bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spatial Imaging, Speciation, and Quantification of Selenium in the Hyperaccumulator PlantsAstragalus bisulcatusandStanleya pinnata
Authors: Freeman John L. , Zhang Li Hong , Marcus Matthew A. , Fakra Sirine , McGrath Steve P. , Pilon-Smits Elizabeth A.H. 
Published: August 2006

AbstractAstragalus bisulcatus and Stanleya pinnata hyperaccumulate selenium (Se) up to 1% of plant dry weight. In the field, Se was mostly present in the young leaves and reproductive tissues of both hyperaccumulators. Microfocused scanning x-ray fluorescence mapping revealed that Se was hyperaccumulated in trichomes in young leaves of A. bisulcatus. None of 10 other elements tested were accumulated in trichomes. Micro x-ray absorption spectroscopy and liquid chromatography-mass spectrometry showed that Se in trichomes was present in the organic forms methylselenocysteine (MeSeCys; 53%) and γ-glutamyl-MeSeCys (47%). In the young leaf itself, there was 30% inorganic Se (selenate and selenite) in addition to 70% MeSeCys. In young S. pinnata leaves, Se was highly concentrated near the leaf edge and surface in globular structures that were shown by energy-dispersive x-ray microanalysis to be mainly in epidermal cells. Liquid chromatography-mass spectrometry revealed both MeSeCys (88%) and selenocystathionine (12%) inside leaf edges. In contrast, both the Se accumulator Brassica juncea and the nonaccumulator Arabidopsis thaliana accumulated Se in their leaf vascular tissues and mesophyll cells. Se in hyperaccumulators appears to be mobile in both the xylem and phloem because Se-treated S. pinnata was found to be highly toxic to phloem-feeding aphids, and MeSeCys was present in the vascular tissues of a S. pinnata young leaf petiole as well as in guttation fluid. The compartmentation of organic selenocompounds in specific storage areas in the plant periphery appears to be a unique property of Se hyperaccumulators. The high concentration of Se in the plant periphery may contribute to Se tolerance and may also serve as an elemental plant defense mechanism.
Computational Estimation and Experimental Verification of Off-Target Silencing during Posttranscriptional Gene Silencing in Plants
Authors: Xu Ping , Zhang Yuanji , Kang Li , Roossinck Marilyn J. , Mysore Kirankumar S. 
Published: August 2006

Abstract
Successful application of posttranscriptional gene silencing (PTGS) for gene function study in both plants and animals depends on high target specificity and silencing efficiency. By computational analysis with genome and/or transcriptome sequences of 25 plant species, we predicted that about 50% to 70% of gene transcripts in plants have potential off-targets when used for PTGS that could obscure experimental results. We have developed a publicly available Web-based computational tool called siRNA Scan to identify potential off-targets during PTGS. Some of the potential off-targets obtained from this tool were tested by measuring the amount of off-target transcripts using quantitative reverse transcription-PCR. Up to 50% of the predicted off-target genes tested in plants were actually silenced when tested experimentally. Our results suggest that a high risk of off-target gene silencing exists during PTGS in plants. Our siRNA Scan tool is useful to design better constructs for PTGS by minimizing off-target gene silencing in both plants and animals.
Self-Compatibility of Two Apricot Selections Is Associated with Two Pollen-Part Mutations of Different Nature
Authors: Vilanova Santiago , Badenes María Luisa , Burgos Lorenzo , Martínez-Calvo José , Llácer Gerardo , Romero Carlos 
Published: August 2006

AbstractLoss of pollen-S function in Prunus self-compatible mutants has recently been associated with deletions or insertions in S-haplotype-specific F-box (SFB) genes. We have studied two self-compatible cultivars of apricot (Prunus armeniaca), Currot (S C S C) and Canino (S 2 S C), sharing the naturally occurring self-compatible (S C)-haplotype. Sequence analysis showed that whereas the S C-RNase is unaltered, a 358-bp insertion is found in the SFB C gene, resulting in the expression of a truncated protein. The alteration of this gene is associated with self-incompatibility (SI) breakdown, supporting previous evidence that points to SFB being the pollen-S gene of the Prunus SI S-locus. On the other hand, PCR analysis of progenies derived from Canino showed that pollen grains carrying the S 2-haplotype were also able to overcome the incompatibility barrier. However, alterations in the SFB 2 gene or evidence of pollen-S duplications were not detected. A new class of F-box genes encoding a previously uncharacterized protein with high sequence similarity (approximately 62%) to Prunus SFB proteins was identified in this work, but the available data rules them out of producing S-heteroallelic pollen and thus the cause of the pollen-part mutation. These results suggest that cv Canino has an additional mutation, not linked to the S-locus, which causes a loss of pollen-S activity when present in pollen. As a whole, these findings support the proposal that the S-locus products besides other S-locus independent factors are required for gametophytic SI in Prunus.
Detection and Quantification of Unbound Phytochelatin 2 in Plant Extracts ofBrassica napusGrown with Different Levels of Mercury
Authors: Iglesia-Turiño Santiago , Febrero Anna , Jauregui Olga , Caldelas Cristina , Araus Jose Luis , Bort Jordi 
Published: August 2006

