bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interaction between Gravitropism and Phototropism in Sporangiophores ofPhycomyces blakesleeanus
Authors: Grolig Franz , Eibel Peter , Schimek Christine , Schapat Tanja , Dennison David S. , Galland Paul A. 
Published: July 2002

AbstractThe interaction between gravitropism and phototropism was analyzed for sporangiophores of Phycomyces blakesleeanus. Fluence rate-response curves for phototropism were generated under three different conditions: (a) for stationary sporangiophores, which reached photogravitropic equilibrium; (b) for sporangiophores, which were clinostated head-over during phototropic stimulation; and (c) for sporangiophores, which were subjected to centrifugal accelerations of 2.3g to 8.4g. For blue light (454 nm), clinostating caused an increase of the slope of the fluence rate-response curves and an increase of the maximal bending angles at saturating fluence rates. The absolute threshold remained, however, practically unaffected. In contrast to the results obtained with blue light, no increase of the slope of the fluence rate-response curves was obtained with near-ultraviolet light at 369 nm. Bilateral irradiation with near-ultraviolet or blue light enhanced gravitropism, whereas symmetric gravitropic stimulation caused a partial suppression of phototropism. Gravitropism and phototropism appear to be tightly linked by a tonic feedback loop that allows the respective transduction chains a mutual influence over each other. The use of tropism mutants allowed conclusions to be drawn about the tonic feedback loop with the gravitropic and phototropic transduction chains. The results from clinostating mutants that lack octahedral crystals (implicated as statoliths) showed that these crystals are not involved in the tonic feedback loop. At elevated centrifugal accelerations, the fluence-rate-response curves for photogravitropic equilibrium were displaced to higher fluence rates and the slope decreased. The results indicate that light transduction possesses a logarithmic transducer, whereas gravi-transduction uses a linear one.
Changes in the Xanthophyll Cycle and Fluorescence Quenching Indicate Light-Dependent Early Events in the Action of Paraquat and the Mechanism of Resistance to Paraquat in Erigeron canadensis(L.) Cronq
Authors: Váradi Gyula , Darkó Éva , Lehoczki Endre 
Published: July 2002

Abstract
Violaxanthin de-epoxidation, chlorophyll fluorescence quenching, and photosynthetic O2 evolution in the presence of paraquat (Pq) were studied in intact attached leaves of Pq-susceptible, and Pq-resistant (PqR) biotypes of Erigeron canadensis under different light conditions. Initially, similar changes were induced in the two biotypes, but the effects relaxed only in the PqR plants, indicating a Pq elimination process. The penetration of Pq into the chloroplasts of PqR plants proved to be somewhat restricted and highly light-dependent, as revealed by both the light response curves of violaxanthin de-epoxidation and fluorescence quenching and the short-term high-light pre-illumination experiments. An irregular down-regulation of the non-photochemical fluorescence quenching processes was observed, reflected by lower steady-state zeaxanthin and non-photochemical fluorescence quenching levels as compared with the corresponding non-treated high-light controls. It is concluded that light is essential not only for the initiation of the mechanism of resistance to Pq, but also for the penetration of Pq into the chloroplasts in the PqR E. canadensis. Also, the Pq elimination process may cause a modification to the regulation of the non-radiative energy dissipation in PqR plants in the presence of Pq.
Trehalose Induces the ADP-Glucose Pyrophosphorylase Gene,ApL3, and Starch Synthesis in Arabidopsis
Authors: Wingler Astrid , Fritzius Thorsten , Wiemken Andres , Boller Thomas , Aeschbacher Roger A. 
Published: July 2002

Abstract
In Arabidopsis, genes encoding functional enzymes for the synthesis and degradation of trehalose have been detected recently. In this study we analyzed how trehalose affects the metabolism and development of Arabidopsis seedlings. Exogenously applied trehalose (25 mm) strongly reduced the elongation of the roots and, concomitantly, induced a strong accumulation of starch in the shoots, whereas the contents of soluble sugars were not increased. When Arabidopsis seedlings were grown on trehalose plus sucrose (Suc), root elongation was restored, but starch still accumulated to a much larger extent than during growth on Suc alone. The accumulation of starch in the shoots of trehalose-treated seedlings was accompanied by an increased activity of ADP-glucose pyrophosphorylase and an induction of the expression of the ADP-glucose pyrophosphorylase gene,ApL3. Even in the presence of 50 mm Suc, which itself also slightly induced ApL3, trehalose (5 mm) led to a further increase in ApL3expression. These results suggest that trehalose interferes with carbon allocation to the sink tissues by inducing starch synthesis in the source tissues. Furthermore, trehalose induced the expression of the β-amylase gene, AT-β-Amy, in combination with Suc but not when trehalose was supplied alone, indicating that trehalose can modulate sugar-mediated gene expression.
Metabolic Modeling Identifies Key Constraints on an Engineered Glycine Betaine Synthesis Pathway in Tobacco
Authors: McNeil Scott D. , Rhodes David , Russell Brenda L. , Nuccio Michael L. , Shachar-Hill Yair , Hanson Andrew D. 
Published: July 2002

