bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of UVB‐irradiated algae on life history traits of Daphnia pulex
Authors: DE LANGE HENDRIKA , VAN DONK ELLEN 
Published: November 2003

1. The impact of ultraviolet‐B (UVB)‐irradiated phytoplankton on the life history parameters of Daphnia was studied. Three species of Chlorophyceae (Chlamydomonas reinhardtii, Scenedesmus acutus and S. subspicatus) and one species of Cryptophyceae (Cryptomonas pyrenoidifera) were cultured with and without exposure to UVB radiation (biologically effective dose of 3 kJ m–2 day–1 DNA weighted) and fed to Daphnia pulex.2. The daphnids feeding on UVB‐irradiated algae tended to be smaller in size, to produce less and smaller offspring, and to have a reduced population growth rate.3. Fatty acid (FA) analysis of the phytoplankton showed a reduced total FA content under UVB radiation for all four species. Changes in the content of unsaturated fatty acids (UFA) were species specific.4. The results indicate that the energy transfer between the primary producers’ and grazers’ level might be negatively influenced by UVB radiation. Direct effects on food quality are modest but detectable, changes in quantity or species composition may be more important in the energy transfer.
Effects of algal food quality on fecundity and population growth rates of Daphnia
Authors: KILHAM SUSAN , KREEGER DANIEL , GOULDEN CLYDE , LYNN SCOTT 
Published: November 2003

1. Food quality was at least as important as food quantity for both fecundity and population growth responses of the cladoceran Daphnia pulicaria fed the green alga Ankistrodesmus falcatus grown under N limitation, P limitation, or non‐limited condition.2. The fecundity of D. pulicaria was reduced under conditions of low food quality (low N or low P) compared with that for animals fed control non‐limited algae regardless of ration size. The reduced fecundity of D. pulicaria fed P‐limited food could be partially alleviated by increasing the ration (hence, compensation), but such was not the case for animals fed N‐limited food.3. Population growth rates of D. pulicaria (rmax) were significantly reduced under conditions of low‐quality food for both N‐limited and P‐limited algae. Population growth rates were unaffected by ration size, indicating no compensation.
Effects of food type on the life history of Daphnia clones from lakes differing in trophic state. I. Daphnia galeata feeding on Scenedesmus and Oscillatoria*
Authors: REPKA SARI 
Published: November 2003

1. Effects of the green alga Scenedesmus obliquus and the filamentous cyanobacterium Oscillatoria limnetica as food sources on the growth and reproduction of nine Daphnia galeata clones were studied. A high concentration of these two algae species was fed to Daphnia clones collected from four lakes with varying trophic conditions in a life history experiment.2. Although Oscillatoria is regarded as a low quality food for Daphnia because of its filamentous morphology and suspected nutritional inadequacy, the cyanobacterium sustained both body growth and reproduction in D. galeata. Growth and reproduction were, however, lower and the onset of reproduction was delayed on a diet of Oscillatoria compared to a diet of Scenedesmus. The intrinsic growth rate, r, for each D. galeata clone was positive on a diet of Oscillatoria, ranging from 0.06 to 0.16 mm day–1, whereas the intrinsic growth rates on a diet of Scenedesmus ranged from 0.27 to 0.34 mm day–1.3. The degree of growth depression on the Oscillatoria diet varied among clones. Clonal responses were correlated with body size; clones with larger body size decreased their growth and reproduction more on a diet of Oscillatoria. The responses of different clones from the same lake to the two diets resembled each other, irrespective of geography or trophic state of the lake.
Manipulation of dietary lipids, fatty acids and vitamins in zooplankton cultures
Authors: COUTTEAU PETER , SORGELOOS PATRICK 
Published: November 2003

