bluuebunny/crossref_metadata_2025 huggingface dataset:
Cloning and expression of the liver and muscle isoforms of ovine carnitine palmitoyltransferase 1: residues within the N-terminus of the muscle isoform influence the kinetic properties of the enzyme
Authors: PRICE Nigel T. , JACKSON Vicky N. , van der LEIJ Feike R. , CAMERON Jacqueline M. , TRAVERS Maureen T. , BARTELDS Beatrijs , HUIJKMAN Nicolette C. , ZAMMIT Victor A.
Published: June 2003

Fatty acid and ketone body metabolism differ considerably between monogastric and ruminant species. The regulation of the key enzymes involved may differ accordingly. Carnitine palmitoyltransferase 1 (CPT 1) is the key locus for the control of long-chain fatty acid β-oxidation and liver ketogenesis. Previously we showed that CPT 1 kinetics in sheep and rat liver mitochondria differ. We cloned cDNAs for both isoforms [liver- (L-) and muscle- (M-)] of ovine CPT 1 in order to elucidate the structural features of these proteins and their genes (CPT1A and CPT1B). Their deduced amino acid sequences show a high degree of conservation compared with orthologues from other mammalian species, with the notable exception of the N-terminus of ovine M-CPT 1. These differences were also present in bovine M-CPT 1, whose N-terminal sequence we determined. In addition, the 5′-end of the sheep CPT1B cDNA suggested a different promoter architecture when compared with previously characterized CPT1B genes. Northern blotting revealed differences in tissue distribution for both CPT1A and CPT1B transcripts compared with other species. In particular, ovine CPT1B mRNA was less tissue restricted, and the predominant transcript in the pancreas was CPT1B. Expression in yeast allowed kinetic characterization of the two native enzymes, and of a chimaera in which the distinctive N-terminal segment of ovine M-CPT 1 was replaced with that from rat M-CPT 1. The ovine N-terminal segment influences the kinetics of the enzyme for both its substrates, such that the Km for palmitoyl-CoA is decreased and that for carnitine is increased for the chimaera, relative to the parental ovine M-CPT 1.
Negative regulation of gp130 signalling mediated through tyrosine-757 is not dependent on the recruitment of SHP2
Authors: FAIRLIE W. Douglas , SOUZA David De , NICOLA Nicos A. , BACA Manuel
Published: June 2003

Cytokines of the interleukin-6 family utilize the shared cytokine receptor gp130 in the formation of active signalling complexes. Tyrosine-757 (Y757) on this receptor is critical for negative regulation of gp130-mediated signalling. Two signalling regulators, suppressor of cytokine signalling 3 (SOCS3) and Src homology 2 domain-containing tyrosine phosphatase-2 (SHP2), are recruited to Y757 following receptor activation; however, the relative contribution made by each of these in down-regulating gp130 signalling is not known. In the present study, we show the design of a mutant gp130 receptor that can recruit SHP2, but not SOCS3. This receptor maintains the critical Y757 residue, but contains mutations in other surrounding residues which are also important for interactions with the Src homology 2 domains of SOCS3 and SHP2. Cells transfected with a chimaeric receptor containing the SHP2-selective gp130 intracellular domain showed an enhanced response to cytokine stimulation, which was similar to that shown by a chimaeric gp130 receptor mutant carrying a Y757F point mutation that failed to recruit either SOCS3 or SHP2. These results demonstrate that the recruitment of SHP2 alone is not sufficient for Y757-dependent negative regulation of gp130 signalling and that this activity must therefore be dependent on SOCS3.
cGMP-dependent protein kinase protects cGMP from hydrolysis by phosphodiesterase-5
Authors: KOTERA Jun , GRIMES Kennard A. , CORBIN Jackie D. , FRANCIS Sharron H.
Published: June 2003

The physiological effects of cGMP are largely determined by the activities of intracellular receptors, including cGMP-dependent protein kinase (PKG) and cGMP-binding cyclic nucleotide phosphodiesterases (PDEs), and the distribution of cGMP among these receptors dictates activity of the signalling pathway. In the present study, the effects of PKG-Iα or PKG-Iβ on the rate of cGMP hydrolysis by the isolated PDE5 catalytic domain were examined. PKG-Iα strongly inhibited cGMP hydrolysis with an IC50 value of 217 nM, which is similar to the physiological concentration of PKG in pig coronary artery reported previously. By contrast, PKG-Iβ, which has lower affinity for cGMP than does PKG-Iα, inhibited cGMP hydrolysis with an IC50 of approx. 1 μM. Inhibition by PKG-Iα was more effective than that by PKG-Iβ, consistent with their relative affinities for cGMP. Autophosphorylation of PKGs increased their cGMP-binding affinities and their inhibitory effects on PDE5 hydrolysis of cGMP. Autophosphorylation of PKG-Iβ increased its inhibitory potency on PDE5 hydrolysis of cGMP by 10-fold compared with a 2-fold increase upon autophosphorylation of PKG-Iα. The results indicate that cGMP bound to allosteric cGMP-binding sites of PKG is protected from hydrolysis by PDE5 and that persistent protection of cGMP by either non-phosphorylated or autophosphorylated PKGs may be a positive-feedback control to sustain cGMP signalling.
Carbonic anhydrase-related protein is a novel binding protein for inositol 1,4,5-trisphosphate receptor type 1
Authors: HIROTA Junji , ANDO Hideaki , HAMADA Kozo , MIKOSHIBA Katsuhiko
Published: June 2003

