Showing papers by "University of Georgia published in 1987"
TL;DR: In this article, the carbon isotope compositions of the polysaccharide and lignin components of a variety of vascular plants, including the salt-marsh grass Spartina alterniflora, were investigated.
Abstract: Stable carbon isotope compositions of organic matter are now widely used to trace carbon flow in ecosystems, and have been instrumental in shaping current perceptions of the importance of terrestrial vegetation to estuarine and coastal marine environments. A general assumption in these and other studies relying on carbon isotope compositions for source identification of organic matter has been that the major biochemical components of plant tissues are isotopically invariant. We report here large differences between the carbon isotope compositions of the polysaccharide and lignin components of a variety of vascular plants, including the salt-marsh grass Spartina alterniflora, and demonstrate that the carbon isotope composition of Spartina detritus gradually changes during biogeochemical processing as polysaccharides are preferentially removed, leaving a material that is relatively enriched in lignin-derived carbon and depleted in 13C.
985 citations
TL;DR: In this paper, the authors clarified and extended the transactional and transformational theories of leadership developed by Burns and Bass by using a constructive/developmental theory to explain how critical personality differences in leaders lead to either transactional or transformational leadership styles.
Abstract: The transactional and transformational theories of leadership developed by Burns (1978) and Bass (1985) are clarified and extended by using a constructive/developmental theory to explain how critical personality differences in leaders lead to either transactional or transformational leadership styles. The distinction between two levels of transactional leadership is expanded, and a three-stage developmental model of leadership is proposed.
920 citations
TL;DR: In this article, the authors examine the determinants of new venture performance and find that success depends not only on the characteristics of the entrepreneur, but also on the structure of the industry entered and the strategy of the venture involved, i.e., NVP = f ( E,IS,S ).
732 citations
TL;DR: In this article, the authors used methods derived from percolation theory to construct neutral landscape models, i.e., models lacking effects due to topography, contagion, disturbance history, and related ecological processes.
Abstract: The relationship between a landscape process and observed patterns can be rigorously tested only if the expected pattern in the absence of the process is known. We used methods derived from percolation theory to construct neutral landscape models,i.e., models lacking effects due to topography, contagion, disturbance history, and related ecological processes. This paper analyzes the patterns generated by these models, and compares the results with observed landscape patterns. The analysis shows that number, size, and shape of patches changes as a function of p, the fraction of the landscape occupied by the habitat type of interest, and m, the linear dimension of the map. The adaptation of percolation theory to finite scales provides a baseline for statistical comparison with landscape data. When USGS land use data (LUDA) maps are compared to random maps produced by percolation models, significant differences in the number, size distribution, and the area/perimeter (fractal dimension) indices of patches were found. These results make it possible to define the appropriate scales at which disturbance and landscape processes interact to affect landscape patterns.
710 citations
TL;DR: The experimental approach is supplemented with theoretical calculations of nitrogen transformations in a shortgrass prairie, which incorporate a wide array of information on decomposer organisms, including their feeding preferences, nitrogen contents, life spans, assimilation efficiencies, productio:assimilation ratios, decomposabilities, and population sizes.
Abstract: Several experimental approaches have been taken to demonstrate the importance of soil fauna in nitrogen mineralization, but there have been difficulties interpreting the results We have supplemented the experimental approach with theoretical calculations of nitrogen transformations in a shortgrass prairie The calculations incorporate a wide array of information on decomposer organisms, including their feeding preferences, nitrogen contents, life spans, assimilation efficiencies, productio:assimilation ratios, decomposabilities, and population sizes The results are estimates of nitrogen transfer rates through the detrital food web, including rates of N mineralization by bacteria, fungi, root-feeding nematodes, collembolans, fungal-feeding mites, fungal-feeding nematodes, flagellates, bacterial-feeding nematodes, amoebae, omnivorous nematodes, predaceous nematodes, nematode-feeding mites, and predaceous mites Bacteria are estimated to mineralize the most N (45 g N m−2 year−1), followed by the fauna (29), and fungi (03) Bacterial-feeding amoebae and nematodes together account for over 83% of N mineralization by the fauna The detrital food web in a shortgrass prairie is similar to that of a desert grassland The shortgrass detrital web seems to be divided into bacteria- and fungus-based components, although these two branches are united at the level of predaceous nematodes and mites
664 citations
Book•
18 Dec 1987TL;DR: The construction of Verbal Unit Items and Lexical and Syntactical Meanings in Children's Counting and the Reorganization of Counting.
