bluuebunny/crossref_metadata_2025_split huggingface dataset:
Formation and diagenesis of bedding cycles in uppermost Cretaceous chalks of the Dan Field, Danish North Sea
Authors: Scholle Peter A. , Albrechtsen Troels , Tirsgaard Henrik 
Published: March 2003

Metre‐scale lithologic cycles, visible in core and on logs from Maastrichtian chalks of the Dan Field, were examined to determine their mechanisms of deposition and relation to hydrocarbon production. The lower parts of cycles consist of porous, cream‐coloured, largely non‐stylolitic, commonly laminated chalk with limited bioturbation (mainly escape burrows). Cycles are capped by thinner intervals of white to grey, hard, stylolitic chalk with concentrations of bioclastic material, intense burrowing and few preserved primary sedimentary structures. The cycle caps contain nearly twice as much Mg as compared to the more porous parts of cycles and also have slightly larger δ18O values (−4·1‰ for the caps; −4·4‰ for porous zones). There is a significant reduction of average cycle thickness, as well as total thickness of the Maastrichtian chalk section, from SW to NE across the Dan Field. The cycle thinning largely results from a reduced thickness of porous chalks from the lower parts of cycles and thus is reflected in lower average porosity and permeability on the NE side of the field. These data indicate that episodic winnowing removed fine‐grained constituents from highstanding northeastern areas. Porous cycle bases were deposited at relatively high rates that precluded complete bioturbation; preserved laminae, coupled with escape burrows, reflect episodic sediment influx in areas that flank the seafloor highs. Cycle tops apparently accumulated more slowly (throughout the region, but especially on seafloor highs), perhaps because of reduced productivity of planktic organisms. Slower sedimentation allowed more complete bioturbation and destruction of sedimentary structures, and also led to incipient high‐magnesium calcite seafloor cementation (sufficient to yield firmer sediment and enhanced burrow preservation, but not to form true hardgrounds). Thus, the elevated magnesium contents and reduced porosity of the cycle caps reflect very early diagenetic processes that were only partially modified by burial diagenesis.Rates of chalk deposition, as inferred from physical and geochemical evidence, appear to be a significant control on reservoir characteristics in North Sea chalks. The highest average porosities and permeabilities are found in areas with the highest sediment accumulation rates where seafloor diagenesis is minimized. Topographic depressions at the time of sedimentation can thus be expected to have the best production characteristics, and synsedimentary topographic highs should have the thinnest sections and the poorest petrophysical properties.
Sedimentation in a fluvially infilling, barrier‐bound estuary on a wave‐dominated, microtidal coast: the Ouémé River estuary, Benin, west Africa
Authors: Anthony Edward J. , Oyédé Lucien M. , Lang Jacques 
Published: March 2003

AbstractThe Ouémé River estuary is located on the seasonally humid tropical coast of Benin, west Africa. A striking feature of this microtidal estuary is the presence of a large sand barrier bounding a 120 km2 circular central basin, Lake Nokoué, that is being infilled by heterogeneous fluvial deposits supplied by a relatively large catchment (50 000 km2). Borehole cores from the lower estuary show basal Pleistocene lowstand alluvial sediments overlain by Holocene transgressive–highstand lagoonal mud and by transgressive to probably early highstand tidal inlet and flood‐tidal delta sand deposited in association with non‐preserved transgressive sand barriers. The change in estuary‐mouth sedimentation from a transgressive barrier‐inlet system to a regressive highstand barrier reflects regional modifications in marine sand supply and in the cross‐barrier tidal flux associated with barrier‐inlet systems. As barrier formation west of the Ouémé River led to an increasingly rectilinear shoreline, the longshore drift cell matured, ensuring voluminous eastward transport of sand from the Volta Delta in Ghana, the major purveyor of sand, to the Ouémé embayment, 200 km east. Concomitantly, the number of tidal inlets, and the tidal flux associated with a hitherto interlinked lagoonal system on this coast, diminished. Complete sealing of Lake Nokoué has produced a large, permanently closed estuary, where tidal intrusion is assured through the interconnected coastal lagoon via an inlet located 60 km east. Since 1885, tides have entered the estuary directly through an artificial outlet cut across the sand barrier. Although precluding the seaward loss of fluvial sediments, permanent estuary‐mouth closure has especially deprived the highstand estuary of marine sand, a potentially important component in estuarine infill on wave‐dominated coasts. In spite of a significant fluvial sediment supply, estuarine infill has been moderate, because of the size of the central basin. Estuarine closure has resulted in two co‐existing highstand sediment suites, with limited admixture, the marine‐derived, estuary‐mouth barrier and upland‐derived back‐barrier sediments. This situation differs from that of mature barrier estuaries characterized by active fluvial‐marine sediment mixing and facies interfingering.
Expression of E. coli inorganic pyrophosphatase in transgenic plants alters photoassimilate partitioning
Authors: Sonnewald Uwe 
Published: March 2003