The inositol 1,4,5-trisphosphate (IP3) receptor (IP3R) is an intracellular IP3-gated Ca2+ channel that is located on intracellular Ca2+ stores and modulates Ca2+ signalling. Using the yeast two-hybrid system, we screened a mouse brain cDNA library with bait constructs for mouse IP3R type 1 (IP3R1) to identify IP3R1-associated proteins. In this way, we found that carbonic anhydrase-related protein (CARP) is a novel IP3R1-binding protein. Western blot analysis revealed that CARP is expressed exclusively in Purkinje cells of the cerebellum, in which IP3R1 is abundantly expressed. Immunohistochemical analysis showed that the subcellular localization of CARP in Purkinje cells is coincident with that of IP3R1. Biochemical analysis also showed that CARP is co-precipitated with IP3R1. Using deletion mutagenesis, we established that amino acids 45–291 of CARP are essential for its association with IP3R1, and that the CARP-binding site is located within the modulatory domain of IP3R1 amino acids 1387–1647. CARP inhibits IP3 binding to IP3R1 by reducing the affinity of the receptor for IP3. As reported previously, sensitivity to IP3 for IP3-induced Ca2+ release in Purkinje cells is low compared with that in other tissues. This could be due to co-expression of CARP with IP3R in Purkinje cells and its inhibitory effects on IP3 binding.
Cytosolic iron superoxide dismutase is a part of the triacylglycerol biosynthetic complex in oleaginous yeast
Authors: RAYCHAUDHURI Sumana , REDDY Mamatha M. , RAJKUMAR Naveen R. , RAJASEKHARAN Ram
Published: June 2003

A novel multienzyme complex for the biosynthesis of triacylglycerol in oleaginous yeast has been identified recently in the cytosol and characterized [Gangar, Karande and Rajasekharan (2001) J. Biol. Chem. 276, 10290–10298]. Screening the library of Rhodotorula glutinis with an oligonucleotide probe derived from the N-terminal sequence of one of the protein components in the complex (21 kDa protein) resulted in the isolation of a 0.7 kb cDNA. Nucleotide sequence analysis revealed that the isolated gene codes for superoxide dismutase (SOD). Atomic absorption spectroscopy and inhibition assays showed that this cytosolic SOD utilizes Fe as its cofactor. Enzymic assays, immunoprecipitation and cross-linking experiments revealed that SOD is a part of the triacylglycerol biosynthetic complex, which could protect the substrate and the complex from oxidative damages. These results indicate for the first time the presence of iron-containing SOD in a soluble form in yeast.
An analysis of the phosphorylation and activation of extracellular-signal-regulated protein kinase 5 (ERK5) by mitogen-activated protein kinase kinase 5 (MKK5) in vitro
Authors: MODY Nimesh , CAMPBELL David G. , MORRICE Nick , PEGGIE Mark , COHEN Philip
Published: June 2003

MKK5 expressed as a glutathione S-transferase fusion protein in human embryonic kidney 293 cells activated full-length extracellular-signal-regulated protein kinase (ERK)5 (ERK5wt) as well as the isolated catalytic domain (ERK5cat) in vitro. Activation was accompanied by the phosphorylation of Thr219 and Tyr221, the former residue being phosphorylated preferentially. ERK5cat phosphorylated at Thr219, but not Tyr221, possessed 10% of the activity of the doubly phosphorylated protein towards myelin basic protein, whereas ERK5cat phosphorylated at Tyr221 alone was much less active. Activated ERK5 phosphorylated itself at a number of residues, including Thr28, Ser421, Ser433, Ser496, Ser731 and Thr733. ERK5 phosphorylated at Thr219, but not Tyr221, phosphorylated itself at a similar rate to ERK5 phosphorylated at both Thr219 and Tyr221. Activated ERK5 also phosphorylated mitogen-activated protein kinase kinase 5 (MKK5) extensively at Ser129, Ser137, Ser142 and Ser149, which are located within the region in MKK5 that is thought to interact with ERK5.
Identification of a novel mannose-capped lipoarabinomannan from Amycolatopsis sulphurea
Authors: GIBSON Kevin J. C. , GILLERON Martine , CONSTANT Patricia , PUZO Germain , NIGOU Jérôme , BESRA Gurdyal S.
Published: June 2003

