bluuebunny/crossref_metadata_2025_split huggingface dataset:
An empirical model for the development and equilibrium morphology of current ripples in fine sand
Authors: Baas Jaco H. 
Published: March 2003

A flume study on the development and equilibrium morphology of current ripples in fine sand (D50 = 0·238 mm) was performed to extend an empirical model for current ripple stability in 0·095 mm sand to larger grain sizes. The results of the flume experiments agree with the very fine sand model that current ripple development from a flat bed is largely independent of flow velocity. At all flow velocities, ripples evolve from incipient, through straight, sinuous and non‐equilibrium linguoid, to equilibrium linguoid plan morphology. The time needed to achieve an equilibrium linguoid plan form is related to an inverse power of flow velocity and ranges from several minutes to more than hundreds of hours. Average equilibrium height and length are 17·0 mm and 141·1 mm respectively. These values are about 20% larger than in very fine sand. Equilibrium ripple height and length are proportional to flow velocity near the stability field of dunes. In the same velocity range, a characteristic grouping of ripples with smaller ripples migrating on the upstream face of larger ripples was observed.Bed‐form development shows a conspicuous two‐phase behaviour at flow velocities < 0·49 m s−1. In the first phase of development, ripple height and length increase along an exponential path, similar to that at higher flow velocities, thus reaching intermediate equilibrium values of 14·8 mm and 124·5 mm respectively. After some time, however, a second phase commences, that involves a rapid increase in bed‐form size to the typical equilibrium values for 0·238 mm sand.A comparison with literature data shows that the results obtained for 0·238 mm sand agree reasonably well with other flume studies at similar grain size. Yet considerable variability in the relationships between ripple dimensions and flow strength ensues from, among others, underestimation of equilibrium time, shallow flow depths and differences in sediment texture.
Electrical resistivity ground imaging (ERGI): a new tool for mapping the lithology and geometry of channel‐belts and valley‐fills
Authors: Baines Dave , Smith Derald G. , Froese Duane G. , Bauman Paul , Nimeck Grant 
Published: March 2003

AbstractEfforts to map the lithology and geometry of sand and gravel channel‐belts and valley‐fills are limited by an inability to easily obtain information about the shallow subsurface. Until recently, boreholes were the only method available to obtain this information; however, borehole programmes are costly, time consuming and always leave in doubt the stratigraphic connection between and beyond the boreholes. Although standard shallow geophysical techniques such as ground‐penetrating radar (GPR) and shallow seismic can rapidly obtain subsurface data with high horizontal resolution, they only function well under select conditions. Electrical resistivity ground imaging (ERGI) is a recently developed shallow geophysical technique that rapidly produces high‐resolution profiles of the shallow subsurface under most field conditions. ERGI uses measurements of the ground's resistance to an electrical current to develop a two‐dimensional model of the shallow subsurface (<200 m) called an ERGI profile. ERGI measurements work equally well in resistive sediments (‘clean’ sand and gravel) and in conductive sediments (silt and clay). This paper tests the effectiveness of ERGI in mapping the lithology and geometry of buried fluvial deposits. ERGI surveys are presented from two channel‐fills and two valley‐fills. ERGI profiles are compared with lithostratigraphic profiles from borehole logs, sediment cores, wireline logs or GPR. Depth, width and lithology of sand and gravel channel‐fills and adjacent sediments can be accurately detected and delineated from the ERGI profiles, even when buried beneath 1–20 m of silt/clay.
Systematic revision of the yucca moths in the Tegeticula yuccasella complex (Lepidoptera: Prodoxidae) north of Mexico
Authors: Pellmyr Olle. 
Published: March 2003

SummaryThe yucca moths (TegeticulaandParategeticula) are of great importance in studies of coevolution because of their obligate mutualism with their yucca hosts. Historically, three species ofTegeticulahave been recognized. One of them,T. yuccasella, has been regarded as the pollinator of all but two yucca species, but morphological, molecular and biological data show that this is a large complex of monophagous and oligophagous species that differ greatly in their biology. It also includes derived ‘cheater’ species that do not pollinate their hosts and oviposit into fruits rather than flowers. Here theyuccasellacomplex north of Mexico is revised. The nominotypic pollinator speciesyuccasellais redescribed, and ten new pollinator species described:altiplanella,baccatella,carnerosanella, cassandra, elatella,maderae,mojavella,rostratella,superficiellaandtreculeanella. Two non‐pollinating cheater species are recognized. One such species originally misidentified as aProdoxusspecies, then synonymised withyuccasella,is re‐erected as the non‐pollinatingintermedia. In addition, the new non‐pollinator speciescorruptrixis described.
Phylogeny of Neotropical Lepidocyrtus (Collembola: Entomobryidae): first assessment of patterns of speciation in Puerto Rico and phylogenetic relevance of some subgeneric diagnostic characters
Authors: Soto‐Adames Felipe N. 
Published: March 2003

