bluuebunny/crossref_metadata_2025_split huggingface dataset:
RNase Activity Prevents the Growth of a Fungal Pathogen in Tobacco Leaves and Increases upon Induction of Systemic Acquired Resistance with Elicitin
Authors: Galiana E. , Bonnet P. , Conrod S. , Keller H. , Panabieres F. , Ponchet M. , Poupet A. , Ricci P. 
Published: July 2002

Abstract
The hypersensitive response and systemic acquired resistance (SAR) can be induced in tobacco (Nicotiana tabacum L.) plants by cryptogein, an elicitin secreted by Phytophthora cryptogea. Stem application of cryptogein leads to the establishment of acquired resistance to subsequent leaf infection with Phytophthora parasitica var nicotianae, the agent of the tobacco black shank disease. We have studied early events that occur after the infection and show here that a tobacco gene encoding the extracellular S-like RNase NE is expressed in response to inoculation with the pathogenic fungus. Upon induction of SAR with cryptogein, the accumulation of NE transcripts coincided with a rapid induction of RNase activity and with the increase in the activity of at least two different extracellular RNases. Moreover, exogenous application of RNase activity in the extracellular space of leaves led to a reduction of the fungus development by up to 90%, independently of any cryptogein treatment and in the absence of apparent necrosis. These results indicate that the up-regulation of apoplastic RNase activity after inoculation could contribute to the control of fungal invasion in plants induced to SAR with cryptogein.
Tomato Fructokinases Exhibit Differential Expression and Substrate Regulation1
Authors: Kanayama Yoshinori , Granot David , Dai Nir , Petreikov Marina , Schaffer Arthur , Powell Ann , Bennett Alan B. 
Published: July 2002

AbstractTwo divergent genes encoding fructokinase, Frk1 andFrk2, have been previously shown to be expressed in tomato (Lycopersicon esculentum L.) and have now been further characterized with regard to their spatial expression and the enzymic properties of the encoded proteins. Frk1 andFrk2 mRNA levels were coordinately induced by exogenous sugar, indicating that both belong to the growing class of sugar-regulated genes. However, in situ hybridization indicated thatFrk1 and Frk2 were expressed in a spatially distinct manner, with Frk2 mRNA primarily localized in cells of the fruit pericarp, which store starch, andFrk1 mRNA distributed ubiquitously in pericarp tissue. To evaluate the biochemical characteristics of the products of theFrk1 and Frk2 genes, each cDNA was expressed in a mutant yeast (Saccharomyces cerevisiae) line defective in hexose phosphorylation and unable to grow on glucose or fructose (Fru). Both Frk1 and Frk2 proteins expressed in yeast conferred the ability to grow on Fru and exhibited fructokinase activity in vitro. Although both Frk1 and Frk2 both utilized Fru as a substrate, only Frk2 activity was inhibited at high Fru concentrations. These results indicate that Frk2 can be distinguished from Frk1 by its sensitivity to substrate inhibition and by its temporal and spatial pattern of expression, which suggests that it plays a primary role in plant cells specialized for starch storage.
Characterization of SU1 Isoamylase, a Determinant of Storage Starch Structure in Maize1
Authors: Rahman Afroza , Wong Kit-sum , Jane Jay-lin , Myers Alan M. , James Martha G. 
Published: July 2002

AbstractFunction of the maize (Zea mays) gene sugary1 (su1) is required for normal starch biosynthesis in endosperm. Homozygoussu1- mutant endosperms accumulate a highly branched polysaccharide, phytoglycogen, at the expense of the normal branched component of starch, amylopectin. These data suggest that both branched polysaccharides share a common precursor, and that the product of thesu1 gene, designated SU1, participates in kernel starch biosynthesis. SU1 is similar in sequence to α-(1→6) glucan hydrolases (starch-debranching enzymes [DBEs]). Specific antibodies were produced and used to demonstrate that SU1 is a 79-kD protein that accumulates in endosperm coincident with the time of starch biosynthesis. Nearly full-length SU1 was expressed inEscherichia coli and purified to apparent homogeneity. Two biochemical assays confirmed that SU1 hydrolyzes α-(1→6) linkages in branched polysaccharides. Determination of the specific activity of SU1 toward various substrates enabled its classification as an isoamylase. Previous studies had shown, however, thatsu1- mutant endosperms are deficient in a different type of DBE, a pullulanase (or R enzyme). Immunoblot analyses revealed that both SU1 and a protein detected by antibodies specific for the rice (Oryza sativa) R enzyme are missing fromsu1- mutant kernels. These data support the hypothesis that DBEs are directly involved in starch biosynthesis.
Flavonoids Promote Haustoria Formation in the Root ParasiteTriphysaria versicolor1
Authors: Albrecht Huguette , Yoder John I. , Phillips Donald A. 
Published: July 2002