SummaryTransgenic plants were constructed expressing a novel cytosolic inorganic pyrophosphatase in order to reduce the cytosolic pyrophosphate content. To this end the Escherichia coli gene ppa encoding inorganic pyrophosphatase was cloned between the 35S CaMV promoter and the poly(A) site of the octopine synthase gene and transferred into tobacco and potato plants by Agrobacterium‐mediated gene transfer. Regenerated plants were tested for the expression of the ppa gene by Northern blots and activity gels. Plants expressing active inorganic pyrophosphatase showed a dramatic change in photoassimilate partitioning. In both transgenic tobacco and potato plants the ratio between soluble sugars and starch was increased by about 3–4‐fold in source leaves as compared with the wild‐type. However, whereas source leaves of transgenic tobacco plants accumulated much higher levels of glucose (up to 68‐fold), fructose (up to 24‐fold), sucrose (up to 12‐fold) and starch (up to 8‐fold) this was not observed in potato plants where the change in assimilate partitioning in source leaves was due to an increase of about 2‐fold in sucrose and a reduction in starch content.Expression of the cytosolic inorganic pyrophosphatase in tobacco results in stunted growth of vegetatively growing plants due to a reduced internode distance. Upon flowering the transgenic plants increase their growth rate, reaching almost the same height as control plants at the end of the growth period. Old source leaves accumulate up to 100‐fold more soluble sugars than control leaves. This increase in soluble sugars is accompanied by a reduction in chlorophyll content (up to 85%).Transgenic potato plants showed a less dramatic change in their growth behaviour. Plants were slightly reduced in size, with stems more highly branched. Tuber number increased 2–3‐fold, but tuber weight was lower resulting in no net increase in fresh weight.
Molecular analysis of the avirulence gene avr9 of the fungal tomato pathogen Cladosporium fulvum fully supports the gene‐for‐gene hypothesis
Authors: Van den Ackerveken Guido F.J.M. , Van Kan Jan A.L. , De Wit Pierre J.G.M. 
Published: March 2003

SummaryThe interaction between the fungal pathogen Cladosporium fulvum and tomato is supposed to have a gene‐for‐gene basis. Races of C. fulvum which have ‘overcome’ the resistance gene Cf9 of tomato, lack the avirulence gene avr9 which encodes a race‐specific peptide elicitor. Races avirulent on tomato genotypes carrying the resistance gene Cf9 produce the racespecific peptide elicitor, which induces the hypersensitive response (HR) on those genotypes. The causal relationship between the presence of a functional avr9 gene and avirulence on tomato genotype Cf9 was demonstrated by cloning of the avr9 gene and subsequent transformation of C. fulvum. A race virulent on tomato genotype Cf9 was shown to become avirulent by transformation with the cloned avr9 gene. These results clearly demonstrate that the avr9 gene is responsible for cultivar specificity on tomato genotype Cf9 and fully support the gene‐for‐gene hypothesis. The avr9 gene is the first fungal avirulence gene to be cloned.
Hormonal content and sensitivity of transgenic tobacco and potato plants expressing single rol genes of Agrobacterium rhizogenes T‐DNA
Authors: Schmülling Thomas , Fladung Matthias , Grossmann Klaus , Schell Jeff 
Published: March 2003