The genus Amycolatopsis is a member of the phylogenetic group nocardioform actinomycetes, which also includes the genus Mycobacterium. Members of this group have a characteristic cell envelope structure, dominated by various complex lipids and polysaccharides. Amongst these, lipoglycans are of particular interest since mycobacterial lipoarabinomannans are important immunomodulatory molecules. In this study we report the isolation and structural characterization of Amycolatopsis sulphurea lipoarabinomannan, designated AsuLAM. SDS/PAGE analysis revealed that AsuLAM was of an intermediate size between Mycobacterium tuberculosis lipoarabinomannan and lipomannan, confirmed by matrix-assisted laser-desorption ionization–time-of-flight mass spectrometry that predicted an average molecular mass of 10 kDa. Using a range of chemical degradations, NMR experiments and capillary electrophoresis analysis, AsuLAM was revealed as an original structure. The mannosyl-phosphatidyl-myo-inositol anchor exhibits a single acyl-form, characterized by a diacylated glycerol moiety, and contains, as one of the main fatty acids, 14-methyl-pentadecanoate, a characteristic fatty acid of the Amycolatopsis genus. AsuLAM also contains a short mannan domain; and is dominated by a multi-branched arabinan domain, composed of an (α1→5)-Araf (arabinofuranose) chain substituted, predominately at the O-2 position, by a single β-Araf. The arabinan domain is further elaborated by manno-oligosaccharide caps, with around one per molecule. This is the first description of manno-oligosaccharide caps found in a non-mycobacterial LAM. AsuLAM was unable to induce the production of the pro-inflammatory cytokine tumour necrosis factor α when tested with human or murine macrophage cell lines, reinforcing the paradigm that mannose-capped LAM are poor inducers of pro-inflammatory cytokines.
c-Jun N-terminal kinase (JNK)-mediated modulation of brain mitochondria function: new target proteins for JNK signalling in mitochondrion-dependent apoptosis
Authors: SCHROETER Hagen , BOYD Clinton S. , AHMED Ruhi , SPENCER Jeremy P. E. , DUNCAN Roger F. , RICE-EVANS Catherine , CADENAS Enrique
Published: June 2003

The molecular mechanisms underlying the initiation and control of the release of cytochrome c during mitochondrion-dependent apoptosis are thought to involve the phosphorylation of mitochondrial Bcl-2 and Bcl-xL. Although the c-Jun N-terminal kinase (JNK) has been proposed to mediate the phosphorylation of Bcl-2/Bcl-xL the mechanisms linking the modification of these proteins and the release of cytochrome c remain to be elucidated. This study was aimed at establishing interdependency between JNK signalling and mitochondrial apoptosis. Using an experimental model consisting of isolated, bioenergetically competent rat brain mitochondria, these studies show that (i) JNK catalysed the phosphorylation of Bcl-2 and Bcl-xL as well as other mitochondrial proteins, as shown by two-dimensional isoelectric focusing/SDS/PAGE; (ii) JNK-induced cytochrome c release, in a process independent of the permeability transition of the inner mitochondrial membrane (imPT) and insensitive to cyclosporin A; (iii) JNK mediated a partial collapse of the mitochondrial inner-membrane potential (Δψm) in an imPT- and cyclosporin A-independent manner; and (iv) JNK was unable to induce imPT/swelling and did not act as a co-inducer, but as an inhibitor of Ca-induced imPT. The results are discussed with regard to the functional link between the Δψm and factors influencing the permeability transition of the inner and outer mitochondrial membranes. Taken together, JNK-dependent phosphorylation of mitochondrial proteins including, but not limited to, Bcl-2/Bcl-xL may represent a potential of the modulation of mitochondrial function during apoptosis.
Regulation of the CDP-choline pathway by sterol regulatory element binding proteins involves transcriptional and post-transcriptional mechanisms
Authors: RIDGWAY Neale D. , LAGACE Thomas A.
Published: June 2003

The synthesis of phosphatidylcholine (PtdCho) by the CDP-choline pathway is under the control of the rate-limiting enzyme CTP:phosphocholine cytidylyltransferase (CCT). Sterol regulatory element binding proteins (SREBPs) have been proposed to regulate CCT at the transcriptional level, or via the synthesis of lipid activators or substrates of the CDP-choline pathway. To assess the contributions of these two mechanisms, we examined CCTα expression and PtdCho synthesis by the CDP-choline pathway in cholesterol and fatty acid auxotrophic CHO M19 cells inducibly expressing constitutively active nuclear forms of SREBP1a or SREBP2. Induction of either SREBP resulted in increased expression of mRNAs for sterol-regulated genes, elevated fatty acid and cholesterol synthesis (>10–50-fold) and increased PtdCho synthesis (2-fold). CCTα mRNA was increased 2-fold by enforced expression of SREBP1a or SREBP2. The resultant increase in CCTα protein and activity (2-fold) was restricted primarily to the soluble fraction of cells, and increased CCTα activity in vivo was not detected. Inhibition of the synthesis of fatty acids or their CoA esters by cerulenin or triacsin C respectively following SREBP induction effectively blocked the accompanying elevation in PtdCho synthesis. Thus PtdCho synthesis was driven by increased synthesis of fatty acids or a product thereof. These data show that transcriptional activation of CCTα is modest relative to that of other SREBP-regulated genes, and that stimulation of PtdCho synthesis by SREBPs in CHO cells is due primarily to increased fatty acid synthesis.
Fossils as Neolithic funereal adornments in County Kerry, south‐west Ireland
Authors: Jackson Patrick N. Wyse , Connolly Michael
Published: June 2003

Argument rages in the media on the effects of road‐building on sites of archaeological importance. Certainly there have been many cases where sites of value have been lost, but others where sites of importance have been revealed that would probably have gone undetected for a considerable time, if not for ever. One example of a lucky discovery arose from a proposal to widen the road between the towns of Tralee and Killarney in County Kerry, south‐west Ireland. A preliminary archaeological survey carried out along the route in 1996 revealed an area of exceptional archaeological richness. What was particularly surprising was that one feature contained a significant collection of fossils used for funereal or ceremonial purposes.
A karst of thousands: Jamaica's limestone scenery
Authors: Donovan Stephen K.
Published: June 2003

