Showing papers by "Oregon State University published in 1999"

Vitamin E: function and metabolism

Abstract: Although vitamin E has been known as an essential nutrient for reproduction since 1922, we are far from understanding the mechanisms of its physiological functions. Vitamin E is the term for a group of tocopherols and tocotrienols, of which alpha-tocopherol has the highest biological activity. Due to the potent antioxidant properties of tocopherols, the impact of alpha-tocopherol in the prevention of chronic diseases believed to be associated with oxidative stress has often been studied, and beneficial effects have been demonstrated. Recent observations that the alpha-tocopherol transfer protein in the liver specifically sorts out RRR-alpha-tocopherol from all incoming tocopherols for incorporation into plasma lipoproteins, and that alpha-tocopherol has signaling functions in vascular smooth muscle cells that cannot be exerted by other forms of tocopherol with similar antioxidative properties, have raised interest in the roles of vitamin E beyond its antioxidative function. Also, gamma-tocopherol might have functions apart from being an antioxidant. It is a nucleophile able to trap electrophilic mutagens in lipophilic compartments and generates a metabolite that facilitates natriuresis. The metabolism of vitamin E is equally unclear. Excess alpha-tocopherol is converted into alpha-CEHC and excreted in the urine. Other tocopherols, like gamma- and delta-tocopherol, are almost quantitatively degraded and excreted in the urine as the corresponding CEHCs. All rac alpha-tocopherol compared to RRR-alpha-tocopherol is preferentially degraded to alpha-CEHC. Thus, there must be a specific, molecular role of RRR-alpha-tocopherol that is regulated by a system that sorts, distributes, and degrades the different forms of vitamin E, but has not yet been identified. In this article we try to summarize current knowledge on the function of vitamin E, with emphasis on its antioxidant vs. other properties, the preference of the organism for RRR-alpha-tocopherol, and its metabolism to CEHCs.

Field management effects on soil enzyme activities

Abstract: There is growing recognition for the need to develop sensitive indicators of soil quality that reflect the effects of land management on soil and assist land managers in promoting long-term sustainability of terrestrial ecosystems. Eleven soil enzymes assays were investigated relative to soil management and soil quality at two study sites. Soils were sampled from the Vegetable Crop Rotation Plots (VRP) (established in 1989 in humid western Oregon) which compared continuous fescue (Festuca arundinacea) and four winter cover crop treatments in annual rotation with a summer vegetable crop. The second site was the Residue Utilization Plots (RUP) (initiated in 1931 in semi-arid Eastern Oregon) which is under a winter wheat–summer fallow and compared inorganic N, green manure and beef manure treatments. Soil also was sampled at the research center from a nearby grass pasture that is on the same soil type. The enzymes were α- and β-glucosidase, α- and β-galactosidase, amidase, arylsulfatase, deaminase, fluorescein diacetate hydrolysis, invertase, cellulase and urease. At both sites there was a significant treatment effect for each enzyme tested (P<0.05). Enzyme activities (except α- and β-glucosidase and α- and β-galactosidase) were generally higher in continuous grass fields than in cultivated fields. In cultivated systems, activity was higher where cover crops or organic residues were added as compared to treatments without organic amendments. It was found that use of air-dried soil samples provided the same ranking of treatments by a number of enzyme assays and would facilitate adoption of these assays for practical or commercial applications. Deaminase was not a good indicator of soil quality, while β-glucosidase was suggested as an assay that reflects soil management effects and has microbial ecological significance because of its role in the C cycle.

Does vitamin C act as a pro-oxidant under physiological conditions?

Abstract: Vitamin C readily scavenges reactive oxygen and nitrogen species and may thereby prevent oxidative damage to important biological macromolecules such as DNA, lipids, and proteins. Vitamin C also reduces redox active transition metal ions in the active sites of specific biosynthetic enzymes. The interaction of vitamin C with ‘free’, catalytically active metal ions could contribute to oxidative damage through the production of hydroxyl and alkoxyl radicals; whether these mechanisms occur in vivo, however, is uncertain. To examine this issue, we reviewed studies that investigated the role of vitamin C, both in the presence and absence of metal ions, in oxidative DNA, lipid, and protein damage. We found compelling evidence for antioxidant protection of lipids by vitamin C in biological fluids, animals, and humans, both with and without iron cosupplementation. Although the data on protein oxidation in humans are sparse and inconclusive, the available data in animals consistently show an antioxidant role of vit...