SummaryThe expression of single rol genes of the TL‐DNA of Agrobacterium rhizogenes strain A4 in transgenic tobacco (Nicotiana tabacum L.) and potato (Solanum tuberosum L.) plants alters the internal concentrations of, and the sensitivity to, several plant hormones. The levels of immunoreactive cytokinins, abscisic acid, gibberellins and indole‐3‐acetic acid were analysed in tissues of the apical shoots, stems, leaves, roots and undifferentiated callus tissue. The addition of the dominant and morphogenetically active rolA, rolB, or rolC genes resulted in alterations in the content of several hormones. rolC overexpression in particular led to an up to fourfold increase in the content of isopentenyladenosine, dihydrozeatin riboside and trans‐zeatin riboside‐type cytokinins in potato plants. This increase correlated well with different levels of expression of the rolC gene in different transgenic plants. Furthermore it was shown that the dwarfism of P35s‐rolC transgenic tobacco and potato plants is correlated with a 28–60% reduction of gibberellic acid A1 concentration in apical shoots. Exogenous addition of gibberellic acid completely restored stem elongation in P35s‐rolC transgenic plants. Apical shoots of dwarf rolA transgenic tobacco plants also contained 22% less gibberellic acid A1 than control plants, but growth cannot be restored completely by exogenously added gibberellic acid. Similarly, the sensitivity of transgenic tobacco seedlings or callus tissues towards different phytohormone concentrations can be altered by the expression of single rol genes. The overexpression of the rolC gene in seedlings led to an altered response to auxins, cytokinins, abscisic acid, gibberellic acid and the ethylene precursor 1‐aminocyclopropane‐carboxylic acid. The overexpression of the rolB gene in tobacco calli led to necrosis at lower auxin concentrations than in the wild‐type, while other parameters of auxin action, like the induction of cell growth, remained unchanged.
The 20 kDa apoprotein of the CP24 complex of photosystem II: An alternative model to study import and intra‐organellar routing of nuclear‐encoded thylakoid proteins
Authors: Cai Daguang , Herrmann Reinhold G. , Klösgen Ralf Bernd 
Published: March 2003

SummaryThe 20 kDa polypeptide, the apoprotein of the chlorophyll a/b antenna complex CP24 associated with photosystem II, is a remote relative of light‐harvesting complex (LHC) apoproteins and thus a member of the extended cab gene family. LHC apoproteins are poly‐topic integral components of the thylakoid membrane with probably three transmembrane segments which originate in nuclear genes and are made in the cytosol as precursors. They possess exclusively stroma‐targeting transit peptides for import into the organelle and integrate into the thylakoid membrane via uncleaved hydrophobic domains of the mature protein. The CP24 apoprotein displays intriguing structural differences to LHC apoproteins with a potential impact on the routing and targeting processes during biogenesis. In particular, it lacks a pronounced second hydrophobic segment in the mature polypeptide chain found in LHCPs, and carries a transit peptide that is reminiscent of thylakoid‐targeting transit peptides. We have used in organello assays with isolated intact chloroplasts and the authentic precursor of the 20 kDa apoprotein from spinach, or appropriate chimaeric polypeptides consisting of a transit peptide and the mature part of various nuclear‐encoded thylakoid proteins of known location and targeting epitopes, in order to resolve the characteristics of its targeting properties, as well as to determine the contribution of the individual parts of the precursor molecule to its import and subsequent intra‐organellar routing. Our experiments demonstrate that the transit peptide of the CP24 apoprotein is required only for the import of the protein into the organelle. All subsequent steps, such as the integration of the protein into the thylakoid membrane, binding of chlorophyll, assembly into the CP24 complex and migration to the grana lamellae, still take place if the authentic transit peptide is replaced by a targeting signal of a nuclear‐encoded stromal protein.
Antisense RNA inhibition of Rubisco activase expression
Authors: Jiang Cai‐Zhong , Quick W. Paul , Alred Rhu , Kliebenstein Daniel , Rodermel Steven R. 
Published: March 2003

SummaryRibulose bisphosphate carboxylase (Rubisco) activase catalyzes the activation of Rubisco in vivo. Activase antisense DNA mutants of tobacco have been generated to explore the control that activase exerts on the photosynthetic process. These mutants have up to 90% reductions in activase protein levels as a consequence of an inhibition of activase mRNA accumulation. It is shown that photosynthesis, measured as the rate of CO2 exchange (CER), is modestly decreased in plants exposed to high irradiances. The decreases in CER in the transgenic plants are accompanied by corresponding decreases in Rubisco activation, indicating that activase has a direct effect on photosynthetic rates in the antisense plants by influencing the activation state of Rubisco. It is concluded that in high light conditions, control of photosynthesis is largely shared between Rubisco and activase. Plant growth is also impaired in mutant plants that have severe reductions in activase. The inhibition of activase in the antisense plants does not have an impact on the accumulation of Rubisco large subunit or small subunit mRNAs or proteins. This indicates that the concerted expression of the genes for activase (Rca) and Rubisco (rbcL and rbcS) in response to light, developmental factors and circadian controls is not due to feedback regulation of rbcL or rbcS by the amount of activase protein.
bZIP proteins bind to a palindromic sequence without an ACGT core located in a seed‐specific element of the pea lectin promoter
Authors: De Pater Sylvia , Katagiri Fumiaki , Kijne Jan , Chua Nam‐Hai 
Published: March 2003

