bluuebunny/crossref_metadata_2025_split huggingface dataset:
Oxidative Stress-Induced Calcium Signaling in Arabidopsis
Authors: Rentel Maike C. , Knight Marc R. 
Published: July 2004

Abstract
Many environmental stresses result in increased generation of active oxygen species in plant cells. This leads to the induction of protective mechanisms, including changes in gene expression, which lead to antioxidant activity, the recovery of redox balance, and recovery from damage/toxicity. Relatively little is known about the signaling events that link perception of increased active oxygen species levels to gene expression in plants. We have investigated the role of calcium signaling in H2O2-induced expression of the GLUTATHIONE-S-TRANSFERASE1 (GST1) gene. Challenge with H2O2 triggered a biphasic Ca2+ elevation in Arabidopsis seedlings. The early Ca2+ peak localized to the cotyledons, whereas the late Ca2+ rise was restricted to the root. The two phases of the Ca2+ response were independent of each other, as shown by severing shoot from root tissues before H2O2 challenge. Modulation of the height of Ca2+ rises had a corresponding effect upon H2O2-induced GST1 expression. Application of the calcium channel blocker lanthanum reduced the height of the first Ca2+ peak and concomitantly inhibited GST1 expression. Conversely, enhancing the height of the H2O2-triggered Ca2+ signature by treatment with l-buthionine-[S,R]-sulfoximine (an inhibitor of glutathione synthesis) lead to enhancement of GST1 induction. This finding also indicates that changes in the cellular redox balance constitute an early event in H2O2 signal transduction as reduction of the cellular redox buffer and thus the cell's ability to maintain a high GSH/GSSG ratio potentiated the plant's antioxidant response.
Phototropins Mediate Blue and Red Light-Induced Chloroplast Movements in Physcomitrella patens
Authors: Kasahara Masahiro , Kagawa Takatoshi , Sato Yoshikatsu , Kiyosue Tomohiro , Wada Masamitsu 
Published: July 2004

Abstract
Phototropin is the blue-light receptor that mediates phototropism, chloroplast movement, and stomatal opening in Arabidopsis. Blue and red light induce chloroplast movement in the moss Physcomitrella patens. To study the photoreceptors for chloroplast movement in P. patens, four phototropin genes (PHOTA1, PHOTA2, PHOTB1, and PHOTB2) were isolated by screening cDNA libraries. These genes were classified into two groups (PHOTA and PHOTB) on the basis of their deduced amino acid sequences. Then phototropin disruptants were generated by homologous recombination and used for analysis of chloroplast movement. Data revealed that blue light-induced chloroplast movement was mediated by phototropins in P. patens. Both photA and photB groups were able to mediate chloroplast avoidance, as has been reported for Arabidopsis phot2, although the photA group contributed more to the response. Red light-induced chloroplast movement was also significantly reduced in photA2photB1photB2 triple disruptants. Because the primary photoreceptor for red light-induced chloroplast movement in P. patens is phytochrome, phototropins may be downstream components of phytochromes in the signaling pathway. To our knowledge, this work is the first to show a function for the phototropin blue-light receptor in a response to wavelengths that it does not absorb.
Transcriptional Programs of Early Reproductive Stages in Arabidopsis
Authors: Hennig Lars , Gruissem Wilhelm , Grossniklaus Ueli , Köhler Claudia 
Published: July 2004

Abstract
The life cycle of flowering plants alternates between a diploid sporophytic and a haploid gametophytic generation. After fertilization of each the egg and central cells by one male gamete, the development of both fertilization products occurs coordinated with the maternally derived seed coat and carpel tissues forming the fruit. The reproduction program is likely to involve the concerted activity of many genes. To identify genes with specific functions during reproduction, we have analyzed the expression profile of more than 22,000 genes present on the Arabidopsis ATH1 microarray during three stages of flower and fruit development. We found 1,886 genes regulated during reproductive development and 1,043 genes that were specifically expressed during reproduction. When compared to cells from an Arabidopsis suspension culture, S-phase genes were underrepresented and G2 and M-phase genes were strongly enriched in the set of specific genes, indicating that important functions during reproduction are exerted in the G2 and M phases of the cell cycle. Many potential signaling components, such as receptor-like protein kinases, phosphatases, and transcription factors, were present in both groups of genes. Members of the YABBY, MADS box, and Myb transcription factor families were significantly overrepresented in the group of specific genes, revealing an important role of these families during reproduction. Furthermore, we found a significant enrichment of predicted secreted proteins smaller than 15 kD that could function directly as signaling molecules or as precursors for peptide hormones. Our study provides a basis for targeted reverse-genetic approaches aimed to identify key genes of reproductive development in plants.
Metabolic Responses to the Reduction in Palmitate Caused by Disruption of the FATB Gene in Arabidopsis
Authors: Bonaventure Gustavo , Bao Xiaoming , Ohlrogge John , Pollard Mike 
Published: July 2004

