bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transient Phases of the Isometric Tetanus in Frog's Striated Muscle
Authors: Mittenthal Jay E. , Carlson Francis D. 
Published: May 2004

In an isometric tetanus in frog's sartorius muscle tension approaches the plateau exponentially with rate constant α. α a depends on sarcomere length, s, and temperature, T, according to the Arrhenius equation
See PDF for Equation
for temperatures between 1 and 20°C and for sarcomere lengths 2.0–2.8 µm. The energy of activation, E, does not vary significantly with s; E = 13.9 ± 2.4 kcal/mole. A(s) decreases monotonically with s; A(2.1 µm) is about three times greater than A(2.8 µm). Late in relaxation active tension approaches zero exponentially with rate constant r. r decreases exponentially with increasing duration of tetanus, D, from r0 in a twitch to r∞ for large D. The rate constant for decrease of r with D increases with s and with T. r0 and r∞ obey the Arrhenius equation and decrease with increasing s.
Energetics of Contraction in Phasic and Tonic Skeletal Muscles of the Chicken
Authors: Rall Jack A. , Schottelius B. A. 
Published: May 2004

Comparative energetics of chicken latissimus dorsi muscles, tonic anterior (ALD) and phasic posterior (PLD), were investigated by measuring initial heat production. Heat components were analyzed in terms of the equation:
E = A + W + αF(Δ¯L) + f(P, t)
As the muscles were stretched by increments, heat produced in isometric twitches and tetani decreased in a linear fashion. Two processes are involved: one tension independent, the activation heat, or A; and the other tension dependent, Wi + αF(Δ¯L) + f(P, t). In twitches, A, per unit tension, is equivalent in the PLD and ALD. Tension-dependent heat, per unit tension, is greater in the PLD due to Wi; but tension-time-related heat, f(P, t), per unit tension, is similar in both muscles. In tetanic contractions, differences in A and f(P, t), per unit tension, are attributed to the greater Vmax in the PLD. The differences in the energetics of isometric contractions in the PLD and ALD, therefore, can be explained by inherent differences in tension development, compliance, and myosin and reticular ATPase activities. Data from isotonic twitches were quantified by means of the equivalent tension technique. Both muscles exhibited an extra heat associated with shortening, αF(Δ¯L). In the PLD, the ratio αF/Pot is greater; it is load independent and ½ the value of a/Po in both muscles. Enthalpy efficiency, We + Wi/E, is comparable in both muscles. A Fenn effect is observed only when isotonic energy liberation is compared to a decreasing isometric energy expenditure base line.
SPIRAL1Encodes a Plant-Specific Microtubule-Localized Protein Required for Directional Control of Rapidly Expanding Arabidopsis Cells[W]
Authors: Nakajima Keiji , Furutani Ikuyo , Tachimoto Hideki , Matsubara Hiroshige , Hashimoto Takashi 
Published: May 2004

AbstractHighly organized interphase cortical microtubule (MT) arrays are essential for anisotropic growth of plant cells, yet little is known about the molecular mechanisms that establish and maintain the order of these arrays. The Arabidopsis thaliana spiral1 (spr1) mutant shows right-handed helical growth in roots and etiolated hypocotyls. Characterization of the mutant phenotypes suggested that SPR1 may control anisotropic cell expansion through MT-dependent processes. SPR1 was identified by map-based cloning and found to encode a small protein with unknown function. Proteins homologous to SPR1 occur specifically and ubiquitously in plants. Genetic complementation with green fluorescent protein fusion proteins indicated that the SPR1 protein colocalizes with cortical MTs and that both MT localization and cell expansion control are conferred by the conserved N- and C-terminal regions. Strong SPR1 expression was found in tissues undergoing rapid cell elongation. Plants overexpressing SPR1 showed enhanced resistance to an MT drug and increased hypocotyl elongation. These observations suggest that SPR1 is a plant-specific MT-localized protein required for the maintenance of growth anisotropy in rapidly elongating cells.
Extracellular Invertase Is an Essential Component of Cytokinin-Mediated Delay of Senescence[W]
Authors: Balibrea Lara Maria Encarnacioén , Gonzalez Garcia Maria-Cruz , Fatima Tahira , Ehneß Rainer , Lee Taek Kyun , Proels Reinhard , Tanner Widmar , Roitsch Thomas 
Published: May 2004