1. A wide range of species that are cultivated in commercial mariculture are planktonic during at least part of their life cycle; for example, the larval stages of shellfish (shrimp and molluscs) and the live feeds (rotifers, brine shrimp, copepods) used in the larviculture of marine fish and shellfish. Over the last decades various techniques have been developed to deliver nutrients to these zooplanktonic organisms either through artificial diets or by manipulating the composition of the live prey fed to the carnivorous stages. This paper reviews the methodology that has allowed aquaculturists to gain knowledge of nutritional requirements and may offer interesting opportunities for ecologists to verify the importance of key nutrients in the natural food chain of marine as well as freshwater ecosystems.2. Live micro‐algae can be replaced partially or completely in the diet of filter‐feeders such as rotifers, Artemia, shrimp larvae and bivalves, by various types of preserved algae, micro‐encapsulated diets and yeast‐based diets, whereas lipid emulsions and liposomes may be utilized to supplement specific lipid‐and water‐soluble nutrients, respectively. Microbound and micro‐encapsulated diets have been designed to supplement live feed in the culture of micro‐predators such as fish and shrimp larvae.3. Live prey organisms, in particular rotifers and Artemia, can be ‘bio‐encapsulated’ with a variety of enrichment diets to manipulate their content in certain nutrients, including ω3 highly unsaturated fatty acids (FA) and the vitamins C, A and E. Nevertheless, the enrichment techniques are not applicable for all nutrients and prey organisms. Phospholipid composition is difficult to manipulate through the diet of live feed and the enrichment of the essential FA docosahexaenoic acid (DHA) is hampered in most Artemia species due to the catabolism of this FA following enrichment.
Effect of physico‐chemical and molecular mobility parameters on Staphylococcus aureus growth
Authors: Vittadini Elena , Chinachoti Pavinee 
Published: November 2003

SummaryThe role played by water activity, ‘mobility’ and physico‐chemical properties of the media in modulating microbial response has been the object of large debate in the scientific community. In this study, Staphylococcus aureus growth parameters (lag phase and cell density at 24 h) in brain heart infusion (BHI) and BHI:NaCl (1:1) were analysed in their correlation with physico‐chemical/mobility parameters descriptive of the media [solid content, aw, kinematic viscosity, 17O NMR (R2, Pbw and )]. In these high moisture content, liquid and ‘homogeneous’ media S.aureus growth related to all the physico‐chemical and molecular mobility parameters analysed in a similar manner and it was found to be influenced more significantly by added NaCl than by the physico‐chemical and molecular mobility of the media. Staphylococcus aureus growth parameters correlated better with aw (relatively independent of NaCl concentration) than with any other parameter considered in this study.
Ssh10b, a conserved thermophilic archaeal protein, binds RNA in vivo
Authors: Guo Rong , Xue Hong , Huang Li 
Published: November 2003

SummaryProteins of the Sac10b family, which is highly conserved among hyperthermophilic archaea, have been regarded as DNA‐binding proteins. Based on their in vitro DNA‐binding properties, these proteins are thought to be involved in chromosomal organization or DNA repair/recombination. We show that Ssh10b, a member of the Sac10b family from Sulfolobus shibatae, bound with similar affinities to double‐stranded DNA, single‐stranded DNA and RNA in vitro. However, the protein was exclusively bound to RNA in S. shibatae cells, as revealed by in vivo UV cross‐linking and co‐immunoprecipitation. Ribosomal RNAs were among the RNA species co‐immunoprecipitated with Ssh10b. Consistent with this observation, Ssh10b was co‐purified with ribosomes under low salt conditions. Furthermore, we demonstrate by UV‐cross‐linking hybridization that, when the cells were irradiated with UV, Ssh10b became cross‐linked to 16S, 23S rRNAs and mRNAs. Our data indicate that RNA is the physiological binding target of the Sac10b family.
Constitutive expression of PcsB suppresses the requirement for the essential VicR (YycF) response regulator in Streptococcus pneumoniae R6§
Authors: Ng Wai‐Leung , Robertson Gregory T. , Kazmierczak Krystyna M. , Zhao Jingyong , Gilmour Raymond , Winkler Malcolm E. 
Published: November 2003