Abstract: I: On the Construction of the Counting Scheme.- Children's Counting.- The Counting Types.- Perceptual Unit Items.- Figural Unit Items.- Motor Unit Items.- Verbal Unit Items.- Abstract Unit Items.- Ontogenetic Analysis.- Stages.- Adaptation.- Counting as a Scheme.- The First Part of the Counting Scheme.- The Third Part of the Counting Scheme.- Other Sources of Numerosity.- Perceptual Mechanisms.- Spatial Patterns.- Meaning Theory.- Reflection and Abstraction.- II: The Construction of Motor Unit Items: Brenda, Tarus, and James.- 1. Brenda.- The Perceptual Period.- The Motor Period.- Discussion of Brenda's Case Study.- The Perceptual Period.- The Motor Period.- 2. Tarus.- The Perceptual Period.- The Motor Period.- Discusion of Tarus's Case Study.- The Perceptual Period.- The Motor Period.- 3. James.- The Perceptual Period.- The Motor Period.- Discussion of James's Case Study.- The Perceptual Period.- The Motor Period.- Perspectives on the Three Case Studies.- Period Criterion.- The Incorporation and Invariant Sequence Criteria.- The Reorganization Criterion.- III: The Construction of Verbal Unit Items: Brenda, Tarus, and James.- 1. Brenda.- Discussion of Brenda's Case Study.- 2. Tarus.- Discussion of Tarus's Case Study.- 3. James.- Discussion of James's Case Study.- Perspectives on the Case Studies.- The Verbal Period as a Subperiod in the Figurative Stage.- Counting-on.- IV: The Construction of Abstract Unit Items: Tyrone, Scenetra, and Jason.- 4. Tyrone.- The Motor Period.- The Abstract Period.- Discussion of Tryone's Case Study.- 5. Scenetra.- The Motor Period.- The Verbal Period.- The Abstract Period.- Discussion of Scenetra's Case Study.- 6. Jason.- The Motor Period.- Creating Verbal Unit Items.- The Abstract Period.- Discussion of Jason's Case Study.- Perspectives on the Case Studies.- Stages.- Incorportation Criterion.- Transition to the Abstract Period.- The Reorganization of Counting.- V: Lexical and Syntactical Meanings: Brenda, Tarus, and James.- 1. Brenda.- The Perceptual Period.- The Motor Period.- The Verbal Period.- Discussion of Brenda's Case Study.- The Perceptual Stage.- The Figurative Stage.- 2. Tarus.- The Perceptual Period.- The Motor Period.- The Verbal Period.- Discussion of Tarus's Case Study.- The Perceptual Stage.- The Figurative Stage.- 3. James.- The Perceptual Period.- The Motor Period.- The Verbal Period.- Discussion of James's Case Study.- The Perceptual Stage.- The Figurative Stage.- Perspectives on the Case Studies.- The Perceptual Stage.- Finger Patterns.- The Figurative Stage.- Mobile Finger Patterns.- Sophisticated Finger Patterns.- Spatio-Auditory Patterns.- Dual Meanings of Number Words.- Counting as the Meaning of Number Words.- Summary of the Types of Preconcepts and Concepts.- Meanings of "Ten".- Ten as an Enactive Concept.- Ten as a Countable Figural Unit.- Ten as a Countable Motor Unit.- Adding Schemes.- The Perceptual Stage.- The Figurative Stage.- Comments on Prenumerical Children.- VI: Lexical and Syntactical Meanings: Tyrone, Scenetra, and Jason.- Systems of Integration.- Integrations.- Sequential Integration Operations.- Progressive Integration Operations.- Part-Whole Operations.- 4. Tyrone.- The Emergence of the Integration Operation.- The Period of Sequential Integration Operations.- The Period of Progressive Integration Operations.- The Period of Part-Whole Operations.- Discussion of Tyrone's Case Study.- The Emergence of the Integration Operation.- The Period of Sequential Integration Operations.- The Period of Progressive Integration Operations.- The Period of Part-Whole Operations.- Unit Types of the Unit of Ten.- 5. Scenetra.- Recognition and Re-Presentation of Patterns.- The Emergence of the Integration Operation.- The Period of Sequential Integration operations.- The Period of Progressive Integreation Operations.- Discussion of Scenetra's Case Study.- The Emergence of the Integratoin Operation.- The Period of Sequential Integration Operations.- The Period of Progressive Integration Operations.- Unit Types of the Unit of Ten.- 6. Jason.- Recognition and Re-Presentation of Patterns.- The Emergence of The Integration Operation.- The Period of Sequential Integration Operations.- The Period of Progressive integration Operations.- The Period of Part-Whole Operations.- Discussion of Jason's Case Study.