Leader–member exchange (LMX) research: A comprehensive review of theory, measurement, and data-analytic practices.

Abstract: Research conducted since the construct of leader-member exchange (LMX) was first investigated in 1972 is reviewed with respect to the theoretical, measurement, and analytic adequacy of LMX studies. It is shown that conceptual definitions of LMX and its subdimensions have evolved over time, often with little reason or rationale given for changes. Likewise, the measures employed to assess LMX have varied widely and have included an almost bewildering array of diverse item content. Finally, LMX research has rarely examined the level of analysis at which its findings hold. All of these shortcomings lead to the conclusion that we may know less than we should about fundamental leader-member exchange processes and that future research must be conducted with greater attention devoted to the key issues outlined in this review.

Teachers' Understanding of the Nature of Science and Classroom Practice: Factors That Facilitate or Impede the Relationship.

Abstract: The purpose of this multiple case study was to investigate the relationship of teachers' understanding of the nature of science and classroom practice and to delineate factors that facilitate or impede a relationship Five high school biology teachers, ranging in experience from 2 to 15 years, comprised the sample for this investigation During one full academic year, multiple data sources were collected and included classroom observations, open-ended questionnaires, semistructured and structured interviews, and instructional plans and materials In addition, students in each of the teachers' classrooms were interviewed with respect to their understanding of the nature of science Using analytical induction, multiple data sources were analyzed independently and together to triangulate data while constructing teacher profiles The results indicated that teachers' conceptions of science do not necessarily influence classroom practice Of critical importance were teachers' level of experience, intentions, and perceptions of students The results have importnat implications for teacher education as well as the successful implementation of current reforms © 1999 John Wiley & Sons, Inc J Res Sci Teach 36: 916–929, 1999

Climate change and plant disease management

Abstract: ▪ Abstract Research on impacts of climate change on plant diseases has been limited, with most work concentrating on the effects of a single atmospheric constituent or meteorological variable on the host, pathogen, or the interaction of the two under controlled conditions. Results indicate that climate change could alter stages and rates of development of the pathogen, modify host resistance, and result in changes in the physiology of host-pathogen interactions. The most likely consequences are shifts in the geographical distribution of host and pathogen and altered crop losses, caused in part by changes in the efficacy of control strategies. Recent developments in experimental and modeling techniques offer considerable promise for developing an improved capability for climate change impact assessment and mitigation. Compared with major technological, environmental, and socioeconomic changes affecting agricultural production during the next century, climate change may be less important; it will, however, ...

Analyzing protein circular dichroism spectra for accurate secondary structures

Abstract: We have developed an algorithm to analyze the circular dichroism of proteins for secondary structure. Its hallmark is tremendous flexibility in creating the basis set, and it also combines the ideas of many previous workers. We also present a new basis set containing the CD spectra of 22 proteins with secondary structures from high quality X-ray diffraction data. High flexibility is obtained by doing the analysis with a variable selection basis set of only eight proteins. Many variable selection basis sets fail to give a good analysis, but good analyses can be selected without any a priori knowledge by using the following criteria: (1) the sum of secondary structures should be close to 1.0, (2) no fraction of secondary structure should be less than -0.03, (3) the reconstructed CD spectrum should fit the original CD spectrum with only a small error, and (4) the fraction of alpha-helix should be similar to that obtained using all the proteins in the basis set. This algorithm gives a root mean square error for the predicted secondary structure for the proteins in the basis set of 3.3% for alpha-helix, 2.6% for 3(10)-helix, 4.2% for beta-strand, 4.2% for beta-turn, 2.7% for poly(L-proline) II type 3(1)-helix, and 5.1% for other structures when compared with the X-ray structure.

Test case prioritization: an empirical study

Abstract: Test case prioritization techniques schedule test cases for execution in an order that attempts to maximize some objective function. A variety of objective functions are applicable; one such function involves rate of fault detection-a measure of how quickly faults are detected within the testing process. An improved rate of fault detection during regression testing can provide faster feedback on a system under regression test and let debuggers begin their work earlier than might otherwise be possible. In this paper we describe several techniques for prioritizing test cases and report our empirical results measuring the effectiveness of these techniques for improving rate of fault detection. The results provide insights into the tradeoffs among various techniques for test case prioritization.