AbstractLeaf senescence is the final stage of leaf development in which the nutrients invested in the leaf are remobilized to other parts of the plant. Whereas senescence is accompanied by a decline in leaf cytokinin content, exogenous application of cytokinins or an increase of the endogenous concentration delays senescence and causes nutrient mobilization. The finding that extracellular invertase and hexose transporters, as the functionally linked enzymes of an apolasmic phloem unloading pathway, are coinduced by cytokinins suggested that delay of senescence is mediated via an effect on source-sink relations. This hypothesis was further substantiated in this study by the finding that delay of senescence in transgenic tobacco (Nicotiana tabacum) plants with autoregulated cytokinin production correlates with an elevated extracellular invertase activity. The finding that the expression of an extracellular invertase under control of the senescence-induced SAG12 promoter results in a delay of senescence demonstrates that effect of cytokinins may be substituted by these metabolic enzymes. The observation that an increase in extracellular invertase is sufficient to delay leaf senescence was further verified by a complementing functional approach. Localized induction of an extracellular invertase under control of a chemically inducible promoter resulted in ectopic delay of senescence, resembling the naturally occurring green islands in autumn leaves. To establish a causal relationship between cytokinins and extracellular invertase for the delay of senescence, transgenic plants were generated that allowed inhibition of extracellular invertase in the presence of cytokinins. For this purpose, an invertase inhibitor was expressed under control of a cytokinin-inducible promoter. It has been shown that senescence is not any more delayed by cytokinin when the expression of the invertase inhibitor is elevated. This finding demonstrates that extracellular invertase is required for the delay of senescence by cytokinins and that it is a key element of the underlying molecular mechanism.
Differential Activation of the Rice Sucrose Nonfermenting1–Related Protein Kinase2 Family by Hyperosmotic Stress and Abscisic Acid[W]
Authors: Kobayashi Yuhko , Yamamoto Shuhei , Minami Hideyuki , Kagaya Yasuaki , Hattori Tsukaho 
Published: May 2004

AbstractTo date, a large number of sequences of protein kinases that belong to the sucrose nonfermenting1–related protein kinase2 (SnRK2) family are found in databases. However, only limited numbers of the family members have been characterized and implicated in abscisic acid (ABA) and hyperosmotic stress signaling. We identified 10 SnRK2 protein kinases encoded by the rice (Oryza sativa) genome. Each of the 10 members was expressed in cultured cell protoplasts, and its regulation was analyzed. Here, we demonstrate that all family members are activated by hyperosmotic stress and that three of them are also activated by ABA. Surprisingly, there were no members that were activated only by ABA. The activation was found to be regulated via phosphorylation. In addition to the functional distinction with respect to ABA regulation, dependence of activation on the hyperosmotic strength was different among the members. We show that the relatively diverged C-terminal domain is mainly responsible for this functional distinction, although the kinase domain also contributes to these differences. The results indicated that the SnRK2 protein kinase family has evolved specifically for hyperosmotic stress signaling and that individual members have acquired distinct regulatory properties, including ABA responsiveness by modifying the C-terminal domain.
Comparative Analysis of the Receptor-Like Kinase Family in Arabidopsis and Rice[W]
Authors: Shiu Shin-Han , Karlowski Wojciech M. , Pan Runsun , Tzeng Yun-Huei , Mayer Klaus F. X. , Li Wen-Hsiung 
Published: May 2004