- The Emergence of the Integration Operation.- The Period of Sequential Integration Operations.- The Period of Progressive Integration Operations.- The Period of Part-Whole Operations.- Unit Types of the Unit of Ten.- Perspectives on the Case Studies.- The Emergence of the Integration Operation.- Numerical Patterns.- Number Sequences.- Stages in the Construction of the Numerical Counting Scheme.- Piaget's Invariant Sequence and Incorporation Criteria.- The Reorganization Criterion.- Units of One.- The Unit of One in Sequential Integration Operations.- The Unit of One in Progressive Integration Operations.- The Unit of One in Part-Whole Operations.- Units of Ten.- The Stage of Sequential Integration Operations.- The Stage of Progressive Integration Operations.- The Stage of Part-Whole Operations.- Other Perspectives.- VII: Strategies for Finding Sums and Differences: Brenda, Tarus, and James.- Brenda.- Independent Solutions.- Number Word Coordinations.- Tarus.- Independent Solutions.- Number Word Coordinations.- James.- Independent Solutions.- Number Word Coordinations.- Perspectives on the Case Studies.- Number Facts.- VIII: Strategies for Finding Sums and Differences: Tyrone, Scenetra, and Jason.- Sequential Integration Operations.- Jason.- Tyrone.- Scenetra.- Discussion: Sequential Integration Operations.- Progressive Integration Operations.- Jason.- Tyrone.- Scenetra.- Discussion: Progressive Integration Operations.- Part-Whole Operations.- Jason.- Tyrone.- Perspective on the Case Studies.- Arithmetical Context.- Thinking Strategies and Integration Operations.- Thinking Strategies and the Basic Facts.- Thinking Strategies and the Construction of Part-Whole Operations.- Goals for Teaching Thinking Strategies.- IX: Modifications of the Counting Scheme.- Predicting Modifications of the Counting Scheme.- Mathematical Learning.- The Perceptual Stage.- Temporary Modifications.- Procedural Accommodations.- Engendering Accommodations.- Isolated Procedural Accommodations.- The Figurative Stage.- Procedural Accommodations.- Temporary Modifications.- Retrospective Accommodations.- Re-presentation and Review of Prior Activity.- The Figurative Stage: Tyrone, Scenetra, and Jason.- Procedural Engendering Accommodations.- Temporary Modifications.- Metamorphic Accommodations.- Stages in the Construction of Part-Whole Operations.- Sequential Integration Operations.- Procedural Accommodations.- Engendering Accommodations.- Progressive Integration Operations.- Internal Reorganizations.- Part-Whole Operations.- Phylogenetic Perspectives.- Zones of Potential Development in Retrospect.- Figurative Stage.- Sequential Integration Operations.- Progressive Integration Operations.- Part-Whole Operations.- Final Comments.- References.
567 citations
TL;DR: It appears that the use of latex microspheres leads to underestimation of protozoa growth rates and that the FLB technique is superior for estimating instantaneous rates of in situ protozoan grazing on bacterioplankton.
Abstract: We have developed a procedure for preparing monodispersed, fluorescently labeled bacteria (FLB), which may be used to measure virtually instantaneous rates of protozoan bacterivory in natural waters. FLB can be prepared both from natural bacterioplankton assemblages and from clonal isolates and can be stored in frozen suspension or freeze-dried without apparent loss of fluorescence intensity. They are not toxic to protozoa and can be metabolized to support bacterivorous protozoan growth rates equal to those on the same strain of unstained, viable bacteria. In experiments comparing uptake of FLB with uptake of fluorescent latex microspheres by protozoan assemblages in a salt marsh tidal creek, we found that both pelagic oligotrichous ciliates and phagotrophic flagellates ingested FLB with a frequency 4- to 10-fold greater than they ingested the microspheres. Consequently, it appears that the use of latex microspheres leads to underestimation of protozoan bacterivory and that the FLB technique is superior for estimating instantaneous rates of in situ protozoan grazing on bacterioplankton. Images
503 citations
TL;DR: In this paper, the authors show that the public announcement of anti-takeover amendments by 600 firms in the period 1979-1985 has an insignificant effect on the value of announcing firms' shares.
