bluuebunny/crossref_metadata_2025_split huggingface dataset:
Functional consequences of trophic specialization in pufferfishes
Authors: RALSTON K. R. , WAINWRIGHT P. C. 
Published: November 2003

1. Trophic breadth may be correlated with behavioural and functional versatility or flexibility (Liem 1984), such that species with limited diets would be predicted to be less versatile or flexible in their feeding capabilities than would trophic generalists. The relationship was examined between the trophic breadth of a species and the degree to which muscle activity is influenced by prey type in two species of pufferfishes: Chilomycterus schoepfi, a specialist on hard‐shelled prey, and Sphoeroides nephalus, a generalist predator. It was predicted that the specialist would show a decreased ability to alter its motor pattern in response to prey type and an increased amount of motor‐pattern variability when feeding on different prey. 2. Electromyographic recordings of five feeding muscles were made from five individuals per species feeding on four prey types that differed in their hardness and escape abilities. Muscle‐activity duration, relative onset and integrated rectified area were analysed for prey capture and manipulation behaviours for each prey type. 3. Prey‐type effects on mean motor‐pattern variables for capture were limited to one of 14 variables in each species. Prey effects on buccal manipulation were not significant for any of the 14 variables for C. schoepfi, but S. nephalus exhibited prey effects for seven out of 14 variables. No differences in motor‐pattern variation were found for the strike, but species differed significantly in overall motor‐pattern variability during buccal manipulation; C. schoepfi, the dietary specialist, exhibited greater motor variability than S. nephalus, the dietary generalist. 4. The results therefore support a direct relationship between the trophic breadth of a species and its functional versatility for buccal manipulation. In contrast, prey capture was a relatively stereotyped behaviour for both species, as few prey‐type effects were found.
In situ effects of elevated CO2 on the carbon and nitrogen status of alpine plants
Authors: SCHÄPPI B. , KÖRNER CH. 
Published: November 2003

1. The effect of elevated CO2 on tissue composition in an alpine grassland (Swiss Central Alps, 2500m) under both natural and increased nutrient supply (NPK) is summarized. 2. During 3 years of CO2 enrichment the concentration of total non‐structural carbohydrates (TNC) in leaves increased by 32% in Leontodon helveticus (largely sugar) and by 56% in Trifolium alpinum (largely starch) but did not change significantly in the dominant sedge Carex curvula and in Poa alpina, currently a rare species at this site. 3. Enhanced mineral nutrient supply (unlike elevated CO2) greatly stimulated growth but did not reduce the CO2‐induced TNC accumulation. 4. Under elevated CO2 nitrogen concentrations (per g TNC‐free dry matter) of green leaves decreased in Leontodon (–21%) and in Trifolium (–24%) but not or only slightly in Carex and in Poa. NPK addition compensated this CO2 effect on nitrogen concentration in Trifolium but not in the other species. 5. In below‐ground tissue neither TNC nor nitrogen concentration responded to CO2 fertilization. 6. The nitrogen pool per unit land area at peak season biomass remained unaffected by the CO2 treatment. 7. Overall our results suggest that the late successional dominant sedge Carex curvula remains unaffected by elevated CO2, independently of mineral nutrient supply, whereas the co‐dominant and sub‐dominant forbs Leontodon helveticus and Trifolium alpinum show both an increase of TNC as well as N depletion under elevated CO2. 8. None of these changes in active plant tissue translate into compositional changes in naturally senesced litter suggesting caution with predictions of CO2 effects on decomposition based on data from green plant material.
Host selection by virgin and inseminated females of the parasitic wasp, Dinarmus basalis (Pteromalidae, Hymenoptera)
Authors: NISHIMURA K. 
Published: November 2003