Abstract
Previous work has shown that tobacco (Nicotiana tabacum) plants engineered to express spinach choline monooxygenase in the chloroplast accumulate very little glycine betaine (GlyBet) unless supplied with choline (Cho). We therefore used metabolic modeling in conjunction with [14C]Cho labeling experiments and in vivo 31P NMR analyses to define the constraints on GlyBet synthesis, and hence the processes likely to require further engineering. The [14C]Cho doses used were large enough to markedly perturb Cho and phosphocholine pool sizes, which enabled development and testing of models with rates dynamically responsive to pool sizes, permitting estimation of the kinetic properties of Cho metabolism enzymes and transport systems in vivo. This revealed that import of Cho into the chloroplast is a major constraint on GlyBet synthesis, the import rate being approximately 100-fold lower than the rates of Cho phosphorylation and transport into the vacuole, with which import competes. Simulation studies suggested that, were the chloroplast transport limitation corrected, additional engineering interventions would still be needed to achieve levels of GlyBet as high as those in plants that accumulate GlyBet naturally. This study reveals the rigidity of the Cho metabolism network and illustrates how computer modeling can help guide rational metabolic engineering design.
Characterization of the 9-Cis-Epoxycarotenoid Dioxygenase Gene Family and the Regulation of Abscisic Acid Biosynthesis in Avocado
Authors: Chernys Jacqueline T. , Zeevaart Jan A.D. 
Published: July 2002

Abstract
Avocado (Persea americana Mill. cv Lula) is a climacteric fruit that exhibits a rise in ethylene as the fruit ripens. This rise in ethylene is followed by an increase in abscisic acid (ABA), with the highest level occurring just after the peak in ethylene production. ABA is synthesized from the cleavage of carotenoid precursors. The cleavage of carotenoid precursors produces xanthoxin, which can subsequently be converted into ABA via ABA-aldehyde. Indirect evidence indicates that the cleavage reaction, catalyzed by 9-cis-epoxycarotenoid dioxygenase (NCED), is the regulatory step in ABA synthesis. Three genes encoding NCED cleavage-like enzymes were cloned from avocado fruit. Two genes, PaNCED1 andPaNCED3, were strongly induced as the fruit ripened. The other gene, PaNCED2, was constitutively expressed during fruit ripening, as well as in leaves. This gene lacks a predicted chloroplast transit peptide. It is therefore unlikely to be involved in ABA biosynthesis. PaNCED1 was induced by water stress, but expression of PaNCED3 was not detectable in dehydrated leaves. Recombinant PaNCED1 and PaNCED3 were capable of in vitro cleavage of 9-cis-xanthophylls into xanthoxin and C25-apocarotenoids, but PaNCED2 was not. Taken together, the results indicate that ABA biosynthesis in avocado is regulated at the level of carotenoid cleavage.
Impact of Post-Anoxia Stress on Membrane Lipids of Anoxia-Pretreated Potato Cells. A Re-Appraisal
Authors: Pavelic Danijela , Arpagaus Silvio , Rawyler André , Brändle Roland 
Published: July 2002

