bluuebunny/crossref_metadata_2025 huggingface dataset:
An amino‐terminal domain of Enterococcus faecalis aggregation substance is required for aggregation, bacterial internalization by epithelial cells and binding to lipoteichoic acid
Authors: Waters Christopher M. , Hirt Helmut , McCormick John K. , Schlievert Patrick M. , Wells Carol L. , Dunny G. M.
Published: May 2004

Aggregation substance (AS), a plasmid‐encoded surface protein of Enterococcus faecalis, plays important roles in virulence and antibiotic resistance transfer. Previous studies have suggested that AS‐mediated aggregation of enterococcal cells could involve the binding of this protein to cell wall lipoteichoic acid (LTA). Here, a method to purify an undegraded form of Asc10, the AS of the plasmid pCF10, is described. Using this purified protein, direct binding of Asc10 to purified E. faecalis LTA was demonstrated. Equivalent binding of Asc10 to LTA purified from INY3000, an E. faecalis strain that is incapable of aggregation, was also observed. Surprisingly, mutations in a previously identified aggregation domain from amino acids 473 to 683 that abolished aggregation had no effect on LTA binding. In frame deletion analysis of Asc10 was used to identify a second aggregation domain located in the N‐terminus of the protein from amino acids 156 to 358. A purified Asc10 mutant protein lacking this domain showed reduced LTA binding, while a purified N‐terminal fragment from amino acids 44–331 had high LTA binding. Like the previously described aggregation domain, the newly identified Asc10(156−358) aggregation domain was also required for efficient internalization of E. faecalis into HT‐29 enterocytes. Thus, Asc10 possess two distinct domains required for aggregation and eukaryotic cell internalization: an N‐terminal domain that promotes binding to LTA and a second domain located near the middle of the protein.
Enhancement and rescue of target capture in Tn10 transposition by site‐specific modifications in target DNA
Authors: Pribil Patrick A. , Wardle Simon J. , Haniford David B.
Published: May 2004

The bacterial transposon Tn10 inserts preferentially into specific target sequences. This insertion specificity appears to be linked to the ability of target sites to adopt symmetrically positioned DNA bends after binding the transposition machinery. Target DNA bending is thought to permit the transposase protein to make additional contacts with the target DNA, thereby stabilizing the target complex so that the joining of transposon and target DNA sequences can occur efficiently. In the current work, we have asked whether the introduction of a discontinuity in a target DNA strand, a modification that is expected to make it easier for a DNA molecule to bend, can enhance or rescue target capture under otherwise suboptimal reaction conditions. We show that either a nick or a missing phosphate specifically at the site of reaction chemistry increases the ability of various target DNAs to form the target capture complex. The result suggests that the bends in the target DNA are highly localized and include the scissile phosphates. This raises the possibility that strand transfer is mechanistically linked to target capture. We have also identified specific residues in the target DNA and in transposase that appear to play an important role in target DNA bending.
Untangling intracellular DNA topology
Authors: Espeli Olivier , Marians Kenneth J.
Published: May 2004

The biochemical steps by which bacterial topoisomerases alter the topology of DNA are well known. However, it has been a more vexing task to establish physiological roles and sites of action of the different topoisomerases within the context of the bacterial cell cycle. This difficulty can be attributed in part to the redundancy among the activities of the different enzymes. In this microreview, we will focus on recent progress in understanding the topological structure of the chromosome, analysis of topoisomerase mechanism in single‐molecule assays and recent data on the regulation and integration of topoisomerase activity within the cell cycle that have all brought a new perspective to the action of topoisomerases in the bacterial cell.
Quantitative proteomics of the human malaria parasite Plasmodium falciparum and its application to studies of development and inhibition
Authors: Nirmalan Niroshini , Sims Paul F. G. , Hyde John E.
Published: May 2004

The ability to measure accurately comparative levels of protein expression after drug challenge, metabolic stress, developmental programming or other perturbation represents one of the most important goals in post‐genomics malaria research. We describe here a simple and robust quantitative methodology that is ideally suited to in vitro experiments designed to study changes in the proteome of the most important of the human parasites, the lethal species Plasmodium falciparum. The metabolic labelling technique we have developed uses parasite uptake of heavy isotope‐containing isoleucine during normal growth followed by two‐dimensional separation of individual proteins and mass spectrometry. The method is applicable to essentially each of the ≈ 5300 proteins of P. falciparum predicted from the completed genome sequence, permitting facile identification and accurate comparative quantification of labelled peptides from any of these proteins synthesized by in vitro cultures subjected to different stimuli. We demonstrate its application to the study of cell cycle changes, where we observe divergent patterns of protein and reported transcript levels indicative of modulation at the translational level. Our data also provide evidence for significant levels of post‐translational modification in the parasite, and we measure differences among variants of phosphoethanolamine N‐methyltransferase and actin‐I across the cell cycle. We have also monitored parasite responses to equipotent doses of the clinical antimalarial inhibitors pyrimethamine and tetracycline and observed differential effects for a number of proteins unrelated to likely targets of these drugs.
Branching sites and morphological abnormalities behave as ectopic poles in shape‐defective Escherichia coli
Authors: Nilsen Trine , Ghosh Anindya S. , Goldberg Marcia B. , Young Kevin D.
Published: May 2004

