bluuebunny/crossref_metadata_2025_split huggingface dataset:
Demand-Driven Control of Root ATP Sulfurylase Activity and SO42- Uptake in Intact Canola (The Role of Phloem-Translocated Glutathione)
Authors: Lappartient A. G. , Touraine B. 
Published: October 2016

Abstract
The activity of ATP sulfurylase extracted from roots of intact canola (Brassica napus L. cv Drakkar) increased after withdrawal of the S source from the nutrient solution and declined after refeeding SO42- to S-starved plants. The rate of SO42- uptake by the roots was similarly influenced. Identical responses were obtained in SO42- -fed roots when one-half of the root system was starved for S. The internal levels of SO42- and glutathione (GSH) declined after S starvation of the whole root system, but only GSH concentration declined in +S roots of plants from split root experiments. The concentration of GSH in phloem exudates decreased upon transfer of plants to S-free solution. Supplying GSH or cysteine to roots, either exogenously or internally via phloem sap, inhibited both ATP sulfurylase activity and SO42- uptake. Buthionine sulfoximine, an inhibitor of GSH synthesis, reversed the inhibitory effect of cysteine on ATP sulfurylase. It is hypothesized that GSH is responsible for mediating the responses to S availability. ATP sulfurylase activity and the SO42- uptake rate are regulated by similar demand-driven processes that involve the translocation of a phloem-transported message (possibly GSH) to the roots that provides information concerning the nutritional status of the leaves.
Differential Localization of Carbohydrate Epitopes in Plant Cell Walls in the Presence and Absence of Arbuscular Mycorrhizal Fungi
Authors: Balestrini R. , Hahn M. G. , Faccio A. , Mendgen K. , Bonfante P. 
Published: October 2016

Abstract
Two monoclonal antibodies (McAbs) generated against rhamnogalacturonan I and characterized as specific for a terminal α--(1-&gt;2)-linked fucosyl-containing epitope (CCRC-M1) and for an arabinosylated β-(1,6)-galactan epitope (CCRC-M7) were used in immunogold experiments to determine the distribution of the epitopes in four plants. Allium porrum, Zea mays, Trifolium repens, and Nicotiana tabacum plants were chosen as representatives of monocots and dicots with different wall structures. Analyses were performed on root tissues in the presence and absence of arbuscular mycorrhizal fungi. A differential localization of the two cell wall epitopes was found between tissues and between species: for example, in leek, CCRC-M1 labeled epidermal and hypodermal cells, whereas CCRC-M7 labeled cortical cells only. Clover walls were labeled by both McAbs, whereas maize and tobacco were only labeled by CCRC-M7. In the presence of the arbuscular mycorrhizal fungi, labeling was additionally found in an apoplastic compartment typical of the symbiosis (the interface) occurring around the intracellular hyphae. Epitopes binding both McAbs were found in the interfacial material, and their distribution mirrored the pattern found in the host cell wall. These findings demonstrate that the composition of the interface zone in a fungus-plant symbiosis reflects the composition of the wall of the host cell.
Purification and Characterization of a Cryoprotective Protein (Cryoprotectin) from the Leaves of Cold-Acclimated Cabbage
Authors: Sieg F. , Schroder W. , Schmitt J. M. , Hincha D. K. 
Published: October 2016

Abstract
We have purified a protein (cryoprotectin) from the leaves of cold-acclimated cabbage (Brassica oleracea L.) that protects thylakoids from nonacclimated spinach (Spinacia oleracea L.) against freeze-thaw damage. The procedure involves precipitations by heat, ammonium sulfate, and the glycosaminoglycan heparin and column chromatography on Polyamide 6 and a C18 reverse-phase matrix. After reverse-phase chromatography we obtained a single band of an apparent molecular mass of 7 kD when fractions that showed cryoprotective activity were analyzed by sodium dodecyl sulfate gel electrophoresis and silver staining. Gel-filtration experiments confirmed that the active protein is a monomer of 7 kD native molecular mass. This 7-kD protein could be purified only from cold-acclimated cabbage, but not from plants grown under nonacclimating conditions. Using peroxidase-labeled lectins, we show that cryoprotectin is a glycoprotein and that the saccharide moiety contains α-1–3-linked fucose.
Regulation of H+ Extrusion and Cytoplasmic pH in Maize Root Tips Acclimated to a Low-Oxygen Environment
Authors: Xia J. H. , Roberts JKM. 
Published: October 2016

