bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Influence of Exogenous Steroids on the Growth of Aspergillus niger and Torula utilis
Authors: Jefferson W. E. , Sisco Gladys 
Published: May 2004

The yield of Aspergillus niger mycelium from a synthetic medium can be increased by the addition of microgram quantities of cholesterol, ergosterol, cholestanol, 7-dehydrocholesterol, stigmasterol, sitosterol, pregnenolone, and the vitamins D. The stimulation is not due to degradation to the acetate level. It is obtained only in highly aerated cultures. The rate of growth of Torula utilis was not increased.
Both organisms were inhibited by desoxycorticosterone, testosterone, androstenedione, cortisone acetate, progesterone, and diethylstilbestrol. T. utilis was also inhibited by estradiol.
A small decrease in progesterone inhibition of T. utilis was obtained by adding ergosterol, cholesterol, or pregnenolone.
Of the compounds which have been adequately tested the order of stimulatory activity for A. niger is: ergosterol &gt; cholesterol &gt; stigmasterol &gt; 7-dehydrocholesterol &gt; cholestanol &gt; pregnenolone. Progesterone was inhibitory at low concentrations but stimulatory at higher ones, while 17-hydroxyprogesterone was neither inhibitory nor stimulatory. Desoxycorticosterone and testosterone were inhibitory at all concentrations. Complete inhibition of the growth of the fungus was not obtained with any of the steroids.
It is concluded that A. niger has a metabolic requirement for a steroid with a hydroxy group on carbon 3, a double bond in the 5–6 position, and a side chain similar to that in ergosterol or cholesterol and that this material is growth-limiting in the early stages of the cultures described.
Na Extrusion by the Sartorius of Rana pipiens
Authors: Steinbach H. Burr 
Published: May 2004

Sartorius muscles of R. pipiens may be enriched in sodium and depleted of potassium by prolonged soaking in the cold in K-free or low K Ringer's solution. Such K-depleted muscles take up potassium and extrude sodium when exposed to Ringer's solution containing 10 mM K at ordinary room temperature (ca. 20°C), with no dependence on external Na ion concentration in either phase within fairly wide limits.
Extrusion of excess fiber Na is demonstrated on single muscles using Na24-loaded tissues. Rate of exchange of excess fiber Na does not differ significantly from the rate of exchange of Na normally present in muscle fibers.
Deoxyribonuclease from Salmon Testes
Authors: McDonald Margaret R. 
Published: May 2004

A procedure is described for the purification of salmon testis deoxyribonuclease II by means of acid extraction, fractional precipitation with ammonium sulfate, heat denaturation of extraneous proteins, and ethanol fractionation. This process separates the deoxyribonuclease activity from that of ribonuclease, phosphatase, phosphodiesterase, and protease. Over 50 per cent of the activity is retained with an over-all enrichment of 20,000-fold. The enzyme degrades both native and heat-denatured DNA, but the rate of degradation of the latter is only one-tenth that of the former. It does not hydrolyze apurinic acid.
The enzyme is most stable in the pH range 4 to 5. Electrolytes are essential for the expression of its activity: monovalent ions satisfy the requirement, but divalent ones are much more effective. Above a certain optimum concentration, each electrolyte is inhibitory. The pH of maximal activity, under conditions of optimal ionic strength, is 4.8; the temperature optimum is near to 55°C.
Muscle Contraction during Hyperpolarizing Currents in the Crab
Authors: Uchitel O. D. , García H. 
Published: May 2004