SummaryPreviously, it has been shown that a trimer of a 22 bp fragment of the promoter of the seed‐specific pea lectin gene confers high expression in seed. Here it is reported that this fragment contains a binding site for the cloned basic domain/leucine zipper (bZIP) proteins TGA1a and Opaque‐2 (02). Gel shift assays, DNasel footprinting and methylation interference assays using purified TGA1a were performed to determine whether additional binding sites are present in the psl promoter. Within the 469 bp upstream region only one other TGAla binding site was found, which is much weaker than the one present in the 22 bp element. Both O2 and TGAla bound to the odd base palindromic C‐box sequence, ATGAGTCAT, present within the 22 bp fragment. The 22 bp fragment also contains the sequence CACGTA, which contains the ACGT core usually found in binding sites for bZIP proteins. However, this sequence did not significantly contribute to bZIP protein binding. The binding affinity of TGAla for the odd base palindromic sequence was low relative to a high‐affinity C‐box (ATGACGTCAT). By contrast, O2 strongly bound to the odd base C‐box; the affinity was comparable with that for high‐affinity G‐(GACACGTGTC) and C‐boxes. It is concluded that the presence of an ACGT core sequence is not a prerequisite for high‐affinity binding of O2.
Expression of a maize proteinase inhibitor gene is induced in response to wounding and fungal infection: systemic wound‐response of a monocot gene
Authors: Cordero Maria José , Raventós Dora , San Segundo Blanca 
Published: March 2003

SummaryThe isolation and characterization of cDNA and genomic clones encoding a proteinase inhibitor protein (MPI) in maize is reported. Accumulation of the MPI mRNA is induced in response to fungal infection in germinating maize embryos. The expression pattern of the MPI gene, in healthy and fungal infected maize tissues, was examined and compared with the expression pattern of a gene that codes for a pathogenesis‐related protein (the PRms protein) from maize. These two genes are induced by fungal infection, however different signals trigger their activation. Accumulation of the proteinase inhibitor mRNA is more a consequence of the wound produced by the penetration and colonization of the host tissues by the pathogen, than the result of a direct molecular recognition of the pathogen by the plant, as is the case for the induction of the PRms gene. Wounding, or treatment with abscisic acid or methyl jasmonate, stimulate MPI mRNA accumulation, but not PRms mRNA accumulation. Local and systemic induction of the MPI gene expression in response to wounding occurs in maize plants. To the authors' knowledge, this is the first example of a gene from a monocotyledonous species that clearly shows a systemic wound response. The possible functional implications for the existence of different signal transduction pathways that simultaneously activate a battery of defense mechanisms against potential pathogens are discussed.
Cloning and expression of soluble epoxide hydrolase from potato
Authors: Stapleton Andrew , Beetham Jeffrey K. , Pinot Franck , Garbarino Joan E. , Rockhold David R. , Friedman Mendel , Hammock Bruce D. , Belknap William R. 
Published: March 2003

SummaryFive cDNAs encoding a putative soluble epoxide hydrolase (sEH) from potato were isolated and characterized. The cDNAs contained open reading frames encoding 36 kDa polypeptides which were highly homologous to the carboxy terminal region of mammalian sEH. When one of the cDNAs was expressed in a baculovirus system a soluble 38 kDa protein with epoxide hydrolase activity was produced. The recombinant enzyme hydrolyzed a commonly used diagnostic substrate for the soluble form of mammalian EH. Inhibitor profiles of the recombinant potato and mammalian sEH were also similar. The expression of sEH in potato was found to be regulated by both developmental and environmental signals. Levels of mRNA for sEH were higher in meristematic tissue than in mature leaves. This mRNA was also observed to accumulate on wounding and application of exogenous methyl jasmonate.
The late‐flowering phenotype of FRIGIDA and mutations in LUMINIDEPENDENS is suppressed in the Landsberg erecta strain of Arabidopsis
Authors: Lee Ilha , Michaels Scott D. , Masshardt Amy S. , Amasino Richard M. 
Published: March 2003