Stratified atmospheric boundary layers

Abstract: Various features of different stability regimes of the stable boundary layer are discussed. Traditional layering is examined in terms of the roughness sublayer, surface layer, local similarity, z-less stratification and the region near the boundary-layer top. In the very stable case, the strongest turbulence may be detached from the surface and generated by shear associated with a low level jet, gravity waves or meandering motions. In this case, similarity theory and the traditional concept of a boundary-layer break down. The elevated turbulence may intermittently recouple to the surface. Inability to adequately measure turbulent fluxes in very stable conditions limits our knowledge of this regime.

Seasonal and annual respiration of a ponderosa pine ecosystem

Abstract: The net ecosystem exchange of CO2 between forests and the atmosphere, measured by eddy covariance, is the small difference between two large fluxes of photosynthesis and respiration Chamber measurements of soil surface CO2 efflux (Fs), wood respiration (Fw) and foliage respiration (Ff) help identify the contributions of these individual components to net ecosystem exchange Models developed from the chamber data also provide independent estimates of respiration costs We measured CO2 efflux with chambers periodically in 1996–97 in a ponderosa pine forest in Oregon, scaled these measurements to the ecosystem, and computed annual totals for respiration by component We also compared estimated half-hourly ecosystem respiration at night (Fnc) with eddy covariance measurements Mean foliage respiration normalized to 10 °C was 020 μmol m–2 (hemi-leaf surface area) s–1, and reached a maximum of 024 μmol m–2 HSA s–1 between days 162 and 208 Mean wood respiration normalized to 10 °C was 59 μmol m–3 sapwood s–1, with slightly higher rates in mid-summer, when growth occurs There was no significant difference (P > 010) between wood respiration of young (45 years) and old trees (250 years) Soil surface respiration normalized to 10 °C ranged from 07 to 30 μmol m–2 (ground) s–1 from days 23 to 329, with the lowest rates in winter and highest rates in late spring Annual CO2 flux from soil surface, foliage and wood was 683, 157, and 54 g C m–2 y–1, with soil fluxes responsible for 76% of ecosystem respiration The ratio of net primary production to gross primary production was 045, consistent with values for conifer sites in Oregon and Australia, but higher than values reported for boreal coniferous forests Below-ground carbon allocation (root turnover and respiration, estimated as Fs– litterfall carbon) consumed 61% of GPP; high ratios such as this are typical of sites with more water and nutrient constraints The chamber estimates were moderately correlated with change in CO2 storage in the canopy (Fstor) on calm nights (friction velocity u* 025 m s–1), the sum of turbulent flux measured above the canopy by eddy covariance and Fstor was only weakly correlated with summed chamber estimates (R2 = 014); the eddy covariance estimates were lower than chamber estimates by 50%

Northern Hemisphere Ice-Sheet Influences on Global Climate Change

Abstract: Large ice sheets actively interact with the rest of the climate system by amplifying, pacing, and potentially driving global climate change over several time scales. Direct and indirect influences of ice sheets on climate cause changes in ocean surface temperatures, ocean circulation, continental water balance, vegetation, and land-surface albedo, which in turn cause additional feedbacks in the climate system and help to synchronize global climate change. The effect of the underlying geological substrate on ice-sheet dynamics may be the missing link in understanding the ice sheet–climate interactions that are integral to the middle Pleistocene transition; the 100,000-year climate cycle; high-amplitude, millennial-scale climate variability; and low–aspect ratio ice sheets of the Last Glacial Maximum.

Regulation of keystone predation by small changes in ocean temperature

Abstract: Key species interactions that are sensitive to temperature may act as leverage points through which small changes in climate could generate large changes in natural communities. Field and laboratory experiments showed that a slight decrease in water temperature dramatically reduced the effects of a keystone predator, the sea star Pisaster ochraceus, on its principal prey. Ongoing changes in patterns of cold water upwelling, associated with El Nino events and longer term geophysical changes, may thus have far-reaching impacts on the composition and diversity of these rocky intertidal communities.