Certain mutants in Escherichia coli lacking multiple penicillin‐binding proteins (PBPs) produce misshapen cells containing kinks, bends and branches. These deformed regions exhibit two structural characteristics of normal cell poles: the peptidoglycan is inert to dilution by new synthesis or turnover, and a similarly stable patch of outer membrane caps the sites. To test the premise that these aberrant sites represent biochemically functional but misplaced cell poles, we assessed the intracellular distribution of proteins that localize specifically to bacterial poles. Green fluorescent protein (GFP) hybrids containing polar localization sequences from the Shigella flexneri IcsA protein or from the Vibrio cholerae EpsM protein formed foci at the poles of wild‐type E. coli and at the poles and morphological abnormalities in PBP mutants. In addition, secreted wild‐type IcsA localized to the outer membrane overlying these aberrant domains. We conclude that the morphologically deformed sites in these mutants represent fully functional poles or pole fragments. The results suggest that prokaryotic morphology is driven, at least in part, by the controlled placement of polar material, and that one or more of the low‐molecular‐weight PBPs participate in this process. Such mutants may help to unravel how particular proteins are targeted to bacterial poles, thereby creating important biochemical and functional asymmetries.
The effect of host‐encoded nucleoid proteins on transposition: H‐NS influences targeting of both IS903 and Tn10
Authors: Swingle Bryan , O'Carroll Michelle , Haniford David , Derbyshire Keith M.
Published: May 2004

Nucleoid proteins are small, abundant, DNA‐binding proteins that profoundly affect the local and global structure of the chromosome, and play a major role in gene regulation. Although several of these proteins have been shown to enhance assembly of transpososomes before initiating transposition, no systematic survey has been carried out examining the in vivo role(s) of these proteins in transposition. We have examined the requirement of the six most abundant nucleoid proteins in transposition for three different transposons, IS903, Tn10 and Tn552. Most notably, H‐NS was required for efficient transposition of all three elements in a papillation assay, suggesting a general role for H‐NS in bacterial transposition. Further studies indicated that H‐NS was exerting its effect on target capture. Targeting preferences for IS903 into the Escherichia coli chromosome were dramatically altered in the absence of H‐NS. In addition, the alterations observed in the IS903 target profile emphasized the important role that H‐NS plays in chromosome organization. A defect in target capture was also inferred for Tn10, as an excised transposon fragment, a precursor to target capture, accumulated in in vivo induction assays. Furthermore, a transposase mutant that is known to increase target DNA bending and to relax target specificity eliminated this block to target capture. Together, these results imply a role for H‐NS in target capture, either by providing regions of DNA more accessible to transposition or by stabilizing transpososome binding to captured targets immediately before strand transfer.
Regulation of type III secretion in Bordetella
Authors: Mattoo Seema , Yuk Ming H. , Huang Lisa L. , Miller Jeff F.
Published: May 2004

The BvgAS virulence control system regulates the expression of type III secretion genes in Bordetella subspecies that infect humans and other mammals. We have identified five open reading frames, btrS, btrU, btrX, btrW and btrV, that are activated by BvgAS and encode regulatory factors that control type III secretion at the levels of transcription, protein expression and secretion. The btrS gene product bears sequence similarity to ECF (extracytoplasmic function) sigma factors and is required for transcription of the bsc locus. btrU, btrW and btrV encode proteins predicted to contain PP2C‐like Ser phosphatase, HPK (His protein kinase)‐like Ser kinase and STAS anti‐sigma factor antagonist domains, respectively, which are characteristic of Gram‐positive partner switching proteins in Bacillus subtilis. BtrU and BtrW are required for secretion of proteins that are exported by the bsc type III secretion system, whereas BtrV is specifically required for protein synthesis and/or stability. Bordetella species have thus evolved a unique cascade to differentially regulate type III secretion that combines a canonical phosphorelay system with an ECF sigma factor and a set of proteins with domain signatures that define partner switchers, which were traditionally thought to function only in Gram‐positive bacteria. The presence of multiple layers and mechanisms of regulation most likely reflects the need to integrate multiple signals in controlling type III secretion. The bsc and btr loci are nearly identical between broad‐host‐range and human‐specific Bordetella. Comparative analysis of Bordetella subspecies revealed that, whereas bsc and btr loci were transcribed in all subspecies, only broad‐host‐range strains expressed a functional type III secretion system in vitro. The block in type III secretion is post‐transcriptional in human‐adapted strains, and signal recognition appears to be a point of divergence between subspecies.
Cell‐to‐cell signalling in Escherichia coli and Salmonella enterica
Authors: Ahmer Brian M. M.
Published: May 2004