Abstract
The importance of lipid peroxidation and its contributing pathways (via reactive oxygen species and lipoxygenase) during post-anoxia was evaluated with respect to the biphasic behavior of membrane lipids under anoxia (A. Rawyler, D. Pavelic, C. Gianinazzi, J. Oberson, R. Brändle [1999] Plant Physiol 120: 293–300), using potato (Solanum tuberosum cv Bintje) cell cultures. When anoxic cells in the pre-lytic phase were re-oxygenated for 2 h, superoxide anion was not detectable, the hydrogen peroxide (H2O2) level remained small and similar to that of controls, and cell viability was preserved. Lipids were intact and no lipid hydroperoxides were detected. However, small amounts of lipid hydroperoxides accumulated upon feeding anoxic cells with H2O2 and incubation for an additional 2 h under anoxia. When cells that entered the lytic phase of anoxia were re-oxygenated for 2 h, the H2O2 and superoxide anion levels were essentially unchanged. However, cell respiration decreased, reflecting the extensive lipid hydrolysis that had already started under anoxia and continued during post-anoxia. Simultaneous with the massive release of free polyunsaturated fatty acids, small amounts of lipid hydroperoxides were formed, reaching 1% to 2% of total fatty acids. Catalase and superoxide dismutase activities were not greatly affected, whereas the amount and activity of lipoxygenase tended to increase during anoxia. Lipid peroxidation in potato cells is therefore low during post-anoxia. It is mainly due to lipoxygenase, whereas the contribution of reactive oxygen species is negligible. But above all, it is a late event that occurs only when irreversible damage is already caused by the anoxia-triggered lipid hydrolysis.
The rib1 Mutant Is Resistant to Indole-3-Butyric Acid, an Endogenous Auxin in Arabidopsis
Authors: Poupart Julie , Waddell Candace S. 
Published: July 2002

Abstract
The presence of indole-3-butyric acid (IBA) as an endogenous auxin in Arabidopsis has been recently demonstrated. However, the in vivo role of IBA remains to be elucidated. We present the characterization of a semi-dominant mutant that is affected in its response to IBA, but shows a wild-type response to indole-3-acetic acid (IAA), the predominant and most studied form of auxin. We have named this mutantrib1 for resistant to IBA. Root elongation assays show that rib1 is specifically resistant to IBA, to the synthetic auxin 2,4-dichlorophenoxyacetic acid, and to auxin transport inhibitors. rib1 does not display increased resistance to IAA, to the synthetic auxin naphthalene acetic acid, or to other classes of plant hormones. rib1individuals also have other root specific phenotypes including a shortened primary root, an increased number of lateral roots, and a more variable response than wild type to a change in gravitational vector. Adult rib1 plants are morphologically indistinguishable from wild-type plants. These phenotypes suggest thatrib1 alters IBA activity in the root, thereby affecting root development and response to environmental stimuli. We propose models in which RIB1 has a function in either IBA transport or response. Our experiments also suggest that IBA does not use the same mechanism to exit cells as does IAA and we propose a model for IBA transport.
Analysis of Phosphate Acquisition Efficiency in Different Arabidopsis Accessions
Authors: Narang Ram A. , Bruene Asja , Altmann Thomas 
Published: July 2002

Abstract
The morphological and physiological characteristics of Arabidopsis accessions differing in their phosphate acquisition efficiencies (PAEs) when grown on a sparingly soluble phosphate source (hydroxylapatite) were analyzed. A set of 36 accessions was subjected to an initial PAE evaluation following cultivation on synthetic, agarose-solidified media containing potassium phosphate (soluble) or hydroxylapatite (sparingly soluble). From the five most divergent accessions identified in this way, C24, Co, and Calexhibited high PAEs, whereas Col-0 and Teexhibited low PAEs. These five accessions were analyzed in detail. Significant differences were found in root morphology, phosphate uptake kinetics, organic acid release, rhizosphere acidification, and the ability of roots to penetrate substrates. Long root hairs at high densities, high uptake per unit root length, and high substrate penetration ability in the efficient accessions C24 andCo mediate their high PAEs. The third accession with high PAE, Cal, exhibits a high shoot-to-root ratio, long roots with long root hairs, and rhizosphere acidification. These results are consistent with previous observations and highlight the suitability of using Arabidopsis accessions to identify and isolate genes determining the PAE in plants.
Evidence for the Involvement of an Oxidative Stress in the Initiation of Infection of Pear by Erwinia amylovora
Authors: Venisse Jean-Stéphane , Gullner Gabor , Brisset Marie-Noëlle 
Published: July 2002