AbstractThe mercury (Hg) accumulation mechanism was studied in rape (Brassica napus) plants grown under a Hg concentration gradient (0 μ m–1,000 μ m). Hg mainly accumulated in roots. Therefore, the presence of phytochelatins (PCs) was studied in the roots of the plants. The high stability of the PC-Hg multicomplexes (mPC-nHg) seems to be the main reason for the lack of previous Hg-PC characterization studies. We propose a modification of the method to detect and quantify unbound PC of Hg in plant extracts via high-performance liquid chromatography coupled to electrospray tandem mass spectrometry and inductively coupled plasma mass spectrometry in parallel. We separated the PC from the Hg by adding the chelating agent sodium 2,3-dimercaptopropanesulfonate monohydrate. We only detected the presence of PC after the addition of the chelating agent. Some multicomplexes mPC-nHg could be formed but, due to their large sizes, could not be detected. In this study, only PC2 was observed in plant samples. Hg accumulation was correlated with PC2 concentration (r 2 = 0.98).
SUMO-Conjugating and SUMO-Deconjugating Enzymes from Arabidopsis
Authors: Colby Thomas , Matthäi Anett , Boeckelmann Astrid , Stuible Hans-Peter 
Published: August 2006

Abstract
Posttranslational protein modification by the small ubiquitin-like modifier (SUMO) is a highly dynamic and reversible process. To analyze the substrate specificity of SUMO-conjugating and -deconjugating enzymes from Arabidopsis (Arabidopsis thaliana), we reconstituted its SUMOylation cascade in vitro and tested the capacity of this system to conjugate the Arabidopsis SUMO isoforms AtSUMO1, 2, and 3 to the model substrate ScPCNA from yeast (Saccharomyces cerevisiae). This protein contains two in vivo SUMOylated lysine residues, namely K127 and K164. Under in vitro conditions, the Arabidopsis SUMOylation system specifically conjugates all tested SUMO isoforms to lysine-127, but not to lysine-164, of ScPCNA. The SUMO isoforms AtSUMO1 and AtSUMO2, but not AtSUMO3, were found to form polymeric chains on ScPCNA due to a self-SUMOylation process. In a complementary approach, we analyzed both the SUMO isopeptidase activity and the pre-SUMO-processing capacity of the putative Arabidopsis SUMO proteases At1g60220, At1g10570, and At5g60190 using the known SUMO isopeptidases ScULP1, XopD, and ESD4 (At4g15880) as reference enzymes. Interestingly, At5g60190 exhibits no SUMO protease activity but processes the pre-form of Arabidopsis Rub1. The other five enzymes represent SUMO isopeptidases that show different substrate preferences. All these enzymes cleave AtSUMO1 and AtSUMO2 conjugates of ScPCNA, whereas only the putative bacterial virulence factor XopD is able to release AtSUMO3. In addition, all five enzymes cleave pre-AtSUMO1 and pre-AtSUMO2 peptides, but none of the proteins efficiently produce mature AtSUMO3 or AtSUMO5 molecules from their precursors.
A Heteromeric RNA-Binding Protein Is Involved in Maintaining Acrophase and Period of the Circadian Clock
Authors: Iliev Dobromir , Voytsekh Olga , Schmidt Eva-Maria , Fiedler Monika , Nykytenko Alla , Mittag Maria 
Published: August 2006