SummaryWe report several new findings about the function of the essential VicRK two‐component regulatory system (TCS) in the human pathogen Streptococcus pneumoniae. The vicR‐encoded response regulator, vicK‐encoded histidine kinase and the protein encoded by the downstream vicX gene are the homologues of the YycF, YycG and YycJ proteins, respectively, studied previously in Bacillus subtilis and Staphylococcus aureus. Using a regulatable promoter, we demonstrated that the VicK histidine kinase is conditionally required for growth of S. pneumoniae. Likewise, we found that the VicX protein is also conditionally required for growth and probably plays a role in the essential signal transduction pathway mediated by VicR and VicK. Recovery of limited substitutions in the conserved aspartate 52 residue (D52) of VicR was consistent with a requirement for phosphorylation of VicR for growth under some conditions. We applied microarrays to characterize the changes in transcription patterns in bacteria depleted for vicRKX operon expression. Our results suggest that the pcsB gene is a target of the VicRK TCS. We present evidence that downregulation of pcsB could account for many of the defects in cell growth, shape, size and morphology observed in bacteria depleted for vicRKX expression. Furthermore, constitutive expression of pcsB+ suppressed the essential requirement for the VicRK TCS and allowed the isolation of vicR null mutants.
Deletion analysis identifies key functional domains of the cytadherence‐associated protein HMW2 of Mycoplasma pneumoniae
Authors: Balish Mitchell F. , Ross Stephanie M. , Fisseha Makda , Krause Duncan C. 
Published: November 2003

Summary Mycoplasma pneumoniae attachment to host cells requires biogenesis of a functional attachment organelle, including proper localization of the adhesion protein P1 to this structure. Mutations in the hmw2 gene result in the inability to cytadhere, failure to localize P1 to the attachment organelle, altered cell morphology and accelerated turnover of the cytadherence‐associated proteins HMW1, HMW3 and P65. The hmw2 gene encodes HMW2 (190 kDa) and P28 (28 kDa), the latter apparently the product of internal translation initiation near the 3′ end of the hmw2 coding region. Transformation of hmw2 mutant I‐2 with recombinant wild‐type hmw2 restores a wild‐type phenotype. In the current study, a severely truncated hmw2 gene with an in frame internal deletion of 80% of the HMW2 coding region that leaves the P28‐encoding region intact restored cytadherence to mutant I‐2. Transformants produced the expected 38 kDa HMW2 derivative (HMW2Δmid) at levels comparable to that of HMW2 in wild‐type cells; like HMW2, HMW2Δmid exhibited marked Triton X‐100 insolubility. HMW3, P65 and P28 were fully restored, but not HMW1. These transformants were morphologically similar to wild‐type M. pneumoniae but failed to localize P1 to the attachment organelle. Finally, a C‐terminally truncated HMW2 derivative was partly Triton X‐100 soluble and incapable of restoring HMW1, HMW3 and P65 to wild‐type levels. These data are consistent with a model in which the C‐terminal domain of HMW2 imparts normal localization to the protein, and this localization itself is required for productive interactions with downstream cytadherence‐associated proteins. Furthermore, these results emphasize the association of HMW1 with P1 clustering.
Distribution of split DnaE inteins in cyanobacteria
Authors: Caspi Jonathan , Amitai Gil , Belenkiy Olga , Pietrokovski Shmuel 
Published: November 2003

SummaryInteins are genetic elements found inside the coding regions of different host proteins and are translated in frame with them. The intein‐encoded protein region is removed by an autocatalytic protein‐splicing reaction that ligates the host protein flanks with a peptide bond. This reaction can also occur in trans with the intein and host protein split in two. After translation of the two genes, the two intein parts ligate their flanking protein parts to each other, producing the mature protein. Naturally split inteins are only known in the DNA polymerase III alpha subunit (polC or dnaE gene) of a few cyanobacteria. Analysing the phylogenetic distribution and probable genetic propagation mode of these split inteins, we conclude that they are genetically fixed in several large cyanobacterial lineages. To test our hypothesis, we sequenced parts of the dnaE genes from five diverse cyanobacteria and found all species to have the same type of split intein. Our results suggest the occurrence of a genetic rearrangement in the ancestor of a large division of cyanobacteria. This event fixed the dnaE gene in a unique two‐genes one‐protein configuration in the progenitor of many cyanobacteria. Our hypothesis, findings and the cloning procedure that we established allow the identification and acquisition of many naturally split inteins. Having a large and diverse repertoire of these unique inteins will enable studies of their distinct activity and enhance their use in biotechnology.
Glutathione peroxidase genes in Arabidopsis are ubiquitous and regulated by abiotic stresses through diverse signaling pathways
Authors: Milla Miguel A. Rodriguez , Maurer Alberto , Huete Alicia Rodriguez , Gustafson J. Perry 
Published: November 2003

