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Showing papers by "Purdue University published in 2000"


Journal ArticleDOI
TL;DR: A simple and highly efficient method to disrupt chromosomal genes in Escherichia coli in which PCR primers provide the homology to the targeted gene(s), which should be widely useful, especially in genome analysis of E. coli and other bacteria.
Abstract: We have developed a simple and highly efficient method to disrupt chromosomal genes in Escherichia coli in which PCR primers provide the homology to the targeted gene(s). In this procedure, recombination requires the phage lambda Red recombinase, which is synthesized under the control of an inducible promoter on an easily curable, low copy number plasmid. To demonstrate the utility of this approach, we generated PCR products by using primers with 36- to 50-nt extensions that are homologous to regions adjacent to the gene to be inactivated and template plasmids carrying antibiotic resistance genes that are flanked by FRT (FLP recognition target) sites. By using the respective PCR products, we made 13 different disruptions of chromosomal genes. Mutants of the arcB, cyaA, lacZYA, ompR-envZ, phnR, pstB, pstCA, pstS, pstSCAB-phoU, recA, and torSTRCAD genes or operons were isolated as antibiotic-resistant colonies after the introduction into bacteria carrying a Red expression plasmid of synthetic (PCR-generated) DNA. The resistance genes were then eliminated by using a helper plasmid encoding the FLP recombinase which is also easily curable. This procedure should be widely useful, especially in genome analysis of E. coli and other bacteria because the procedure can be done in wild-type cells.

14,389 citations


Journal Article
Carol L. Baird1
TL;DR: A randomized controlled experiment is designed to test whether access to affordable day care (in the form of subsidies, for example) would incentivize Saudi mothers to search actively for employment and to remain employed once they are hired.
Abstract: This pilot aims to better understand the market for childcare in Saudi Arabia – both the supply and demand sides – and to design a randomized controlled experiment to test whether access to affordable day care (in the form of subsidies, for example) would incentivize Saudi mothers to search actively for employment and to remain employed once they are hired. In addition, the study seeks to understand the degree to which employment early on in one’s life impacts employment in later stages. The pilot will provide information on the groups of women the experiment should target, appropriate levels for the childcare subsidy, and the quality and current geographic locations of daycare sites. Expected Impact Determine the effects of facilitating childcare access on Saudi women’s employment. PRINCIPAL INVESTIGATORS  Boston University Patricia Cortes  Harvard University Claudia Goldin  Swarthmore College Jennifer Peck

9,609 citations


Journal ArticleDOI
01 Jun 2000
TL;DR: Evidence for plant stress signaling systems is summarized, some of which have components analogous to those that regulate osmotic stress responses of yeast, some that presumably function in intercellular coordination or regulation of effector genes in a cell-/tissue-specific context required for tolerance of plants.
Abstract: ▪ Abstract Plant responses to salinity stress are reviewed with emphasis on molecular mechanisms of signal transduction and on the physiological consequences of altered gene expression that affect biochemical reactions downstream of stress sensing. We make extensive use of comparisons with model organisms, halophytic plants, and yeast, which provide a paradigm for many responses to salinity exhibited by stress-sensitive plants. Among biochemical responses, we emphasize osmolyte biosynthesis and function, water flux control, and membrane transport of ions for maintenance and re-establishment of homeostasis. The advances in understanding the effectiveness of stress responses, and distinctions between pathology and adaptive advantage, are increasingly based on transgenic plant and mutant analyses, in particular the analysis of Arabidopsis mutants defective in elements of stress signal transduction pathways. We summarize evidence for plant stress signaling systems, some of which have components analogous to t...

4,596 citations


Journal ArticleDOI
TL;DR: The aim of this article is to present a concise review on the applications of hydrogels in the pharmaceutical field, hydrogel characterization and analysis of drug release from such devices.