About two‐thirds of the surface‐rock outcrop of Jamaica consists of Cretaceous and Cenozoic, particularly mid‐Tertiary, limestones. The island has been subaerially exposed for less than 10 million years. During this time, a combination of high tropical temperatures and high seasonal rainfall, coupled with widespread jointing and faulting related to the island's position within the North Caribbean Plate Boundary Zone, has led to the development of an impressive karst topography over much of Jamaica.
Effect of underground fungus‐growing termites on carbon dioxide emission at the point‐ and landscape‐scales in an African savanna
Authors: Konaté S. , Roux X. Le , Verdier B. , Lepage M.
Published: June 2003

The rate of CO2 emission by two major termite species (Ancistrotermes cavithorax and Odontotermes n. pauperans) was studied in a West African savanna (Lamto, Côte d’Ivoire). First, in three major savanna types (grassy, shrubby and woody savannas), CO2 emission from the soil surface was measured using a closed container system. Control soil without termite fungus‐comb chambers, and soil of eroded termite mound with or without Odontotermes fungus‐comb chambers was sampled in each savanna type. Second, the mass‐specific respiration rate of the different components of termite fungus‐comb chambers (i.e. workers, soldiers, fungus comb and chamber walls) was measured under laboratory conditions. CO2 emission by termites at the landscape‐scale was computed from both field biomass data and laboratory measurements.

Whatever the savanna type, CO2 emission from the soil surface was not different between control soil and soil of eroded termite mound without termite fungus‐comb chambers, but was significantly higher in areas with fungus‐comb chambers than in areas without fungus‐comb chambers (10–19 µmol CO2 m−2 s−1vs 5–10 µmol CO2 m−2 s−1).

The mass‐specific respiration rates were higher for individuals of O. pauperans than for individuals of A. cavithorax. Total respiration rate from an individual fungus‐comb chamber was around 56 and 143 µmol CO2 h−1 for Ancistrotermes and Odontotermes, respectively.

Despite a low mass‐specific respiration rate, fungus comb accounted for 51% of the total respiration flux from whole chambers in Odontotermes and for 82% in Ancistrotermes. The laboratory‐derived respiration rate from individual Odontotermes chambers was consistent with the field estimates.

At the landscape‐scale, the CO2 emission due to A. cavithorax and O. pauperans was 0·022 and 0·050 µmol CO2 m−2 s−1, respectively. This total (27·2 g C m−2 years−1) represented 4·9% of the total above‐ground net primary production in this ecosystem and 11·3% of the carbon not mineralized by annual fires.
Fractal index captures the role of vegetation clumping in locust swarming
Authors: Despland E.
Published: June 2003

This paper evaluates box‐counting dimension as a quantitative clumping index for discontinuous plant cover, and applies it to studies of both small‐ and large‐scale ecological processes in desert locust (Schistocerca gregaria) swarming.

The quadrat under study is tiled with squares of increasing size, and the relationship between the number of occupied squares and square size gives the box‐counting dimension. This index is high for random distributions and decreases when the vegetation is clumped; it is also positively linked to the abundance of vegetation.

At the scale of individual locusts, this index captures the space‐filling properties of vegetation that promote change to the gregarious phase and the onset of swarming. At the very large scale, box‐counting dimension measured from satellite imagery reflects topography, which influences the concentration and migration of locust swarms.

Fractal geometry considers scale of measurement in quantifying pattern and provides a framework to interpret ecological phenomena across spatial scales. Demonstration of a statistically significant relationship between the box‐counting exponent and locust behaviour shows how this approach can be applied to ecological studies.
The effect of wasps and ants on the reproductive success of the extrafloral nectaried plantTurnera ulmifolia(Turneraceae)
Authors: Cuautle M. , Rico‐Gray V.
Published: June 2003

1. To assess the effectiveness of extrafloral nectaries (EFN) as a defensive mechanism of plants it is vital to use a multiple interactions approach and assess the contribution of all visiting species and their interactions.

2. The effect of EFN‐visiting ants (Camponotus planatus,C.abdominalis,Conomyrmasp.,Crematogaster brevispinosa,Foreliussp.,Pseudomyrmexsp.) and wasps (Polistes instabilis,Polybia occidentalis) on the reproductive success (estimated as the number of reproductive structures) ofTurnera ulmifolia(Turneraceae) was experimentally evaluated. Herbivory effects were tested usingEuptoieta hegesialarvae (caterpillars), which is the main herbivore of this plant. The study was done in a coastal sand dune scrub in Veracruz, México.

3. Wasps and ants were selectively excluded using a two‐factor design (Wasps, Ants) block design, both factors with two levels (absent, present). The response variables were an index of herbivory per branch and the number of buds, flowers, ripe and unripe fruit per plant, and the seed/fruit ratio per branch.

4. After a week of placing the larvae on experimental plants, they were significantly more frequent on plants where wasps and ants had been experimentally excluded.

5. Wasp presence was associated significantly with greater numbers of buds, flowers, ripe fruit and seeds. When acting separately, wasps and ants exerted a positive effect in decreasing herbivory levels and increasing the number of unripe fruit; when acting together, however, their effect was not additive.