SummaryGlutathione peroxidases (GPXs) are a group of enzymes that protect cells against oxidative damage generated by reactive oxygen species (ROS). The presence of GPXs in plants has been reported by several groups, but the roles of individual members of this family in a single plant species have not been studied. A family of seven related proteins named AtGPX1– AtGPX7 in Arabidopsis was identified, and the genomic organization of this family was reported. The putative subcellular localizations of the encoded proteins are the cytosol, chloroplast, mitochondria, and endoplasmic reticulum. Expressed sequence tags (ESTs) for all the genes except AtGPX7 were identified. Expression analysis of AtGPX genes in Arabidopsis tissues was performed, and different patterns were detected. Interestingly, several genes were up‐regulated coordinately in response to abiotic stresses. AtGPX6, like human phospholipid hydroperoxide GPX (PHGPX), possibly encodes mitochondrial and cytosolic isoforms by alternative initiation. In addition, this gene showed the strongest responses under most abiotic stresses tested. AtGPX6::GUS analysis in transgenic Arabidopsis showed that AtGPX6 is highly expressed throughout development in most tissues, thus supporting an important role for this gene in protection against oxidative damage. The different effects of salicylic acid (SA), jasmonic acid (JA), abscisic acid (ABA), and auxin on the expression of the genes indicate that the AtGPX family is regulated by multiple signaling pathways. Analysis of the upstream region of the AtGPX genes revealed the presence of multiple conserved motifs, and some of them resembled antioxidant‐responsive elements found in plant and human promoters. The potential regulatory role of specific sequences is discussed.
Temporal and spatial control of gene silencing in transgenic plants by inducible expression of double‐stranded RNA
Authors: Chen Shuai , Hofius Daniel , Sonnewald Uwe , Börnke Frederik 
Published: November 2003

SummaryDownregulation of endogenous genes via post‐transcriptional gene silencing (PTGS) is a key to the characterization of gene function in plants. The recent discovery that double‐stranded RNA (dsRNA) is an extremely effective trigger of gene silencing greatly enhanced the predictability of this approach. However, strong constitutive silencing often leads to pleiotropic effects, which make it difficult to directly relate phenotype to gene function, or even interferes with the recovery of viable transgenic plants. Here, we show that strong genetic interference can be achieved in a chemically inducible fashion, allowing for temporal and spatial control of gene silencing in transgenic plants. To this end, transgenic tobacco plants were established expressing dsRNA in the form of intron‐spliced hairpin structures under the control of the ethanol‐inducible alc gene expression system. Targeting magnesium (Mg)‐chelatase subunit I (Chl I) and glutamate 1‐semialdehyde aminotransferase (GSA), both involved in chlorophyll (chl) biosynthesis, resulted in rapid and specific mRNA degradation upon induction with ethanol. Ethanol‐inducible silencing of the target genes caused strong but transient phenotypical alterations featured by a progressive loss of chl in young leaves, which persisted for about 7–9 days before newly growing leaves completely recovered. About 10–30% of the primary transformants showed phenotype development upon induction. Local silencing of Chl I could be achieved by confined ethanol treatment of a single leaf without affecting any other part of the plant. Inducible gene silencing using the alc system promises to obviate the problems associated with constitutive RNA silencing and enables to dissect primary and secondary effects of PTGS at temporal and spatial resolution.
A chloroplast‐localized PPR protein required for plastid ribosome accumulation
Authors: Williams Pascale M. , Barkan Alice 
Published: November 2003

SummaryThe pentatricopeptide repeat (PPR) is a degenerate 35‐amino acid repeating motif that is found in animal, fungal, and plant proteins. The PPR protein family is particularly large in plants, where the majority of family members are predicted to be targeted to mitochondria or chloroplasts. PPR proteins are believed to fall into the larger family of helical repeat proteins, which typically bind macromolecules through a surface formed by the stacking of consecutive helical repeating units. Prior findings implicate several PPR proteins in organellar RNA metabolism, but the biological functions of few PPR proteins have been explored and in no case has a direct substrate been definitively identified. We present a characterization of the maize nuclear gene ppr2, which encodes a chloroplast PPR protein. PPR2 is found in large, heterogeneous protein complexes in the chloroplast stroma, some of which may be associated with RNA. Null ppr2 mutants have albino leaves and lack plastid rRNA and translation products. Plastid rRNAs are absent in both dark‐ and light‐grown leaf tissues, indicating that their absence does not result from photo‐oxidative damage. The population of plastid transcripts in ppr2 mutants is similar to that in other maize mutants lacking plastid ribosomes, and no ppr2‐specific defects in plastid RNA metabolism have been detected. Taken together, the results suggest that ppr2 functions in the synthesis or assembly of one or more component of the plastid translation machinery.
Novel isoforms of NADPH oxidase in vascular physiology and pathophysiology
Authors: Bengtsson Sara HM , Gulluyan Lerna M , Dusting Gregory J , Drummond Grant R 
Published: November 2003