Cell‐to‐cell signalling in prokaryotes that leads to co‐ordinated behaviour has been termed quorum sensing. This type of signalling can have profound impacts on microbial community structure and host–microbe interactions. The Gram‐negative quorum‐sensing systems were first discovered and extensively characterized in the marine Vibrios. Some components of the Vibrio systems are present in the classical genetic model organisms Escherichia coli and Salmonella enterica. Both organisms encode a signal receptor of the LuxR family, SdiA, but not a corresponding signal‐generating enzyme. Instead, SdiA of Salmonella detects and responds to signals generated only by other microbial species. Conversely, E. coli and Salmonella encode the signal‐generating component of a second system (a LuxS homologue that generates AI‐2), but the sensory apparatus for AI‐2 differs substantially from the Vibrio system. The only genes currently known to be regulated by AI‐2 in Salmonella encode an active uptake and modification system for AI‐2. Therefore, it is not yet clear whether Salmonella uses AI‐2 as a signal molecule or whether AI‐2 has some other function. In E. coli, the functions of both SdiA and AI‐2 are unclear due to pleiotropy. Genetic strategies to identify novel signalling systems have been performed with E. coli and Providencia stuartii. Several putative signalling systems have been identified, one that uses indole as a signal and another that releases what appears to be a peptide. The latter system has homologues in E. coli and Salmonella, as well as other bacteria, plants and animals. In fact, the protease components from Providencia and Drosophila are functionally interchangeable.
Plasmid partitioning and the spreading of P1 partition protein ParB
Authors: Rodionov Oleg , Yarmolinsky Michael
Published: May 2004

Bacterial plasmids of low copy number, P1 prophage among them, are actively partitioned to nascent daughter cells. The process is typically mediated by a pair of plasmid‐encoded proteins and a cis‐acting DNA site or cluster of sites, referred to as the plasmid centromere. P1 ParB protein, which binds to the P1 centromere (parS), can spread for several kilobases along flanking DNA. We argue that studies of mutant ParB that demonstrated a strong correlation between spreading capacity and the ability to engage in partitioning may be misleading, and describe here a critical test of the dependence of partitioning on the spreading of the wild‐type protein. Physical constraints imposed on the spreading of P1 ParB were found to have only a minor, but reproducible, effect on partitioning. We conclude that, whereas extensive ParB spreading is not required for partitioning, spreading may have an auxiliary role in the process.
The AberdeenChildren of the 1950scohort study: background, methods and follow‐up information on a new resource for the study of life course and intergenerational influences on health
Authors: Batty G. David , Morton Susan M. B. , Campbell Doris , Clark Heather , Smith George Davey , Hall Marison , Macintyre Sally , Leon David A.
Published: May 2004

In this paper we introduce and describe in detail an addition to the UK's population‐based resources for the investigation of biological and social influences on health across the life course and between generations: the AberdeenChildren of the 1950sstudy. We also provide an account of postwar Aberdeen when study members were growing up, report on findings of analyses of data from the original survey on which this study is based and its follow‐up, assess the strengths and limitations of the study, and outline current and future research directions.

This cohort comprises individuals born in Aberdeen, Scotland (UK) between 1950 and 1956, and is derived from 15 thousand subjects who took part in the Aberdeen Child Development Survey, a cross‐sectional study of ‘mental subnormality’ (learning disability) in a population of all children who were attending Aberdeen primary schools in December 1962. Data collection included information on birthweight, gestational age, childhood height and weight, tests of cognition and behavioural disorder, and a range of multilevel socio‐economic indicators. In 1998 we began the process of revitalising this cohort (now termed the AberdeenChildren of the 1950sstudy). We have been successful in ascertaining the current vital status and whereabouts of 98.5% of a target population of 12 150 subjects (6276 males, 5874 females) with full baseline data. The large majority (81%) of study participants still reside in Scotland and many (73%) have remained in the Grampian region which incorporates Aberdeen. At the present time, a total of almost 500 subjects are known to have died. Linkages to hospital admissions and other health endpoints captured through the Scottish Morbidity Records system have been completed. This includes an intergenerational linkage to approximately eight thousand deliveries in Scotland occurring to female members of the study population. A postal questionnaire to all traced surviving cohort members has also been distributed.
Impact of pregnancy‐induced hypertension on birthweight by gestational age
Authors: Xiong Xu , Fraser William D.
Published: May 2004

Few studies to date have examined the effect of severe pre‐eclampsia, pre‐eclampsia, and gestational hypertension on birthweight according to gestational age. We conducted a population‐based retrospective cohort study of 16 936 pregnant women in Suzhou, China. Analysis of variance and multivariable linear regression were performed to compare the mean birthweights of babies born to mothers with gestational hypertension, pre‐eclampsia, and severe pre‐eclampsia with birthweights of infants born to mothers with normal blood pressure at each week of gestation.

The differences in mean birthweight between women with severe pre‐eclampsia and women with normal blood pressure ranged between −467.7 g and 189.1 g. The birthweights were statistically significantly lower in women with severe pre‐eclampsia than in women with normal blood pressure for gestational age categories ≤ 35 and 36 weeks. However, after adjustment for confounding variables, the birthweights were not statistically significantly different in women with severe pre‐eclampsia when compared with women with normal blood pressure even at ≤ 35 and 36 weeks. The differences in mean birthweight between women with pre‐eclampsia and women with normal blood pressure ranged between −132.2 g and 174.6 g. These differences were not statistically significant, before or after adjusting for confounding variables. There were no differences in mean birthweight between women with gestational hypertension and women with normal blood pressure.