6. This is the first demonstration of a positive effect on the plant by wasps associated with EFN. The ecological implication of this finding is that the function of EFN and the ultimate effects on a plant will probably depend on the array of organisms visiting its EFN.
Tropospheric O3 moderates responses of temperate hardwood forests to elevated CO2: a synthesis of molecular to ecosystem results from the Aspen FACE project
Authors: Karnosky D. F. , Zak D. R. , Pregitzer K. S. , Awmack C. S. , Bockheim J. G. , Dickson R. E. , Hendrey G. R. , Host G. E. , King J. S. , Kopper B. J. , Kruger E. L. , Kubiske M. E. , Lindroth R. L. , Mattson W. J. , Mcdonald E. P. , Noormets A. , Oksanen E. , Parsons W. F. J. , Percy K. E. , Podila G. K. , Riemenschneider D. E. , Sharma P. , Thakur R. , Sôber A. , Sôber J. , Jones W. S. , Anttonen S. , Vapaavuori E. , Mankovska B. , Heilman W. , Isebrands J. G.
Published: June 2003

The impacts of elevated atmospheric CO2 and/or O3 have been examined over 4 years using an open‐air exposure system in an aggrading northern temperate forest containing two different functional groups (the indeterminate, pioneer, O3‐sensitive species Trembling Aspen, Populus tremuloides and Paper Birch, Betula papyrifera, and the determinate, late successional, O3‐tolerant species Sugar Maple, Acer saccharum).

The responses to these interacting greenhouse gases have been remarkably consistent in pure Aspen stands and in mixed Aspen/Birch and Aspen/Maple stands, from leaf to ecosystem level, for O3‐tolerant as well as O3‐sensitive genotypes and across various trophic levels. These two gases act in opposing ways, and even at low concentrations (1·5 × ambient, with ambient averaging 34–36 nL L−1 during the summer daylight hours), O3 offsets or moderates the responses induced by elevated CO2.

After 3 years of exposure to 560 µmol mol−1 CO2, the above‐ground volume of Aspen stands was 40% above those grown at ambient CO2, and there was no indication of a diminishing growth trend. In contrast, O3 at 1·5 × ambient completely offset the growth enhancement by CO2, both for O3‐sensitive and O3‐tolerant clones. Implications of this finding for carbon sequestration, plantations to reduce excess CO2, and global models of forest productivity and climate change are presented.
Anther arrangement influences pollen deposition and removal in hermaphrodite flowers
Authors: Kudo G.
Published: June 2003

Effects of anther arrangement on pollen deposition and removal in hermaphrodite flowers were experimentally quantified to assess the ecological significance of stamen structure. The anther arrangement of Brassica rapa was modified into six types with respect to anther number and the spatial arrangement of long and short stamens. Each anther treatment was combined with a nectar‐intact and nectar‐depleted treatment. After single visits by bumblebees in a glasshouse, the visit duration to each flower and the number of pollen grains deposited on stigmas and pollen grains remaining in long and short anthers were measured.

Visits were significantly shorter in nectar‐depleted flowers. Short anthers also extended visit duration, but modification of the long anther arrangement had no effect. Pollen deposition on stigmas depended on the number of long anthers and on visit duration. Although an increase in long anther number accelerated self‐pollination, removal of short anthers did not influence pollen deposition.

Pollen removal from long anthers depended on anther treatment and visit duration, but not on nectar availability. Any modification of anther arrangement tended to increase pollen removal during single visits. Long anthers contributed to the decrease in pollen removal per visit, while pollen removal from short anthers depended only on visit duration. Short anthers appeared to have a different function from the restriction of pollen removal during single visits by bumblebees.

Thus, long and short anthers made different contributions to pollination efficiency of nectar‐feeding bumblebees. The maintenance of different types of stamens in Brassicaceae plants (tetradynamous stamens) may reflect functional advantages for a diverse pollination syndrome if the pollination efficiency of long and short anthers varies depending on the type of pollinator.
Reduced burst speed is a cost of rapid growth in anuran tadpoles: problems of autocorrelation and inferences about growth rates
Authors: Arendt J. D.
Published: June 2003

It is becoming clear that individual growth rates are optimized to suit local conditions rather than maximized to be as fast as possible. To understand this adaptive variation in growth rates, we need to understand the costs of rapid growth.

Recent work in teleost fish suggests that a trade‐off between growth rate and critical swimming speed may be common. The current study demonstrates that the trade‐off also occurs in anuran tadpoles with regard to burst speed.

Individual growth rate and burst speed were compared in Bufo americanus and Scaphiopus hamondi, representatives of two distantly related anuran families. Path analysis showed that growth rate is negatively correlated with burst speed. Because the trade‐off between growth rate and swimming speed occurs in two such distantly related anuran species as well as teleosts, it may be general for all vertebrates.

However, identifying costs of rapid growth is complicated by the indirect effects of growth rate on body size which will also often correlate with performance factors. Distinguishing between direct effects of growth rate and indirect effects through body size is difficult because the two necessarily result in collinearity. A randomization test shows just how severe this problem can be.
Attack strategy of an ambush predator: which attributes of the prey trigger a pit‐viper's strike?
Authors: Shine R. , Sun L.‐X.
Published: June 2003

Why do larger predators generally consume larger prey items? Endemic pit‐vipers (Gloydius shedaoensis) on a small island in north‐eastern China ambush passerine birds, usually from the branches of small trees. Both minimum and maximum prey sizes increase with predator size.

To clarify the reasons for this ontogenetic shift, 251 snakes in ambush postures were approached and offered potential prey items (dead birds, or models covered in feathers) to clarify the cues that trigger a foraging strike.

The snakes struck at the prey item in 101 of these trials, and this ‘decision’ was influenced by the size, movement and temperature of the prey item. A pit‐viper's body size influenced its prey‐size selectivity, with larger snakes refusing to strike at smaller prey items. Larger snakes also scavenge dead birds too large for smaller snakes to ingest, but do not ignore live birds: even the largest snakes use prey movement and prey temperature as cues to elicit feeding strikes.