Summary1. Vascular cells have evolved to use reactive oxygen species (ROS), such as superoxide and hydrogen peroxide, as signalling molecules. Under physiological conditions, ROS are important regulators of cell cycle, protein kinase activity and gene expression. However, in vascular disease states, such as hypertension and hypercholesterolaemia, excessive production of ROS may overwhelm the anti‐oxidant defence mechanisms of cells, resulting in ‘oxidative stress’, damage to the artery wall and, ultimately, development of atherosclerotic plaques.2. The primary source of ROS in the vasculature is NADPH oxidase. There appear to be at least three isoforms of NADPH oxidase expressed in the vascular wall, each differing with respect to the flavin‐containing catalytic subunit it uses to transfer electrons from NADPH to molecular oxygen. Thus, although endothelial cells and adventitial fibroblasts express a gp91phox‐containing NADPH oxidase similar to that originally identified in phagocytes, vascular smooth muscle cells may rely on novel homologues of gp91phox, namely Nox1 and Nox4, to produce superoxide.3. Controversy remains over which isoform(s) of NADPH oxidase is responsible for the oxidative stress associated with vascular diseases. We and others have shown that although gp91phox mRNA expression is upregulated during atherogenesis in human and animal models, expression of the Nox4 subunit remains unchanged. Nox1 expression is also likely to be increased in diseased arteries; however, its relative level of expression, at least at the mRNA level, appears to be markedly lower than that of the other gp91phox homologues, even after upregulation.4. Whether these findings suggest that a gp91phox‐containing NADPH oxidase is more important than either Nox4 or Nox1 in vascular disease awaits studies examining relative protein expression and enzyme kinetics of each subunit, as well as the effects of targeted gene deletion of each of these gp91phox homologues on atherogenesis.
The contractile response of the mesenteric resistance arteries to prostaglandin F2α; effects of simultaneous hyperlipemia–diabetes
Authors: Georgescu Adriana , Popov Doina 
Published: November 2003

AbstractThe effect of hyperlipemia associated with diabetes on the contractility of resistance arteries to prostaglandin F2α (PGF2α) was investigated employing 4 weeks simultaneously hyperlipemic–diabetic (HD), hyperlipemic (H), diabetic (D) and normal hamsters (controls, C). The isometric force produced by explanted arteries in the presence of 10−8 to 10−5 m PGF2α was recorded by the myograph technique. The results showed that compared with controls, the contractile response to 10−5 m PGF2α was approx. 2 fold increased in HD group, and approx. 1.75 and 1.62‐fold enhanced in H and D groups, respectively. Activation of protein kinase C with 10−6 m phorbol 12‐myristate 13‐acetate increased the contractility to PGF2α in all groups and particularly in HD hamsters (approx. 10.16‐fold). Inhibition of cyclooxygenase by indomethacin increased approx. 1.81‐fold the arterial contractility to PGF2α in C group, whereas in H, D and HD hamsters had no effect. Blockage of Ca2+‐activated K+‐channels with 10−3 m tetraethylammonium augmented the contraction to PGF2α approx. 6.43‐fold in C group, and at significantly lower levels in H, D and HD groups, i.e. approx. 3.84, 3.72 and 3.33‐fold, respectively. The results validate two conclusions: (i) simultaneous insult of hyperlipemia‐hyperglycemia is associated with the highest contractility of the resistance arteries to PGF2α; the highest circulating glucose and cholesterol levels, and the enhancement in the protein kinase C pathway underlay the augmented contractility; (ii) no matter the pathology induced (hyperlipemia, diabetes or both simultaneously) a common dysfunctional response to PGF2α was installed; this consists in a reduced effect of cyclooxygenase inhibition, and a altered activity of Ca2+ dependent K+ channels.