Abstract
Parasitic plants in the Scrophulariaceae develop infective root structures called haustoria in response to chemical signals released from host-plant roots. This study used a simple in vitro assay to characterize natural and synthetic molecules that induce haustoria in the facultative parasiteTriphysaria versicolor. Several phenolic acids, flavonoids, and the quinone 2,6-dimethoxy-p-benzoquinone induced haustoria in T. versicolor root tips within hours after treatment. The concentration at which different molecules were active varied widely, the most active being 2,6-dimethoxy-p-benzoquinone and the anthocyanidin peonidin. Maize (Zea mays) seeds are rich sources of molecules that induce T. versicolor haustoria in vitro, and chromatographic analyses indicated that the active molecules present in maize-seed rinses include anthocyanins, other flavonoids, and simple phenolics. The presence of different classes of inducing molecules in seed rinses was substantiated by the observation that maize kernels deficient in chalcone synthase, a key enzyme in flavonoid biosynthesis, released haustoria-inducing molecules, although at reduced levels compared with wild-type kernels. We discuss these results in light of existing models for host perception in the related parasitic plant Striga.
Curvature Induced by Amyloplast Magnetophoresis in Protonemata of the Moss Ceratodon purpureus1
Authors: Kuznetsov Oleg A. , Schwuchow Jochen , Sack Fred D. , Hasenstein Karl H. 
Published: July 2002

Abstract
After gravistimulation ofCeratodon purpureus (Hedw.) Brid. protonemata in the dark, amyloplast sedimentation was followed by upward curvature in the wild-type (WT) and downward curvature in the wwr mutant (wrongwayresponse). We used ponderomotive forces induced by high-gradient magnetic fields (HGMF) to simulate the effect of gravity and displace the presumptive statoliths. The field was applied by placing protonemata either between two permanent magnets at the edge of the gap, close to the edge of a magnetized ferromagnetic wedge, or close to a small (&lt;1 mm) permanent magnet. Continuous application of an HGMF in all three configurations resulted in plastid displacement and induced curvature in tip cells of WT and wwr protonemata. WT cells curved toward the HGMF, and wwr cells curved away from the HGMF, comparable to gravitropism. Plastids isolated from protonemal cultures had densities ranging from 1.24 to 1.38 g cm−3. Plastid density was similar for both genotypes, but the mutant contained larger plastids than the WT. The size difference might explain the stronger response of the wwr protonemata to the HGMF. Our data support the plastid-based theory of gravitropic sensing and suggest that HGMF-induced ponderomotive forces can substitute for gravity.
The MADS-Domain Protein AGAMOUS-Like 15 Accumulates in Embryonic Tissues with Diverse Origins1
Authors: Perry Sharyn E. , Lehti Melissa D. , Fernandez Donna E. 
Published: July 2002

Abstract
AGL15 (AGAMOUS-like 15), a member of the MADS-domain family of regulatory factors, accumulates preferentially in the organs and tissues derived from double fertilization in flowering plants (i.e. the embryo, suspensor, and endosperm). The developmental role of AGL15 is still undefined. If it is involved in embryogenesis rather than some other aspect of seed biology, then AGL15 protein should accumulate whenever development proceeds in the embryonic mode, regardless of the origin of those embryos or their developmental context. To test this, we used AGL15-specific antibodies to analyze apomictic embryogenesis in dandelion (Taraxacum officinale), microspore embryogenesis in oilseed rape (Brassica napus), and somatic embryogenesis in alfalfa (Medicago sativa). In every case, AGL15 accumulated to relatively high levels in the nuclei of the embryos. AGL15 also accumulated in cotyledon-like organs produced by thextc2(extracotyledon2) mutant of Arabidopsis and during precocious germination in oilseed rape. Furthermore, the subcellular localization of AGL15 appeared to be developmentally regulated in all embryogenic situations. AGL15 was initially present in the cytoplasm of cells and became nuclear localized before or soon after embryogenic cell divisions began. These results support the hypothesis that AGL15 participates in the regulation of programs active during the early stages of embryo development.
Cloning and Characterization of the DihydrolipoamideS-Acetyltransferase Subunit of the Plastid Pyruvate Dehydrogenase Complex (E2) from Arabidopsis1
Authors: Mooney Brian P. , Miernyk Jan A. , Randall Douglas D. 
Published: July 2002