3,484 citations


Proceedings ArticleDOI
16 Jul 2000
TL;DR: It is concluded that the best approach is to use the constriction factor while limiting the maximum velocity Vmax to the dynamic range of the variable Xmax on each dimension.
Abstract: The performance of particle swarm optimization using an inertia weight is compared with performance using a constriction factor. Five benchmark functions are used for the comparison. It is concluded that the best approach is to use the constriction factor while limiting the maximum velocity Vmax to the dynamic range of the variable Xmax on each dimension. This approach provides performance on the benchmark functions superior to any other published results known by the authors.

2,922 citations


Journal ArticleDOI
TL;DR: In this article, the authors quantify the effect of the bullwhip effect on simple two-stage supply chains consisting of a single retailer and a single manufacturer and demonstrate that the effect can be reduced by centralizing demand information.
Abstract: An important observation in supply chain management, known as the bullwhip effect, suggests that demand variability increases as one moves up a supply chain. In this paper we quantify this effect for simple, two-stage supply chains consisting of a single retailer and a single manufacturer. Our model includes two of the factors commonly assumed to cause the bullwhip effect: demand forecasting and order lead times. We extend these results to multiple-stage supply chains with and without centralized customer demand information and demonstrate that the bullwhip effect can be reduced, but not completely eliminated, by centralizing demand information.

1,726 citations


Journal ArticleDOI
01 Jul 2000
TL;DR: In this paper, the authors introduce the concept of hybrid systems and some of the challenges associated with the stability of such systems, including the issues of guaranteeing stability of switched stable systems and finding conditions for the existence of switched controllers for stabilizing switched unstable systems.
Abstract: This paper introduces the concept of a hybrid system and some of the challenges associated with the stability of such systems, including the issues of guaranteeing stability of switched stable systems and finding conditions for the existence of switched controllers for stabilizing switched unstable systems. In this endeavour, this paper surveys the major results in the (Lyapunov) stability of finite-dimensional hybrid systems and then discusses the stronger, more specialized results of switched linear (stable and unstable) systems. A section detailing how some of the results can be formulated as linear matrix inequalities is given. Stability analyses on the regulation of the angle of attack of an aircraft and on the PI control of a vehicle with an automatic transmission are given. Other examples are included to illustrate various results in this paper.

1,647 citations


Journal ArticleDOI
TL;DR: A new conceptual model of the 2 processing modes is advanced, supported by psychological and neuropsychological evidence, that humans possess 2 memory systems and involves the intentional retrieval of explicit, symbolically represented rules from either memory system and their use to guide processing.
Abstract: Models postulating 2 distinct processing modes have been proposed in several topic areas within social and cognitive psychology. We advance a new conceptual model of the 2 processing modes. The structural basis of the new model is the idea, supported by psychological and neuropsychological evidence, that humans possess 2 memory systems. One system slowly learns general regularities, whereas the other can quickly form representations of unique or novel events. Associative retrieval or pattern completion in the slow-learning system elicited by a salient cue constitutes the effortless processing mode. The second processing mode is more conscious and effortful; it involves the intentional retrieval of explicit, symbolically represented rulesfrom either memory system and their use to guide processing. After presenting our model, we review existing dual-process models in several areas, emphasizing their similar assumptions of a quick, effortless processing mode that rests on well-learned prior associations and ...

1,373 citations


Book ChapterDOI
TL;DR: In this article, a review of previous work in the development of freezing and thawing processes focusing on the implications of such materials for a variety of applications is presented, and future directions involving the further development of freeze/thawed PVA hydrogels are addressed.
Abstract: Poly(vinyl alcohol) (PVA) is a polymer of great interest because of its many desirable characteristics specifically for various pharmaceutical and biomedical applications. The crystalline nature of PVA has been of specific interest particularly for physically cross-linked hydrogels prepared by repeated cycles of freezing and thawing. This review includes details on the structure and properties of PVA, the synthesis of its hydrogels, the crystallization of PVA, as well as its applications. An analysis of previous work in the development of freezing and thawing processes is presented focusing on the implications of such materials for a variety of applications. PVA blends that have been developed with enhanced properties for specific applications will also be discussed briefly. Finally, the future directions involving the further development of freeze/thawed PVA hydrogels are addressed.