Further analysis suggested that pre‐eclampsia and gestational hypertension were associated with increased rates of both small‐for‐gestational‐age and large‐for‐gestational‐age infants. The majority of the babies born to mothers with different types of pregnancy‐induced hypertension were appropriate‐for‐gestational‐age or even large‐for‐gestational‐ age.  In  this  Chinese  population,  most  babies  born  to  mothers with severe pre‐eclampsia or pre‐eclampsia and gestational hypertension had similar fetal growth to those born to normotensive mothers.
Parental exposure to medical radiation and neuroblastoma in offspring
Authors: Patton Tara , Olshan Andrew F. , Neglia Joseph P. , Castleberry Robert P. , Smith Joanna
Published: May 2004

Previous studies have suggested an association between parental medical radiation exposure and increased incidence of certain childhood cancers. We investigated the relationship between medical radiation and risk of neuroblastoma in offspring using data from a North American case–control study. Cases were children diagnosed with neuroblastoma from 1 May 1992, to 30 April 1994, at Children's Cancer Group and Pediatric Oncology Group institutions throughout the United States and Canada. One matched control per case was selected using random‐digit dialling. Telephone interviews were conducted with parents to collect data on any medical radiation examinations and treatments in the 2 years before conception or during pregnancy. We included 500 maternal and 339 paternal matched pairs. Overall, no association was found between maternal exposure to radiation and neuroblastoma risk (odds ratio [OR] = 1.0; 95% confidence interval [CI]: 0.7, 1.3). Analysis of maternal exposure by specific anatomical site showed no association for gonadal sites [OR = 1.0; 95% CI = 0.5, 2.0]. Little association was found with paternal radiation exposure [OR = 1.2; 95% CI = 0.8, 1.8]. No consistent exposure‐response gradient was found based upon the number of maternal or paternal medical radiation examinations. The data presented here, coupled with the lower radiation doses currently used, indicate that any further study of this question will require larger studies with improved exposure assessment.
Recent decelerated decline in perinatal mortality rate of unlike‐sexed twins in Japan
Authors: Kato Noriko
Published: May 2004

The effect of assisted reproductive technology is more pronounced in unlike‐sexed twins than in like‐sexed. Trends in perinatal mortality of twins were compared between the two types of sex combination. Certificates for births (478 276 cases), stillbirths (50 542 cases), and early neonatal deaths (8747 cases) were the subjects of this analysis. Since 1984, the decline in the perinatal mortality of unlike‐sexed twins has been slower than that of like‐sexed twins. In both light‐for‐dates (LFD) and non‐LFD, the decline in the gestational age standardised mortality ratio has been slower in unlike‐sexed twins. We suggest this is due to the introduction of assisted reproductive technologies.
Parental growth at different life stages and offspring birthweight: an intergenerational cohort study
Authors: Hyppönen Elina , Power Chris , Smith George Davey
Published: May 2004

Using three generations of the 1958 British national birth cohort we investigated ways in which parental size is related to offspring birthweight. By age 41 years, 4566 singleton female and 4050 male cohort members (born 3–9 March, 1958) had become parents and provided information on their singleton offspring.

Mother's birthweight (standardised for gestational age and sex) was the strongest determinant of offspring birthweight (effect size [ES] per SDS 112 g [95% CI 97, 128]), which was little affected by adjustment for maternal height or BMI (ES 95 g and 105 g respectively). The intergenerational birthweight association was not observed for mothers born very small or large. Mother's childhood height at age 7 (ES 46 g [24, 67]), but not BMI (ES 3 g [−18, 23]), was associated with offspring birthweight after adjustment for grandparental size, own birthweight, and adult size. Controlling for other growth measures strongly attenuated the association between mother's adult height and offspring birthweight: (ES 90 g, unadjusted, and 25 g, adjusted), while the association between adult BMI and offspring birthweight was little affected (ES 55 g and 51 g respectively). Father's BMI did not affect offspring birthweight, while the associations for height were similar, albeit weaker, than those observed for the mother. Our results suggest that intergenerational associations in birthweights are largely independent of postnatal size. Maternal height in childhood was positively related to offspring birthweight, while the effect of her BMI was restricted to adulthood.
Maternal obesity as an independent risk factor for caesarean delivery
Authors: Sheiner Eyal , Levy Amalia , Menes Tehillah S. , Silverberg Daniel , Katz Miriam , Mazor Moshe
Published: May 2004

The present study was aimed to investigate pregnancy outcome among obese women and specifically the correlation between maternal obesity and incidence of caesarean section (CS) while controlling for the potential confounding effects of other variables associated with obesity. A population‐based study was performed comparing all pregnancies of obese (maternal pre‐pregnancy body mass index (BMI) of 30 kg/m2 or more) and non‐obese patients, between the years 1988 and 2002. Patients with hypertensive disorders and diabetes mellitus as well as patients lacking prenatal care were excluded from the analysis. Stratified analyses, using the Mantel‐Haenszel technique, and a multiple logistic regression model were performed to control for confounders. During the study period there were 126 080 deliveries meeting the inclusion criteria, of which 1769 (1.4%) occurred in obese patients.