AbstractAn Arabidopsis cDNA encoding the dihydrolipoamide S-acetyltransferase subunit of the plastid pyruvate dehydrogenase complex (E2) was isolated from a λPRL2 library. The cDNA is 1709 bp in length, with a continuous open reading frame of 1440 bp encoding a protein of 480 amino acids with a calculated molecular mass of 50,079 D. Southern analysis suggests that a single gene encodes plastid E2. The amino acid sequence has characteristic features of an acetyltransferase, namely, distinct lipoyl, subunit-binding, and catalytic domains, although it is unusual in having only a single lipoyl domain. The in vitro synthesized plastid E2 precursor protein has a relative molecular weight of 67,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Upon incubation of the precursor with pea (Pisum sativum) chloroplasts, it was imported and processed to a mature-sized relative molecular weight of 60,000. The imported protein was located in the chloroplast stroma, associated with the endogenous pyruvate dehydrogenase. Catalytically active recombinant plastid E2 was purified as a glutathione S-transferase fusion protein. Analysis of plastid E2 mRNA by reverse transcriptase-polymerase chain reaction showed highest expression in flowers, followed by leaves, siliques, and roots. The results of immunoblot analysis indicate that protein expression was similar in roots and flowers, less similar in leaves, and even less similar in siliques. This is the first report, to our knowledge, describing a plastid E2.
EAF1 Regulates Vegetative-Phase Change and Flowering Time in Arabidopsis1
Authors: Scott Derek B. , Jin Wei , Ledford Heidi K. , Jung Hou-Sung , Honma Mary A. 
Published: July 2002

Abstract
We have identified a new locus that regulates vegetative phase change and flowering time in Arabidopsis. An early-flowering mutant, eaf1(earlyflowering1) was isolated and characterized.eaf1 plants flowered earlier than the wild type under either short-day or long-day conditions, and showed a reduction in the juvenile and adult vegetative phases. When grown under short-day conditions, eaf1 plants were slightly pale green and had elongated petioles, phenotypes that are observed in mutants altered in either phytochrome or the gibberellin (GA) response.eaf1 seed showed increased resistance to the GA biosynthesis inhibitor paclobutrazol, suggesting that GA metabolism and/or response had been altered. Comparison of eaf1 to other early-flowering mutants revealed that eaf1 shifts to the adult phase early and flowers early, similarly to thephyB(phytochromeB) and spy(spindly) mutants. eaf1 maps to chromosome 2, but defines a locus distinct from phyB, clf(curlyleaf), and elf3(early-flowering3). These results demonstrate thateaf1 defines a new locus involved in an autonomous pathway and may affect GA regulation of flowering.
Auxin Is Required for Leaf Vein Pattern in Arabidopsis
Authors: Sieburth Leslie E. 
Published: July 2002

Abstract
To investigate possible roles of polar auxin transport in vein patterning, cotyledon and leaf vein patterns were compared for plants grown in medium containing polar auxin transport inhibitors (N-1-naphthylphthalamic acid, 9-hydroxyfluorene-9-carboxylic acid, and 2,3,5-triiodobenzoic acid) and in medium containing a less well-characterized inhibitor of auxin-mediated processes, 2-(p-chlorophynoxy)-2-methylpropionic acid. Cotyledon vein pattern was not affected by any inhibitor treatments, although vein morphology was altered. In contrast, leaf vein pattern was affected by inhibitor treatments. Growth in polar auxin transport inhibitors resulted in leaves that lacked vascular continuity through the petiole and had broad, loosely organized midveins, an increased number of secondary veins, and a dense band of misshapen tracheary elements adjacent to the leaf margin. Analysis of leaf vein pattern developmental time courses suggested that the primary vein did not develop in polar auxin transport inhibitor-grown plants, and that the broad midvein observed in these seedlings resulted from the coalescence of proximal regions of secondary veins. Possible models for leaf vein patterning that could account for these observations are discussed.
Mutation in the Threonine Synthase Gene Results in an Over-Accumulation of Soluble Methionine in Arabidopsis
Authors: Bartlem Derek , Lambein Ingrid , Okamoto Takashi , Itaya Asuka , Uda Yukie , Kijima Fumiko , Tamaki Yuko , Nambara Eiji , Naito Satoshi 
Published: July 2002