493 citations
TL;DR: In this article, a modified micro-pipette method for mechanical analysis was evaluated that eliminated the need for bulky laboratory equipment and long settling times associated with standard pipette and hydrometer methods, using 2 to 4 g soil with 40 mL of dilute dispersant, shaken overnight in 50 mL centrifuge tubes.
Abstract: Determination of soil texture, particularly the clay (<2 μm) fraction, is an important measurement in most soil investigations. In this study a modified method for mechanical analysis was evaluated that eliminated the need for bulky laboratory equipment and long settling times associated with standard pipette and hydrometer methods. Termed a “micro‐pipette”; method, the modified procedure uses 2 to 4 g soil with 40 mL of dilute dispersant, shaken overnight in 50 mL centrifuge tubes. Clay is determined by sampling 2.5 mL using an adjustable volume pipettor from a depth of 2.5 cm after approximately 2 h of settling, as calculated from Stokes’ law. The dried suspension weight is used to compute clay content after correction for salt content of the dispersant. Sand can be determined by sieving at 50 μm after clay analysis, with silt calculated by difference. Using 12 soils with a range of particle sizes, the proposed method was found to give textural values nearly identical to those found with the st...
436 citations
TL;DR: Scrap loading and sonication loading are two recently described methods of introducing macromolecules into living cells as discussed by the authors, which can be employed to generate cell lines that express the gene product of the transfected DNA molecules both transiently and stably.
Abstract: Scrape loading and sonication loading are two recently described methods of introducing macromolecules into living cells. We have tested the efficacy of these methods for transfection of mammalian cells with exogenous DNA, using selection systems based either on resistance to the drug G418 (Geneticin) or on acquisition of the ability to utilize the salvage pathway of pyrimidine biosynthesis. These loading methods can be employed to generate cell lines that express the gene product of the transfected DNA molecules both transiently and stably. Optimal transfection is observed when the DNA is added to cells in physiological saline lacking divalent cations and containing K+ in place of Na+. DNA molecules 7.1 to 30 kilobases long have been introduced by the scrape loading procedure. In addition, the scrape loading procedure has been employed for cotransfection and subsequent expression of nonselectable genes encoded on DNA molecules added in a mixture with DNA molecules whose expression is selected. Cell lines expressing oncogenes or proteins that are important for regulation of cell growth and division have been obtained by this procedure. The scrape loading procedure is also useful for studies of the cellular changes that occur upon expression of an exogenous gene. As many as 80% of cells scrape loaded with the plasmid pC6, which encodes the simian virus 40 large tumor antigen, contained this protein in the nucleus between 1 and 5 days after transfection. Thus, scrape loading and sonication loading are simple, economical, and reproducible methods for introduction of DNA molecules into adherent and nonadherent cells, and these methods may be useful in the future for experimentation at both fundamental and applied levels.
389 citations
TL;DR: Bacterial clearance rates for pelagic ciliates are measured which are 10–100 times greater than earlier estimates and may 'short-circuit' the microbial loop in aquatic ecosystems by making bacterioplankton production available to metazoan grazers via a simple, two-step food chain.
Abstract: It has been thought that ciliate protozoans that consume bacteria are not found in open waters except at micro-sites of high bacterial density1,2. Previous laboratory studies, using ciliates isolated from benthic habitats have suggested that (1), ciliates that can ingest bacterial-sized particles have cell-specific clearance rates too low to obtain sufficient food for growth at the bacterial abundances found in most marine and fresh waters3,4, and (2), spirotrichous ciliates cannot ingest particles of less than 1–2 µm in diameter3,4. New data on uptake rates of pelagic ciliates at low bacterial concentrations refute both of these ideas. We and others have found that ciliates, including spirotrichous forms, present in the plankton of both coastal marine waters and lakes can be voracious consumers of bacteria5–8. Using a new method for preparing monodisperse, fluorescently labelled 'marker' bacteria, we have measured bacterial clearance rates for pelagic ciliates which are 10–100 times greater than earlier estimates. In waters of a salt marsh estuary, ciliate grazing can account for 100% of estimated protozoan bacterivory. Ciliate bacterivory may 'short-circuit' the microbial loop in aquatic ecosystems by making bacterioplankton production available to metazoan grazers via a simple, two-step food chain.
