compared with vector-transformed controls at −180 mV, which resulted in reduction in light-induced stomatal opening by 38% to 45% compared with vector-transformed controls. Analyses of intracellular K+ content using both sodium hexanitrocobaltate (III) and elemental x-ray microanalyses showed that light-induced K+ uptake was also significantly reduced in guard cells of K+ in channel depressor lines. These findings support the model that K+ inchannels contribute to K+ uptake during light-induced stomatal opening. Furthermore, transpirational water loss from leaves was reduced in the K+ in channel depressor lines. Comparisons of guard cell K+ in current magnitudes among four different transgenic lines with different K+ in current magnitudes show the range of activities of K+ in channels required for guard cell K+ uptake during light-induced stomatal opening.
Phosphoenolpyruvate Carboxykinase Assayed at Physiological Concentrations of Metal Ions Has a High Affinity for CO2
Authors: Chen Zhi-Hui , Walker Robert P. , Acheson Richard M. , Leegood Richard C. 
Published: November 2008

Abstract
The effect of Mn2+/Mg2+ concentration on the activity of intact, homogeneous phosphoenolpyruvate carboxykinase (PEPCK) from leaves of the C4 grass, Guinea grass (Panicum maximum), have been investigated. Assay conditions were optimized so that PEPCK activity could be measured at concentrations of Mn2+/Mg2+ similar to those found in the cytosol (low micromolar Mn2+ and millimolar Mg2+). PEPCK activity was totally dependent on Mn2+ and was activated at low micromolar concentrations of Mn2+ by millimolar concentrations of Mg2+. Therefore, at physiological concentrations of Mn2+, PEPCK has a requirement for Mg2+. Assay at physiological concentrations of Mn2+/Mg2+ led to a marked decrease in its affinity for ATP and a 13-fold increase in its affinity for CO2. The K m(CO2) was further decreased by assay at physiological ATP to ADP ratios, reaching values as low as 20 μmCO2, comparable with the K m(CO2) of ribulose 1,5-bisphosphate carboxylase-oxygenase. This means that PEPCK will catalyze a reversible reaction and that it could operate as a carboxylase in vivo, a feature that could be particularly important in algal CO2-concentrating systems.
Antisense Inhibition of Threonine Synthase Leads to High Methionine Content in Transgenic Potato Plants
Authors: Zeh Michaela , Casazza Anna Paola , Kreft Oliver , Roessner Ute , Bieberich Katrin , Willmitzer Lothar , Hoefgen Rainer , Hesse Holger 
Published: November 2008

Abstract
Methionine (Met) and threonine (Thr) are members of the aspartate family of amino acids. In plants, their biosynthetic pathways diverge at the level of O-phosphohomo-serine (Ser). The enzymes cystathionine gamma-synthase and Thr synthase (TS) compete for the common substrate O-phosphohomo-Ser with the notable feature that plant TS is activated through S-adenosyl-Met, a metabolite derived from Met. To investigate the regulation of this branch point, we engineered TS antisense potato (Solanum tuberosum cv Désirée) plants using the constitutive cauliflower mosaic virus 35S promoter. In leaf tissues, these transgenics exhibit a reduction of TS activity down to 6% of wild-type levels. Thr levels are reduced to 45% wild-type controls, whereas Met levels increase up to 239-fold depending on the transgenic line and environmental conditions. Increased levels of homo-Ser and homo-cysteine indicate increased carbon allocation into the aspartate pathway. In contrast to findings in Arabidopsis, increased Met content has no detectable effect on mRNA or protein levels or on the enzymatic activity of cystathionine gamma-synthase in potato. Tubers of TS antisense potato plants contain a Met level increased by a factor of 30 and no reduction in Thr. These plants offer a major biotechnological advance toward the development of crop plants with improved nutritional quality.
A Novel Phospholipase D of Arabidopsis That Is Activated by Oleic Acid and Associated with the Plasma Membrane
Authors: Wang Cunxi , Wang Xuemin 
Published: November 2008

AbstractOleate-dependent phospholipase D (PLD; EC 3.1.4.4) has been reported in animal systems, but its molecular nature is unkown. Multiple PLDs have been characterized in plants, but none of the previously cloned PLDs exhibits the oleate-activated activity. Here, we describe the biochemical and molecular identification and characterization of an oleate-activated PLD in Arabidopsis. This PLD, designated PLDδ, was associated tightly with the plasma membrane, and its level of expression was higher in old leaves, stems, flowers, and roots than in young leaves and siliques. A cDNA encoding the oleate-activated PLD was identified, and catalytically active PLDδ was expressed from its cDNA inEscherichia coli. PLDδ was activated by free oleic acid in a dose-dependent manner, with the optimal concentration being 0.5 mm. Other unsaturated fatty acids, linoleic and linolenic acids, were less effective than oleic acid, whereas the saturated fatty acids, stearic and palmitic acids, were totally ineffective. Phosphatidylinositol 4,5-bisphosphate stimulated PLDδ to a lesser extent than oleate. Mutation at arginine (Arg)-611 led to a differential loss of the phosphatidylinositol 4,5-bisphosphate-stimulated activity of PLDδ, indicating that separate sites mediate the oleate regulation of PLDδ. Oleate stimulated PLDδ's binding to phosphatidylcholine. Mutation at Arg-399 resulted in a decrease in oleate binding by PLDδ and a loss of PLDδ activity. However, this mutation bound similar levels of phosphatidylcholine as wild type, suggesting that Arg-399 is not required for PC binding. These results provide the molecular information on oleate-activated PLD and also suggest a mechanism for the oleate stimulation of this enzyme.
Distinct But Conserved Functions for Two Chloroplastic NADP-Malic Enzyme Isoforms in C3 and C4 Flaveria Species
Authors: Lai Lien B. , Wang Lin , Nelson Timothy M. 
Published: November 2008

Abstract
In the most common C4 pathway for carbon fixation, an NADP-malic enzyme (NADP-ME) decarboxylates malate in the chloroplasts of bundle sheath cells. Isoforms of plastidic NADP-ME are encoded by two genes in all species of Flaveria, including C3, C3-C4 intermediate, and C4 types. However, only one of these genes,ChlMe1, encodes the enzyme that functions in the C4 pathway. We compared the expression patterns of theChlMe1 and ChlMe2 genes in developing leaves of Flaveria pringlei (C3) andFlaveria trinervia (C4) and in transgenicFlaveria bidentis (C4).ChlMe1 expression in C4 species increases in leaves with high C4 pathway activity. In the C3species F. pringlei, ChlMe1 expression is transient and limited to early leaf development. In contrast,ChlMe2 is expressed in C3 and C4species concurrent with stages in chloroplast biogenesis. Because previous studies suggest that NADP-ME activities generally reflect the level of its mRNA abundance, we discuss possible roles ofChlMe1 and ChlMe2 based on these expression patterns.