1. Fitness is related to reproduction and survival. There apparently exists a negative correlation between the numbers of male and female offspring. There also exists a trade‐off between survival and reproduction. This paper investigates optimal decisions with the reproduction and survival trade‐off in host selection by wasps. 2. Whereas inseminated female wasps could manipulate the sex of their offspring, virgin females produced only male offspring. I surveyed behavioural differences and the consequences of oviposition by inseminated and virgin females of a solitary parasitic wasp in host choice situations. 3. Two host types were available at the same time to both inseminated and virgin female wasps: one (a 17‐day‐old host in one bean) presenting difficulties for the laying of eggs, but more benefits for the offspring and the other (five 12‐ or 13‐day‐old hosts in one bean) easier for the female wasp for laying of eggs but less beneficial for the offspring. 4. Inseminated female wasps chose more 17‐day‐old hosts than 12‐day‐old hosts, but more 13‐day‐old hosts than 17‐day‐old hosts in each pair‐wise choice. Virgin females chose the smaller hosts in both situations. 5. Virgin females, having greater longevity than inseminated females, laid larger numbers of eggs than the inseminated females during their lifetime by adopting an energy‐saving host choice that had little effect on male offspring fitness.
Light stress effects and antioxidative protection in two desert plants
Authors: STREB P. , TEL‐OR E. , FEIERABEND J. 
Published: November 2003

1. The enzyme catalase was investigated as a sensitive marker of light stress in Retama raetam stems and Atriplex halimus leaves. While the activity of catalase was readily photoinactivated in vitro when crude extracts from these tissues were exposed to a photon flux of 500μmolm–2s–1 photosynthetic active radiation (PAR), no apparent losses of the extractable catalase activities were observed when tissues were harvested from desert plants at noon when light levels were as high as 2200μmolm–2s–1 PAR. 2. When stems of R. raetam or leaves of A. halimus were exposed to natural daylight of 1000μmolm–2s–1 PAR in the presence of cycloheximide (CHI), in order to prevent the new synthesis of catalase, or at a temperature of 42–44°C, only minor losses of catalase activity occurred in stems of R. raetam, but a marked apparent photoinactivation of catalase was observed in leaves of A. halimus. 3. Similarly, stronger declines of the ratio Fv/Fm, indicating more severe photoinhibition of photosystem II (PSII), were observed in A. halimus, compared with R. raetam. 4. For R. raetam, activities of some antioxidative enzymes and the carotenoid contents were higher in plants growing in the desert than in plants collected from non‐desert locations. 5. During the daily increase of light and temperature the antioxidants ascorbate and glutathione became more oxidized and violaxanthin was converted to zeaxanthin in R. raetam stems, while these antioxidants became more reduced and zeaxanthin was not notably accumulated in A. halimus leaves. 6. The results suggest that the desert plants R. raetam and A. halimus apply different strategies of protection against light‐stress damage. In the stems of R. raetam antioxidative protection appears to play the major role, while A. halimus appears to avoid light damage in the field by the mutual shading of leaves and reflection of light at the leaf surface.
Role of foliar nitrogen in light harvesting and shade tolerance of four temperate deciduous woody species
Authors: NIINEMETS Ü. 
Published: November 2003

1. Distribution of leaf chlorophyll (Chl), nitrogen and non‐structural carbohydrates (NSC, ethanol‐soluble sugars and starch) in leaves along a natural light gradient was studied in saplings of four deciduous woody species: Acer platanoides, Padus avium, Populus tremula and Quercus robur (from most shade tolerant to intolerant). 2. Leaf dry mass per area (LMA) increased linearly with increasing relative irradiance (RI) in all species and therefore it may be considered as a species‐specific estimate of long‐term light conditions. 3. Decreasing irradiance enhanced chlorophyll synthesis, and consistently resulted in highest Chl per leaf dry mass in low‐light environments. Chl content per leaf area was correlated negatively with RI in A. platanoides and was independent of RI in three other species. 4. Leaf nitrogen content per leaf area (Na) increased linearly with LMA in all species, and with RI in all except A. platanoides. 5. The slopes and intercepts of Na vs LMA relationships were negatively correlated. Moreover, it appeared that the slope decreased and the intercept increased with increasing species shade tolerance. Thus, average nitrogen content per mass (Nm) increases and maximum concentrations of leaf nitrogen shift towards more open habitats with decreasing shade tolerance. Distribution of foliar nitrogen in this way is likely to contribute to greater photosynthetic potentials at higher irradiances in shade‐intolerant species. Inversely, more tolerant species have greater concentrations of foliar nitrogen at low irradiance — an investment pattern, which provides resources to enhance the capacity of light harvesting in light‐limited conditions. 6. NSC per leaf dry mass was positively related to relative irradiance and the slope of this relationship was highest for shade‐intolerant species, which have intrinsically higher photosynthetic capacities. Nevertheless, the conclusions were robust and were not significantly biased by using the parameters expressed either on a total or on a NSC‐free dry mass. 7. The analysis was further extended by including a number of other species from several independent studies. Examination of both sets of data resulted in identical conclusions. Based on this evidence it may be concluded that the variability in leaf nitrogen concentration in relation to irradiance plays a central role in species shade tolerance.
The effects of novel and stressful environments on trait distribution
Authors: HOLLOWAY G. J. , CROCKER H. J. , CALLAGHAN A. 
Published: November 2003