Isolated muscle fibers from the motor legs of the crab Trichodactilus dilocarcinus were submitted to strong hyperpolarizing currents of varied intensities which produced tension during the current pulse. Threshold for tension was obtained with intensities of about 0.2 x 10–5 A, changing Em to ca. –150 mV (starting from a resting potential ofca. –80 mV). At the closure of the anodic square pulse, a second phase of tension usually appeared superimposed upon the one obtained during hyperpolarization. The first phase of tension increased with the increase of Ca++ concentration in the bath. Sr++ produced the same type of mechanical output as Ca++. When added to the normal Ca++ concentration, Ba++ and Mn++ in low concentrations (up to 21.5 mM) also increased the tension of this phase, but at higher concentrations they blocked both phases while Mg++ did not alter the tension. Of all the divalent cations employed, only Sr++ is capable of developing tension as a substitute for Ca++ in the external media. Procaine administered in a dosage (5 x 10–3 W/V)which would suppress the contracture due to caffeine (10 mM), did not modify the tension developed during the hyperpolarization.
The preceding data indicate that the Ca++ required for tension during hyperpolarization comes from sites which would differ from those usually postulated for tension due to depolarization in the muscle fibers of other crustaceans (American crayfish). Furthermore, the external source of Ca++ appears to be one mainly implicated in the induction of tension due to inward current pulses.
The resistance of the septum of the medium giant axon of the earthworm
Authors: Brink P , Barr L 
Published: May 2004

It is generally thought that nexuses constitute low-resistance pathways between cell interiors in epithelial, neural, muscular, and even connective tissues. However, there are no reliable estimates of the specific resistance of a nexus. The reason for this is that in most cases the surfaces of nexuses between cells are geometrically complex and therefore it has been very hard to accurately estimate nexal areas. However, the septa of the median giant axon have a relatively simple shape. Moreover, in this preparation, it is possible to make a measuring current flow parallel to the axon axis so that from the voltage difference appearing between intracellular electrodes during current flow, the specific septal membrane resistance could be calculated. The average specific nexal resistance obtained was 5.9 ω cm(2) if one assumes that 100 percent of the septum is nexus. The steady state I-V curve for the septum is linear (+/- 10 mV). Placement of electrodes was validated by septa even though the septa were found to be permeable to fluorescein and TEA. Exposure of the axon to hypertonic saline impedes the movement of fluorescein across the septa. By analogy with other tissues it is concluded that hypertonic solutions disrupt nexuses.
A mathematical model was derived which predicts the steady- state transmembrane potential vs. distance from a point source of intracellular current. When the specific nexal membrane resistance is 5.9 ω cm(2), the prediction closely approximates the fall of transmembrane potential vs. distance in an ordinary infinite cable. This is commensurate with the electrophysiological behavior of this multicellular "axon".
Acute Alcohol Use and Suicidal Behavior: A Review of the Literature
Authors: Cherpitel Cheryl J. , Borges Guilherme L.G. , Wilcox Holly C. 
Published: May 2004

Abstract: Background: Both acute and chronic use of alcohol are associated with suicidal behavior. However, the differing relationship of each component of alcohol use and possible causal mechanisms remain unclear.Methods: This article reviews and summarizes associations between acute alcohol consumption (with and without intoxication) and suicidal behavior (both completed suicide and suicide attempts) among adults 19 years and older, as presented in literature published between 1991 and 2001. Possible mechanisms and methodologic challenges for evaluating the association are also discussed. An application of a research design (the case‐crossover study) that has the potential for addressing the effects of acute alcohol use over and above usual or chronic use is presented.Results: The majority of articles reviewed were restricted to descriptive studies that documented the prevalence of suicide completers or attempters who tested positive for alcohol use. A wide range of alcohol‐positive cases were found for both completed suicide (10–69%) and suicide attempts (10–73%). Common methodologic limitations included the lack of control groups (for evaluating risk conferred by alcohol use), selection and ascertainment bias, and small sample sizes. The results of the case‐crossover pilot study indicated substantially higher risk of suicide during or shortly after use of alcohol compared with alcohol‐free periods.Conclusions: Although there is a substantial literature of published studies on acute alcohol use and suicidal behavior, the majority of studies focus on completed suicide and report prevalence estimates. Findings from such studies are subject to several possible sources of bias and have not advanced our knowledge of mechanisms in the association between acute alcohol use and suicidal behavior. The case‐crossover design may help to overcome some limitations of these studies and facilitate evaluation of associations and possible causal mechanisms by which acute alcohol use is linked to suicidal behavior.
Serotonergic and Noradrenergic Neurobiology of Alcoholic Suicide
Authors: Underwood Mark D. , Mann J. John , Arango Victoria 
Published: May 2004