AbstractReceptor-like kinases (RLKs) belong to the large RLK/Pelle gene family, and it is known that the Arabidopsis thaliana genome contains &gt;600 such members, which play important roles in plant growth, development, and defense responses. Surprisingly, we found that rice (Oryza sativa) has nearly twice as many RLK/Pelle members as Arabidopsis does, and it is not simply a consequence of a larger predicted gene number in rice. From the inferred phylogeny of all Arabidopsis and rice RLK/Pelle members, we estimated that the common ancestor of Arabidopsis and rice had &gt;440 RLK/Pelles and that large-scale expansions of certain RLK/Pelle members and fusions of novel domains have occurred in both the Arabidopsis and rice lineages since their divergence. In addition, the extracellular domains have higher nonsynonymous substitution rates than the intracellular domains, consistent with the role of extracellular domains in sensing diverse signals. The lineage-specific expansions in Arabidopsis can be attributed to both tandem and large-scale duplications, whereas tandem duplication seems to be the major mechanism for recent expansions in rice. Interestingly, although the RLKs that are involved in development seem to have rarely been duplicated after the Arabidopsis–rice split, those that are involved in defense/disease resistance apparently have undergone many duplication events. These findings led us to hypothesize that most of the recent expansions of the RLK/Pelle family have involved defense/resistance-related genes.
Small‐seeded species produce more seeds per square metre of canopy per year, but not per individual per lifetime
Authors: MOLES ANGELA T. , FALSTER DANIEL S. , LEISHMAN MICHELLE R. , WESTOBY MARK 
Published: May 2004

SummaryThe trade‐off between seed mass and the number of seeds a plant can make for a given amount of energy underpins our understanding of seed ecology. However, there is little information on the magnitude of the fecundity advantage of small‐seeded species over an entire plant lifetime.We compiled data from the literature to quantify the relationships between: (i) seed mass and plant size (because the photosynthetic area of a plant determines how much energy is available for allocation to seed production); (ii) seed mass and plant reproductive lifetime (the number of years a plant has to produce seeds); and (iii) seed mass and the number of seeds produced per individual per year, and per lifetime.Seed mass was positively related to all measures of plant size (canopy area, plant height, stem diameter, plant mass and canopy volume). There were also positive correlations between seed mass and time to first reproduction, plant life span, and reproductive life span. Thus, although small‐seeded species produce more seeds per unit canopy area per year than large‐seeded species, large‐seeded species tend to have larger canopies and more reproductive years.These patterns accord well with independently gathered data on annual and lifetime seed production. The negative relationship between seed mass and the number of seeds produced per year was much shallower on a per individual basis than on a per unit canopy basis. Seed mass was not significantly related to the total number of seeds produced by an individual plant throughout its lifetime.Our previous understanding of seed mass as a spectrum from production of many small seeds, each with low establishment probability, to a few large seeds each with higher establishment probability, was missing some important elements. To understand the forces shaping the evolution of seed mass, we will need to consider plant size and longevity, as well as seedling survival rates and the number of seeds that can be produced for a given amount of energy.
Ground cover recovery patterns and life‐history traits: implications for restoration obstacles and opportunities in a species‐rich savanna
Authors: KIRKMAN L. K. , COFFEY K. L. , MITCHELL R. J. , MOSER E. B. 
Published: May 2004

Summary

We identified species with low re‐colonization potential, which could be used as indicators of recovery of species‐rich pine savannas, by comparing the ground‐cover flora of a 64‐year‐old slash pine plantation (recovery site) with that of a nearby natural longleaf pine savanna (reference site). We also determined life‐history traits that were useful predictors of recolonization potential.
The high floristic overlap in species between reference and recovery sites and similar species richness at scales ≥ 10 m2 suggests that substantial vegetation recovery occurred over the 65‐year period. However, for areas < 10 m2 the lower species packing in the recovery sites indicates that coexistence of a high number of species at small scales is dependent on local dispersal and establishment, and may take much longer to achieve.
The absence, or near absence, of some species from the recovery site, even after 65 years, suggests that some species may be particularly vulnerable to disturbance and may re‐establish infrequently, if ever. Several dispersal distance‐restricted species were identified that require active reintroduction. While no particular guild of species was a strong indicator of recovery in this study, we identified a group of species that assess the absence of or the degree of recovery from, prior soil disturbance.
Local dispersal appears to be an important factor structuring species richness patterns in pine savannas. Limitations of dispersal distance in some species, particularly those with gravity and ant‐dispersal mechanisms, represent an obstacle to passive restoration that can only be overcome either by introduction of propagules in the restoration process or by allowing for longer periods of recruitment.
This study demonstrates a method for identifying a suite of species that may be unsuccessful at recolonization. The method would be applicable to numerous degraded ecosystems, particularly similar species‐rich savannas, grasslands and forests.
Seedling survival and seed size: a synthesis of the literature
Authors: MOLES ANGELA T. , WESTOBY MARK 
Published: May 2004