TL;DR: In this paper, a conceptual model of how training can impact the acceptance of information systems within the organization is presented and empirically evaluated via an extensive field study of 100 middle-and upper-level managers from 20 companies.
Abstract: This article presents and empirically evaluates a conceptual model of how training can impact the acceptance of information systems within the organization. Specifically, the training of end users is explored via an extensive field study of 100 middle- and upper-level managers from 20 companies. The results indicate that (1) a positive relationship exists between the computer-related training an individual receives and his/her computer-related ability, and (2) a positive relationship exists between the computer-related ability of an end user and his/her acceptance of information systems products and technologies.
TL;DR: Mussels, clams, and tube worms collected in the vicinity of hydrocarbon seeps on the Louisiana slope contain mostly "dead" carbon, indicating that dietary carbon is largely derived from seeping oil and gas.
Abstract: Mussels, clams, and tube worms collected in the vicinity of hydrocarbon seeps on the Louisiana slope contain mostly "dead" carbon, indicating that dietary carbon is largely derived from seeping oil and gas. Enzyme assays, elemental sulfur analysis, and carbon dioxide fixation studies demonstrate that vestimentiferan tube worms and three clam species contain intracellular, autotrophic sulfur bacterial symbionts. Carbon isotopic ratios of 246 individual animal tissues were used to differentiate heterotrophic (8(13)C = -14 to -20 per mil), sulfur-based (8(13)C = -30 to -42 per mil), and methane-based (8(13)C = <-40 per mil) energy sources. Mussels with symbiotic methanotrophic bacteria reflect the carbon isotopic composition of the methane source. Isotopically light nitrogen and sulfur confirm the chemoautotrophic nature of the seep animals. Sulfur-based chemosynthetic animals contain isotopically light sulfur, whereas methane-based symbiotic mussels more closely reflect the heavier oceanic sulfate pool. The nitrogen requirement of some seep animals may be supported by nitrogen-fixing bacteria. Some grazing neogastropods have isotopic values characteristic of chemosynthetic animals, suggesting the transfer of carbon into the background deep-sea fauna.
TL;DR: Characterization of the minimum components necessary for the functional organization of pigments in these membrane complexes reveals that xanthophylls are essential structural components.
Abstract: A method for in vitro reconstitution of the chlorophyll a/b light-harvesting complex from LiDodSO4/heat-denatured or acetone-extracted photosynthetic membranes has been developed. Characterization of the minimum components necessary for the functional organization of pigments in these membrane complexes reveals that xanthophylls are essential structural components.
TL;DR: New analysis of the number of reported cases of AIDS in a defined population to the proportion of that population infected with the virus as a specified time point reveals age-related differences in the mean and median incubation period.
Abstract: Temporal trends in the prevalence of HIV (human immunodeficiency virus) infection are uncertain because of the reluctance of most governments to embark on large-scale programmes of serological surveillance. In the absence of such data, attempts have been made to relate the number of reported cases of AIDS (acquired immune deficiency syndrome) in a defined population to the proportion of that population infected with the virus as a specified time point. One crucial determinant of this relationship is the probability distribution of the incubation period of the disease, with the period defined as the time interval from infection to diagnosis. Recent statistical analysis suggests a mean incubation period of 4.5 years with wide confidence limits, whereas a more heuristic study reports a mean of 15 years. Here we report on a new analysis which reveals age-related differences in the mean (and median) incubation period: 1.97 (1.90) years for children (0-4 yrs old at infection), 8.23 (7.97) years for adults (5-59 yrs old), 5.50 (5.44) years for elderly patients (60 yrs and older).
TL;DR: In this article, a two-step model describing the thermal dependence of the dormancy breaking phenomenon is developed, which assumes that the level of dormancy completion is proportional to the amount of a certain dormancy-breaking factor which accumulates in plants by a 2-step process.
TL;DR: Chicken may be the principal vehicle of transmission for sporadic Campylobacter enteritis among college students and three risk factors were identified: eating fully cooked chicken, eating chicken reported to be raw or undercooked, and contact with a cat or kitten.