Abstract
We tested the hypothesis that H+ extrusion contributes to cytoplasmic pH regulation and tolerance of anoxia in maize (Zea mays) root tips. We studied root tips of whole seedlings that were acclimated to a low-oxygen environment by pretreatment in 3% (v/v) O2. Acclimated root tips characteristically regulate cytoplasmic pH near neutrality and survive prolonged anoxia, whereas nonacclimated tips undergo severe cytoplasmic acidosis and die much more quickly. We show that the plasma membrane H+-ATPase can operate under anoxia and that net H+ extrusion increases when cytoplasmic pH falls. However, at an external pH near 6.0, H+ extrusion contributes little to cytoplasmic pH regulation. At more acidic external pH values, net H+ flux into root tips increases dramatically, leading to a decrease in cytoplasmic pH and reduced tolerance of anoxia. We present evidence that, under these conditions, H+ pumps are activated to partly offset acidosis due to H+ influx and, thereby, contribute to cytoplasmic pH regulation and tolerance of anoxia. The regulation of H+ extrusion under anoxia is discussed with respect to the acclimation response and mechanisms of intracellular pH regulation in aerobic plant cells.
Highly Branched Phenotype of the Petunia dad1-1 Mutant Is Reversed by Grafting
Authors: Napoli C. 
Published: October 2016

Abstract
The recessive dad1–1 allele conditions a highly branched growth habit resulting from a proliferation of first- and second-order branches. Unlike the wild-type parent, which has lateral branching delayed until the third or fourth leaf node distal to the cotyledons, dad1–1 initiates lateral branching from each cotyledon axil. In addition to initiating lateral branching sooner than the wild type, dad1–1 sustains branching through more nodes on the main shoot axis than the wild type. In keeping with a propensity for branching at basal nodes, dad1–1 produces second-order branches at the proximal-most nodes on first-order branches and small shoots from accessory buds at basal nodes on the main shoot axis. Additional traits associated with the mutation are late flowering, adventitious root formation, shortened internodes, and mild leaf chlorosis. Graft studies show that a dad1–1 scion, when grafted onto wild-type stock, is converted to a phenotype resembling the wild type. Furthermore, a small wild-type interstock fragment inserted between a mutant root stock and a mutant scion is sufficient to convert the dad1–1 scion from mutant to a near wild-type appearance. The recessive dad1–1 phenotype combines traits associated with cytokinin overexpression, auxin overexpression, and gibberellin limitation, which suggests a complex interaction of hormones in establishing the mutant phenotype.
The Loss of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Caused by 24-Hour Rain Treatment Fully Explains the Decrease in the Photosynthetic Rate in Bean Leaves
Authors: Ishibashi M. , Usuda H. , Terashima I. 
Published: October 2016

Abstract
Recently, we have found that simulated rainfall causes a chronic inhibition of leaf photosynthesis in Phaseolus vulgaris (M. Ishibashi and I. Terashima [1995] Plant Cell Environ 18: 431–438). Mechanisms of this inhibition were examined in the present study. After the plants were treated with continuous mist for 24 h and then dried to unwet conditions, light-saturated photosynthetic rates of the leaves measured at 35 Pa ambient CO2 decreased to one-half of the control level. The extractable activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) also decreased to the same extent. Unexpectedly, this decline was due not to the lowered activation state but to the decrease in the amount of Rubisco. Before or after the “rain” treatment, the relationship between the net photosynthetic rate and the amount of Rubisco was expressed as a unique linear function with a small intercept (r2 = 0.84). From these it was inferred that the main cause of the rain-induced decline in photo-synthetic rate was the loss in amount of Rubisco.
Isolation of a Microsomal Enzyme System Involved in Glucosinolate Biosynthesis from Seedlings of Tropaeolum majus L
Authors: Du L. , Halkier B. A. 
Published: October 2016