Abstract
The RNA-binding protein CHLAMY1 from the green alga Chlamydomonas reinhardtii consists of two subunits. One (named C1) contains three lysine homology motifs and the other (named C3) has three RNA recognition motifs. CHLAMY1 binds specifically to uridine-guanine-repeat sequences and its circadian-binding activity is controlled at the posttranslational level, presumably by time-dependent formation of protein complexes consisting of C1 and C3 or C1 alone. Here we have characterized the role of the two subunits within the circadian system by measurements of a circadian rhythm of phototaxis in strains where C1 or C3 are either up- or down-regulated. Further, we have measured the rhythm of nitrite reductase activity in strains with reduced levels of C1 or C3. In case of changes in the C3 level (both increases and decreases), the acrophase of the phototaxis rhythm and of the nitrite reductase rhythm (C3 decrease) was shifted by several hours from subjective day (maximum in wild-type cells) back towards the night. In contrast, both silencing and overexpression of C1 resulted in disturbed circadian rhythms and arrhythmicity. Interestingly, the expression of C1 is interconnected with that of C3. Our data suggest that CHLAMY1 is involved in the control of the phase angle and period of the circadian clock in C. reinhardtii.
Mutations in an Auxin Receptor Homolog AFB5 and in SGT1b Confer Resistance to Synthetic Picolinate Auxins and Not to 2,4-Dichlorophenoxyacetic Acid or Indole-3-Acetic Acid in Arabidopsis
Authors: Walsh Terence A. , Neal Roben , Merlo Ann Owens , Honma Mary , Hicks Glenn R. , Wolff Karen , Matsumura Wendy , Davies John P. 
Published: August 2006

Abstract
Although a wide range of structurally diverse small molecules can act as auxins, it is unclear whether all of these compounds act via the same mechanisms that have been characterized for 2,4-dichlorophenoxyacetic acid (2,4-D) and indole-3-acetic acid (IAA). To address this question, we used a novel member of the picolinate class of synthetic auxins that is structurally distinct from 2,4-D to screen for Arabidopsis (Arabidopsis thaliana) mutants that show chemically selective auxin resistance. We identified seven alleles at two distinct genetic loci that conferred significant resistance to picolinate auxins such as picloram, yet had minimal cross-resistance to 2,4-D or IAA. Double mutants had the same level and selectivity of resistance as single mutants. The sites of the mutations were identified by positional mapping as At4g11260 and At5g49980. At5g49980 is previously uncharacterized and encodes auxin signaling F-box protein 5, one of five homologs of TIR1 in the Arabidopsis genome. TIR1 is the recognition component of the Skp1-cullin-F-box complex associated with the ubiquitin-proteasome pathway involved in auxin signaling and has recently been shown to be a receptor for IAA and 2,4-D. At4g11260 encodes the tetratricopeptide protein SGT1b that has also been associated with Skp1-cullin-F-box-mediated ubiquitination in auxin signaling and other pathways. Complementation of mutant lines with their corresponding wild-type genes restored picolinate auxin sensitivity. These results show that chemical specificity in auxin signaling can be conferred by upstream components of the auxin response pathway. They also demonstrate the utility of genetic screens using structurally diverse chemistries to uncover novel pathway components.
Mitochondria-Associated Hexokinases Play a Role in the Control of Programmed Cell Death inNicotiana benthamiana
Authors: Kim Moonil , Lim Jeong-Hwa , Ahn Chang Sook , Park Kyoungsook , Kim Gyung Tae , Kim Woo Taek , Pai Hyun-Sook 
Published: August 2006

AbstractRecent findings suggest a pivotal role for mitochondria-associated hexokinase in the regulation of apoptosis in animal cells. In this study, virus-induced gene silencing (VIGS) of a hexokinase-encoding Hxk1 caused necrotic lesions on leaves, abnormal leaf morphology, and retarded plant growth in Nicotiana benthamiana. Hxk1 was associated with the mitochondria, and this association required the N-terminal membrane anchor. VIGS of Hxk1 reduced the cellular glucose-phosphorylating activity to ∼31% of control levels without changing the fructose-phosphorylating activity and did not alter hexose phosphate content severely. The affected cells showed programmed cell death (PCD) morphological markers, including nuclear condensation and DNA fragmentation. Similar to animal cell apoptosis, cytochrome c was released into the cytosol and caspase-9– and caspase-3–like proteolytic activities were strongly induced. Furthermore, based on flow cytometry, Arabidopsis thaliana plants overexpressing Arabidopsis HXK1 and HXK2, both of which are predominantly associated with mitochondria, exhibited enhanced resistance to H2O2- and α-picolinic acid–induced PCD. Finally, the addition of recombinant Hxk1 to mitochondria-enriched fractions prevented H2O2/clotrimazole-induced cytochrome c release and loss of mitochondrial membrane potential. Together, these results show that hexokinase critically regulates the execution of PCD in plant cells, suggesting a link between glucose metabolism and apoptosis.
GA4 Is the Active Gibberellin in the Regulation ofLEAFYTranscription andArabidopsisFloral Initiation
Authors: Eriksson Sven , Böhlenius Henrik , Moritz Thomas , Nilsson Ove 
Published: August 2006