1. Ecotoxicology seeks to blend the disciplines of toxicology and ecology to provide a means of assessing the risk that natural populations of organisms are exposed to when confronted by an environmental stress, such as a pollutant. The LC50 of a compound is usually used to assess this risk with little or no consideration of the importance of the variation about the mean. 2. Several populations of the Rice Weevil, Sitophilus oryzae, were examined that had been bred on toxic (Yellow Split‐pea) or non‐toxic (Wheat) foodstuffs, or transferred between the two. The goal was to establish the effect of stress on the levels of activity of two detoxification enzyme systems, esterases and glutathione‐S‐transferases, and the variation about the mean enzyme activity. 3. Populations kept on their original foodstuffs showed similar levels of enzyme activity irrespective of whether they bred on toxic or non‐toxic foods. When transferred to a novel food stuff there was a small increase in enzyme activity, perhaps reflecting induction, but transfer to a more toxic food did not produce a greater increase in activity than transfer to a non‐toxic food. 4. Populations on their original foodstuff showed similar levels of variation about the mean, but the variation about the mean increased considerably following transfer to a novel food. There was some evidence that this increase was greater when the transfer was to the more toxic food. 5. The increase in variation following transfer was largely due to a small number of individuals showing particularly high levels of enzyme activity. The consequence of the generation of this type of distribution in response to an environmental stress is discussed.
The influence of thermoregulation on behavioural recovery from exercise in a lizard
Authors: WAGNER E. L. , GLEESON T. T. 
Published: November 2003

1. Past work on the thermal preferences of Dipsosaurus dorsalis (Biard & Giard) has indicated that intense, exhaustive exercise causes these lizards to select a body temperature (33·5 °C) which is cooler than their preferred activity temperature of 40°C during the first 1–2 h of exercise recovery. 2. In order to test the hypothesis that the thermal regime selected by exhausted D. dorsalis is beneficial to the process of exercise recovery, lizards were forced to undergo both exhaustive and sprinting exercise at their preferred body temperature of 40°C. The peak speeds attained and the total distances travelled by these animals during these two different exercise protocols were measured and the animals were then forced to undergo a second bout of either sprinting or exhaustive exercise, following a 30–330 min recovery at either 20°C, 40°C or under a variable thermal regime which duplicated that selected by animals following exercise. 3. Animals recovering at a constant 40°C regained their ability to repeat exhaustive activity in less than 85 min, while animals recovering under the other two thermal regimes required between 85 and 100 min of recovery to be able to repeat this activity. Animals recovering at both 40°C and under the variable thermal regime regained their ability to repeat sprint behaviour within 60 min of recovery, while animals recovering at 20°C required more than 100 min of recovery to be able to repeat sprint behaviour. 4. These results formed the basis of the conclusion that the post‐exercise behaviour selected by D. dorsalis retards the rate at which the animals recover their ability to repeat exhaustive exercise when compared with recovery at a constant 40°C but does not retard their ability to repeat sprint exercise.
The probabilities of supercoil removal and decatenation by yeast DNA topoisomerase II
Authors: Roca Joaquim , Wang James C. 
Published: November 2003

Background:  In yeast a single type II DNA topoisomerase is involved in both the removal of DNA supercoils and the unlinking of intertwined pairs of newly replicated chromosomes or plasmids; in bacteria, two type II enzymes, DNA gyrase and DNA topoisomerase IV, function separately in the passage of DNA segments in cis and in trans. To deduce the molecular characteristics of these enzyme‐mediated reactions, the efficiencies of supercoil removal and decatenation by the yeast enzyme upon the addition of a nonhydrolysable ATP analogue were determined. Results:  The probability that a bound enzyme transports a DNA segment in cis increases with positive or negative supercoiling of the DNA, and transport is nearly quantitative at high degrees of supercoiling. The relative probabilities of transporting a contiguous and noncontiguous DNA segment by a yeast enzyme bound to one member of a singly linked pair of 3.6‐kb rings were calculated from the observed efficiency of decatenation. When the enzyme‐bound ring is highly supercoiled, transport of a noncontiguous segment is more probable than a contiguous one. Conclusion:  A DNA‐bound yeast enzyme has no intrinsic bias in its selection of a contiguous or noncontiguous DNA segment for transport, and the selection is determined by DNA conformations. For the singly linked dimeric catenane studied, a high degree of supercoiling of the enzyme‐bound DNA does not make supercoil removal more favourable than decatenation. In the case of bacterial gyrase, however, wrapping of a DNA segment around the enzyme is expected to strongly favour the transport of a contiguous segment.
Compartmentalized distribution of the proteins controlling the prespore‐specific transcription factor σF of Bacillus subtilis
Authors: Lewis Peter J. , Magnin Thierry , Errington Jeffery 
Published: November 2003