Abstract
An in vitro system that converts phenylalanine to phenylacetaldoxime in the biosynthesis of the glucosinolate glucotropaeolin has been established in seedlings of Tropaeolum majus L. exposed to the combined treatment of jasmonic acid, ethanol, and light. The treatment resulted in a 9-fold induction, compared with untreated, dark-grown seedlings, of de novo biosynthesis measured as incorporation of radioactively labeled phenylalanine into glucotropaeolin. Formation of the inhibitory degradation product benzylisothiocyanate during tissue homogenization was prevented by inactivation of the thioglucosidase myrosinase by addition of 100 mM ascorbic acid to the isolation buffer. This allowed the isolation of a biosynthetically active microsomal preparation from the induced T. majus plant material. The enzyme, which catalyzes the conversion of phenylalanine to the corresponding oxime, was sensitive to cytochrome P450 inhibitors, indicating the involvement of a cytochrome P450 in the biosynthetic pathway. It has previously been shown that the oxime-producing enzyme in the biosynthesis of p-hydroxybenzylglucosinolate in Sinapis alba L. is dependent on cytochrome P450, whereas the oxime-producing enzymes in Brassica species have been suggested to be flavin monooxygenases or peroxidase-type enzymes. The result with T. majus provides additional experimental documentation for a similarity between the enzymes converting amino acids into the corresponding oximes in the biosynthesis of glucosinolates and cyanogenic glucosides.
Cytoplasmic Orientation of the Naphthylphthalamic Acid-Binding Protein in Zucchini Plasma Membrane Vesicles
Authors: Dixon M. W. , Jacobson J. A. , Cady C. T. , Muday G. K. 
Published: October 2016

Abstract
Polar transport of the plant hormone auxin is blocked by substances such as N-1-naphthylphthalamic acid (NPA), which inhibit auxin efflux and block polar auxin transport. To understand how auxin transport is regulated in vivo, it is necessary to discern whether auxin transport inhibitors act at the intra- or extracellular side of the plasma membrane. Populations of predominantly in-side-in plasma membrane vesicles were subjected to treatments that reverse the orientation. These treatments, which included osmotic shock, cycles of freezing and thawing, and incubation with 0.05% Brij-58, all increased NPA-binding activity and the accessibility of the binding protein to protease digestion. Marker activities for inside-out vesicles also increased, indicating that these treatments act by altering the membrane orientation. Finally, binding data were analyzed by multiple analyses and indicated that neither the affinity nor abundance of binding sites changed. Kinetic analyses indicated that the change in NPA-binding activity by Brij-58 treatment was due to an increase in the initial rates of both association and dissociation of this ligand. These experiments indicated that the NPA-binding site is on the cytoplasmic face of the plasma membrane in zucchini (Cucurbita pepo L. cv Burpee Fordhook).
Partial Purification and Characterization of an Inducible Indole-3-Acetyl-L-Aspartic Acid Hydrolase from Enterobacter agglomerans
Authors: Chou J. C. , Kuleck G. A. , Cohen J. D. , Mulbry W. W. 
Published: October 2016

Abstract
Indole-3-acetyl-amino acid conjugate hydrolases are believed to be important in the regulation of indole-3-acetic acid (IAA) metabolism in plants and therefore have potential uses for the alteration of plant IAA metabolism. To isolate bacterial strains exhibiting significant indole-3-acetyl-aspartate (IAA-Asp) hydrolase activity, a sewage sludge inoculation was cultured under conditions in which IAA-Asp served as the sole source of carbon and nitrogen. One isolate, Enterobacter agglomerans, showed hydrolase activity inducible by IAA-L-Asp or N-acetyl-L-Asp but not by IAA, (NH4)2SO4, urea, or indoleacetamide. Among a total of 17 IAA conjugates tested as potential substrates, the enzyme had an exclusively high substrate specificity for IAA-L-Asp. Substrate concentration curves and Lineweaver-Burk plots of the kinetic data showed a Michaelis constant value for IAA-L-Asp of 13.5 mM. The optimal pH for this enzyme was between 8.0 and 8.5. In extraction buffer containing 0.8 mM Mg2+ the hydrolase activity was inhibited to 80% by 1 mM dithiothreitol and to 60% by 1 mm CuSO4; the activity was increased by 40% with 1 mM MnSO4. However, in extraction buffer with no trace elements, the hydrolase activity was inhibited to 50% by either 1 mM dithiothreitol or 1% Triton X-100 (Sigma). These results suggest that disulfide bonding might be essential for enzyme activity. Purification of the hydrolase by hydroxyapatite and TSK-phenyl (HP-Genenchem, South San Francisco, CA) preparative high-performance liquid chromatography yielded a major 45-kD polypeptide as shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis.
Maize Root Phytase (Purification, Characterization, and Localization of Enzyme Activity and Its Putative Substrate)
Authors: Hubel F. , Beck E. 
Published: October 2016