Using a multivariable analysis, the following conditions were significantly associated with maternal obesity: failure to progress during the first stage (odds ratio (OR) = 3.1; 95% confidence interval [CI] 2.5, 3.8; P < 0.001), fertility treatments (OR = 2.0; [95% CI 1.6, 2.5]; P < 0.001), previous CS (OR = 1.7; [95% CI 1.5, 1.9]; P < 0.001), malpresentations (OR = 1.4; [95% CI 1.2, 1.6]; P < 0.001), recurrent miscarriages (OR = 1.4; [95% CI 1.2, 1.7]; P < 0.001) and fetal macrosomia (OR = 1.4; [95% CI 1.2, 1.7]; P < 0.001). Higher rates of caesarean deliveries were found among obese parturients (27.8% vs. 10.8%; OR = 3.2; [95% CI 2.9, 3.5]; P < 0.001). When controlling for possible confounders, using the Mantel‐Haenszel technique, the association between maternal obesity and CS remained significant. No significant differences were noted between the groups regarding perinatal complications such as perinatal mortality, congenital malformations, shoulder dystocia and low Apgar scores.

In conclusion, a significant association was found between obesity and CS even after the exclusion of hypertensive disorders and diabetes mellitus. Importantly, obesity alone was not associated with adverse perinatal outcome. Obstetricians should be encouraged to allow obese patients not suffering from diabetes or hypertensive disorders an adequate trial of labour.
Early discharge: no evidence of adverse outcomes in three consecutive population‐based Australian surveys of recent mothers, conducted in 1989, 1994 and 2000
Authors: Brown Stephanie , Bruinsma Fiona , Darcy Mary‐Ann , Small Rhonda , Lumley Judith
Published: May 2004

Length of postnatal hospital stay has declined dramatically since the 1970s, with ongoing controversy about potential harmful effects. Three population‐based surveys of recent mothers conducted in the State of Victoria, Australia have been analysed to assess the impact of shorter length of stay on breast feeding and women's psychological well‐being. Women giving birth in Victoria, Australia in 1 week in 1989, 2 weeks in 1993 and 2 weeks in 1999, excluding those who had a stillbirth or neonatal death, were mailed surveys 5–8 months postpartum. Adjusted response fractions were: 71.4% in 1989 (n = 790), 62.5% in 1994 (n = 1313), and 67% in 2000 (n = 1616). Participants were representative in terms of method of birth, parity and infant birthweight. Younger women, single women and women of non‐English‐speaking background (born outside Australia) were under‐represented.

The primary outcome measures were infant feeding at 6 weeks postpartum and maternal depression at 5–8 months postpartum (Edinburgh Postnatal Depression Scale ≥ 13). There was no significant association between length of stay (1–2 days vs. ≥ 5 days, 3–4 days vs. ≥ 5 days) and primary outcome measures in univariable analyses of the 1989 Survey, or multivariable analyses of the 1994 and 2000 Surveys adjusting for relevant social and obstetric factors. For stays of 3–4 days, the adjusted odds ratio for formula feeding at 6 weeks was 1.35 [95% CI 0.9, 1.9] in 1994 and 1.22 [95% CI 0.9, 1.7] in 2000. The confidence intervals are compatible with a very small reduction or a large increase in formula feeding, neither reaching statistical significance. For depressive symptoms at 5–7 months postpartum (EPDS score ≥ 13), the adjusted odds ratio for women staying 3–4 days was 0.96 [95% CI 0.7, 1.4] in 1994 and 0.90 [95% CI 0.6, 1.3] in 2000. These confidence intervals are compatible with a 30–40% reduction or a 30–40% increase in odds of depressive symptoms. Based on these findings shorter length of stay does not appear to have an adverse impact on breast feeding or women's emotional well‐being. Testing early discharge policies in well‐designed randomised trials remains a priority for developing stronger evidence to inform practice.
Cerebral palsy of post‐neonatal origin: characteristics and risk factors
Authors: Cans Christine , McManus Vicki , Crowley Michael , Guillem Pascale , Platt Mary‐Jane , Johnson Ann , Arnaud Catherine ,   SCPE (Surveillance of Cerebral Palsy in Europe) collaborative group
Published: May 2004

We aimed to study the rates and trends over time of children with cerebral palsy (CP) of post‐neonatal origin (arising more than 28 days after birth, and before the age of 25 months), to examine their aetiology and associated significant risk factors, and to compare them with other CP cases. Children with post‐neonatal CP born 1976–90 were identified from a European database and seven registers were included (Surveillance of Cerebral Palsy in Europe collaboration). Using a previously published classification it was possible to allocate an aetiology to 99% of cases. The prevalence rate of post‐neonatal CP was 1.26 per 10 000 live births and a significant decrease was observed over the period 1976–90 (P = 0.011). Infection accounted for 50%, vascular episodes for 20% and head injury for 18% of the cases. Although there has been little change in the profile of underlying causes in this period, within the infection group, a significant downward trend was observed for Reye's syndrome (P < 0.001) and non‐central nervous system (non‐CNS) infection (P = 0.004), but not for meningitis/encephalitis. There was evidence of some increased risk of post‐neonatal CP among children with low birthweight (<2500 g) (P < 0.001). Overall children with CP of post‐neonatal origin showed a more severe functional pattern than non‐post‐neonatal CP children. In order to ascertain the impact of public health and other preventive measures aimed at reducing the frequency of brain injury in the first 2 years after birth, it is necessary to continue to monitor the frequency and characteristics of children with post‐neonatal CP into the 1990s.
Transcriptome of Arabidopsis leaf senescence
Authors: GUO Y. , CAI Z. , GAN S.
Published: May 2004