The ontogenetic shift in prey size thus reflects a combination of processes. The absence of large prey from the diet of small snakes is due to gape‐limitation (these snakes strike and attempt to swallow much larger prey). The absence of small prey items from the diet of larger snakes is due to active refusal to strike at small prey, as well as a behavioural shift to scavenging and to terrestrial rather than arboreal ambush‐sites (and thus, higher rates of encounter with large prey items) by larger pit‐vipers.
Defoliation alters water uptake by deep and shallow roots of Prosopis velutina (Velvet Mesquite)
Authors: Snyder K. A. , Williams D. G.
Published: June 2003

Prosopis velutina Woot. (Velvet Mesquite) at a site with limited groundwater availability derived a greater percentage of water from shallow soil at the onset of the summer rainy season than did trees at a site with greater availability of groundwater. Predawn leaf water potentials (Ψpd) were not a strong indicator of shallow water use for this species with roots in multiple soil layers.

We experimentally defoliated P. velutina plants to determine if reduced‐canopy photosynthesis would alter vertical patterns of root activity. After natural rain events, hydrogen isotope ratios of xylem sap indicated that defoliated P. velutina took up a greater percentage of its water from shallow soils than did undefoliated plants.

Irrigation with deuterium‐labelled water further demonstrated that undefoliated plants were able to use shallow soil water. Defoliation appeared to affect the ability of trees to use deep‐water sources.

Reduced carbon assimilation limited water uptake from deep soil layers. These data highlight that there are internal physiological controls on carbon allocation that may limit water uptake from different soil layers. During periods of high vapour pressure deficit or soil drought, when leaf gas exchange and carbon assimilation decline, this may create positive feedbacks where plants are unable to forage for deep water due to carbon limitations.
High daily energy expenditure of incubating shorebirds on High Arctic tundra: a circumpolar study
Authors: Piersma T. , Lindström Å. , Drent R. H. , Tulp I. , Jukema J. , Morrison R. I. G. , Reneerkens J. , Schekkerman H. , Visser G. H.
Published: June 2003

Given the allometric scaling of thermoregulatory capacity in birds, and the cold and exposed Arctic environment, it was predicted that Arctic‐breeding shorebirds should incur high costs during incubation. Using doubly labelled water (DLW), daily energy expenditure (DEE) during incubation was measured in eight shorebird species weighing between 29 and 142 g at various sites in the Eurasian and Canadian High Arctic. The results are compared with a compilation of similar data for birds at lower latitudes.

There was a significant positive correlation between species average DEE and body mass (DEE (kJ day−1) = 28·12 BM (g)0·524, r2 = 0·90). The slopes of the allometric regression lines for DEE on body mass of tundra‐breeding birds and lower latitude species (a sample mostly of passerines but including several shorebirds) are similar (0·548 vs 0·545). DEE is about 50% higher in birds on the tundra than in temperate breeding areas.

Data for radiomarked Red Knots for which the time budgets during DLW measurements were known, indicated that foraging away from the nest on open tundra is almost twice as costly as incubating a four‐egg clutch.

During the incubation phase in the High Arctic, tundra‐breeding shorebirds appear to incur among the highest DEE levels of any time of the year. The rates of energy expenditure measured here are among the highest reported in the literature so far, reaching inferred ceilings of sustainable energy turnover rates.
Body size and the timing of egg production in parasitoid wasps: a comparative analysis
Authors: Jervis M. A. , Ferns P. N. , Heimpel G. E.
Published: June 2003

1. The ovigeny index, previously identified as both a significant fitness variable in parasitoid wasps and an important factor in parasitoid–host population dynamics, is the proportion of the maximum potential lifetime complement of eggs that is mature when the female emerges into the environment following pupal development. We tested the hypothesis that ovigeny index varies with female body size in parasitoid wasps. Body size measurements were obtained for 40 species in 13 families, representing a broad taxonomic and morphological diversity of parasitoid wasps. There was an almost 18‐fold difference in size between the smallest and the largest species.

2. Ovigeny index is shown to be negatively correlated with body size across species – smaller wasps have a higher proportion of eggs mature at emergence than do larger wasps – a result supporting the hypothesis. This relationship has previously been observed within species.

3. The previously reported cross‐species negative correlation between life‐span and ovigeny index is robust, as it still holds when variation in body size is controlled for.

4. We discuss the likely selective factors in the evolution of a link between ovigeny index and body size across species.
Density‐dependent growth of Sea Lamprey larvae: evidence for chemical interference
Authors: Rodríguez‐Muñoz R. , Nicieza A. G. , Braña F.
Published: June 2003

Density can influence growth through exploitation competition and behavioural or chemical interference. Negative effects of population density on the growth rate of Sea Lamprey larvae have been reported in several field and laboratory studies, but the mechanisms involved are poorly understood.

In this study the role of population density and waterborne‐mediated interference on the growth rate of Sea Lamprey larvae was assessed in two laboratory experiments. The effects of these factors were evaluated by comparing growth of larvae reared at three different densities (27, 75 and 128 individuals m−2) or in preconditioned water (i.e. containing Sea Lamprey larvae at the same three densities).