SummaryThe late‐flowering phenotype of mutations in the LUMINIDEPENDENS (LD) gene and the late flowering caused by the naturally occurring dominant gene FRIGIDA (FRI) are suppressed in the Landsberg erecta (Ler) strain of Arabidopsis thaliana. This suppression is dependent on a locus on chromosome 5 designated FLC. Of the ecotypes tested, only the Ler strain contains the suppressor allele of FLC; ld mutations and FRI cause late flowering in the other genetic backgrounds. The allele at FLC also has a moderate effect on flowering time in the absence of FRI or ld mutations. The flowering time effects of FLC are gene dosage dependent.
Recombinant stigmatic self‐incompatibility (S‐) protein elicits a Ca2+ transient in pollen of Papaver rhoeas
Authors: Franklin‐Tong Vernonica E. , Ride Jon P. , Franklin F. Christopher H. 
Published: March 2003

Evidence for Ca2+ signalling in pollen during the self‐incompatibility (SI) response in Papaver rhoeas L. has been presented previously. However, it was not known whether the S‐protein alone could act as an elicitor of the response or whether the presence of other stigmatic components was required, since relatively crude stigmatic extracts had been used. The S1 gene has since been cloned and its product expressed in Escherichia coli has been shown to exhibit biological activity. In this paper it is reported that the recombinant protein (S1e) elicits a transient rise in [Ca2+]i in incompatible pollen. The Ca2+ signal appears indistinguishable from that elicited by S‐gene products partially purified from plant extracts in terms of both its timing and spatial distribution. Pollen tube growth is arrested directly after the rise in [Ca2+]i.The results provide direct evidence that the S‐protein alone acts as an elicitor which triggers the Ca2+ signal for the pollen SI response. In addition, it is now clear that the recombinant S‐protein does not require several post‐translational processing events which take place in the plant to act as an elicitor. With respect to the spatial distribution of the Ca2+ transient, data are presented which correlate the localized rise in intracellular Ca2+ ([Ca2+]i) with the ‘nuclear complex’ and the endoplasmic reticulum which is associated with this region.
Induction of intrachromosomal homologous recombination in whole plants
Authors: Puchta Holger , Swoboda Peter , Hohn Barbara 
Published: March 2003

SummaryThe influence of different factors on frequencies of intrachromosomal homologous recombination in whole Arabidopsis thaliana and tobacco plants was analyzed using a disrupted β‐glucuronidase marker gene. Recombination frequencies were enhanced severalfold by DNA damaging agents like UV‐light or MMS (methyl methanesulfonate). Applying 3‐methoxybenzamide (3‐MB), an inhibitor of poly(ADP)ribose polymerase (PARP), an enzyme that is postulated to be involved in DNA repair, enhanced homologous recombination frequencies strongly. These findings indicate that homologous recombination is involved in DNA repair and can (at least partially) compensate for other DNA repair pathways. Indications that recombination in plants can be induced by environmental stress factors that are not likely to be involved in DNA metabolism were also found; Arabidopsis plants growing in a medium containing 0.1 M NaCl exhibited elevated recombination frequencies. The possible general effects of ‘environmental’ challenges on genome flexibility are discussed.
Differential in vitro DNA binding activity to a promoter element of the gn1β‐1,3‐glucanase gene in hypersensitively reacting tobacco plants
Authors: Alonso Elena , De Carvalho Niebel Fernanda , Obregón Patricia , Gheysen Godelieve , Inzé Dirk , Van Montagu Marc , Castresana Carmen 
Published: March 2003

SummaryIn a hypersensitive reaction to pathogen infection, expression of the β‐1,3‐glucanase gn1 gene is induced in cells surrounding the necrotic lesions. The 5′‐flanking sequence of gn1 was examined to investigate the molecular basis controlling activation of gene expression during this plant defense response. Studies on transgenic tobacco plants containing gn1 promoter deletions fused to the β‐glucuronidase reporter gene revealed the presence of negative and positive regulatory sequences mediating both the level and the spatial distribution of gn1 expression. Promoter sequences to −138 bp were sufficient to confer increased gene expression around the necrotic lesions produced in response to Pseudomonas syringae pv. syringae inoculation. It is demonstrated by electrophoretic mobility shift assays that nuclear proteins in both healthy and hypersensitively reacting tobacco leaves interact with DNA sequences within the regulatory elements identified. Among the binding sequences characterized, the promoter region extending from −250 to −217 bp contained the DNA motif ‐GGCGGC‐ found to be conserved in most if not all promoters of genes encoding pathogenesis‐related basic proteins. The activity bound by this promoter sequence was stronger in hypersensitively responding tissues than in healthy untreated tobacco leaves.