Background: Differential gene expression during sporulation in the prespore and mother cell of Bacillus subtilis is dependent on the correct timing and localization of the activity of specific transcription (σ) factors. The first σ factor activated is σF, which directs gene expression specifically in the prespore compartment. Release of σF activity is tightly controlled through a series of complex interactions involving an anti‐σ factor, SpoIIAB, an anti‐anti‐σ factor SpoIIAA and a phosphoprotein phosphatase SpoIIE. In vitro studies have shown that SpoIIAB binds to σF, preventing transcription of the σF regulon, and that it can also phosphorylate SpoIIAA, thereby inactivating it. However, non‐phosphorylated SpoIIAA can displace σF from SpoIIAB. The SpoIIE phosphatase provides a means of reactivating SpoIIAA‐P. Results: We have directly determined the cellular distibutions of σF, SpoIIAB, SpoIIAA‐P and SpoIIAA during sporulation, using recently developed immunofluorescence methods. While σF activity is restricted to the prespore, the protein is present in both compartments. As development proceeds the σF signal disappears. The anti‐σ factor SpoIIAB is also distributed throughout both cells and rapidly disappears from both cellular compartments soon after σF becomes active. Disappearance of SpoIIAB seems to be closely associated with the activation of the second prespore‐specific σ factor σF. The distribution of phosphorylated SpoIIAA closely mimics that of SpoIIAB, being non‐compartmentalized and disappearing soon after σF activation occurs. Significantly, the active, non‐phosphorylated form of the anti‐anti‐σ factor, SpoIIAA, accumulates in the prespore just before σF becomes active. Conclusion: These results support the hypothesis that the accumulation of SpoIIAA within the prespore is the single most important requirement for activation of σF.
Genetic interactions between CDC7 and CDC28: growth inhibition of cdc28‐1N by Cdc7 point mutants
Authors: Ohtoshi Akihira , Arai Ken‐ichi , Masai Hisao 
Published: November 2003

Background: Cdc7 kinase of Saccharomyces cerevisiae, a nuclear phosphoprotein, regulates initiation of chromosomal DNA replication. Overexpression of kinase‐negative Cdc7 point mutants (T281E, D182N and D163N) arrests the cell cycle of the wild‐type Saccharomyces cerevisiae cells at the G1/S boundary. This is caused by titration of a regulatory protein, Dbf4, from the wild‐type Cdc7, which leads to inactivation of its kinase activity. Results: We report here that kinase‐negative Cdc7 mutants, when overexpressed in cdc28‐1N(ts) at a permissive temperature, not only inhibit DNA replication by inactivating the wild‐type Cdc7 but may also disturb coordination between DNA replication and cell division. Suppression of growth inhibition under this condition requires co‐expression of both Dbf4 and Cdc28, whereas Dbf4 alone can counteract the growth inhibition in the wild‐type cells. In cdc28‐1N(ts), co‐expression of the wild‐type Dbf4 rescues only the G1/S defect and results in accumulation of those cells with less than 1C DNA as well as 2C DNA. On the other hand, co‐expression of Cdc28 alone leads to increase of those cells arrested at the G1/S boundary, as found typically in the wild‐type. We also report that overexpression of T281A, a ‘weak’ allele of Cdc7, causes growth arrest in cdc28‐1N(ts) cells, but not in the CDC28 wild‐type cells. This suggests that T281A is inactive in cdc28‐1N(ts) and is consistent with the idea that Cdc28 activates Cdc7 by phosphorylation. Conclusion: We conclude that two essential serine‐threonine kinases, Cdc28 and Cdc7, genetically inter‐act for initiation of the S phase and possibly for G2/M progression and/or S phase checkpoint control.
Complete growth inhibition of Escherichia coli by ribosome trapping with truncated cspA mRNA at low temperature
Authors: Jiang Weining , Fang Li , Inouye Masayori 
Published: November 2003