Patterns of historical earthquake rupture in the iranian plateau

Abstract: The Iranian plateau accommodates the 35 mrn/yr convergence rate be- tween the Eurasian and Arabian plates by strike-slip and reverse faults with relatively low slip rates in a zone 1000 km across. Although these faults have only locally been the subject of paleoseismological studies, a rich historical and archeological record spans several thousand years, long enough to establish recurrence intervals of 1000 to 5000 yr on individual fault segments. Several clusters of earthquakes provide evidence of interaction among reverse and strike-slip faults, probably due to adjacent faults being loaded by individual earthquakes. The Dasht-e-Bayaz sequence of 1936 to 1997 includes earthquakes on left-lateral, right-lateral, and reverse faults. The Neyshabur sequence of four earthquakes between 1209 and 1405 respected the seg- ment boundary between the Neyshabur and Binalud reverse fault systems. The two pairs of earthquakes may have ruptured different faults in each segment, similar to the 1971 and 1994 San Fernando, California, earthquakes. The 1978 Tabas reverse- fault earthquake was preceded by the 1968 Ferdows earthquake, part of the Dasht- e-Bayaz sequence. The North Tabriz fault system ruptured from southeast to north- west in three earthquakes from 1721 to 1786; a previous cluster may have struck this region in 855 to 958. The Mosha fault north of Tehran ruptured in three earthquakes in 958, 1665, and 1830. Five large earthquakes struck the Tehran region from 743 to 1177, but only two that large have struck the area since 1177. Other earthquakes occurred in pairs in the Talesh Mountains near the Caspian Sea (1863, 1896), the Iran-Turkey border (1840, 1843), and the Nayband-Gowk fault system (both 1981). Other historical events did not occur as parts of sequences. The historic seismic moment release in Iran accounts for only a small part of the plate convergence rate, which may be due to aseismic slip or to the Iranian historical record, long as it is, being too short to sample long-term deformation across the plateau. No historic earthquakes of M --> 8 have struck Iran. However, several long, straight strike-slip faults (Doruneh, West Neh, East Neh, and Nayband) have not sustained large historical earthquakes, raising the possibility that these long faults could produce earthquakes of M => 8, thereby removing at least part of the apparent slip deficit. An increased understanding of Iran's seismic hazard could be obtained by an extensive paleoseismology program and space-geodetic arrays, supplementing the abundant historical and archaeological record.

Founding Family Control and Capital Structure: The Risk of Loss of Control and the Aversion to Debt

Abstract: This paper tests the hypothesis that Founding Family Controlled Firms (FFCFs) are more averse to control risk than similar non-FFCFs and therefore avoid debt. Higher levels of debt increase the lik...

Multiscale thermal refugia and stream habitat associations of chinook salmon in northeastern oregon

Abstract: We quantified distribution and behavior of adult spring chinook salmon (Oncorhynchus tshawytscha ) related to patterns of stream temperature and physical habitat at channel-unit, reach-, and section-level spatial scales in a wilderness stream and a disturbed stream in the John Day River basin in northeastern Oregon. We investigated the effectiveness of thermal remote sensing for analyzing spatial patterns of stream temperature and assessed habitat selection by spring chinook salmon, evaluating whether thermal refugia might be responsible for the persistence of these stocks in rivers where water temperatures frequently exceed their upper tolerance levels (258C) during spawning migration. By presenting stream temperature and the ecology of chinook salmon in a historical context, we could evaluate how changes in riverine habitat and thermal spatial structure, which can be caused by land- use practices, may influence distributional patterns of chinook salmon. Thermal remote sensing provided spatially continuous maps of stream temperature for reaches used by chinook salmon in the upper subbasins of the Middle Fork and North Fork John Day River. Electivity analysis and logistic regression were used to test for associations between the longitudinal distribution of salmon and cool-water areas and stream habitat characteristics. Chinook salmon were distributed nonuniformly in reaches throughout each stream. Salmon distribution and cool water temperature patterns were most strongly related at reach-level spatial scales in the warm stream, the Middle Fork (maximum likelihood ratio: P , 0.01), and most weakly related in the cold stream, the North Fork (P. 0.30). Pools were preferred by adult chinook salmon in both subbasins (Bonferroni confidence interval: P # 0.05); however, riffles were used proportionately more frequently in the North Fork than in the Middle Fork. Our observations of thermal refugia and their use by chinook salmon at multiple spatial scales reveal that, although heterogeneity in the longitudinal stream tem- perature profile may be viewed as an ecological warning sign, thermal patchiness in streams also should be recognized for its biological potential to provide habitat for species existing at the margin of their environmental tolerances.