Abstract
Disruption of the FATB gene in Arabidopsis results in a two-thirds reduction in saturated fatty acids, largely palmitate, in the leaf extra-plastidic phospholipids and a reduction in the growth rate of the mutant compared to wild type (Bonaventure G, Salas JJ, Pollard MR, Ohlrogge JB [2003] Plant Cell 15: 1020–1033). In this study, we report that although fatb-ko seedlings grow more slowly than wild type, the rate of fatty acid synthesis in leaves of the mutant increases by 40%. This results in approximately the same amount of palmitate exported from the plastid as in wild type but an increase in oleate export of about 55%. To maintain constant amounts of fatty acids in leaves, thereby counterbalancing their higher rate of production, the mutant also increases its rate of fatty acid degradation. Although fatb-ko leaves have higher rates of fatty acid synthesis and turnover, the relative proportions of membrane lipids are similar to wild type. Thus, homeostatic mechanisms to preserve membrane compositions compensate for substantial changes in rates of fatty acid and glycerolipid metabolism in the mutant. Pulse-chase labeling studies show that in fatb-ko leaves there is a net increase in the synthesis of both prokaryotic and eukaryotic lipids and consequently of their turnover. The net loss of palmitate from phosphatidylcholine plus phosphatidylethanolamine is similar for wild type and mutant, suggesting that mechanisms are not present that can preferentially preserve the saturated fatty acids. In summary, the leaf cell responds to the loss of saturated fatty acid production in the fatb-ko mutant by increasing both fatty acid synthesis and degradation, but in doing so the mechanisms for increased fatty acid turnover contribute to the lowering of the percentage of saturated fatty acids found in eukaryotic lipids.
Abscisic Acid Induces CBF Gene Transcription and Subsequent Induction of Cold-Regulated Genes via the CRT Promoter Element
Authors: Knight Heather , Zarka Daniel G. , Okamoto Haruko , Thomashow Michael F. , Knight Marc R. 
Published: July 2004

Abstract
Many cold-regulated genes of Arabidopsis are inducible by abscisic acid (ABA) as well as by cold. This has been thought to occur via two separate signaling pathways, with ABA acting via ABA-responsive promoter elements and low temperature activating the C-repeat element (CRT; dehydration-responsive) promoter element via CBF (DREB1) transcription factors. We show here that ABA is also capable of activating the CRT promoter element. Although the more recently discovered ABA-inducible CBF4 transcription factor might have accounted for this, we show here that CBF1-3 transcript levels also increase in response to elevated ABA levels. This increase in CBF1-3 transcript levels appears to be at least in part due to increased activity of the CBF promoters in response to ABA. A total of 125 bp of the CBF2 promoter, which has previously been shown to be sufficient for cold-, mechanical-, and cycloheximide-induced expression, was also sufficient for ABA-induced expression. However, the ABA-responsive promoter element-like motif within this region is not needed for ABA-induced expression. An observed increase in CBF protein levels after ABA treatment, together with previous data showing that increased CBF levels are sufficient for cold-regulated gene induction, suggests that ABA-induced increases in CBF1-3 transcript levels do have the potential to activate the CRT. Our data indicate therefore that activation of the CRT may also occur via a novel ABA-inducible signaling pathway using the normally cold-inducible CBFs.
A Plant-Specific Subclass of C-Terminal Kinesins Contains a Conserved A-Type Cyclin-Dependent Kinase Site Implicated in Folding and Dimerization
Authors: Vanstraelen Marleen , Torres Acosta Juan Antonio , De Veylder Lieven , Inzé Dirk , Geelen Danny 
Published: July 2004