Abstract
Involvement of an oxidative burst, usually related to incompatible plant/pathogen interactions leading to hypersensitive reactions, was investigated with Erwinia amylovora, the causal agent of fire blight of Maloideae subfamily of Rosaceae, in interaction with pear (Pyrus communis; compatible situation) and tobacco (Nicotiana tabacum; incompatible situation). As expected, this necrogenic bacterium induced in tobacco a sustained production of superoxide anion, lipid peroxidation, electrolyte leakage, and concomitant increases of several antioxidative enzymes (ascorbate peroxidases, glutathion reductases, glutathion-S-transferases, and peroxidases), in contrast to the compatible pathogen Pseudomonas syringae pvtabaci, which did not cause such reactions. In pear leaves, however, inoculations with both the disease- and the hypersensitive reaction-inducing bacteria (E. amylovoraand P. syringae pv tabaci, respectively) resulted in superoxide accumulation, lipid peroxidation, electrolyte leakage, and enzyme induction at similar rates and according to equivalent time courses. The unexpected ability of E. amylovora to generate an oxidative stress even in compatible situation was linked to its functional hrp (for hypersensitive reaction and pathogenicity) cluster because an Hrp secretion mutant of the bacteria did not induce any plant response. It is suggested that E. amylovora uses the production of reactive oxygen species as a tool to provoke host cell death during pathogenesis to invade plant tissues. The bacterial exopolysaccharide could protect this pathogen against the toxic effects of oxygen species since a non-capsular mutant of E. amylovora induced locally the same responses than the wild type but was unable to further colonize the plant.
Molecular Interactions between the Specialist HerbivoreManduca sexta (Lepidoptera, Sphingidae) and Its Natural Host Nicotiana attenuata. IV. Insect-Induced Ethylene Reduces Jasmonate-Induced Nicotine Accumulation by Regulating Putrescine N-Methyltransferase Transcripts,
Authors: Winz Robert A. , Baldwin Ian T. 
Published: July 2002

Abstract
Attack by the specialist herbivore, Manduca sexta, on its native host Nicotiana attenuata Torr. ex Wats. produces a dramatic ethylene release, a jasmonate burst, and a suppression of the nicotine accumulation that results from careful simulations of the herbivore's damage. Methyl-jasmonate (MeJA) treatment induces nicotine biosynthesis. However, this induction can be suppressed by ethylene as pretreatment of plants with 1-methylcyclopropene (1-MCP), a competitive inhibitor of ethylene receptors, restores the full MeJA-induced nicotine response in herbivore attacked plants (J. Kahl, D.H. Siemens, R.J. Aerts, R. Gäbler, F. Kühnemann, C.A. Preston, I.T. Baldwin [2000] Planta 210: 336–342). To understand whether this herbivore-induced signal cross-talk occurs at the level of transcript accumulation, we cloned the putrescine methyltransferase genes (NaPMT1 and NaPMT2) ofN. attenuata, which are thought to represent the rate limiting step in nicotine biosynthesis, and measured transcript accumulations by northern analysis after various jasmonate, 1-MCP, ethephon, and herbivory treatments. Transcripts of both root putrescineN-methyltransferase (PMT) genes and nicotine accumulation increased dramatically within 10 h of shoot MeJA treatment and immediately after root treatments. Root ethephon treatments suppressed this response, which could be reversed by 1-MCP pretreatment. Moreover, 1-MCP pretreatment dramatically amplified the transcript accumulation resulting from both wounding and M. sexta herbivory. We conclude that attack from this nicotine-tolerant specialist insect causes N. attenuatato produce ethylene, which directly suppresses the nitrogen-intensive biosynthesis of nicotine.
Phytochrome-Mediated Photoperiod Perception, Shoot Growth, Glutamine, Calcium, and Protein Phosphorylation Influence the Activity of the Poplar Bark Storage Protein Gene Promoter (bspA)
Authors: Zhu Baolong , Coleman Gary D. 
Published: July 2002

Abstract
In poplars (Populus), bspA encodes a 32-kD bark storage protein that accumulates in the inner bark of plants exposed to either short-day (SD) photoperiods or elevated levels of nitrogen. In this study, poplars transformed with a chimeric gene consisting of the bspA promoter fused to β-glucuronidase (uidA) were used to investigate the transcriptional regulation of the bspA promoter. Photoperiodic activation of the bspA promoter was shown to involve perception by phytochrome and likely involves both a low fluence response and a parallel very low fluence response pathway. Activity of the bspA promoter was also influenced by shoot growth. High levels of bspA expression usually occur in the bark of plants during SD but not long day orSD with a night break. When growth was inhibited under growth permissive photoperiods (SD with night break) levels of bark β-glucuronidase (GUS) activity increased. Stimulating shoot growth in plants treated with SD inhibited SD-induced increases in bark GUS activity. Because changes in photoperiod and growth also alter carbon and nitrogen partitioning, the role of carbon and nitrogen metabolites in modulating the activity of thebspA promoter were investigated by treating excised stems with amino acids or NH4NO3 with or without sucrose. Treatment with either glutamine or NH4NO3 resulted in increased stem GUS activity. The addition of sucrose with either glutamine or NH4NO3 resulted in synergistic induction of GUS, whereas sucrose alone had no effect. Glutamine plus sucrose induction of GUS activity was inhibited by EGTA, okadaic acid, or K-252A. Inhibition by EGTA was partially relieved by the addition of Ca2+. The Ca2+ ionophore, ionomycin, also induced GUS activity in excised shoots. These results indicate that transcriptional activation of bspA is complex. It is likely that SD activation of bspA involves perception by phytochrome coupled to changes in growth. These growth changes may then alter carbon and nitrogen partitioning that somehow signals bspA induction by a yet undefined mechanism that involves carbon and nitrogen metabolites, Ca2+, and protein phosphorylation/dephosphorylation.
Fatty Acid Synthesis in Pea Root Plastids Is Inhibited by the Action of Long-Chain Acyl- Coenzyme As on Metabolite Transporters
Authors: Fox Simon R. , Rawsthorne Stephen , Hills Matthew J. 
Published: July 2002