Abstract
Three phytase (EC 3.1.3.26) isoforms from the roots of 8-d-old maize (Zea mays L. var Consul) seedlings were separated from phosphatases and purified to near homogeneity. The molecular mass of the native protein was 71 kD, and the isoelectric points of the three isoforms were pH 5.0, 4.9, and 4.8. Each of the three isoforms consisted of two subunits with a molecular mass of 38 kD. The temperature and pH optima (40[deg]C, pH 5.0) of these three isoforms, as well as the apparent Michaelis constants for sodium inositol hexakisphosphate (phytate) (43, 25, and 24 [mu]M) as determined by the release of inorganic phosphate, were only slightly different. Phytate concentrations higher than 300 [mu]M were inhibitory to all three isoforms. In contrast, the dephosphorylation of 4-nitrophenyl phosphate was not inhibited by any substrate concentration, but the Michaelis constants for this substrate were considerably higher (137–157 [mu]M). Hydrolysis of phytate by the phytase isoforms is a nonrandom reaction. D/L-Inositol-1,2,3,4,5- pentakisphosphate was identified as the first and D/L-inositol-1,2,5,6-tetrakisphosphate as the second intermediate in phytate hydrolysis. Phytase activity was localized in root slices. Although phosphatase activity was present in the stele and the cortex of the primary root, phytase activity was confined to the endodermis. Phytate was identified as the putative native substrate in maize roots (45 [mu]g P g-1 dry matter). It was readily labeled upon supplying [32P]phosphate to the roots.
In Vitro Prenylation of the Small GTPase Rac13 of Cotton
Authors: Trainin T. , Shmuel M. , Delmer D. P. 
Published: October 2016

Abstract
Previous work (D.P. Delmer, J. Pear, A. Andrawis, D. Stalker [1995] Mol Gen Genet 248: 43–51) has identified a gene in cotton (Gossypium hirsutum), Rac13, that encodes a small, signal-transducing GTPase and shows high expression in the fiber at the time of transition from primary to secondary wall synthesis. Since Rac13 may be important in signal transduction pathway(s), regulating the onset of fiber secondary wall synthesis, we continue to characterize Rac13 by determining its ability to undergo posttranslational modification. In animals Rac proteins contain the C-terminal consensus sequence CaaL (where “a” can be any aliphatic residue), which is a site for geranylgeranylation (B.T. Kinsella, R.A. Erdman, W.A. Maltese [1994] J Biol Chem 266: 9786–9794). We have identified activities in developing cotton fibers that resemble in specificity the geranylgeranyl- and farnesyltransferases of animals and yeast. In addition, using prenyltransferases from rabbit reticulocytes, we show that Rac13, having a C-terminal sequence of CAFL, can serve as an in vitro substrate for geranylgeranylation but not farnesylation. However, the presence of the uncommon penultimate F residue appears to slow the rate of prenylation considerably compared with other acceptors.
Evidence for a UDP-Glucose Transporter in Golgi Apparatus-Derived Vesicles from Pea and Its Possible Role in Polysaccharide Biosynthesis
Authors: Munoz P. , Norambuena L. , Orellana A. 
Published: October 2016

Abstract
The Golgi apparatus in plant cells is involved in hemicellulose and pectin biosynthesis. While it is known that glucan synthase I is responsible for the formation of β-l-4-linked glucose (Glc) polymers and uses UDP-Glc as a substrate, very little is known about the topography of reactions leading to the biosynthesis of polysaccharides in this organelle. We isolated from pea (Pisum sativum) stems a fraction highly enriched in Golgi apparatus-derived vesicles that are sealed and have the same topographical orientation that the membranes have in vivo. Using these vesicles and UDP-Glc, we reconstituted polysaccharide biosynthesis in vitro and found evidence for a luminal location of the active site of glucan synthase I. In addition, we identified a UDP-Glc transport activity, which is likely to be involved in supplying substrate for glucan synthase I. We found that UDP-Glc transport is protein mediated. Moreover, our results suggest that UDP-Glc transport is coupled to the exit of a luminal uridine-containing nucleotide via an antiporter mechanism. We suggest that UDP-Glc is transported into the lumen of Golgi and that Glc is transferred to a polysaccharide chain, whereas the nucleotide moiety leaves the vesicle by an antiporter mechanism.
Effect of Xyloglucan Oligosaccharides on Growth, Viscoelastic Properties, and Long-Term Extension of Pea Shoots
Authors: Cutillas-Iturralde A. , Lorences E. P. 
Published: October 2016