AbstractFlower initiation in Arabidopsis thaliana under noninductive short-day conditions is dependent on the biosynthesis of the plant hormone gibberellin (GA). This dependency can be explained, at least partly, by GA regulation of the flower meristem identity gene LEAFY (LFY) and the flowering time gene SUPPRESSOR OF CONSTANS1. Although it is well established that GA4 is the active GA in the regulation of Arabidopsis shoot elongation, the identity of the GA responsible for the regulation of Arabidopsis flowering has not been established. Through a combination of GA quantifications and sensitivity assays, we show that GA4 is the active GA in the regulation of LFY transcription and Arabidopsis flowering time under short-day conditions. The levels of GA4 and sucrose increase dramatically in the shoot apex shortly before floral initiation, and the regulation of genes involved in GA metabolism suggests that this increase is possibly due to transport of GAs and sucrose from outside sources to the shoot apex. Our results demonstrate that in the dicot Arabidopsis, in contrast with the monocot Lolium temulentum, GA4 is the active GA in the regulation of both shoot elongation and flower initiation.
The Clp1 Protein Is Required for Clamp Formation and Pathogenic Development ofUstilago maydis
Authors: Scherer Mario , Heimel Kai , Starke Verena , Kämper Jörg 
Published: August 2006

AbstractIn the phytopathogenic fungus Ustilago maydis, pathogenic development is controlled by a heterodimer of the two homeodomain proteins bE and bW, encoded by the b-mating-type locus. We have identified a b-dependently induced gene, clampless1 (clp1), that is required for the proliferation of dikaryotic filaments in planta. We show that U. maydis hyphae develop structures functionally equivalent to clamp cells that participate in the distribution of nuclei during cell division. In clp1 mutant strains, dikaryotic filaments penetrate the plant cuticle, but development is stalled before the first mitotic division, and the clamp-like structures are not formed. Although clp1 is immediately activated upon b-induction on the transcriptional level, nuclear-localized Clp1 protein is first observed at the stage of plant penetration prior to the first cell division. Induced expression of clp1 strongly interferes with b-dependent gene regulation and blocks b-dependent filament formation and b-dependent cell cycle arrest. We speculate that the Clp1 protein inhibits the activity of the bE/bW heterodimer to facilitate the cell cycle progression during hyphal growth.
Tung Tree DGAT1 and DGAT2 Have Nonredundant Functions in Triacylglycerol Biosynthesis and Are Localized to Different Subdomains of the Endoplasmic Reticulum
Authors: Shockey Jay M. , Gidda Satinder K. , Chapital Dorselyn C. , Kuan Jui-Chang , Dhanoa Preetinder K. , Bland John M. , Rothstein Steven J. , Mullen Robert T. , Dyer John M. 
Published: August 2006

Abstract
Seeds of the tung tree (Vernicia fordii) produce large quantities of triacylglycerols (TAGs) containing ∼80% eleostearic acid, an unusual conjugated fatty acid. We present a comparative analysis of the genetic, functional, and cellular properties of tung type 1 and type 2 diacylglycerol acyltransferases (DGAT1 and DGAT2), two unrelated enzymes that catalyze the committed step in TAG biosynthesis. We show that both enzymes are encoded by single genes and that DGAT1 is expressed at similar levels in various organs, whereas DGAT2 is strongly induced in developing seeds at the onset of oil biosynthesis. Expression of DGAT1 and DGAT2 in yeast produced different types and proportions of TAGs containing eleostearic acid, with DGAT2 possessing an enhanced propensity for the synthesis of trieleostearin, the main component of tung oil. Both DGAT1 and DGAT2 are located in distinct, dynamic regions of the endoplasmic reticulum (ER), and surprisingly, these regions do not overlap. Furthermore, although both DGAT1 and DGAT2 contain a similar C-terminal pentapeptide ER retrieval motif, this motif alone is not sufficient for their localization to specific regions of the ER. These data suggest that DGAT1 and DGAT2 have nonredundant functions in plants and that the production of storage oils, including those containing unusual fatty acids, occurs in distinct ER subdomains.
Oscillatory Increases in Alkalinity Anticipate Growth and May Regulate Actin Dynamics in Pollen Tubes of Lily
Authors: Lovy-Wheeler Alenka , Kunkel Joseph G. , Allwood Ellen G. , Hussey Patrick J. , Hepler Peter K. 
Published: August 2006