1,284 citations


Journal ArticleDOI
Supriyo Datta1
TL;DR: The non-equilibrium Green's function (NEGF) formalism provides a sound conceptual basis for the devlopment of atomic-level quantum mechanical simulators that will be needed for nanoscale devices of the future as discussed by the authors.

1,094 citations


Journal ArticleDOI
Sidney Diamond1
TL;DR: In this article, the conditions that must be met for MIP measurements to provide valid estimates of the pore size distribution of porous solids are reviewed and evidence is presented indicating that these conditions are not satisfied in cement-based systems.

Journal ArticleDOI
TL;DR: This review discusses the molecular structure, dynamic behavior, and structural modifications of hydrogels as well as the various applications of these biohydrogels.
Abstract: ▪ Abstract Hydrogels are cross-linked hydrophilic polymers that can imbibe water or biological fluids. Their biomedical and pharmaceutical applications include a very wide range of systems and processes that utilize several molecular design characteristics. This review discusses the molecular structure, dynamic behavior, and structural modifications of hydrogels as well as the various applications of these biohydrogels. Recent advances in the preparation of three-dimensional structures with exact chain conformations, as well as tethering of functional groups, allow for the preparation of promising new hydrogels. Meanwhile, intelligent biohydrogels with pH- or temperature-sensitivity continue to be important materials in medical applications.

Journal ArticleDOI
TL;DR: According to social role theory, groups should have dynamic stereotypes to the extent that their typical social roles are perceived to change over time as discussed by the authors, and the female stereotype should be particularly dynamic because of greater change in the roles of women than of men.
Abstract: Dynamic stereotypes characterize social groups that are thought to have changed from the attributes they manifested in the past and even to continue to change in the future. According to social role theory’s assumption that the role behavior of group members shapes their stereotype, groups should have dynamic stereotypes to the extent that their typical social roles are perceived to change over time. Applied to men and women, this theory makes two predictions about perceived change: (a) perceivers should think that sex differences are eroding because of increasing similarity of the roles of men and women and (b) the female stereotype should be particularly dynamic because of greater change in the roles of women than of men. This theory was tested and confirmed in five experiments that examined perceptions of the roles and the personality, cognitive, and physical attributes of men and women of the past, present, and future.

Journal ArticleDOI
TL;DR: It is indicated that liquid carbohydrate promotes positive energy balance, whereas a comparable solid carbohydrate elicits precise dietary compensation and increased consumption of energy-yielding fluids may promotepositive energy balance.
Abstract: BACKGROUND: Beverages are contributing an increased proportion of energy to the diet. Because they elicit a weak compensatory dietary response, they may increase risk of positive energy balance. OBJECTIVES: This study aimed to document the differential effects of matched liquid and solid carbohydrate loads on diet and body weight. DESIGN: In a cross-over design, seven males and eight females consumed dietary carbohydrate loads of 1880 kJ/day as a liquid (soda) or solid (jelly beans) during two 4 week periods separated by a 4 week washout. Subjects were permitted to consume the loads however they chose. In addition to baseline measurements, diet records were obtained on random days throughout the study, body composition was measured weekly, physical activity was assessed before and after treatments and hunger was assessed during washout and midway through each treatment. RESULTS: Free-feeding energy intake during the solid period was significantly lower than intake prior to this period. Dietary energy compensation was precise (118%). No decrease in free-feeding energy intake occurred during the liquid period. Total daily energy intake increased by an amount equal to the load resulting in dietary compensation of −17%. Consequently, body weight and BMI increased significantly only during the liquid period. Physical activity and hunger were unchanged. CONCLUSIONS: This study indicates that liquid carbohydrate promotes positive energy balance, whereas a comparable solid carbohydrate elicits precise dietary compensation. Increased consumption of energy-yielding fluids may promote positive energy balance.