SummaryA phylogenetic analysis of the Neotropical members of genusLepidocyrtuswas conducted to assess the pattern of speciation in Puerto Rico while testing the phylogenetic information content of two characters used to diagnose subgenera. The analysis included twenty‐two species ofLepidocyrtusfrom the Neotropical Region for which information on the tergal chaetotaxy of the trunk was available, two species of HolarcticLepidocyrtus, three species ofPseudosinella, two species ofMetasinellaused in outgroup analysis and ninety‐two informative characters. The results do not support a monophyletic origin for the Puerto RicanLepidocyrtus, suggesting the current fauna originated through repeated invasions from abroad. Three instances of endemic speciation can be inferred from the cladograms. The geographical distribution and diversity of colour forms suggest thatL. caprilesi and L. paracaprilesispeciated sympatrically, whereas vicariance can explain speciation forL. lepargusandL. maldonadoi. The mode of speciation forL. dispar and L. biphasisremains unclear because the proportion of morphological variation between these species does not fit the proportions expected under the sympatric model suggested by their geographical distribution. The results support an early conclusion regarding appendicular scale distribution as a poor indicator of phylogenetic relationships. Taxa defined using this character are likely to be polyphyletic. The results disagree with a previous study in documenting low levels of homoplasy for the dental tubercle, implying that this character contains phylogenetic information useful in defining subgenera. However, the presence or absence of a dental tubercle is not diagnostic and should be used in combination with other characters. Comparisons of levels of homoplasy in Neotropical and HawaiianLepidocyrtussuggest that the relative position of two setae on the second abdominal tergum may be a better subgeneric character than other characters currently in use.
Revision and phylogenetic analysis of the New World genus Neoclypeodytes Young (Coleoptera: Dytiscidae: Hydroporinae: Bidessini)
Authors: Miller Kelly B. 
Published: March 2003

SummaryThe western North American and northern Central American genusNeoclypeodytesYoung is revised. Twenty‐five valid species are recognized in the genus. One additional name,N. luctuosus(Guignot) is treated as species of uncertain status. Eleven new species are described:N. amybethae,N. anasinus,N. astrapus,N. challeti,N. edithae,N. haroldi,N. megalus,N. nanus,N. roughleyi,N. similisandN. tumulus. Six new synonymies are established:N. centralis(Sharp) = N. cinctellus(LeConte);N. substriatus(Sharp) = N. discedens(Sharp);N. americanus(Guignot),N. decoratus(Fall) andN. quadrisignatus(Sharp) = N. fryii(Clark); andN. rugulosus(Guignot) = N. obesus(Sharp). Lectotypes are designated forN. curtulus(Sharp),N. discedens,N. discretus(Sharp),N. lynceus(Sharp),N. obesus,N. ornatellus(Fall),N. pictodes(Sharp),N. plicipennis(Crotch),N. quadrinotatus(Sharp),N. quadripustulatus,N. quadrisignatusandN. substriatus. A key is provided for the known species ofNeoclypeodytes. Distribution maps, illustrations of important morphological features and natural history notes are provided for each species. A single possible synapomorphy was found supporting the monophyly ofNeoclypeodytes, a pattern of two maculae on each elytron. The perplexing and unresolved relationships ofNeoclypeodytesto other bidessine genera are discussed. A cladistic analysis using twenty‐two characters of adult morphology is presented for twenty‐five species ofNeoclypeodytes, withUvarus lacustris(Say) andLiodessus affinis(Say) as outgroup taxa (rooted atU. lacustris). A single most parsimonious cladogram was obtained.
Review: Stratigraphy, meta‐stratigraphy and chaos
Authors: Bailey R.J. 
Published: March 2003