Abstract
The growth-promoting effect of xyloglucan-derived oligosaccharides was investigated using a bioassay with entire pea (Pisum sativum L., var Alaska) shoots. After a 24-h incubation period at 25[deg]C, xyloglucan oligosaccharide (XGO) solutions with concentrations of 10–6 M notably increased the growth rate of pea shoots, whereas the same oligosaccharides at 10–7 M were less effective. To investigate the possible correlation between growth rate changes in the XGO-treated shoots and changes in the wall mechanical properties of their growing regions (third internodes), we used a short-term creep assay. The promotion of elongation by XGOs was reflected in an enhancement of the viscoelasticity of the growing regions of the shoots. To show whether this effect on wall viscoelastic properties was the cause or a consequence of their growth promotion, we tested the effect of XGOs on the long-term extension of isolated cell walls. We characterized an acid-induced extension in isolated cell walls from pea shoots that was not inhibited by preincubation in neutral buffers. Exogenously added XGOs did not alter the pattern of pea segment extension at any pH tested, indicating that XGOs have no direct effect on cell wall viscoelasticity. Finally, preincubation of pea segments in neutral buffers with XGOs enhanced their capacity to extend under acidic conditions. This finding suggests that XGOs at a neutral pH can act via transglycosylation, weakening the wall matrix and making the wall more responsive to other mechanisms of acid-induced extension as an expansin-mediated extension.
Water Deficit Rapidly Stimulates the Activity of a Protein Kinase in the Elongation Zone of the Maize Primary Root
Authors: Conley T. R. , Sharp R. E. , Walker J. C. 
Published: October 2016

Abstract
The mechanisms by which plants detect water deficit and transduce that signal into adaptive responses is unknown. In maize (Zea mays L.) seedlings, primary roots adapt to low water potentials such that substantial rates of elongation continue when shoot growth is completely inhibited. In this study, in-gel protein kinase assays were used to determine whether protein kinases in the elongation zone of the primary root undergo activation or inactivation in response to water deficit. Multiple differences were detected in the phosphoprotein content of root tips of water-stressed compared with well-watered seedlings. Protein kinase assays identified water-deficit-activated protein kinases, including a 45-kD, Ca2+-independent serine/threonine protein kinase. Water-deficit activation of this kinase occurred within 30 min after transplanting seedlings to conditions of low water potential and was localized to the elongation zone, was independent of ABA accumulation, and was unaffected by cycloheximide-mediated inhibition of protein translation. These results provide evidence that the 45-kD protein kinase acts at an early step in the response of maize primary roots to water deficit and is possibly involved in regulating the adaptation of root growth to low water potential.
Sugar-Dependent Gibberellin-Induced Chalcone Synthase Gene Expression in Petunia Corollas
Authors: Moalem-Beno D. , Tamari G. , Leitner-Dagan Y. , Borochov A. , Weiss D. 
Published: October 2016

Abstract
The induction of anthocyanin synthesis and anthocyanin biosynthetic gene expression in detached petunia (Petunia hybrida) corollas by gibberellic acid (GA3) requires sucrose. Neither sucrose nor GA3 alone can induce these processes. We found that GA3 enhances sucrose uptake by 20 to 30%, and we tested whether this is the mechanism by which the hormone induces gene expression. Changing the intracellular level of sucrose with the inhibitors p-chloromercuribenzenesulfonic acid and vanadate did not inhibit the induction of chalcone synthase gene (chs) expression by GA3. Growing detached corollas in various sucrose concentrations did not affect the induction of the gene but did affect its level of expression and the level of anthocyanin accumulated. Only metabolic sugars promoted GA3-induced anthocyanin accumulation. Mannitol and sorbitol had no effect and 3-O-methylglucose only slightly promoted chs expression and anthocyanin accumulation. Our results do not support the suggestion that sugars act as specific signals in the activation of anthocyanin biosynthetic gene expression during petunia corolla development. We suggest that sugars are essential as general sources of carbohydrates for carbon metabolism, upon which the induction of pigmentation is dependent.