Abstract: Background: Alcoholism is associated with alterations in the serotonergic and noradrenergic systems. Alcoholics are at a significantly higher risk for suicide than the general population. Altered serotonin (5‐HT) function is associated with suicide and serious suicide attempts. We hypothesized patterns of abnormality associated independently with suicide and with alcoholism.Methods: Quantitative autoradiographic experiments were performed in human postmortem brain tissue sections from alcoholics, alcoholic‐suicide decedents, nonalcoholic suicide decedents, and normal controls diagnosed by psychological autopsy.Results: Binding to 5‐HT1A receptors is lower in both alcoholic suicides and alcoholic nonsuicides, suggesting that this effect is related to alcoholism and not suicide. In nonalcoholic suicides, there is a localized increase in 5‐HT1A binding in ventral prefrontal cortex, hypothesized to be a response to less serotonin input. Therefore, alcoholic suicides may fail to up‐regulate ventral prefrontal 5‐HT1A receptors in response to decreased serotonergic transmission, failing to mitigate the impact of less serotonin upon signal transduction and thereby increasing the risk of suicidal behavior. Binding to the serotonin transporter is low in alcoholic suicides but not in alcoholic nonsuicides, suggesting an association with suicide, as nonalcoholic suicides also have decreased binding compared with controls. Evidence of impaired serotonergic innervation associated with alcoholism is also manifested by less 5‐HT1D terminal autoreceptor binding in alcoholics. Nonalcoholic suicides do not have lower 5‐HT1D binding.In the noradrenergic system, alcoholics (suicide and nonsuicide) and nonalcoholic suicide victims all have fewer pigmented locus ceruleus neurons compared with controls, yet β1‐adrenergic binding is low in both alcoholic groups, whereas α1‐and α2‐adrenergic binding decreases are more pronounced in the alcoholic suicide group. These noradrenergic findings differ from those in nonalcoholic suicides, which have a common feature with alcoholics in having less α2‐and β1‐adrenergic binding but more α1‐adrenergic binding in ventrolateral and orbital cortex.Conclusion: Extensive but different abnormalities in both the serotonergic and noradrenergic systems have been identified in alcoholics and suicides, suggesting two separate patterns: one related to alcoholism and the other related to suicide. The different patterns suggest different causes and homeostatic responses for alcoholism and suicide.
cis-Regulatory Elements for Mesophyll-Specific Gene Expression in the C4 PlantFlaveria trinervia, the Promoter of the C4 Phosphoenolpyruvate Carboxylase Gene[W]
Authors: Gowik Udo , Burscheidt Janet , Akyildiz Meryem , Schlue Ute , Koczor Maria , Streubel Monika , Westhoff Peter 
Published: May 2004

AbstractC4 photosynthesis depends on the strict compartmentalization of CO2 assimilatory enzymes. cis-regulatory mechanisms are described that ensure mesophyll-specific expression of the gene encoding the C4 isoform of phosphoenolpyruvate carboxylase (ppcA1) of the C4 dicot Flaveria trinervia. To elucidate and understand the anatomy of the C4 ppcA1 promoter, detailed promoter/reporter gene studies were performed in the closely related C4 species F. bidentis, revealing that the C4 promoter contains two regions, a proximal segment up to −570 and a distal part from −1566 to −2141, which are necessary but also sufficient for high mesophyll-specific expression of the β-glucuronidase reporter gene. The distal region behaves as an enhancer-like expression module that can direct mesophyll-specific expression when inserted into the ppcA1 promoter of the C3 plant F. pringlei. Mesophyll expression determinants were restricted to a 41-bp segment, referred to as mesophyll expression module 1 (Mem1). Evolutionary and functional studies identified the tetranucleotide sequence CACT as a key component of Mem1.
Intermediate disturbance in a late‐successional hemlock‐northern hardwood forest
Authors: WOODS KERRY D. 
Published: May 2004