Leaf senescence is a complex developmental process during which essential nutrients are recycled. In order to unravel the biochemical pathways and regulatory mechanisms that underlie this process, it would be valuable to examine the transcriptome associated with leaf senescence. Accordingly, an Arabidopsis thaliana leaf senescence cDNA library with approximately 104 recombinant clones was subjected to large‐scale single‐pass sequencing. Approximately 6200 expressed sequence tags (ESTs) were obtained, corresponding to 2491 unique genes. These included 134 genes encoding transcription factors and 182 genes whose products are components of signal transduction pathways, such as the mitogen‐activated protein kinase (MAPK) cascades. A total of 116 of these genes are predicted to be involved in protein turnover, including 75 genes associated with the ubiquitin–proteasome pathway and 35 proteinases. Many of the genes are predicted to encode transporters for ions, amino acids and sugars, consistent with the substantial nutrient recycling during leaf senescence. In addition, this study revealed ESTs for 98 annotated genes for which ESTs did not previously exist and 46 novel transcribed units that have not previously been annotated in the Arabidopsis genome. Approximately one‐third of the 2491 genes are predicted to encode proteins with unknown functions. The genes are distributed evenly on the five chromosomes.
Whole tree xylem sap flow responses to multiple environmental variables in a wet tropical forest
Authors: O'BRIEN J. J. , OBERBAUER S. F. , CLARK D. B.
Published: May 2004

In order to quantify and characterize the variance in rainforest tree physiology, whole tree sap flow responses to local environmental conditions were investigated in 10 species of trees with diverse traits at La Selva Biological Station, Costa Rica. A simple model was developed to predict tree sap flow responses to a synthetic environmental variable generated by a principle components analysis. The best fit was obtained with a sigmoid function which explained between 74 and 93% of the variation in sap flux of individual trees. Sap flow reached an asymptote where higher light and evaporative demand did not cause sap flux to increase further. Soil moisture had little influence on sap flux. The morphological characteristics of the trees significantly affected sap flow; taller trees responded to changes in environmental variables sooner than shorter trees and high liana cover buffered tree sap flow responses to weather. The effect of species‐specific differences on the model was small; the mean effectiveness of the model was reduced by 6% when parameters were estimated from a single pool of measurements taken from all individuals. The results indicate that sap flow response could be effectively estimated using a simple general model and composite environmental index for these 10 diverse tree species.
Canopy gradients in leaf intercellular CO2 mole fractions revisited: interactions between leaf irradiance and water stress need consideration
Authors: NIINEMETS Ü. , SONNINEN E. , TOBIAS M.
Published: May 2004

Intercellular CO2 mole fractions (Ci) are lower in the upper canopy relative to the lower canopy leaves. This canopy gradient in Ci has been associated with enhanced rates of carbon assimilation at high light, and concomitant greater draw‐downs in Ci. However, increases in irradiance in the canopy are generally also associated with decreases in leaf water availability. Thus, stress effects on photosynthesis rates (A) and stomatal conductance (G), may provide a further explanation for the observed Ci gradients. To test the hypotheses of the sources of canopy variation in Ci, and quantitatively assess the influence of within‐canopy differences in stomatal regulation on A, the seasonal and diurnal variation in G was studied in relation to seasonal average daily integrated quantum flux density (Qint) in tall shade‐intolerant Populus tremula L. trees. Daily time‐courses of A were simulated using the photosynthesis model of Farquhar et al. (Planta 149, 78–90, 1980). Stable carbon isotope composition of a leaf carbon fraction with rapid turnover rate was used to estimate canopy gradient in Ci during the simulations. Daily maximum G (Gmax) consistently increased with increasing Qint. However, canopy differences in Gmax decreased as soil water availability became limiting during the season. In water‐stressed leaves, there were strong mid‐day decreases in G that were poorly associated with vapour pressure deficits between the leaf and atmosphere, and the magnitude of the mid‐day decreases in G occasionally interacted with long‐term leaf light environment. Simulations indicated that the percentage of carbon lost due to mid‐day stomatal closure was of the order of 5–10%, and seasonal water stress increased this percentage up to 20%. The percentage of carbon lost due to stomatal closure increased with increasing Qint. Canopy differences in light environment resulted in a gradient of daily average Ci of approximately 20 µmol mol−1. The canopy variation in seasonal and diurnal reductions in G led to a Ci gradient of approximately 100 µmol mol−1, and the actual canopy Ci gradient was of the same magnitude according to leaf carbon isotope composition. This study demonstrates that stress effects influence Ci more strongly than within‐canopy light gradients, and also that leaves acclimated to different irradiance and water stress conditions may regulate water use largely independent of foliar photosynthetic potentials.
Hybridization of European oaks (Quercus ilex × Q. robur) results in a mixed isoprenoid emitter type
Authors: SCHNITZLER J.‐P. , STEINBRECHER R. , ZIMMER I. , STEIGNER D. , FLADUNG M.
Published: May 2004