Larval density had a negative effect on growth rates. Water conditioning had a negative but weaker effect on growth. Larvae reared in water preconditioned at the two higher densities showed a lower mass increase than those growing in water preconditioned at the lowest density.

The results are consistent with the existence of some chemical or biological agent released into the surrounding water and influencing growth in larval Sea Lampreys. However, chemical interference is not the only factor influencing density‐dependent growth.
Is rate of ontogenetic growth constrained by resource supply or tissue growth potential? A comment on Westet al.'s model
Authors: Ricklefs R. E.
Published: June 2003

Westet al. (2001) describe a general model of ontogenetic growth in which growth represents the surplus of energy acquisition over maintenance energy requirement, which themselves are allometric (power) functions of body mass with exponents3/4and 1, respectively. Furthermore, the intercept of the maintenance requirement decreases with the –1/4power of adult mass.

These relationships determine the sigmoid shape of the postnatal growth curve and the3/4allometric slope of time to complete growth as a function of adult mass.

Westet al.'s growth function is a particular form of the generalized Pütter growth model dm/dt = amy − bmz, which includes other familiar growth functions, such as the logistic and von Bertalanffy equations.

Empirical estimates of the allometry of resting metabolism in growing birds are close toz = 1 in some precocial species, but are approximately 50% higher in altricial and semiprecocial birds, which challenges the generality of any single growth function for birds.

Rather than growth rate being limited by the difference between energy acquisition and maintenance expenditure, it may also be determined by the growth potential of tissues, which is traded off against functional capacity. Predicted growth curves based on increasing tissue function with age are indistinguishable from the Westet al. and related equations.

Models based on growth rate–functional maturity trade‐offs also can produce observed allometric relationships of growth rate to adult mass by incorporating the relative size of the chick at hatching.

In contrast to Westet al.'s model, declining variance in size among individuals as chicks approach adult size implies targeted growth and control of growth rate by feedbacks of body size itself on growth rate.

The existence of plausible alternative hypotheses for the control of postnatal growth should stimulate additional experimental studies to elucidate mechanisms of growth rate regulation and to understand the evolutionary diversification of postnatal growth.
Structural requirements for the perception of ambient temperature signals in homeothermic heat production of skunk cabbage (Symlocarpus foetidus)
Authors: ITO K. , ONDA Y. , SATO T. , ABE Y. , UEMURA M.
Published: June 2003

The spadix of skunk cabbage, Symplocarpus foetidus, is capable of maintaining an internal temperature of around 20 °C even when the ambient temperature drops to around 0 °C. To determine the crucial structure that is required for detection of ambient temperature signals, detailed measurements of the temperatures of the spadix were made under field conditions. The spadix temperature was well regulated even when the spathe or the leaf of the plant was removed. Furthermore, maintenance of the temperature of the central stalk at either 10 or 20 °C had no effect on the thermoregulation when the ambient temperature increased from 10 to 25 °C or decreased from 20 to 8 °C. Therefore, it seemed that the heat production in the spadix required neither the spathe, the leaf, nor the central stalk for perception of the external temperature signals. Finally, analysis of sugar composition in xylem exudates showed that the concentrations of sucrose, glucose, and fructose, all of which are potential energy sources of thermogenesis, did not change significantly at different ambient temperatures. It is concluded that the spadix is a unique organ in which the perception of ambient temperature signals and heat production occurs in S. foetidus.
Root structure and cellular chloride, sodium and potassium distribution in salinized grapevines
Authors: STOREY R. , SCHACHTMAN D. P. , THOMAS M. R.
Published: June 2003

X‐ray microanalysis was used to study the patterns of K+, Na+ and Cl– accumulation in salinized (25 mm NaCl) and non‐salinized grapevine (Vitis) roots. The aim was to determine whether NaCl affects patterns of Cl– accumulation differentially in the roots of a Cl–‐excluding genotype and a non‐excluding genotype. Two regions of fibrous roots were analysed: (1) a region 2–3 mm basipetal to the root tip; and (2) a region of the root 10–12 mm basipetal to the root tip where the outermost layer is the hypodermis. The ion contents of the hypodermis, cortex, endodermis and pericycle vacuoles were analysed. Data were also collected from the cytoplasm of the endodermal and pericycle cells. The analyses showed that the ion profiles of the hypodermis and the endodermis were significantly different from those of the cortex and pericycle. The hypodermis and endodermis had higher K+ and lower Na+ and Cl– than surrounding cells. Some changes due to salinity such as increased K+ concentrations in the hypodermis were also noted. Chloride concentrations did not differ between the genotypes in the hypodermis, across the cortex or in the endodermis, but were higher in the pericycle of the excluder in comparison with the non‐excluding genotype. However, K+/Na+ ratios of the cortex and endodermis were higher in the excluder. The pericycle cells exhibited the greatest ability to sequester Na+ and Cl– in vacuoles. Overall the data show cell‐type‐specific ion accumulation patterns and small but significant differences were found between genotypes. The possibility that these accumulation patterns arise from differences in uptake properties of cell types and/or result from the spatial distribution of the cell types along the competing symplastic and apoplastic ion transport pathways across the root is discussed.
On the progressive enrichment of the oxygen isotopic composition of water along a leaf
Authors: FARQUHAR G. D. , GAN K. S.
Published: June 2003