An alternative approach to stratigraphic analysis is proposed. It takes as its starting point the simple general characteristics of the stratigraphic record and the complex, chaotic behaviours of the systems that combine to generate this record. In this context, Smith’s Stratigraphy Machine (SM) concept is developed. The SM is a chaotic global system, combining the operations of the atmosphere, hydrosphere, lithosphere and asthenosphere, which everywhere tends to self‐organize towards a critical state in which continuous loading of the system with rock waste, over time, is balanced by the unloading that creates the record. The outputs of the SM are simple and nonscale dependent in character, with residence times in the record ranging from a second, or less, to 1 billion years. However, only those long‐lived in the human time‐frame are judged to be of stratigraphic significance; and the range of residence times entails that the stratigraphic record embraces a similar range of hiatuses, or gaps. The value of the SM, as developed here, is that it can be regarded as a meta‐stratigraphic concept that transcends the usual frameworks of stratigraphic classification and interpretation and thus allows a reappraisal of significant features of the record such as its perceived cycles and sequences. There are three outcomes of this meta‐stratigraphic analysis. First, the geometric units employed in sequence stratigraphy are components of a self‐similar series of essentially lenticular bodies, with no fundamental characteristics to distinguish them from larger and smaller bodies in the generally self‐similar series. Secondly, the interactions and feedbacks within the SM are so complex, and its outputs so repetitive in general character, that it is dangerous to assume that any perceived cyclicity provides an unambiguous chronicle of process cyclicity, whether eustatic, climatic or tectonic. The classic coarsening upward cyclicity of shallow marine facies can, for example, be viewed solely as the outcome of the lack of phasing between the chaotic behaviours tending to unload the SM and those creating accommodation space. Finally, the meta‐stratigraphic approach reinforces the view that, in the absence of demonstrable stratal continuity, chronostratigraphic correlation must continue to rely on sample‐based, mainly biostratigraphical, methods, rather than sequence stratigraphy.
Methane hydrate in the global organic carbon cycle
Authors: Kvenvolden Keith A. 
Published: March 2003

The global occurrence of methane hydrate in outer continental margins and in polar regions, and the magnitude of the amount of methane sequestered in methane hydrate suggest that methane hydrate is an important component in the global organic carbon cycle. Various versions of this cycle have emphasized the importance of methane hydrate, and in the latest version the role of methane hydrate is considered to be analogous to the workings of an electrical circuit. In this circuit the methane hydrate is a condenser and the consequences of methane hydrate dissociation are depicted as a resistor and inductor, reflecting temperature change and changes in earth surface history. These consequences may have implications for global change including global climate change.Terra Nova, 14, 302–306, 2002
Maize C4 photosynthesis involves differential regulation of phosphoenolpyruvate carboxylase genes
Authors: Schaffner Anton R. , Sheen Jen 
Published: March 2003

SummaryMaize as a C4 plant partitions CO2 fixation in two consecutive, spatially separated steps, thus eliminating photorespiration. The crucial enzyme for primary CO2 fixation is a C4‐specific phosphoenolpyruvate carboxylase (PEPC). The differential expression of the unique C4‐specific gene pepcZml and two non‐specific genes, pepcZm2A and pepcZm3B, in leaf, root, and stem is reported here. It is shown, in a transient homologous system, that this tissue‐specific regulation is mainly controlled by their distinct promoters. The light induction of the C4‐specific pepcZml in illuminated etiolated (greening) leaves probably relies on light‐dependent developmental changes instead of an immediate responsiveness found for other maize genes. Analyses of deleted, mutated, and hybrid promoters revealed the redundant nature of a 14mer which is repeated four times and a decisive function of the TATA box‐like motif, TATTT, and the sequences directly preceding it. No consensus sequences to other photosynthetic gene promoters were uncovered. Although light induces the expression of C4 PEPC and other photosynthetic genes in maize, this co‐ordination is apparently mediated through different signal transduction pathways and distinct regulatory elements. This study indicates that the acquisition of a new promoter is at least partially responsible for the C4‐specific expression of pepcZml essential for C4 photosynthesis.
The barley 60 kDa jasmonate‐induced protein (JIP60) is a novel ribosome‐inactivating protein
Authors: Chaudhry Bushra , Müller‐Uri Frieder , Cameron‐Mills Verena , Gough Simon , Simpson David , Skriver Karen , Mundy John 
Published: March 2003