Journal ArticleDOI
TL;DR: Transposable elements were first discovered in plants because they can have tremendous effects on genome structure and gene function and may be responsible for the rate at which incompatibility is generated in separated populations.
Abstract: Transposable elements were first discovered in plants because they can have tremendous effects on genome structure and gene function. Although only a few or no elements may be active within a genome at any time in any individual, the genomic alterations they cause can have major outcomes for a species. All major element types appear to be present in all plant species, but their quantitative and qualitative contributions are enormously variable even between closely related lineages. In some large-genome plants, mobile DNAs make up the majority of the nuclear genome. They can rearrange genomes and alter individual gene structure and regulation through any of the activities they promote: transposition, insertion, excision, chromosome breakage, and ectopic recombination. Many genes may have been assembled or amplified through the action of transposable elements, and it is likely that most plant genes contain legacies of multiple transposable element insertions into promoters. Because chromosomal rearrangements can lead to speciating infertility in heterozygous progeny, transposable elements may be responsible for the rate at which such incompatibility is generated in separated populations. For these reasons, understanding plant gene and genome evolution is only possible if we comprehend the contributions of transposable elements.

Proceedings ArticleDOI
01 Aug 2000
TL;DR: Results indicate that gated-Vdd together with a novel resizable cache architecture reduces energy-delay by 62% with minimal impact on performance.
Abstract: Deep-submicron CMOS designs have resulted in large leakage energy dissipation in microprocessors. While SRAM cells in on-chip cache memories always contribute to this leakage, there is a large variability in active cell usage both within and across applications. This paper explores an integrated architectural and circuit-level approach to reducing leakage energy dissipation in instruction caches. We propose, gated-V/sub dd/, a circuit-level technique to gate the supply voltage and reduce leakage in unused SRAM cells. Our results indicate that gated-V/sub dd/ together with a novel resizable cache architecture reduces energy-delay by 62% with minimal impact on performance.

Journal ArticleDOI
TL;DR: A game theoretic framework for bandwidth allocation for elastic services in high-speed networks based on the Nash bargaining solution from cooperative game theory that can be used to characterize a rate allocation and a pricing policy which takes into account users' budget in a fair way.
Abstract: In this paper, we present a game theoretic framework for bandwidth allocation for elastic services in high-speed networks. The framework is based on the idea of the Nash bargaining solution from cooperative game theory, which not only provides the rate settings of users that are Pareto optimal from the point of view of the whole system, but are also consistent with the fairness axioms of game theory. We first consider the centralized problem and then show that this procedure can be decentralized so that greedy optimization by users yields the system optimal bandwidth allocations. We propose a distributed algorithm for implementing the optimal and fair bandwidth allocation and provide conditions for its convergence. The paper concludes with the pricing of elastic connections based on users' bandwidth requirements and users' budget. We show that the above bargaining framework can be used to characterize a rate allocation and a pricing policy which takes into account users' budget in a fair way and such that the total network revenue is maximized.

Journal ArticleDOI
TL;DR: The structure and morphology of polyvinyl alcohol (PVA) gels prepared by repeated cycles of 8 h freezing at −20 °C and 4 h thawing at +25 °C were examined in this paper.
Abstract: The structure and morphology of poly(vinyl alcohol) (PVA) gels prepared by repeated cycles of 8 h freezing at −20 °C and 4 h thawing at +25 °C were examined. Long-term morphological changes of such gels were determined upon swelling in water at 37 °C for 6 months. The preparation conditions were examined by varying such parameters as the number of freezing and thawing cycles, the concentration of aqueous solution, and the PVA molecular weight. The overall structure and stability were examined in terms of water content, fractional PVA dissolution, degree of crystallinity, and crystal size distribution. An increase in the number of freezing and thawing cycles served to reinforce existing crystals within the structure. Increased initial concentrations of aqueous PVA solutions resulted in hydrogels that contained initially higher crystallinity and added stability upon swelling. An increase in the PVA molecular weight resulted in crystals of higher lamellar thickness and a broadening of the crystal size distri...