Summary

An old‐growth mesic forest in northern Michigan, USA, experienced an unusually intense storm in July 2002. Permanent inventory plots and a 2.9‐ha mapped stand allow comparison of effects of this rare disturbance with patterns of ‘baseline’ mortality.
Tree mortality attributable to immediate effects of the storm was of similar magnitude to mortality over the previous decade, amounting to about 9% of basal area and 7% of stem density (mean of 88 inventory plots).
Storm mortality differed from baseline mortality in patterns related to species and size. Tsuga canadensis suffered little mortality of either type. Betula alleghaniensis had high baseline mortality in all size classes, but very low storm mortality. Acer spp. and Fagus grandifolia showed similar overall levels of baseline and storm mortality, but storm mortality was higher for larger stems.
Spatial patterns of mortality differed between baseline and storm‐caused disturbance, with storm mortality patterns related to composition and to substrate variation over the stand. Baseline canopy mortality was hyperdispersed at local scales, but mortality due to the storm was strongly clustered at distances up to 30 m.
Properties of rare, intermediate disturbances cannot be predicted by simply scaling up patterns due to frequent, less intense, events. They may have distinctive influences on community dynamics, countering trends towards dominance by shade‐tolerant species, generating demographic and spatial structure in the canopy, and distinctively affecting understorey environment.
These results suggest that climate change may induce changes in forest ecosystems by changing disturbance patterns even when species are not close to limits of physiological tolerance. Forest management for natural regeneration may need to take the effects of rare, intermediate disturbance into account.
Propagule pools mediate community assembly and diversity‐ecosystem regulation along a grassland productivity gradient
Authors: FOSTER BRYAN L. , DICKSON TIMOTHY L. , MURPHY CHERYL A. , KAREL IRENE S. , SMITH VAL H. 
Published: May 2004

SummaryThe relative importance of regional species pools and local ecological processes in governing landscape variation in plant species diversity and productivity was evaluated in a Kansas grassland.We examined the impact of multispecies sowing treatments and experimental canopy disturbances on plant species diversity and ecosystem processes along a complex natural gradient of plant standing crop.Data collected 4 years after sowing showed that plant invasion and diversity were seed limited in unproductive sites, but microsite limited in productive sites. Effects of sowing on plant diversity along the natural landscape gradient were paralleled by significant effects of sowing on measures of local plant production and community resilience to disturbance.These results support the shifting limitations hypothesis (SLH) that landscape gradients in local plant diversity should reflect shifts in the major regulating factor, from species pools to local ecological processes, as one moves from sites of inherently low to inherently high productivity.Our findings also indicate that diversity at the level of the available propagule pool acts to constrain ecosystem productivity and stability by mediating local community assembly, by determining the availability of key species, and by governing opportunities for functional compensation within the community.In total, our results support an emerging view that community processes and ecosystem functions are dynamically linked and act reciprocally to constrain each other.
Relative importance of suppression‐based and tolerance‐based competition in an invaded oak savanna
Authors: MacDOUGALL ANDREW S. , TURKINGTON ROY 
Published: May 2004

SummaryInvasive species dominate many ecosystems but the competitive strategies underlying this dominance are unclear. Are invasive species generalist competitors, or do they only thrive in certain environments? Do they occur mainly post‐disturbance or can they persist throughout succession?We tested the relative importance of resource acquisition (competitive suppression ability) and the ability to tolerate reduced resource levels (competitive tolerance ability) among four C3 perennial grass species in an invaded oak savanna. Two species (Poa pratensisandDactylis glomerata) are exotic invaders and are thought to have replaced the two native species (Bromus carinatusandElymus glaucus) as dominants.Using glasshouse and field experiments we tested whether the two strategies were maintained with changing resource levels and successional conditions, and their relative roles in explaining exotic dominance.The relative importance of suppression‐ and tolerance‐based competition shifted with neighbour density, burning and planting order. Further, the relative importance of particular plant traits changed depending on the imposed conditions, and the exotic dominants were only competitively superior under certain circumstances.Competitive suppression ability was maintained with changing resource levels but was confined to post‐disturbance conditions. When planting of neighbours was delayed, the early establishing targets were dominant regardless of species, fertility and neighbour density.Competitive tolerance ability determined long‐term patterns of relative abundance and coexistence, but only under the current field conditions of low fertility and limited disturbance. Alteration of these conditions changed the relative abundance of the four grasses, and would probably reconfigure species patterns in the oak savanna community generally.Exotic dominance is presently determined by tolerance‐based competitive traits interacting with the long‐term absence of disturbance. Dominance is therefore contingent on the interaction of competitive strategies, resource availability and disturbance history rather than any one factor alone.Exotic flora dominate all stages of succession in this savanna because there exists both early (suppression) and late (tolerance) successional specialists. The identity of the dominant changes with succession based on the competitive strategy it employs. This result highlights the importance of examining the historical context of invaded communities and tracking their successional status over time.
Induction of two indirect defences benefits Lima bean (Phaseolus lunatus, Fabaceae) in nature
Authors: HEIL MARTIN 
Published: May 2004