Summary

Large‐seeded species have long been known to have higher survivorship during establishment than small‐seeded species. Here, we assessed the size of this advantage by compiling published data on survival through seedling emergence, seedling establishment and sapling establishment.
We found no relationship between seed mass and survival through the transition from viable seed in or on the soil to newly emerged seedlings (P = 0.47, n = 33 species).
Synthesis of data from experimental studies on the advantages of large‐seeded species establishing under particular hazards (such as shade, drought or herbivory) confirmed that seedlings of large‐seeded species perform better than those of small‐seeded species in most situations. However, the magnitude of this advantage was not sufficient to counterbalance the greater number of seeds produced by small‐seeded species m−2 of canopy outline year−1.
Synthesis of data from field studies of populations under natural conditions also showed that large‐seeded species have higher survival through early seedling establishment than small‐seeded species (P = 0.006, n = 112 species). However, the magnitude of this advantage would only be sufficient to counterbalance the greater number of seeds produced by small‐seeded species m−2 of canopy outline year−1 if mortality continued at the same rate for some time.
The time required for a species with 10‐fold larger seeds to recoup the advantage gained by a smaller‐seeded species during seed production ranged from 8.8 weeks for the smallest seeded species in the data set, up to an implausible 4.2 years for the largest‐seeded species. Thus, while large‐seeded species do have a survival advantage over small‐seeded species during seedling establishment, the available evidence suggests that advantages must also accrue during other stages in the life cycle. One possibility is that the greater seed production of small‐seeded species (m−2 of canopy outline year−1) is partly offset by larger canopies and longer reproductive life spans in large‐seeded species.
The relative dominance hypothesis explains interaction dynamics in mixed speciesAlnus rubra/Pseudotsuga menziesiistands
Authors: ANTHONY W. D’AMATO , KLAUS J. PUETTMANN 
Published: May 2004

SummaryWe used repeated measurements of tree growth and population‐level and neighbourhood conditions from three mixedAlnus rubra/Pseudotsuga menziesiiforests in the Pacific Northwest, USA to investigate why previous results regarding the importance of neighbourhood competition as a determinant of plant growth were inconsistent.We propose that relative dominance of a particular species determines the importance of neighbourhood interactions, and tested whether growth performance of both species at various stand ages agrees with this relative dominance hypothesis.Neighbourhood and relative dominance interaction indices were modified to accommodate two‐species mixtures and were incorporated into a growth model predicting relative diameter growth rates. The corrected Akaike Information Criterion (AICc) was used to identify the optimum interaction measures and model forms for each species and measurement period.Interaction indices reflecting the size of a tree relative to the population were the best predictors of growth of the dominant (i.e. taller) species and neighbourhood interaction indices of the subordinate species.Performance of interaction measures as predictors of relative growth rates in our study varied in agreement with the relative dominance hypothesis for both species and on all sites. Results from other studies suggest that the hypothesis may explain growth performances on a species and individual plant level and for a variety of life forms.These findings suggest that the spatial scale of plant interactions is influenced by the size structure of plant populations. The relative dominance hypothesis offers a framework to provide insight into the mechanism of competition, based on the relative performance of competition indices.
Seed–seedling allometry in tropical rain forest trees: seed mass‐related patterns of resource allocation and the ‘reserve effect’
Authors: GREEN PETER T. , JUNIPER PETER A. 
Published: May 2004