Journal ArticleDOI
TL;DR: This paper presented a model of relational leadership based on a review of leader-member exchange (LMX) and interpersonal trust, which asserts that the LMX relationship is built through interpersonal exchanges in which parties to the relationship evaluate the ability, benevolence, and integrity of each other.
Abstract: This article presents a model of relational leadership based on a review of leader-member exchange (LMX) and interpersonal trust. This model asserts that the LMX relationship is built through interpersonal exchanges in which parties to the relationship evaluate the ability, benevolence, and integrity of each other. These perceptions, in turn, influence the behaviors predicted by LMX researchers. This integrated model of relational leadership provides insights into the dynamics of leader-subordinate relationships and resolves some of the inconsistencies in the LMX research without losing the richness and uniqueness of the exchange theory. A number of propositions for future research in relational leadership are also suggested.

Book ChapterDOI
01 Jan 2000
TL;DR: In this article, the authors argue that students' self-regulatory competence can be enhanced through systematic interventions that are designed to teach skills and raise student's selfefficacy for learning.
Abstract: Publisher Summary This chapter argues that students' self-regulatory competence can be enhanced through systematic interventions that are designed to teach skills and raise students' self-efficacy for learning. Self-regulation (or self-regulated learning) refers to self-generated thoughts, feelings, and actions that are planned and systematically adapted as needed to affect one's learning and motivation. Self-regulation comprises such processes as setting goals for learning, attending to and concentrating on instruction, using effective strategies to organize, code, and rehearse information to be remembered, establishing a productive work environment, using resources effectively, monitoring performance, managing time effectively, seeking assistance when needed, holding positive beliefs about one's capabilities, the value of learning, the factors influencing learning and the anticipated outcomes of actions, and experiencing pride and satisfaction with one's efforts. Self-regulation is not an all-or-none phenomenon; rather, it refers to the degree that students are metacognitively, motivationally, and behaviorally active in their learning. Students may self-regulate different dimensions of learning, including their motives for learning, the methods they employ, the performance outcomes they strive for, and the social and environmental resources they use. Thus, self-regulation has both qualitative and quantitative aspects because it involves which processes students use, how frequently they use them, and how well they employ them. The hallmarks of self-regulation are choice and control: Students cannot self-regulate unless they have options available for learning and can control essential dimensions of learning. Students have little opportunity for self-regulation when teachers dictate what students do, when and where they do it, and how they accomplish it.

Journal ArticleDOI
TL;DR: In this paper, the authors empirically examined the relationship between trust for a business unit's general manager and organizational performance and found that trust was significantly related to sales, profits and employee turnover in the restaurant industry.
Abstract: Employee trust for the general manager is proposed as an internal organizational characteristic that provides a competitive advantage for the firm. This paper empirically examines the relationship between trust for a business unit's general manager and organizational performance. Trust was found to be significantly related to sales, profits and employee turnover in the restaurant industry. Managers who were either more or less trusted differed significantly in perceptions of their ability, benevolence and integrity. Copyright © 2000 John Wiley & Sons, Ltd.


Journal ArticleDOI
TL;DR: In this paper, the authors provide a general method for constructing model category structures for categories of ring, algebra, and module spectra, and provide the necessary input for obtaining model categories of symmetric ring spectra and functors with smash product.
Abstract: In recent years the theory of structured ring spectra (formerly known as A$_{\infty}$- and E$_{\infty}$-ring spectra) has been simplified by the discovery of categories of spectra with strictly associative and commutative smash products. Now a ring spectrum can simply be defined as a monoid with respect to the smash product in one of these new categories of spectra. In this paper we provide a general method for constructing model category structures for categories of ring, algebra, and module spectra. This provides the necessary input for obtaining model categories of symmetric ring spectra, functors with smash product, $\Gamma$-rings, and diagram ring spectra. Algebraic examples to which our methods apply include the stable module category over the group algebra of a finite group and unbounded chain complexes over a differential graded algebra. 1991 Mathematics Subject Classification: primary 55U35; secondary 18D10.