European oaks have been reported to emit isoprene or monoterpenes derived from recently fixed photosynthetic carbon. The emission type is plant species specific and can be used as chemo‐taxonomic marker. In the present article the isoprenoid biochemical properties of mature Quercus × turneri‘Pseudoturneri’ hybrids resulting from a crossing of a Mediterranean evergreen monoterpene‐emitting species (subgenus Sclerophyllodrys; Quercus ilex L.) and an isoprene‐emitting deciduous oak species (subgenus Lepidobalanus; Quercus robur L.) are described. Both species are compared with respect to the capacity for isoprenoid synthesis and the actual isoprenoid emission pattern of different tree‐types. The analysis showed that the oak hybrid combines properties of both parental species. Furthermore, it could be shown that the enzyme activities of isoprene synthase and monoterpene synthases are reflected in the isoprenoid emission pattern of the hybrids as well as in the observed emission rates.
Sulphide intrusion in eelgrass (Zostera marinaL.)
Authors: PEDERSEN O. , BINZER T. , BORUM J.
Published: May 2004

Sudden events of seagrass die‐off have been suggested to be induced by invasion of the phytotoxin sulphide under environmental stress generating low oxygen supply in seagrass tissues. Laboratory experiments were conducted with eelgrass (Zostera marinaL.) to measure intra‐plant changes in oxygen and sulphide by means of microelectrodes at different oxygen concentrations in the water column. The objectives were to examine whether sulphide intrusion into seagrass tissues can be induced, to determine the role of plant oxygen status for sulphide intrusion and to determine how fast internal sulphide pools are depleted after internal oxygen supplies have been restored. Under conditions with oxygen partial pressures (pO2) above 7.4 kPa (> 35% of air saturation) within eelgrass rhizomes or meristematic tissues no intrusion of sulphide occurred in spite of high sediment concentrations of gaseous sulphide (> 1000 µm). Lack of sulphide intrusion at high internal pO2suggested that oxygen release from the roots ensured complete re‐oxidation of sulphide in the rhizosphere. Under oxygen stress, however, the experiments clearly demonstrated intrusion of sulphide in eelgrass rhizomes and meristematic tissues. Rates of sulphide intrusion were controlled by internal pO2, which in turn was controlled by water column oxygen concentrations. Maximum internal sulphide content reached 325 µmwhich by far exceeded the 1–10 µmknown to inhibit mitochondrial activity in eukaryotic cells. Sulphide and low levels of oxygen could coexist in the eelgrass tissues reflecting fast internal transport of sulphide and slow rates of sulphide re‐oxidation. Upon re‐establishment of high internal oxygen concentrations the depletion of the sulphide pool was slow (half‐life = 20–30 min) indicating, that sulphide re‐oxidation within the eelgrass tissue was not bacterially or enzymatically facilitated but occurred by simple chemical oxidation. The results of this study are consistent with the proposed detrimental role of sulphide intrusion in events of sudden seagrass die‐off.
A novel stress‐acclimation response in Spirodela punctata (Lemnaceae): 2,4,6‐trichlorophenol triggers an increase in the level of an extracellular peroxidase, capable of the oxidative dechlorination of this xenobiotic pollutant
Authors: JANSEN M. A. K. , HILL L. M. , THORNELEY R. N. F.
Published: May 2004

Peroxidases are haem‐containing enzymes capable of oxidizing a wide range of substrates. This article describes the presence of peroxidase activity in the growth medium of axenic Spirodela punctata (Lemnaceae) cultures. It was found that the release of extracellular peroxidase activity is specifically enhanced by phytotoxic, halogenated phenols but not by other abiotic stress‐factors, elicitors or plant metabolites. Based on the concentration dependence of 2,4,6‐trichlorophenol (TCP)‐enhanced peroxidase release, it is concluded that release is not simply a consequence of physiological damage, but rather requires metabolically healthy fronds. In vitro studies (UV/VIS spectroscopy and liquid chromatography/mass spectrometry) show that the extracellular duckweed peroxidase (SpEx), which was partially purified from Spirodela growth medium, is capable of catalysing the oxidative dechlorination of TCP with hydrogen peroxide as the electron acceptor. It is proposed that the ability of S. punctata to specifically sense environmentally persistent phytotoxic chlorophenols, and to respond by increasing extracellular levels of a peroxidase capable of catalysing their oxidative dechlorination, is part of the protection strategy of this aquatic plant against xenobiotic stress.
High light enhances the expression of low‐CO2‐inducible transcripts involved in the CO2‐concentrating mechanism in Synechocystis sp. PCC6803
Authors: MCGINN P. J. , PRICE G. D. , BADGER M. R.
Published: May 2004

The relative abundances of key gene transcripts encoding proteins involved in inducible inorganic carbon (Ci) transport in the cyanobacterium Synechocystis PCC6803 were quantified by real‐time reverse‐transcriptase‐polymerase chain reaction under conditions of varying Ci and light levels. Significant increases in CO2‐concentrating mechanism (CCM)‐related transcript abundance were observed only in cells aerated with CO2‐free air for 30 min in the light, but not in the dark, relative to illuminated cells grown at high CO2 levels (high‐Ci cells). Cells were incubated under precisely defined conditions in a cuvette attached to a mass spectrometer to allow for the measurement of photosynthetic gas exchange rates, [Ci] and [O2], in combination with quantitative analysis of transcripts. Under conditions of increasing irradiance and low [Ci], or under conditions of decreasing [Ci] at constant irradiance, the abundances of cmpA (encoding part of the BCT1 HCO3– transporter), ndhF3 (encoding subunit of high‐affinity CO2 uptake system) and sbtA (encoding Na+‐dependent HCO3– transporter) transcripts tended to increase, relative to illuminated cells grown at high‐CO2. The cmpA transcript appeared to be less responsive to decreasing [Ci] than either ndhF3 or sbtA. The induction of cmpA and ndhF3 transcripts was completely inhibited by 10 µm 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) compared to untreated control cells. This inhibitor had no effect on sbtA expression. In the presence of 2,6‐dichlorobenzoquinone (DCBQ), the expression of the cmpA transcript tracked the apparent rate of O2 evolution from photosystem II closely as the irradiance was increased, reaching maximum levels of expression approximately 16‐fold higher than control cells. Under the same conditions, the ndhF3 transcript increased by two‐ to three‐fold, whereas the sbtA transcript did not respond to this treatment. The regulation of CCM induction in this strain is discussed in relation to current hypotheses on the sensing of Ci limitation.
Environmental regulation of photosynthetic metabolism in the amphibious sedge Eleocharis baldwinii and comparisons with related species
Authors: UENO O.
Published: May 2004