Abstract
In higher plants, O-phosphohomoserine (OPH) represents a branch point between the methionine (Met) and threonine (Thr) biosynthetic pathways. It is believed that the enzymes Thr synthase (TS) and cystathionine γ-synthase (CGS) actively compete for the OPH substrate for Thr and Met biosynthesis, respectively. We have isolated a mutant of Arabidopsis, designated mto2-1, that over-accumulates soluble Met 22-fold and contains markedly reduced levels of soluble Thr in young rosettes. The mto2-1mutant carries a single base pair mutation within the gene encoding TS, resulting in a leucine-204 to arginine change. Accumulation of TS mRNA and protein was normal in young rosettes of mto2-1, whereas functional complementation analysis of an Escherichia coli thrC mutation suggested that the ability ofmto2-1 TS to synthesize Thr is impaired. We concluded that the mutation within the TS gene is responsible for themto2-1 phenotype, resulting in decreased Thr biosynthesis and a channeling of OPH to Met biosynthesis in young rosettes. Analysis of the mto2-1 mutant suggested that, in vivo, the feedback regulation of CGS is not sufficient alone for the control of Met biosynthesis in young rosettes and is dependent on TS activity. In addition, developmental analysis of soluble Met and Thr concentrations indicated that the accumulation of these amino acids is regulated in a temporal and spatial manner.
Variation in the Oxygen Isotope Ratio of Phloem Sap Sucrose from Castor Bean. Evidence in Support of the Péclet Effect
Authors: Barbour Margaret M. , Schurr Ulrich , Henry Beverley K. , Wong S. Chin , Farquhar Graham D. 
Published: July 2002

Abstract
Theory suggests that the level of enrichment of18O above source water in plant organic material (Δ) may provide an integrative indicator of control of water loss. However, there are still gaps in our understanding of the processes affecting Δ. One such gap is the observed discrepancy between modeled enrichment of water at the sites of evaporation within the leaf and measured enrichment of the leaf water as a whole (ΔL). Farquhar and Lloyd (1993) suggested that this may be caused by a Péclet effect. It is also unclear whether organic material formed in the leaf reflects enrichment of water at the sites of evaporation within the leaf or ΔL. To investigate this question castor bean (Ricinus communis L.) leaves, still attached to the plant, were sealed into a controlled-environment gas exchange chamber and subjected to a step change in leaf-to-air vapor pressure difference. Sucrose was collected from a cut on the petiole of the leaf in the chamber under equilibrium conditions and every hour for 6 h after the change in leaf-to-air vapor pressure difference. Oxygen isotope composition of sucrose in the phloem sap (Δsuc) reflected modeled ΔL. A model is presented describing Δsuc at isotopic steady state, and accounts for 96% of variation in measured Δsuc. The data strongly support the Péclet effect theory.
Cytochrome P450-Dependent Metabolism of Oxylipins in Tomato. Cloning and Expression of Allene Oxide Synthase and Fatty Acid Hydroperoxide Lyase
Authors: Howe Gregg A. , Lee Gyu In , Itoh Aya , Li Lei , DeRocher Amy E. 
Published: July 2002

Abstract
Allene oxide synthase (AOS) and fatty acid hydroperoxide lyase (HPL) are plant-specific cytochrome P450s that commit fatty acid hydroperoxides to different branches of oxylipin metabolism. Here we report the cloning and characterization of AOS (LeAOS) and HPL (LeHPL) cDNAs from tomato (Lycopersicon esculentum). Functional expression of the cDNAs inEscherichia coli showed that LeAOS andLeHPL encode enzymes that metabolize 13- but not 9-hydroperoxide derivatives of C18 fatty acids. LeAOS was active against both 13S-hydroperoxy-9(Z),11(E),15(Z)-octadecatrienoic acid (13-HPOT) and 13S-hydroperoxy-9(Z),11(E)-octadecadienoic acid, whereas LeHPL showed a strong preference for 13-HPOT. These results suggest a role for LeAOS andLeHPL in the metabolism of 13-HPOT to jasmonic acid and hexenal/traumatin, respectively. LeAOS expression was detected in all organs of the plant. In contrast, LeHPLexpression was predominant in leaves and flowers. Damage inflicted to leaves by chewing insect larvae led to an increase in the local and systemic expression of both genes, with LeAOS showing the strongest induction. Wound-induced expression ofLeAOS also occurred in the def-1 mutant that is deficient in octadecanoid-based signaling of defensive proteinase inhibitor genes. These results demonstrate that tomato uses genetically distinct signaling pathways for the regulation of different classes of wound responsive genes.
Blue Light Activates Potassium-Efflux Channels in Flexor Cells from Samanea saman Motor Organs via Two Mechanisms
Authors: Suh SuJeong , Moran Nava , Lee Youngsook 
Published: July 2002