Journal ArticleDOI
TL;DR: In this paper, a discontinuous projection-based adaptive robust controller (ARC) is proposed for the swing motion control of a single-rod hydraulic actuator with constant unknown inertia load, which takes into account not only the effect of parameter variations coming from the inertia load and various hydraulic parameters, but also the effects of hard to model nonlinearities such as uncompensated friction forces and external disturbances.
Abstract: High-performance robust motion control of single-rod hydraulic actuators with constant unknown inertia load is considered. The two chambers of a single-rod actuator have different areas, so the dynamic equations describing the pressure changes in them cannot be combined into a single load pressure equation. This complicates controller design since it not only increases the system dimension but also brings in the stability issue of the added internal dynamics. A discontinuous projection-based adaptive robust controller (ARC) is constructed. The controller takes into account not only the effect of parameter variations coming from the inertia load and various hydraulic parameters but also the effect of hard-to-model nonlinearities such as uncompensated friction forces and external disturbances. It guarantees a prescribed output tracking transient performance and final tracking accuracy in general while achieving asymptotic output tracking in the presence of parametric uncertainties. In addition, the zero error dynamics for tracking any nonzero constant velocity trajectory is shown to be globally uniformly stable. Experimental results are obtained for the swing motion control of a hydraulic arm and verify the high-performance nature of the proposed strategy. In comparison to a state-of-the-art industrial motion controller, the proposed algorithm achieves more than a magnitude reduction of tracking errors. Furthermore, during the constant velocity portion of the motion, it reduces the tracking errors almost down to the measurement resolution level.

Journal ArticleDOI
TL;DR: It is shown that activation of endogenous EphA2 kinase induces an inactive conformation of integrins and inhibits cell spreading, migration and integrin-mediated adhesion in resting cells.
Abstract: Interactions between receptor tyrosine kinases of the Eph family and their ligands, ephrins, are implicated in establishment of organ boundaries and repulsive guidance of cell migration during development, but the mechanisms by which this is achieved are unclear Here we show that activation of endogenous EphA2 kinase induces an inactive conformation of integrins and inhibits cell spreading, migration and integrin-mediated adhesion Moreover, EphA2 is constitutively associated with focal-adhesion kinase (FAK) in resting cells Within one minute after stimulation of EphA2 with its ligand, ephrin-A1, the protein tyrosine phosphatase SHP2 is recruited to EphA2; this is followed by dephosphorylation of FAK and paxillin, and dissociation of the FAK-EphA2 complex We conclude that Eph kinases mediate some of their functions by negatively regulating integrins and FAK

Journal ArticleDOI
TL;DR: The success of cryo-electron microscopy in combination with three-dimensional image reconstruction for icosahedral viruses provides a firm foundation for future explorations of more-complex viral pathogens, including the vast number that are nonspherical or nonsymmetrical.
Abstract: Viruses are cellular parasites. The linkage between viral and host functions makes the study of a viral life cycle an important key to cellular functions. A deeper understanding of many aspects of viral life cycles has emerged from coordinated molecular and structural studies carried out with a wide range of viral pathogens. Structural studies of viruses by means of cryo-electron microscopy and three-dimensional image reconstruction methods have grown explosively in the last decade. Here we review the use of cryo-electron microscopy for the determination of the structures of a number of icosahedral viruses. These studies span more than 20 virus families. Representative examples illustrate the use of moderate- to low-resolution (7- to 35-A) structural analyses to illuminate functional aspects of viral life cycles including host recognition, viral attachment, entry, genome release, viral transcription, translation, proassembly, maturation, release, and transmission, as well as mechanisms of host defense. The success of cryo-electron microscopy in combination with three-dimensional image reconstruction for icosahedral viruses provides a firm foundation for future explorations of more-complex viral pathogens, including the vast number that are nonspherical or nonsymmetrical.