AbstractThe uptake in vitro of glucose (Glc)-6-phosphate (Glc-6-P) into plastids from the roots of 10- to 14-d-old pea (Pisum sativum L. cv Puget) plants was inhibited by oleoyl-coenzyme A (CoA) concentrations in the low micromolar range (1–2 μm). The IC50 (the concentration of inhibitor that reduces enzyme activity by 50%) for the inhibition of Glc-6-P uptake was approximately 750 nm; inhibition was reversed by recombinant rapeseed (Brassica napus) acyl-CoA binding protein. In the presence of ATP (3 mm) and CoASH (coenzyme A; 0.3 mm), Glc-6-P uptake was inhibited by 60%, due to long-chain acyl-CoA synthesis, presumably from endogenous sources of fatty acids present in the preparations. Addition of oleoyl-CoA (1 μm) decreased carbon flux from Glc-6-P into the synthesis of starch and through the oxidative pentose phosphate (OPP) pathway by up to 73% and 40%, respectively. The incorporation of carbon from Glc-6-P into fatty acids was not detected under any conditions. Oleoyl-CoA inhibited the incorporation of acetate into fatty acids by 67%, a decrease similar to that when ATP was excluded from incubations. The oleoyl-CoA-dependent inhibition of fatty acid synthesis was attributable to a direct inhibition of the adenine nucleotide translocator by oleoyl-CoA, which indirectly reduced fatty acid synthesis by ATP deprivation. The Glc-6-P-dependent stimulation of acetate incorporation into fatty acids was reversed by the addition of oleoyl-CoA.
BetaCore, a designed water soluble four‐stranded antiparallel β‐sheet protein
Authors: Carulla Natàlia , Woodward Clare , Barany George 
Published: July 2002

AbstractBetaCore is a designed ∼50‐residue protein in which two BPTI‐derived core modules, CMIand CMII, are connected by a 22‐atom cross‐link. At low temperature and pH 3, homo‐ and heteronuclear NMR data report a dominant folded (′f') conformation with well‐dispersed chemical shifts,i, i+1 periodicity, numerous long‐range NOEs, and slowed amide hydrogen isotope exchange patterns that is a four‐stranded antiparallel β‐sheet with nonsymmetrical and specific association of CMIand CMII. BetaCore 'f' conformations undergo reversible, global, moderately cooperative, non‐two‐state thermal transitions to an equilibrium ensemble of unfolded 'u' conformations. There is a significant energy barrier between 'f' and 'u' conformations. This is the first designed four‐stranded antiparallel β‐sheet that folds in water.
On the Optimal Damping of a Vibrating Shape Memory Alloy Rod
Authors: Oberaigner Eduard R. , Fischer Franz D. , Tanaka Kikuaki 
Published: July 2002

AbstractVibration damping through phase transformation is one major area of application of shape memory alloys in smart systems and structures. The authors of this study have shown in earlier publications, how damping of vibrating rods can be accomplished. This paper is an extension and generalization. On the one side it uses the proper description of the stress-wave phenomenon instead of a quasi-static approximation, on the other side it describes, how the damping could be optimized. The basic equations of the underlying mathematical model are the stress-wave equation, the heat conduction equation, a kinetic and a constitutive law as well as a condition to ensure maximal damping. The major results are the heating history, which governs the phase transformation, and the domain splitting along the rod into elastic and inelastic regions.