Summary

Herbivore damage often induces the release of herbivore‐induced plant volatiles (HIPVs) or the secretion of extrafloral nectar (EFN). The purpose of this study was to induce such proposed indirect defence responses in plants growing in their natural environment and to monitor the effects on vegetative and generative traits such as herbivory, plant growth and fruit set.
I tested whether mature wild Lima beans (Phaseolus lunatus, Fabaceae) growing in Mexico could be reliably induced to produce HIPVs and EFN in response to application of the phytohormone, jasmonic acid (JA), and investigated whether this treatment leads to any benefit to the plants.
Eleven HIPVs were released from JA‐treated leaves at significantly higher amounts than from control leaves, and only one (methylsalicylate) at significantly lower amounts than from controls. Treatment with JA increased EFN secretion on leaves on average by more than 30 times and on bracts by more than 20 times. EFN production, which has not previously been described in Lima bean, represents a second induced indirect resistance trait of this species.
JA treatment reduced both the number of dead shoot tips and leaf damage by herbivores. Treated tendrils grew faster and produced more leaves than controls. At the end of the experiment, treated tendrils bore c. two times more inflorescences and three times more fruits than controls.
Repeated treatment with JA resulted in a combined induction of HIPVs and EFN and strongly benefited wild Lima beans. The plants suffered less from the consequences of herbivore attack, supporting the use of the term ‘induced defences’ for these traits. JA‐induced defences thus can significantly benefit Lima bean under natural conditions.
Variation in wood density determines spatial patterns inAmazonian forest biomass
Authors: Baker Timothy R. , Phillips Oliver L. , Malhi Yadvinder , Almeida Samuel , Arroyo Luzmila , Di Fiore Anthony , Erwin Terry , Killeen Timothy J. , Laurance Susan G. , Laurance William F. , Lewis Simon L. , Lloyd Jon , Monteagudo Abel , Neill David A. , Patiño Sandra , Pitman Nigel C. A. , M. Silva J. Natalino , Vásquez Martínez Rodolfo 
Published: May 2004

AbstractUncertainty in biomass estimates is one of the greatest limitations to models of carbon flux in tropical forests. Previous comparisons of field‐based estimates of the aboveground biomass (AGB) of trees greater than 10 cm diameter within Amazonia have been limited by the paucity of data for western Amazon forests, and the use of site‐specific methods to estimate biomass from inventory data. In addition, the role of regional variation in stand‐level wood specific gravity has not previously been considered. Using data from 56 mature forest plots across Amazonia, we consider the relative roles of species composition (wood specific gravity) and forest structure (basal area) in determining variation in AGB.Mean stand‐level wood specific gravity, on a per stem basis, is 15.8% higher in forests in central and eastern, compared with northwestern Amazonia. This pattern is due to the higher diversity and abundance of taxa with high specific gravity values in central and eastern Amazonia, and the greater diversity and abundance of taxa with low specific gravity values in western Amazonia. For two estimates of AGB derived using different allometric equations, basal area explains 51.7% and 63.4%, and stand‐level specific gravity 45.4% and 29.7%, of the total variation in AGB. The variation in specific gravity is important because it determines the regional scale, spatial pattern of AGB. When weighting by specific gravity is included, central and eastern Amazon forests have significantly higher AGB than stands in northwest or southwest Amazonia. The regional‐scale pattern of species composition therefore defines a broad gradient of AGB across Amazonia.