SummaryThe N‐terminal region of a 60 kDa, jasmonate‐induced protein of barley leaves (JIP60) is shown to be homologous to the catalytic domains of plant ribosome‐inactivating proteins (RIP). Western blotting of leaf extracts and in vitro reconstitution experiments indicate that JIP60 is synthesized as a precursor which is processed in vivo. This is in keeping with in vitro translation experiments indicating that a deletion derivative of the N‐terminal region, but not the putative precursor, strongly inhibits protein synthesis on reticulocyte ribosomes. The inhibition of ribosome function is associated with depurination of 26S rRNA, characteristic of plant RIPs. This indicates that JIP60 is a novel ribosome‐inactivating protein requiring at least two processing events for full activation. JIP60 derivatives do not significantly inhibit in vitro protein synthesis on wheat germ ribosomes. These and other results suggest that JIP60 may be involved in plant defence.
Control of de novo purine biosynthesis genes in ureide‐producing legumes: induction of glutamine phosphoribosylpyrophosphate amidotransferase gene and characterization of its cDNA from soybean and Vigna
Authors: Kim Jong H. , Delauney Ashton J. , Verma Desh Pal S. 
Published: March 2003

Soybean (Glycine max) and mothbean (Vigna aconitifolia) cDNA clones encoding glutamine phosphoribosylpyrophosphate amidotransferase (PRAT), the first enzyme of the de novo purine biosynthesis pathway, have been isolated from nodule cDNA libraries. The amino acid sequence deduced from soybean clone showed> 85% homology to the PRAT sequence of mothbean and 33–47% homology to those of bacteria, yeast, chicken, rat and human. The soybean clone encodes a protein with an N‐terminal sequence resembling a plastid‐targeting peptide. Downstream from this peptide is a sequence similar to the 11 amino acid propeptide found in the Bacillus subtilis, chicken, rat and human PRAT proteins. The mothbean cDNA, although lacking most of the plastid presequence, encodes the putative propeptide and efficiently complements purine auxotrophy in an Escherichia coli purF mutant. Both the soybean and mothbean clones encode characteristic cysteine residues that are known to be involved in the assembly of a [Fe‐S] cluster near the C‐terminus of this protein. Levels of PRAT mRNA in mothbean nodules were found to increase steadily as the nodules matured from 13 days to 23 days.PRAT mRNA was not detectable in uninfected root tissue but a low level of transcript was detected in leaves. Treatment of uninfected root with l‐glutamine induced the PRAT mRNA transcript suggesting that glutamine produced as a result of assimilation of fixed nitrogen is funnelled into the de novo purine biosynthesis and controls the expression of this pathway in root nodules.
Molecular evolution of plant β‐glucan endohydrolases
Authors: Høj Peter B. , Fincher Geoffrey B. 
Published: March 2003

SummaryThe evolutionary relationships of two classes of plant β‐glucan endohydrolases have been examined by comparison of their substrate specificities, their three‐dimensional conformations and the structural features of their corresponding genes. These comparative studies provide compelling evidence that the (1→3)‐β‐glucanases and (1→3,1→4)‐β‐glucanases from higher plants share a common ancestry and, in all likelihood, that the (1→3,1→4)‐β‐glucanases diverged from the (1→3)‐β‐glucanases during the appearance of the graminaceous monocotyledons. The evolution of (1→3,1→4)‐β‐glucanases from (1→3)‐β‐glucanases does not appear to have invoked ‘modular’ mechanisms of change, such as those caused by exon shuffling or recombination. Instead, the shift in specificity has been acquired through a limited number of point mutations that have resulted in amino acid substitutions along the substrate‐binding cleft. This is consistent with current theories that the evolution of new enzymic activity is often achieved through duplication of the gene encoding an existing enzyme which is capable of performing the required chemistry, in this case the hydrolysis of a glycosidic linkage, followed by the mutational alteration and fine‐tuning of substrate specificity.The evolution of a new specificity has enabled a dramatic shift in the functional capabilities of the enzymes. (1→3)‐β‐Glucanases that play a major role, inter alia, in the protection of the plant against pathogenic microorganisms through their ability to hydrolyse the (1→3)‐β‐glucans of fungal cell walls, appear to have been recruited to generate (1→3,1→4)‐β‐glucanases, which quite specifically hydrolyse plant cell wall (1→3,1→4)‐β‐glucans in the graminaecous monocotyledons during normal wall metabolism. Thus, one class of β‐glucan endohydrolase can degrade β‐glucans in fungal walls, while the other hydrolyses structurally distinct β‐glucans of plant cell walls. Detailed information on the three‐dimensional structures of the enzymes and the identification of catalytic amino acids now present opportunities to explore the precise molecular and atomic details of substrate‐binding, catalytic mechanisms and the sequence of molecular events that resulted in the evolution of the substrate specificities of the two classes of enzyme.
Reduction in phosphoribulokinase activity by antisense RNA in transgenic tobacco: effect on CO2 assimilation and growth in low irradiance
Authors: Paul Matthew J. , Knight Jacqui S. , Habash Dimah , Parry Martin A.J. , Lawlor David W. , Barnes Simon A. , Loynes Andy , Gray John C. 
Published: March 2003