Journal ArticleDOI
23 Jun 2000-Science
TL;DR: Through locally focused management strategies, biodiversity and forest resources will be sustained, and downstream regions will be better protected from flooding.
Abstract: A half-century policy of forest exploitation and monoculture in China has led to disastrous consequences, including degradation of forests and landscapes, loss of biodiversity, unacceptable levels of soil erosion, and catastrophic flooding. A new forest policy had been adopted in China called the Natural Forest conservation Program (NFCP), which emphasizes expansion of natural forests and increasing the productivity of forest plantations. Through locally focused management strategies, biodiversity and forest resources will be sustained, and downstream regions will be better protected from flooding. This new policy is being implemented with a new combination of policy tools, including technical training and education, land management planning, mandatory conversion of marginal farmlands to forest, resettlement and retaining of forest dwellers, share in private ownership, and expanded research. These policy tools may have wider relevance for other countries, particularly developing countries.

Journal ArticleDOI
TL;DR: In this paper, a PIV algorithm is presented for estimating time-averaged or phaseaveraged velocity fields, which can be applied to situations where signal strength is not sufficient for standard cross correlation techniques, such as a low number of particle images in an interrogation spot, or poor image quality.
Abstract: A PIV algorithm is presented for estimating time-averaged or phase-averaged velocity fields. The algorithm can be applied to situations where signal strength is not sufficient for standard cross correlation techniques, such as a low number of particle images in an interrogation spot, or poor image quality. The algorithm can also be used to increase the spatial resolution of measurements by allowing smaller interrogation spots than those required for standard cross correlation techniques. The quality of the velocity measurements can be dramatically increased by averaging a series of instantaneous corelation functions, before determining the location of the signal peak, as opposed to the commonly used technique of estimating instantaneous velocity fields first and then averaging the velocity fields. The algorithm is applied to a 30 μm×300 μm microchannel flow

Journal ArticleDOI
TL;DR: Data demonstrate that oxalate may inhibit a signaling step positioned upstream of oxidase assembly/activation but downstream of Ca2+ fluxes into the plant cell cytosol, and indicate that the inhibitory effects of oxalates are largely independent of both its acidity and its affinity for Ca2+.
Abstract: Effective pathogenesis by the fungus Sclerotinia sclerotiorum requires the secretion of oxalic acid. Studies were conducted to determine whether oxalate aids pathogen compatibility by modulating the oxidative burst of the host plant. Inoculation of tobacco leaves with an oxalate-deficient nonpathogenic mutant of S. sclerotiorum induced measurable oxidant biosynthesis, but inoculation with an oxalate-secreting strain did not. Oxalate inhibited production of H2O2 in tobacco and soybean cultured cell lines with a median inhibitory concentration of ∼4 to 5 mM, a concentration less than that measured in preparations of the virulent fungus. Several observations also indicate that the inhibitory effects of oxalate are largely independent of both its acidity and its affinity for Ca2+. These and other data demonstrate that oxalate may inhibit a signaling step positioned upstream of oxidase assembly/activation but downstream of Ca2+ fluxes into the plant cell cytosol.

Journal ArticleDOI
01 Jun 2000
TL;DR: What is currently known about the functions of virulence and plant proteins in several aspects of the Agrobacterium transformation process is reviewed.
Abstract: The phytopathogenic bacterium Agrobacterium tumefaciens genetically transforms plants by transferring a portion of the resident Ti-plasmid, the T-DNA, to the plant. Accompanying the T-DNA into the plant cell is a number of virulence (Vir) proteins. These proteins may aid in T-DNA transfer, nuclear targeting, and integration into the plant genome. Other virulence proteins on the bacterial surface form a pilus through which the T-DNA and the transferred proteins may translocate. Although the roles of these virulence proteins within the bacterium are relatively well understood, less is known about their roles in the plant cell. In addition, the role of plant-encoded proteins in the transformation process is virtually unknown. In this article, I review what is currently known about the functions of virulence and plant proteins in several aspects of the Agrobacterium transformation process.