Abstract: Campylobacter jejuni is the most common enteric pathogen isolated from university and college students in the United States. During the fall and winter quarters of the 1983-1984 academic year, the authors conducted a case-control study at the University of Georgia, Athens, Georgia, to identify risk factors for C. jejuni enteritis. Students with diarrhea whose cultures yielded C. jejuni were compared with controls matched by age, sex, and residence. A total of 45 case-control pairs were interviewed about exposures during the week before the case's onset of illness. The infections occurred sporadically and were caused by a wide variety of C. jejuni serotypes. Three risk factors were identified: eating fully cooked chicken, eating chicken reported to be raw or undercooked, and contact with a cat or kitten. No case reported drinking raw milk. No significant association was found between illness and the places where chicken meals were prepared or the specific manner in which chicken was cooked. Chicken may be the principal vehicle of transmission for sporadic Campylobacter enteritis among college students.
TL;DR: In this paper, the authors developed spatial simulation models to predict temporal changes in land use patterns in a piedmont county in Georgia (USA) using historical aerial photography and digitized into a matrix based on 1 ha grid cell format.
Abstract: Spatial simulation models were developed to predict temporal changes in land use patterns in a piedmont county in Georgia (USA). Five land use categories were included: urban, cropland, abandoned cropland, pasture, and forest. Land use data were obtained from historical aerial photography and digitized into a matrix based on a 1 ha grid cell format. Three different types of spatial simulation were compared: (1) random simulations based solely on transition probabilities; (2) spatial simulations in which the four nearest neighbors (adjacent cells only) influence transitions; and (3) spatial simulations in which the eight nearest neighbors (adjacent and diagonal cells) influence transitions. Models and data were compared using the mean number and size of patches, fractal dimension of patches, and amount of edge between land uses. The random model simulated a highly fragmented landscape having numerous, small patches with relatively complex shapes. The two versions of the spatial model simulated cropland well, but simulated patches of forest and abandoned cropland were fewer, larger, and more simple than those in the real landscape. Several possible modifications of model structure are proposed. The modeling approach presented here is a potentially general one for simulating human-influenced landscapes.
TL;DR: This article found that 30% of men and 32% of women reported engaging in some form of physical aggression against a current steady dating partner and 49% of the women reported being the victims of their current dating partner's physical aggression.
Abstract: A total of 95 males and 175 females provided information about whether they had engaged in or been victims of physical aggression in past and/or current dating relationships. Some 30% of the men and 32% of the women reported engaging in some form of physical aggression against a current steady dating partner. Additionally, 49% of the men and 26% of the women reported being the victims of their current dating partner's physical aggression. Length of the dating relationship was associated with men's physical aggression and their victimization was associated with decreased liking for their partners. Women's experiences with physical aggression in a dating relationship as both victims and aggressors were related to the length of the relationship, less liking for the partner, and less positive affect for the partner.
TL;DR: The cell walls of Douglas fir were more similar to dicot (sycamore) cell walls than to those of graminaceous monocots, because they had a predominance of xyloglucan over xylan as the principle hemicellulose and because they possessed relatively large amounts of rhamnogalacturonan-like pectic polysaccharides.
Abstract: The partial purification and characterization of cell wall polysaccharides isolated from suspension-cultured Douglas fir (Pseudotsuga menziesii) cells are described. Extraction of isolated cell walls with 1.0 m LiCl solubilized pectic polysaccharides with glycosyl-linkage compositions similar to those of rhamnogalacturonans I and II, pectic polysaccharides isolated from walls of suspension-cultured sycamore cells. Treatment of LiCl-extracted Douglas fir walls with an endo-alpha-1,4-polygalacturonase released only small, additional amounts of pectic polysaccharide, which had a glycosyl-linkage composition similar to that of rhamnogalacturonan I. Xyloglucan oligosaccharides were released from the endo-alpha-1,4-polygalacturonase-treated walls by treatment with an endo-beta-1,4-glucanase. These oligosaccharides included hepta- and nonasaccharides similar or identical to those released from sycamore cell walls by the same enzyme, and structurally related octa- and decasaccharides similar to those isolated from various angiosperms. Finally, additional xyloglucan and small amounts of xylan were extracted from the endo-beta-1,4-glucanase-treated walls by 0.5 n NaOH. The xylan resembled that extracted by NaOH from dicot cell walls in that it contained 2,4- but not 3,4-linked xylosyl residues. In this study, a total of 15% of the cell wall was isolated as pectic material, 10% as xyloglucan, and less than 1% as xylan. The noncellulosic polysaccharides accounted for 26% of the cell walls, cellulose for 23%, protein for 34%, and ash for 5%, for a total of 88% of the cell wall. The cell walls of Douglas fir were more similar to dicot (sycamore) cell walls than to those of graminaceous monocots, because they had a predominance of xyloglucan over xylan as the principle hemicellulose and because they possessed relatively large amounts of rhamnogalacturonan-like pectic polysaccharides.