Abstract
Cyclin-dependent kinases (CDKs) control cell cycle progression through timely coordinated phosphorylation events. Two kinesin-like proteins that interact with CDKA;1 were identified and designated KCA1 and KCA2. They are 81% identical and have a similar three-partite domain organization. The N-terminal domain contains an ATP and microtubule-binding site typical for kinesin motors. A green fluorescent protein (GFP) fusion of the N-terminal domain of KCA1 decorated microtubules in Bright Yellow-2 cells, demonstrating microtubule-binding activity. During cytokinesis the full-length GFP-fusion protein accumulated at the midline of young and mature expanding phragmoplasts. Two-hybrid analysis and coimmunoprecipitation experiments showed that coiled-coil structures of the central stalk were responsible for homo- and heterodimerization of KCA1 and KCA2. By western-blot analysis, high molecular mass KCA molecules were detected in extracts from Bright Yellow-2 cells overproducing the full-length GFP fusion. Treatment of these cultures with the phosphatase inhibitor vanadate caused an accumulation of these KCA molecules. In addition to dimerization, interactions within the C-terminally located tail domain were revealed, indicating that the tail could fold onto itself. The tail domains of KCA1 and KCA2 contained two adjacent putative CDKA;1 phosphorylation sites, one of which is conserved in KCA homologs from other plant species. Site-directed mutagenesis of the conserved phosphorylation sites in KCA1 resulted in a reduced binding with CDKA;1 and abolished intramolecular tail interactions. The data show that phosphorylation of the CDKA;1 site provokes a conformational change in the structure of KCA with implications in folding and dimerization.
Identification of Genes Required for Embryo Development in Arabidopsis
Authors: Tzafrir Iris , Pena-Muralla Rosanna , Dickerman Allan , Berg Michael , Rogers Rebecca , Hutchens Steven , Sweeney T. Colleen , McElver John , Aux George , Patton David , Meinke David 
Published: July 2004

Abstract
A long-term goal of Arabidopsis research is to define the minimal gene set needed to produce a viable plant with a normal phenotype under diverse conditions. This will require both forward and reverse genetics along with novel strategies to characterize multigene families and redundant biochemical pathways. Here we describe an initial dataset of 250 EMB genes required for normal embryo development in Arabidopsis. This represents the first large-scale dataset of essential genes in a flowering plant. When compared with 550 genes with other knockout phenotypes, EMB genes are enriched for basal cellular functions, deficient in transcription factors and signaling components, have fewer paralogs, and are more likely to have counterparts among essential genes of yeast (Saccharomyces cerevisiae) and worm (Caenorhabditis elegans). EMB genes also represent a valuable source of plant-specific proteins with unknown functions required for growth and development. Analyzing such unknowns is a central objective of genomics efforts worldwide. We focus here on 34 confirmed EMB genes with unknown functions, demonstrate that expression of these genes is not embryo-specific, validate a strategy for identifying interacting proteins through complementation with epitope-tagged proteins, and discuss the value of EMB genes in identifying novel proteins associated with important plant processes. Based on sequence comparison with essential genes in other model eukaryotes, we identify 244 candidate EMB genes without paralogs that represent promising targets for reverse genetics. These candidates should facilitate the recovery of additional genes required for seed development.
Assessing applications for collaboration: from collaboratively usable applications to collaborative technology
Authors: Lipponen Lasse , Lallimo Jiri 
Published: July 2004

AbstractThe continually increasing number of applications said to facilitate collaboration makes it very difficult for educators to identify and evaluate the ones that are suitable for educational purposes. In this paper we argue that from the educational point of view, it is meaningful to make a distinction between collaboratively usable applications and collaborative technology. Collaboratively usable applications are systems that can be used for collaboration, whilst collaborative technology is technology that is especially designed to support and establish collaboration. To distinguish between these two kinds of technologies, we propose four criteria for collaborative technology: its design is grounded on some explicitly argued theory of learning or pedagogical model; it relies on the idea of groupware; it provides procedural facilitation; and it offers representational and community‐building tools.
Information and communication technology (ICT) in secondary schools: the role of the computer coordinator
Authors: Lai Kwok‐Wing , Pratt Keryn 
Published: July 2004