Summary

The seedlings of larger seeded species generally perform better than those of smaller seeded species under a variety of hazards. The reserve effect proposes that larger seeded species retain a greater proportion of their initial seed resources and their seedlings are therefore better provisioned to cope with post‐deployment resource deficits.
This hypothesis was tested with a suite of 32 Australian rain forest species with storage cotyledons, and seed reserve mass ranging from 36 mg to 25 g. Seedlings germinated in dim light were harvested as their first set of leaves became fully expanded, dissected into shoot, root and left‐over cotyledons, dried and weighed.
In cross‐species, allometric analyses, the mean mass of the shoot‐plus‐root scaled less than proportionately (slope c. 0.8), and mean cotyledon mass more than proportionately (slope c. 1.1) with either initial seed mass or seedling mass. These slopes were significantly different from each other. Both conditions for a reserve effect were therefore fulfilled. Cotyledons ranged from 45% of total seedling mass in the smallest species, to 92% in the largest.
Solid evidence for a reserve effect was detected within two of four families tested (Lauraceae and Myrtaceae), but only in 7 of the 22 species for which there were sufficient data.
Even if the reserve effect has present day utility for enhanced seedling performance in larger seeded species, it may have evolved in response to selection for a greater relative retention of initial seed mass during seedling deployment in larger seeded species, combined with selection for greater deployment of seed reserves to the initial shoot and root of smaller seeded species.
The Three R's of Pastoral Care: Relationships, Respect and Responsibility
Authors: Grove Michael 
Published: May 2004

The author argues that over the last twenty years we have witnessed an evolution in pastoral care that is unparalleled in any other field of education. There has been controversy over the definition and these different views are discussed. The paucity of research and literature in the field and particularly in relation to the pastoral needs of teachers andstaff is emphasized.In this paper it is suggested that the needs of school staff in respect of pastoral care are relatively neglected in the literature. Using the three R's of pastoral care – relationships, respect and responsibility – this paper focuses attention on teachers and their needs in the workplace. It is argued that attention to relationships, respect and responsibility enablesa proactive collaborative approach in which all members of the school community play a crucial role in the pastoral care of students.
Effects of an experimental drought on soil emissions of carbon dioxide, methane, nitrous oxide, and nitric oxide in a moist tropical forest
Authors: Davidson Eric A. , Ishida Françoise Yoko , Nepstad Daniel C. 
Published: May 2004

AbstractChanges in precipitation in the Amazon Basin resulting from regional deforestation, global warming, and El Niño events may affect emissions of carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and nitric oxide (NO) from soils. Changes in soil emissions of radiatively important gases could have feedback implications for regional and global climates. Here we report results of a large‐scale (1 ha) throughfall exclusion experiment conducted in a mature evergreen forest near Santarém, Brazil. The exclusion manipulation lowered annual N2O emissions by >40% and increased rates of consumption of atmospheric CH4 by a factor of >4. No treatment effect has yet been detected for NO and CO2 fluxes. The responses of these microbial processes after three rainy seasons of the exclusion treatment are characteristic of a direct effect of soil aeration on denitrification, methanogenesis, and methanotrophy. An anticipated second phase response, in which drought‐induced plant mortality is followed by increased mineralization of C and N substrates from dead fine roots and by increased foraging of termites on dead coarse roots, has not yet been detected. Analyses of depth profiles of N2O and CO2 concentrations with a diffusivity model revealed that the top 25 cm soil is the site of most of the wet season production of N2O, whereas significant CO2 production occurs down to 100 cm in both seasons, and small production of CO2 occurs to at least 1100 cm depth. The diffusivity‐based estimates of CO2 production as a function of depth were strongly correlated with fine root biomass, indicating that trends in belowground C allocation may be inferred from monitoring and modeling profiles of H2O and CO2.