01 Jan 1987
TL;DR: This article found that divergent responses toward abortion, as measured in two consecutive surveys, were caused not by a change of opinion over time but by the presence or absence of a particular question before the target question.
Abstract: The central goal of asking questions in a survey is to obtain reliable information about characteristics of the respondent. Asking, and consequently answering questions, however, never occurs in a vacuum. Rather, it occurs in a specific social and cognitive context that may influence responses in undesired ways (e.g., Schuman & Presser, 1981). Thus, a change in the answer to a particular question may not necessarily reflect an attitude change on the part of the respondent but simply may be the influence of a different context. Schuman, Presser, and Ludwig (1981), for example, found that divergent responses toward abortion, as measured in two consecutive surveys, were caused not by a change of opinion over time but by the presence or absence of a particular question before the target question.
TL;DR: It is unlikely that spatial resources were limiting during the investigation of microhabitat use among fishes in Coweeta Creek, North Carolina, because there was no evidence of either exploitation or interference competition for microhabITat, consequently it is unlikely to have changed markedly during the study.
Abstract: We examined microhabitat use among fishes in a 37-m section of Coweeta Creek, North Carolina. Numerical abundances of species changed substantially during the 17-month study period. Microhabitat availability, however, did not change markedly during our investigation. Seasonal principal component analyses of microhabitat availability and fish microhabitat use data extracted two main patterns of non-random microhabitat use. Clinostomus funduloides, Notropis eoccogenis and Semotilus atromaculatm were significantly over-represented in deep areas with low to intermediate velocities and depositional substrata. Campostoma oligolepis, Coitus bairdi, Etheostoma blennioides, Rhinichthys cataractae and Salmo gairdneri all occurred in intermediate to deep microhabitats with moderate to high velocities and erosional substrata. Five of seven species exhibited seasonal variation in microhabitat utilization, whereas six species displayed size-related variation in use. Size-related variation was probably ontogenetic. We attributed most seasonal changes in microhabitat use to variations in microhabitat availability.
We used canonical analysis of discriminants to identify factors maximizing interspecific differences in microhabitat use. This analysis indicated that species could be assigned to either a benthic or a water column guild. Species within a guild generally could not be differentiated statistically, whereas members of different guilds were readily separable. These patterns persisted throughout the study, despite changes in numerical abundances of assemblage members. There was no evidence of either exploitation or interference competition for microhabitat, consequently it is unlikely that spatial resources were limiting during our study.
TL;DR: Human cathepsin G is a serine proteinase with chymotrypsin-like specificity found in both polymorphonuclear leukocytes (neutrophils) and the U937 leukemic cell line and a cDNA library is constructed and a clone is isolated which apparently codes for the complete amino acid sequence of this enzyme.
Abstract: Human cathepsin G is a serine proteinase with chymotrypsin-like specificity found in both polymorphonuclear leukocytes (neutrophils) and the U937 leukemic cell line. Utilizing RNA from the latter, we have constructed a cDNA library in lambda gt11 and isolated a clone which apparently codes for the complete amino acid sequence of this enzyme. Analysis of the sequence reveals homology with rat mast cell proteinase II (47%) but a greater degree of identity (56%) with a product of activated mouse cytotoxic T lymphocytes. The close relationship between the three proteins indicates similarities in substrate specificity and in biosynthesis which we predict involves removal of a two amino acid activation peptide during or just before packaging into their respective storage granules.
TL;DR: Results show that soybean calcium-dependentprotein kinase represents a new class of protein kinase which requires calcium but not calmodulin for activity.