AbstractA study was conducted in 2002 to evaluate the use of information and communication technology (ICT) in 21 secondary schools in one region of New Zealand. As part of the study, the role of the ICT coordinator was investigated. All the ICT coordinators were surveyed and 14 of them were interviewed in‐depth. It is found that they were all well‐equipped to take up a significant leadership role in their schools and some of them have already demonstrated visible leadership. This paper also identifies some obstacles that have reduced their effective leadership in ICT use in their schools.
Interacting with layered dynamic media—some educational aspects of MPEG‐4
Authors: Whalley Peter 
Published: July 2004

AbstractThe role that layered, time‐synchronised media might play in the design of interactive learning environments is examined both in terms of their initial construction, and also in regard to how they might be later re‐engineered and shared. Although the eventual scale of adoption of the new Moving Picture Experts Group (MPEG) media types will be governed by commercial factors, their wide availability would offer considerable benefit to the development of innovative forms of educational interactive multimedia.
Morphology in perch affects habitat specific feeding efficiency
Authors: SVANBÄCK R. , EKLÖV P. 
Published: July 2004

Summary

Trophic polymorphism is a common phenomenon in many species. Trade‐offs in foraging efficiency on different resources are thought to be a primary cause of such polymorphism.
To test for a trade‐off in foraging efficiency perch (Perca fluviatilis L.) were used from a population that differs in morphology between the littoral and pelagic habitat of a lake. Indoor aquarium experiments were performed with three different prey types in two different environments. It was predicted that the morphology of the individual would affect foraging efficiency in the different environments and on the different prey types through search and attack behaviour.
Overall the foraging efficiency of perch was found to be related to individual morphology. A connection was also found between individual morphology and search and attack behaviour. Search behaviour but not attack behaviour was affected by the structure in the aquaria. Furthermore our results show that there are relations between search behaviour and detection rates and between attack behaviour and attack success.
Our results give a mechanistic explanation for the differences in foraging efficiency between littoral and pelagic perch. These differences are probably driven by a functional trade‐off between foraging performance and general body form.
Short‐term diet changes revealed using stable carbon isotopes in horse tail‐hair
Authors: WEST A. G. , AYLIFFE L. K. , CERLING T. E. , ROBINSON T. F. , KARREN B. , DEARING M. D. , EHLERINGER J. R. 
Published: July 2004

Summary

We demonstrate the potential of extracting high‐resolution dietary information from stable carbon isotopes (δ13C) in horse tail‐hair, in response to short‐term changes in diet in controlled feeding experiments.
Tail hairs were sampled from six horses that had been equilibrated to C3 forage and were then subjected to a series of short‐term diet switches to the C4 Coastal Bermuda Grass (Cynodon dactylon L.). Four of these horses were equilibrated to Alfalfa (Medicago sativa L.) and were then subjected to 1‐, 3‐ and 7‐day diet spikes of the C4 grass. The remaining two horses were equilibrated to a C3 grass mix (Dactylis glomerata L. and Festuca arundinacea Schreb.) and then subjected to a 7‐day diet spike of C4 grass.
The effects of the short‐term diet switches were easily observable in the hair. The 1‐, 3‐ and 7‐day spikes showed an increasing deviation from the prespike equilibrium value of 1·0, 2·9 and 5·6 (7‐day treatments averaged).
Isotopic chronologies of individual hairs were created and plotted against a three‐pool, exponential‐decay model. With small alterations to the original model parameters, our data are well explained by this model.
This study indicates that information about diet is recorded with high resolution in hair. This method could be applied to both modern and ancient samples, greatly enhancing the temporal resolution of diet reconstruction studies.
Elevated CO2 alters functional attributes of nematode communities in forest soils
Authors: NEHER D. A. , WEICHT T. R. , MOORHEAD D. L. , SINSABAUGH R. L. 
Published: July 2004