Cutting edge: 4-1BB is a bona fide CD8 T cell survival signal.

Abstract: After recognition of Ag/MHC and ligation of a costimulatory molecule, resting T cells will clonally expand and then delete to very low levels. Previously, it was shown that deletion can be prevented by coinjection of cytokines or proinflammatory agents such as adjuvants. Here, we demonstrate that ligation of 4-1BB blocks deletion of superantigen-activated T cells in the absence of adjuvant or additional cytokine treatment. Nearly 10 times as many staphylococcal enterotoxin A-specific T cells were detected in the spleens of mice injected 21 days previously with staphylococcal enterotoxin A and an agonist anti-4-1BB Ab compared with mice given staphylococcal enterotoxin A and a control IgG. Even though both CD4- and CD8-activated T cells expressed 4-1BB, a higher proportion of CD8 T cells were rescued compared CD4 T cells. These data suggest that although 4-1BB provides costimulation, it may also promote long-term T cell survival.

Evidence that hydraulic conductance limits photosynthesis in old Pinus ponderosa trees.

Abstract: We tested the hypotheses that hydraulic conductance is lower in old (about 250 years old and 30 m tall) compared to young (about 40 years old and 10 m tall) Pinus ponderosa Dougl. ex Laws. trees and that lower hydraulic conductance of old trees limits their photosynthesis. Hydraulic conductance at the end of summer 1995, calculated from leaf water potential and leaf gas exchange measurements on one-year-old needles, was 44% lower in old trees compared to young trees growing in a mixed age-class stand on the east slope of the Oregon Cascades. Whole-tree sapflow per unit leaf area averaged 53% lower in old trees compared to young trees and mean hydraulic conductance calculated from sapflow and water potential data was 63% lower in old trees than in young trees. For the entire summer, stomatal conductance (g s ) and assimilation (A) declined more steeply with air saturation deficit (D) in old trees than in young trees. For both old and young trees, mean g s and A were approximately 32 and 21% lower, respectively, at typical midday D values (2.5-3.0 kPa). We hypothesized that if hydraulic conductance limits g s and A, then increasing or decreasing the leaf specific conductance of a branch will result in proportional changes in the responses of g s and A with D. Removal of 50% of the foliage from a set of experimental branches on old trees caused g s and A to decline less steeply with D in early summer, but values were not significantly different from control values in late summer. Cutting transverse notches in branches on young trees had no effect on the responses of g s and A with D. Leaf nitrogen content and photosynthetic capacity were similar suggesting that differences in g s and A between old and young trees were not caused by differences in photosynthetic capacity.

Lipid synthesis under hydrothermal conditions by Fischer-Tropsch-type reactions.

Abstract: Ever since their discovery in the late 1970's, mid-ocean-ridge hydrothermal systems have received a great deal of attention as a possible site for the origin of life on Earth (and environments analogous to mid-ocean-ridge hydrothermal systems are postulated to have been sites where life could have originated or Mars and elsewhere as well) Because no modern-day terrestrial hydrothermal systems are free from the influence of organic compounds derived from biologic processes, laboratory experiments provide the best opportunity for confirmation of the potential for organic synthesis in hydrothermal systems Here we report on the formation of lipid compounds during Fischer-Tropsch-type synthesis from aqueous solutions of formic acid or oxalic acid Optimum synthesis occurs in stainless steel vessels by heating at 175 degrees C for 2-3 days and produces lipid compounds ranging from C2 to > C35 which consist of n-alkanols, n-alkanoic acids, n-alkenes, n-alkanes and alkanones The precursor carbon sources used are either formic acid or oxalic acid, which disproportionate to H2, CO2 and probably CO Both carbon sources yield the same lipid classes with essentially the same ranges of compounds The synthesis reactions were confirmed by using 13C labeled precursor acids