Abstract: A calcium-dependent protein kinase activity from suspension-cultured soybean cells (Glycine max L. Wayne) was shown to be dependent on calcium but not calmodulin. The concentrations of free calcium required for half-maximal histone H1 phosphorylation and autophosphorylation were similar (≈2 micromolar). The protein kinase activity was stimulated 100-fold by ≥10 micromolar-free calcium. When exogenous soybean or bovine brain calmodulin was added in high concentration (1 micromolar) to the purified kinase, calcium-dependent and -independent activities were weakly stimulated (≤2-fold). Bovine serum albumin had a similar effect on both activities. The kinase was separated from a small amount of contaminating calmodulin by sodium dodecyl sulfate polyacrylamide gel electrophoresis. After renaturation the protein kinase autophosphorylated and phosphorylated histone H1 in a calcium-dependent manner. Following electroblotting onto nitrocellulose, the kinase bound 45Ca2+ in the presence of KCl and MgCl2, which indicates that the kinase itself is a high-affinity calcium-binding protein. Also, the mobility of one of two kinase bands in SDS gels was dependent on the presence of calcium. Autophosphorylation of the calmodulin-free kinase was inhibited by the calmodulin-binding compound N-(6-aminohexyl)-5-chloro-1-naphthalene sulfonamide (W-7), showing that the inhibition of activity by W-7 is independent of calmodulin. These results show that soybean calcium-dependent protein kinase represents a new class of protein kinase which requires calcium but not calmodulin for activity.
TL;DR: Cloned and characterized three genes from Aspergillusnidulans, designated brlA, abaA and wetA, whose activities are required to complete different stages of conidiophore development and confirm genetic predictions as to the temporal and spatial patterns of expression and demonstrate that these patterns are specified at the level of RNA accumulation.
Abstract: We cloned and characterized three genes from Aspergillusnidulans, designated brlA, abaA and wetA, whose activities are required to complete different stages of conidiophore development. Inactivation of these genes causes major abnormalities in conidiophore morphology and prevents expression of many unrelated, developmentally regulated genes, without affecting expression of nonregulated genes. The three genes code for poly(A)+RNAs that begin to accumulate at different times during conidiation. The brlA-and abaA-encoded RNAs accumulate specifically in cells of the conidiophore. The wetA-encoded RNA accumulates in mature conidia. Inactivation of the brlA gene prevents expression of the abaA and wetA genes, whereas inactivation of the abaA gene prevents expression of the wetA gene. Our results confirm genetic predictions as to the temporal and spatial patterns of expression of these genes and demonstrate that these patterns are specified at the level of RNA accumulation.
TL;DR: The molecular mechanics (MMP2) program and procedures for the treatment of conjugated hydrocarbons, and some of the results which they can achieve are described in this article.
Abstract: The molecular mechanics (MMP2) program and procedures for the treatment of conjugated hydrocarbons, and some of the results which they can achieve are described. The program is an updated version of the similar MMP1 program, but contains some differences. It is based on an SCF π system calculation, rather than on the VESCF method used earlier. All parameters are compatible with those in the MM2 program. Hence it is possible to calculate heats of formation, resonance energies, and structures for conjugated hydrocarbons in a way that is consistent with the calculations on non-conjugated molecules. The overall results as far as structure and energy are somewhat better than they were with the MMP1 program.
TL;DR: Simulation of the dormancy breaking at cycled temperature regimes of a dynamic two-step model involving a cooperative transition shows the bell-shaped dependence on temperature for dormancy completion and the negation of the chilling effect by high temperatures, and the enhancement of the effect by short applications of high temperatures.
TL;DR: Bacteria produced at the expense of abundant riverine DOC provide a trophic resource for protozoa and higher levels of the microbial food web of a blackwater river.
Abstract: Different nominal molecular weight (nMW) fractions of DOC from a southeastern blackwater river were concentrated by ultrafiltration and added to sieved river water to assess each fraction's ability to stimulate bacterial growth. Bacterial growth was measured using change in bacterial biomass from direct counts and using3H-thymidine incorporated into DNA. Bacterial growth and amount of DOC used was greatest in the low MW enrichment ( 10,000 nMW) supported more growth than did the intermediate MW fraction, apparently because of lower MW compounds complexed with a high MW refractory core. The low MW fraction of DOC from a clearwater mountain stream, a boreal blackwater river, and leachate from water oak and willow leaves also stimulated more bacterial growth than did other fractions. However, the high MW DOC from these other sources was not as biologically available as high MW DOC from a blackwater river. Bacteria converted blackwater river DOC to bacterial biomass with an efficiency of 31%. Bacteria produced at the expense of abundant riverine DOC provide a trophic resource for protozoa and higher levels of the microbial food web of a blackwater river.