Summary

We tested the effects of elevated concentrations of atmospheric CO2 on herbivorous nematodes in soil supporting plantations of Loblolly Pine (Pinus taeda) or Sweet Gum (Liquidambar styraciflua) trees in FACE experiments in the Eastern USA. We expected any net increase in carbon allocation to the rhizosphere to increase the abundance, biomass or respiration of the nematode community.
Data were analysed with effect of CO2 concentration nested within month and year to isolate the maximum potential effect of CO2 treatment on soil nematode communities.
Elevated CO2 decreased total abundance of nematodes in both forests, but impacts were greater in Sweet Gum than Loblolly Pine forests. Soil nematode community respiration and biomass increased with elevated CO2 in Loblolly Pine, but decreased with fumigation in Sweet Gum forests.
Fungivores were the only trophic group showing a consistent response at both sites, with reduced abundance, biomass and respiration at elevated CO2.
Estimated total respiration of soil nematode communities ranged from 2·9–11·2 g C m−2 year−1 in Pine soils and 0·6–4·7 g C m−2 year−1 in Sweet Gum soils, representing ≤1% of net primary production in these forests.
Our results indicate that effects of elevated CO2 on soil nematode communities will not necessarily have a simple functional relationship with rhizosphere carbon allocation.
Hydraulic redistribution by a dominant, warm‐desert phreatophyte: seasonal patterns and response to precipitation pulses
Authors: HULTINE K. R. , SCOTT R. L. , CABLE W. L. , GOODRICH D. C. , WILLIAMS D. G. 
Published: July 2004

Summary

Hydraulic redistribution may have important consequences for ecosystem water balance where plant root systems span large gradients in soil water potential. To assess seasonal patterns of hydraulic redistribution, we measured the direction and rate of sap flow in tap‐roots, lateral roots and main stems of three mature Prosopis velutina Woot. trees occurring on a floodplain terrace in semiarid south‐eastern Arizona, USA. Sap‐flow measurements on two of the trees were initiated before the end of the winter dormancy period, prior to leaf flush.
Despite the absence of crown transpiration during the dormant season, sap flow was detected in lateral roots and tap‐roots of P. velutina. Reverse flow (away from the stem) in the lateral root and positive flow (towards the stem) in the tap‐root was observed in one tree, indicating the presence of hydraulic lift. Conversely, reverse flow in the tap‐root and positive flow in the lateral root was observed in the second tree, indicating hydraulic descent.
Hydraulic descent was induced in the roots of the former tree by wetting the rooting zone in the upper 70 cm of the soil surface with 50 mm of irrigation.
Patterns and rates of nocturnal sap flow in roots of a third tree measured during the growing season were similar to those observed during the dormant season. Nocturnal reverse flow in the lateral root and positive flow in the tap‐root was observed prior to the onset of the summer monsoon. Hydraulic descent commenced immediately following the first large monsoon rain event, and continued after subsequent rain events. After adjusting for differences in sapwood area, maximum diurnal rates of hydraulic descent in the tap‐roots of trees instrumented during the dormant season were 73 and 69% of the maximum night‐time rate of hydraulic descent observed during the growing season.
Despite very limited potential for direct infiltration, volumetric soil moisture content in deep soil layers (1·5–9·5 m) increased 2–8% by the end of the monsoon (late September), indicating that plant roots were redistributing non‐trivial amounts of water to deep soil layers.
Roots of P. velutina apparently redistribute significant amounts of soil water during the growing season, but also during periods of crown dormancy in winter. In arid regions dormant‐season hydraulic descent may buffer plants from water and nutrient deficits during initial stages of the growing season by transferring soil water derived from winter precipitation to deep soil layers and away from zones of evaporation in surface layers and shallow‐rooted herbaceous plants.
Mites attack males of the sexually polymorphic tree Acer opalus more harmfully and more often
Authors: VERDÚ M. , GARCÍA‐FAYOS P. , GLEISER G. 
Published: July 2004

Summary

Theory predicts that plants that achieve fitness more through male function may be less tolerant of herbivory than those that achieve fitness through the female function. We tested this hypothesis by measuring the degree of infection and damage inflicted by the gall‐forming eriophyid mite Aceria macrorhynchus on three different sexual morphs (males, protandrous bisexuals and protogynous bisexuals) of the Mediterranean tree Acer opalus.
The dependence of each morph on male function, estimated by registering gender changes over 5 years and quantifying male function, decreased in the order males, protandrous, protogynous.
The same decreasing order was found in the degree of gall infection produced by the mite, and in the reduction of photosynthetic rates and shoot growth, but not in the carbon‐isotope discrimination caused by the mites.
Mites attack the morphs of A. opalus that rely more on the male function more often and more harmfully than they do other morphs. Male‐biased herbivory is a selective force that could have been driving the separation of sexes in the genus Acer.