SummaryTo quantify the importance of the Calvin cycle enzyme phosphoribulokinase (PRK) in photosynthesis and to perturb photosynthesis without large direct reductions in leaf protein content, tobacco plants (Nicotiana tabacum L.) were transformed with an inverted cDNA encoding tobacco PRK. A population of plants expressing antisense RNA and a range of PRK activities from wild‐type to less than 5% of wild‐type were obtained. CO2 assimilation under the growing conditions (330 µmol photons m−2 sec−1, 350 µbar CO2, 25°C) was not inhibited until more than 85% of PRK activity had been removed. With reduction in PRK activity of between 85 and 95%, assimilation rates and amounts of chlorophyll compared with wild‐type were reduced by up to half. Decreased absorption of light by leaves with less chlorophyll accounte0d for only a small part of the reduction in assimilation rate. When PRK activity was below 15% of wild‐type, amounts of ribulose‐5‐phosphate, ribose‐5‐phosphate, ATP and fructose‐6‐phosphate were 1.5‐ to fivefold higher and levels of ribulose‐1,5‐bisphosphate, 3‐phosphoglyceric acid and ADP 1.5‐ to fourfold lower than in wild‐type. It is estimated that these changes maintained flux through PRK to realise the assimilation rates observed. A possible shift of control within the Calvin cycle towards fructose‐1,6‐bisphosphatase in plants with low PRK is discussed. Amounts of hexoses and starch in particular were reduced in plants expressing the lowest PRK activities; amounts of sucrose were little affected. Lower CO2 assimilation in plants with low PRK activity correlated with reduced relative growth rate of shoots and delayed flowering, but there was no effect on specific leaf area. It is concluded that (i) in wild‐type plants grown in constant low light, PRK has a flux‐control coefficient for CO2 assimilation of zero, and that even when amounts of PRK are reduced 20‐fold relative to wild‐type, altered amounts of metabolites compensate for much of the reduction in PRK protein; (ii) in plants where there is a 95% reduction in amounts of PRK, photosynthesis was reduced twofold without large changes in leaf protein content or leaf geometry.
Characterization of a maize G‐box binding factor that is induced by hypoxia
Authors: De Vetten Nick C. , Ferl Robert J. 
Published: March 2003

SummaryG‐box cis‐acting DNA sequence elements are present in the promoter region of a number of signal‐inducible plant genes. In many cases this motif is essential for gene expression. Maize nuclear extracts contain a protein complex that binds specifically to the G‐box sequence. Previously, a protein called GF14 was described that is physically associated with the G‐box binding complex, but is not a DNA‐binding factor in and of itself. This paper reports the isolation of a cDNA encoding a maize G‐box binding factor (GBF). The deduced amino acid sequence indicates that maize GBF1 is a basic region‐leucine zipper protein. GBF1 binds to the G‐box element with specificity similar to that of the binding activity in nuclear extracts. Furthermore, maize GBF1 and the factor detected in nuclear extract are identical in their molecular weight and are immunologically related. GBF1 mRNA accumulates rapidly in hypoxically induced maize cells prior to the increase in Adh1 mRNA levels. Taken together with results that indicate that GBF1 binds to the hypoxia‐responsive promoter of maize Adh1, these observations suggest that GBF1 may be one of the factors involved in the activation of Adh1.