Background: CspA, the major cold‐shock protein of Escherichia coli, is transiently induced upon temperature downshift and considered to play an important role in low‐temperature adaptation. Results: Overproduction of truncated cspA mRNAs retaining translational ability was found to completely block cell growth at low temperatures. This effect was termed ‘low‐temperature antibiotic effect of truncated cspA expression (LACE)’. In contrast to the significant reduction of polysomes in normal cells upon cold shock, cells under LACE maintained a high polysome profile, producing only truncated cspA products. Growth inhibition of cells under LACE was suppressed when CspA was overproduced together with the truncated cspA mRNA. Conclusion: LACE is caused by the overproduction of a truncated cspA mRNA in the absence of CspA production, which in turn traps all the cellular ribosomes in a non‐adaptive form incapable of forming initiation complexes with other cellular mRNAs. LACE may provide a novel approach to the development of a new antibiotic.
A single point mutation of hamster aminoacyl‐tRNA synthetase causes apoptosis by deprivation of cognate amino acid residue
Authors: Fukushima Kohtaro , Motomura Seiichi , Kuraoka Akio , Nakano Hitoo , Nishimoto Takeharu 
Published: November 2003

Background:
We have isolated a series of temperature‐sensitive mutants for cell‐proliferation from the BHK21 cell line derived from the golden hamster (Nishimoto & Basilico 1978; Nishimoto et al. 1982). Using these mutants as a recipient of DNA‐mediated gene transfer, we have been cloning human genes which complement these ts mutants.
Results:
Cultures of tsBN269 cells, a temperature‐sensitive mutant of the BHK21 cell line, underwent apoptosis at 39.5 °C, a nonpermissive temperature. The gene complementing the tsBN269 cells was cloned and found to encode lysyl‐tRNA synthetase. Indeed, tsBN269 cells were found to have a single cytosine to a thymine point mutation at the first nucleotide of codon 542 in hamster lysyl‐tRNA synthetases. Due to this mutation, the activity of lysyl‐tRNA synthetase was reduced—even at 33.5 °C, a permissive temperature. Consistent with these findings, while supplementation with lysine permitted tsBN269 cells to grow at a nonpermissive temperature, the deprivation of lysine caused apoptosis in tsBN269 cells, even at 33.5 °C. Cycloheximide inhibited the apoptosis caused by lysine starvation at 33.5 °C, but not at 39.5 °C. We also found that another hamster temperature‐sensitive mutant, tsBN250, which is defective in histidyl‐tRNA synthetase, entered apoptosis with the deprivation of histidine.
Conclusion:
Our data suggested that the defect in aminoacyl‐tRNA synthetase turned on the cascade of apoptosis that was already present in the cells.
DNA nicking by Escherichia coli topoisomerase IV with a substitution mutation from tyrosine to histidine at the active site
Authors: Yokochi Tomoki , Kato Jun‐ichi , Ikeda Hideo 
Published: November 2003

Background:

Escherichia coli topoisomerase IV is a type II topoisomerase composed of ParC and ParE subunits and plays a major role in the decatenation of replicated molecules. The reaction with type II topoisomerases involves the cutting through transesterification between an active‐site tyrosine and a DNA phosphodiester bond and a rejoining of cleaved DNA.
Results:
To genetically analyse the mechanism of this reaction, we isolated dominant‐negative topoisomerase IV mutants. In one of them, the parC10 mutant, there was a substitution by histidine of the active‐site tyrosine. Purified mutant topoisomerase IV did not show normal DNA cutting activity but retained DNA nicking activity, even in the absence of ATP. The DNA ends of the product were not covalently bound to the ParC subunits, suggesting that the DNA is not cut via transesterification but by hydrolysis.
Conclusions:
We have shown genetically that the 120th tyrosine residue is important for the DNA cutting step in the topoisomerase reaction. The 120th amino acid residue, tyrosine or histidine, appears to be activated and the histidine residue forces the hydrogen‐bonded water to attack the phosphoryl group of the DNA in hydrolysis, while the tyrosine residue directly attacks the phosphoryl group during transesterification.