AbstractLily (Lilium formosanum or Lilium longiflorum) pollen tubes, microinjected with a low concentration of the pH-sensitive dye bis-carboxyethyl carboxyfluorescein dextran, show oscillating pH changes in their apical domain relative to growth. An increase in pH in the apex precedes the fastest growth velocities, whereas a decline follows growth, suggesting a possible relationship between alkalinity and cell extension. A target for pH may be the actin cytoskeleton, because the apical cortical actin fringe resides in the same region as the alkaline band in lily pollen tubes and elongation requires actin polymerization. A pH-sensitive actin binding protein, actin-depolymerizing factor (ADF), together with actin-interacting protein (AIP) localize to the cortical actin fringe region. Modifying intracellular pH leads to reorganization of the actin cytoskeleton, especially in the apical domain. Acidification causes actin filament destabilization and inhibits growth by 80%. Upon complete growth inhibition, the actin fringe is the first actin cytoskeleton component to disappear. We propose that during normal growth, the pH increase in the alkaline band stimulates the fragmenting activity of ADF/AIP, which in turn generates more sites for actin polymerization. Increased actin polymerization supports faster growth rates and a proton influx, which inactivates ADF/AIP, decreases actin polymerization, and retards growth. As pH stabilizes and increases, the activity of ADF/AIP again increases, repeating the cycle of events.
Uncertainties in Canning Process Calculations
Authors: HICKS E. W. 
Published: August 2006

SUMMARYThe nature of safety factors in canning processes and the uncertainties in calculating lethal values are discussed. The nature, extent, and consequences of these uncertainties are examined. Uncertainties in both the thermal data, obtained from heat penetration measurements, and the bacteriological data contribute significantly to the over‐all uncertainty, that in bacteriological data generally being greater. Although experimental error may be large, most of the uncertainty in thermal data is due to real variations from can to can. These uncertainties should be taken into account whenever calculations are made in canning processes, particularly in deciding the safety factor to employ in any particular case.
The Volatile Flavor Substances of Celery
Authors: GOLD HARVEY J. , WILSON CHARLES W. 
Published: August 2006

SUMMARYThe isolation and identification of the volatile compounds of celery are described. Non‐linear temperature‐programmed gas chromatography was found to give resolution superior to that of either isothermal operation or linear temperature programming. The identification of 24 compounds from celery is reported. Of the 38 compounds thus far identified from celery distillates, the following six compounds are primarily responsible for the characteristic flavor and aroma of celery: 3‐isobutylidene‐3a,4‐dihydrophthalide; 3‐isovalidene‐ 3a,4‐dihydrophthalide; 3‐isobutylidene phthalide; 3‐isovalidene phthalide; cis‐3‐hexen‐l‐yl pyruvate; and diacetyl. The phthalide derivatives are also implicated in the occurrence of certain celery off‐flavors reported in the literature.
Nutrient Content of Morel Mushroom Mycelium: Amino Acid Composition of the Protein
Authors: LITCHFTELD J. H. , VELY V. G. , OVERBECK R. C. 
Published: August 2006

SUMMARYMycelia of three species of morel mushrooms, Morchella crassipes, M. esculenta, and M. hortensis, were grown in submerged culture in a glucose‐ammonium phosphate‐corn steep liquor medium. The dried mycelia were subjected to proximate analyses and amino acid determinations. A commercial morel mushroom powder was also analyzed for the same constituents. The dry samples contained 22.8–51.0% protein and 2.18–7.55% fat, depending upon the species. Amino aeid contents were similar to those reported in the literature for other fungi.
Polyphenoloxidase in Bartlett Pearsa
Authors: TATE J. N. , LUH B. S. , YORK G. K. 
Published: August 2006

SUMMARYThe characteristics of polyphenoloxidase in Bartlett pears were investigated. In a citrate‐phosphate buffer containing 0.03M catechol as the substrate, activity of the pear polyphenoloxidase was greatest in the pH range 5.8‐6.4, being optimum at pH 6.2. The Michaelis constant of the enzyme was 0.048M at pH 6.2 in a citrate‐phosphate buffer. It was active only on phenolic compounds having an ortho‐diphenolic configuration. Neither the meta‐ nor para‐dihydroxy phenolic compounds nor phenol was attacked. The energy of activation for pear polyphenoloxidase on catechol was 4.9 kcal per mole. Oxygen was necessary for browning of catechol to take place in the presence of pear polyphenoloxidase, and the activity was greatly decreased when the concentration of oxygen in the reaction mixture was lowered. Diethyldithiocarbamate, a copper‐chelating agent, and phloroglucinol, a competitive inhibitor, reduced browning markedly, but ascorbic acid was most effective of all. It was noted that ascorbic acid acts as an antioxidant rather than as a true enzyme inhibitor. Iodoacet‐amide, a sulfhydryl inhibitor, had no effect on rate of browning. Methods for preventing brown discoloration in canned pears are discussed.