The amphibious leafless sedge, Eleocharis baldwinii, expresses C4 characteristics in the terrestrial form and intermediate characteristics between C3 and C4 photosynthesis in the submerged form. This study examined the immunocytochemical localization of C3 and C4 enzymes in culms of the two forms to elucidate the regulatory mechanism of photosynthetic metabolism and compared the activities and amounts of C3 and C4 enzymes with those in other Eleocharis species, E. vivipara and E. retroflexa, which show C4 characteristics on land but C3 and C4 characteristics under water. The terrestrial form of E. baldwinii exhibited a C4‐like pattern of enzyme localization. The submerged form exhibited a modified anatomy with well‐developed mesophyll cells and small Kranz cells. The C4 enzyme levels declined conspicuously in outer mesophyll cells adjacent to the epidermis, whereas Rubisco levels increased throughout the mesophyll in the submerged form. These results suggest that intermediate photosynthesis between C3 and C4 photosynthesis in the submerged form results from the predominant operation of the C3 pathway in the outer mesophyll cells and the C4 pathway in both the inner mesophyll and Kranz cells. Differences in the degree of C4 expression in terrestrial forms of Eleocharis species may cause the differences in the expression of photosynthetic modes under water.
Sites of actin filament initiation and reorganization in cold‐treated tobacco cells
Authors: POKORNÁ J. , SCHWARZEROVÁ K. , ZELENKOVÁ S. , PETRÁŠEK J. , JANOTOVÁ I. , ČAPKOVÁ V. , OPATRNÝ Z.
Published: May 2004

Cytoskeletal proteins assemble into dynamic polymers that play many roles in nuclear and cell division, signal transduction, and determination of cell shape and polarity. The distribution and dynamics of microtubules (MTs) and actin filaments (AFs) are determined, among other factors, by the location of their nucleation sites. Whereas the sites of microtubule nucleation in plants are known to be located under the plasma membrane and on the nuclear envelope during interphase, there is a striking lack of information about nucleation sites of AFs. In the studies reported herein, low temperature (0 °C) was used to de‐polymerize AFs and MTs in tobacco BY‐2 (Nicotiana tabacum L.) cells at interphase. The extent of de‐polymerization of cytoskeletal filaments in interphase cells during cold treatment and the subcellular distribution of nucleation sites during subsequent recovery at 25 °C were monitored by means of fluorescence microscopy. The results show that AFs re‐polymerized rapidly from sites located in the cortical region and on the nuclear envelope, similarly to the initiation sites of MTs. In contrast to MTs, however, complete reconstitution of AFs was preceded by the formation of transient actin structures including actin dots, rods, and filaments with a dotted signal. Immunoblotting of soluble and sedimentable protein fractions showed no changes in the relative amounts of free and membrane‐bound actin or tubulin.
The Effects of Density on the Learned Recognition of Heterospecific Alarm Cues
Authors: Pollock Michael S. , Chivers Douglas P.
Published: May 2004

Numerous species, both aquatic and terrestrial, use alarm cues to mediate predation risk. These cues may be either intentionally or inadvertently released, and may be received by either conspecifics or heterospecifics. In aquatic systems, alarm cues are often chemical in nature and are released when an organism is disturbed or damaged by a predator. In some cases the recognition of alarm cues from conspecifics, or closely related heterospecifics, is innate, while the recognition of alarm cues from distantly related species must be learned. Many studies have documented the use of heterospecific alarm cues, but few have explored the manner in which these cues come to be recognized as an indication of predation. In the current study, we examined the fathead minnow (Pimephales promelas)/brook stickleback (Culaea inconstans) alarm system. We tested the effect of density on the ability of minnows to learn to recognize stickleback alarm cues as a threat. We hypothesized that the ability of minnows to learn to recognize stickleback alarm cues should increase with increasing stickleback density because there would be more opportunity for minnows to associate the heterospecific alarm cue with the threat. To test this hypothesis we stocked minnows into large outdoor pools with no stickleback, low numbers of stickleback, or high numbers of stickleback. All pools contained a predator (pike, Esox lucius) known to the minnows. Following a 14 d conditioning period, minnows were tested for a response to skin extract from stickleback, minnow, and an unknown heterospecific (swordtail, Xiphophorus helleri). Minnows from pools with large numbers of stickleback learned to respond to stickleback alarm cues while minnows from pools with low numbers of stickleback, or no stickleback, did not.