Abstract
Light-induced leaflet movement of Samanea samandepends on the regulation of membrane transporters in motor cells. Blue light (BL) stimulates leaflet opening by inducing K+release from the flexor motor cells. To elucidate the mechanism of K+-efflux (KD)-channel regulation by light, flexor motor cell protoplasts were patch-clamped in a cell-attached configuration during varying illumination. Depolarization elicited outward currents through single open KD channels. Changes in cell membrane potential (E M) were estimated by applying voltage ramps and tracking the change of the apparent reversal potential of KD-channel current. BL shifted E M in a positive direction (i.e. depolarized the cell) by about 10 mV. Subsequent red light pulse followed by darkness shifted E M oppositely (i.e. hyperpolarized the cell). The BL-induced shifts ofE M were not observed in cells pretreated with a hydrogen-pump inhibitor, suggesting a contribution by hydrogen-pump to the shift. BL also increased KD-channel activity in a voltage-independent manner as reflected in the increase of the mean net steady-state patch conductance at a depolarization of 40 mV relative to the apparent reversal potential (G @40). G @40increased by approximately 12 pS without a change of the single-channel conductance, possibly by increasing the probability of channel opening. Subsequent red-light and darkness reversed the change inG @40. Thus, K+ efflux, a determining factor for the cell-volume decrease of flexor cells, is regulated by BL in a dual manner via membrane potential and by an independent signaling pathway.
Modular Domain Structure of Arabidopsis COP1. Reconstitution of Activity by Fragment Complementation and Mutational Analysis of a Nuclear Localization Signal in Planta
Authors: Stacey Minviluz G. , Kopp Olga R. , Kim Tae-Houn , von Arnim Albrecht G. 
Published: July 2002

Abstract
The Arabidopsis COP1 protein functions as a developmental regulator, in part by repressing photomorphogenesis in darkness. Using complementation of a cop1 loss-of-function allele with transgenes expressing fusions of cop1 mutant proteins and β-glucuronidase, it was confirmed that COP1 consists of two modules, an amino terminal module conferring a basal function during development and a carboxyl terminal module conferring repression of photomorphogenesis. The amino-terminal zinc-binding domain of COP1 was indispensable for COP1 function. In contrast, the debilitating effects of site-directed mutations in the single nuclear localization signal of COP1 were partially compensated by high-level transgene expression. The carboxyl-terminal module of COP1, though unable to substantially ameliorate a cop1 loss-of-function allele on its own, was sufficient for conferring a light-quality-dependent hyperetiolation phenotype in the presence of wild-type COP1. Moreover, partial COP1 activity could be reconstituted in vivo from two non-covalently linked, complementary polypeptides that represent the two functional modules of COP1. Evidence is presented for efficient association of the two sub-fragments of the split COP1 protein in Arabidopsis and in a yeast two-hybrid assay.
Malate-Permeable Channels and Cation Channels Activated by Aluminum in the Apical Cells of Wheat Roots
Authors: Zhang Wen-Hao , Ryan Peter R. , Tyerman Stephen D. 
Published: July 2002

Abstract
Aluminum (Al3+)-dependent efflux of malate from root apices is a mechanism for Al3+ tolerance in wheat (Triticum aestivum). The malate anions protect the sensitive root tips by chelating the toxic Al3+ cations in the rhizosphere to form non-toxic complexes. Activation of malate-permeable channels in the plasma membrane could be critical in regulating this malate efflux. We examined this by investigating Al3+-activated channels in protoplasts from root apices of near-isogenic wheat differing in Al3+ tolerance at a single locus. Using whole-cell patch clamp we found that Al3+stimulated an electrical current carried by anion efflux across the plasma membrane in the Al3+-tolerant (ET8) and Al3+-sensitive (ES8) genotypes. This current occurred more frequently, had a greater current density, and remained active for longer in ET8 protoplasts than for ES8 protoplasts. The Al3+-activated current exhibited higher permeability to malate2− than to Cl−(P mal/P Cl ≥ 2.6) and was inhibited by anion channel antagonists, niflumate and diphenylamine-2-carboxylic acid. In ET8, but not ES8, protoplasts an outward-rectifying K+ current was activated in the presence of Al3+ when cAMP was included in the pipette solution. These findings provide evidence that the difference in Al3+-induced malate efflux between Al3+-tolerant and Al3+-sensitive genotypes lies in the differing capacity for Al3+ to activate malate permeable channels and cation channels for sustained malate release.