A model has been derived for the enrichment of heavy isotopes of water in leaves, including progressive enrichment along the leaf. In the model, lighter water is preferentially transpired leaving heavier water to diffuse back into the xylem and be carried further along the leaf. For this pattern to be pronounced, the ratio of advection to diffusion (Péclet number) has to be large in the longitudinal direction, and small in the radial direction. The progressive enrichment along the xylem is less than that occurring at the sites of evaporation in the mesophyll, depending on the isolation afforded by the radial Péclet number. There is an upper bound on enrichment, and effects of ground tissue associated with major veins are included. When transpiration rate is spatially nonuniform, averaging of enrichment occurs more naturally with transpiration weighting than with area‐based weighting. This gives zero average enrichment of transpired water, the modified Craig–Gordon equation for average enrichment at the sites of evaporation and the Farquhar and Lloyd (In Stable Isotopes and Plant Carbon‐Water Relations, pp. 47–70. Academic Press, New York, USA, 1993) prediction for mesophyll water. Earlier results on the isotopic composition of evolved oxygen and of retro‐diffused carbon dioxide are preserved if these processes vary in parallel with transpiration rate. Parallel variation should be indicated approximately by uniform carbon isotope discrimination across the leaf.
Alterations in Cd‐induced gene expression under nitrogen deficiency in Hordeum vulgare
Authors: FINKEMEIER I. , KLUGE C. , METWALLY A. , GEORGI M. , GROTJOHANN N. , DIETZ K.‐J.
Published: June 2003

The inter‐relation between nitrogen availability and cadmium toxicity was studied in roots of barley seedlings with emphasis on the analysis of expression of 10 selected genes relevant for growth in the presence of toxic Cd concentrations. The response to Cd exposure differed quantitatively or qualitatively for the 10 genes in dependence of the N supply. Transcripts of glutathione synthase, glutathione reductase, glutathione peroxidase and dehydroascorbate reductase were measured as parameters involved in antioxidant defence, metallothionein, phosphoenolpyruvate carboxylase and phytochelatin synthase (PCS) were analysed as genes related to heavy metal binding, and vacuolar ATPase subunits VHA‐E and VHA‐c and a NRAMP‐transporter as genes being implicated in Cd transport. Reprogramming of the Cd response was most obvious for PCS and NRAMP whose transcript levels were unaltered and down‐regulated, respectively, in the presence of Cd at adequate N, but strongly up‐regulated upon Cd exposure under conditions of nitrogen deficiency. Different responses to Cd at varying N supply were also seen for the antioxidant genes. The results on gene expression are discussed in context with the changes in biochemical parameters, and underline the importance of evaluating the general growth conditions of a plant when discussing its specific response to a stressor such as Cd.

The sequence of the nramp cDNA was filed at the EMBL/GenBank/DDBJ Databases under the accession number AJ514946.
Increases of chlorophyll a/b ratios during acclimation of tropical woody seedlings to nitrogen limitation and high light
Authors: KITAJIMA K. , HOGAN K. P.
Published: June 2003

According to the theory of optimal nitrogen partitioning within a leaf, the chlorophyll (Chl) a/b ratio is expected to increase when leaf N content decreases. Here, we report the first empirical support for this prediction. The Chl a/b ratio increased while Chl content decreased in response to N limitation in photosynthetic cotyledons and leaves of seedlings of four tropical woody species in the Bignoniaceae. The responses of all four species were in the same direction, but differed in magnitude. For Tabebuia rosea, the species that exhibited the greatest increase in Chl a/b ratios (up to values of 5.9), detailed photosynthetic characteristics were also examined. Light and N availability were positively correlated with the light‐ and CO2‐saturated photosynthetic O2 evolution rate, as well as with leaf carboxylation capacity (Vcmax) and electron transport rate (Vj). Severe N limitation and high light did not cause chronic photo‐inhibition (i.e. no change in quantum yield or in dark‐acclimated Fv/Fm). The observed change in the ratio of Vcmax to leaf N in response to N availability was consistent with likely functional reasons for change in the Chl a/b ratio. Adjustment of the Chl a/b ratio was apparently an integral feature of acclimation to high light conditions and low N availability.
Responses of selected birch (Betula pendula Roth) clones to ozone change over time
Authors: OKSANEN E.
Published: June 2003

A long‐term free air ozone fumigation experiment was conducted to study changes in physiological ozone responses during tree ontogeny and exposure time in ozone sensitive and tolerant clones of European white birch (Betula pendula Roth), originated from south and central Finland. The trees were grown in soil in natural microclimatic conditions under ambient ozone (control) and 1.4–1.7 × ambient (elevated) ozone from May 1996 to October 2001, and were measured for stem and foliage growth, net photosynthesis, stomatal conductance, stomatal density, visible injuries, foliar starch content and bud formation. After 6 years of exposure, the magnitude of ozone‐induced growth reductions in the sensitive clone was 12–48% (significant difference), levels similar or greater than those reported earlier for 2‐ and 3‐year‐old saplings undergoing shorter exposures. In the tolerant clone, growth of these larger trees was reduced by 1–38% (significant difference in stem volume), although the saplings had previously been unaffected. In both clones, ozone stress led to significantly reduced leaf‐level net photosynthesis but significantly increased stomatal conductance rates during the late summer, resulting in a lower carbon gain for bud formation and the onset of visible foliar injuries. Increasing ozone sensitivity with duration of exposure was explained by a change in growth form (relatively reduced foliage mass), a lower photosynthesis to stomatal conductance ratio during the late summer, and deleterious carry‐over effects arising from the reduced number of over‐wintering buds.