bluuebunny/crossref_metadata_2025_split huggingface dataset:
MPB2C, a Microtubule-Associated Plant Protein Binds to and Interferes with Cell-to-Cell Transport of Tobacco Mosaic Virus Movement Protein
Authors: Kragler Friedrich , Curin Mirela , Trutnyeva Kateryna , Gansch Andreas , Waigmann Elisabeth 
Published: August 2003

Abstract
The movement protein of tobacco mosaic virus, MP30, mediates viral cell-to-cell transport via plasmodesmata. The complex MP30 intra- and intercellular distribution pattern includes localization to the endoplasmic reticulum, cytoplasmic bodies, microtubules, and plasmodesmata and likely requires interaction with plant endogenous factors. We have identified and analyzed an MP30-interacting protein, MPB2C, from the host plant Nicotiana tabacum. MPB2C constitutes a previously uncharacterized microtubule-associated protein that binds to and colocalizes with MP30 at microtubules. In vivo studies indicate that MPB2C mediates accumulation of MP30 at microtubules and interferes with MP30 cell-to-cell movement. In contrast, intercellular transport of a functionally enhanced MP30 mutant, which does not accumulate and colocalize with MP30 at microtubules, is not impaired by MPB2C. Together, these data support the concept that MPB2C is not required for MP30 cell-to-cell movement but may act as a negative effector of MP30 cell-to-cell transport activity.
Enhanced Formaldehyde Detoxification by Overexpression of Glutathione-Dependent Formaldehyde Dehydrogenase from Arabidopsis
Authors: Achkor Hakima , Díaz Maykelis , Fernández M. Rosario , Biosca Josep Antoni , Parés Xavier , Martínez M. Carmen 
Published: August 2003

Abstract
The ADH2 gene codes for the Arabidopsis glutathione-dependent formaldehyde dehydrogenase (FALDH), an enzyme involved in formaldehyde metabolism in eukaryotes. In the present work, we have investigated the potential role of FALDH in detoxification of exogenous formaldehyde. We have generated a yeast (Saccharomyces cerevisiae) mutant strain (sfa1Δ) by in vivo deletion of the SFA1 gene that codes for the endogenous FALDH. Overexpression of Arabidopsis FALDH in this mutant confers high resistance to formaldehyde added exogenously, which demonstrates the functional conservation of the enzyme through evolution and supports its essential role in formaldehyde metabolism. To investigate the role of the enzyme in plants, we have generated Arabidopsis transgenic lines with modified levels of FALDH. Plants overexpressing the enzyme show a 25% increase in their efficiency to take up exogenous formaldehyde, whereas plants with reduced levels of FALDH (due to either a cosuppression phenotype or to the expression of an antisense construct) show a marked slower rate and reduced ability for formaldehyde detoxification as compared with the wild-type Arabidopsis. These results show that the capacity to take up and detoxify high concentrations of formaldehyde is proportionally related to the FALDH activity in the plant, revealing the essential role of this enzyme in formaldehyde detoxification.
Fructans, But Not the Sucrosyl-Galactosides, Raffinose and Loliose, Are Affected by Drought Stress in Perennial Ryegrass
Authors: Amiard Véronique , Morvan-Bertrand Annette , Billard Jean-Pierre , Huault Claude , Keller Felix , Prud'homme Marie-Pascale 
Published: August 2003

Abstract
The aim of this study was to evaluate the putative role of the sucrosyl-galactosides, loliose [α-d-Gal (1,3) α-d-Glc (1,2) β-d-Fru] and raffinose [α-d-Gal (1,6) α-d-Glc (1,2) β-d-Fru], in drought tolerance of perennial ryegrass and to compare it with that of fructans. To that end, the loliose biosynthetic pathway was first established and shown to operate by a UDP-Gal: sucrose (Suc) 3-galactosyltransferase, tentatively termed loliose synthase. Drought stress increased neither the concentrations of loliose and raffinose nor the activities of loliose synthase and raffinose synthase (EC 2.4.1.82). Moreover, the concentrations of the raffinose precursors, myoinositol and galactinol, as well as the gene expressions of myoinositol 1-phosphate synthase (EC 5.5.1.4) and galactinol synthase (EC 2.4.1.123) were either decreased or unaffected by drought stress. Taken together, these data are not in favor of an obvious role of sucrosyl-galactosides in drought tolerance of perennial ryegrass at the vegetative stage. By contrast, drought stress caused fructans to accumulate in leaf tissues, mainly in leaf sheaths and elongating leaf bases. This increase was mainly due to the accumulation of long-chain fructans (degree of polymerization &gt; 8) and was not accompanied by a Suc increase. Interestingly, Suc but not fructan concentrations greatly increased in drought-stressed roots. Putative roles of fructans and sucrosyl-galactosides are discussed in relation to the acquisition of stress tolerance.
PAUSED, a Putative Exportin-t, Acts Pleiotropically in Arabidopsis Development But Is Dispensable for Viability
Authors: Li Junjie , Chen Xuemei 
Published: August 2003

AbstractExportin-t was first identified in humans as a protein that mediates the export of tRNAs from the nucleus to the cytoplasm. Mutations in Los1p, the Saccharomyces cerevisiae exportin-t homolog, result in nuclear accumulation of tRNAs. Because no exportin-t mutants have been reported in multicellular organisms, the developmental functions of exportin-t have not been determined. Here, we report the isolation and characterization of two Arabidopsis exportin-t mutants, paused-5 and paused-6. The mutant phenotypes indicate that exportin-t acts pleiotropically in plant development. In particular, paused-5 and paused-6 result in delayed leaf formation during vegetative development. The two paused mutations also cause the transformation of reproductive organs into perianth organs in the hua1-1 hua2-1 background, which is partially defective in reproductive organ identity specification. The floral phenotypes of hua1-1 hua2-1 paused mutants resemble those of mutations in the floral homeotic gene AGAMOUS. Moreover, paused-5 enhances the mutant phenotypes of two floral meristem identity genes, LEAFY and APETALA1. The developmental defects caused by paused mutations confirm the important roles of exportin-t in gene expression in multicellular organisms. In addition, a paused null allele, paused-6, is still viable, suggesting the presence of redundant tRNA export pathway(s) in Arabidopsis.
Stomatal Closure during Leaf Dehydration, Correlation with Other Leaf Physiological Traits
Authors: Brodribb Tim J. , Holbrook N. Michele 
Published: August 2003

Abstract
The question as to what triggers stomatal closure during leaf desiccation remains controversial. This paper examines characteristics of the vascular and photosynthetic functions of the leaf to determine which responds most similarly to stomata during desiccation. Leaf hydraulic conductance (Kleaf) was measured from the relaxation kinetics of leaf water potential (Ψl), and a novel application of this technique allowed the response of Kleaf to Ψl to be determined. These “vulnerability curves” show that Kleaf is highly sensitive to Ψl and that the response of stomatal conductance to Ψl is closely correlated with the response of Kleaf to Ψl. The turgor loss point of leaves was also correlated with Kleaf and stomatal closure, whereas the decline in PSII quantum yield during leaf drying occurred at a lower Ψl than stomatal closure. These results indicate that stomatal closure is primarily coordinated with Kleaf. However, the close proximity of Ψl at initial stomatal closure and initial loss of Kleaf suggest that partial loss of Kleaf might occur regularly, presumably necessitating repair of embolisms.
Modulation of Citrate Metabolism Alters Aluminum Tolerance in Yeast and Transgenic Canola Overexpressing a Mitochondrial Citrate Synthase
Authors: Anoop Valar M. , Basu Urmila , McCammon Mark T. , McAlister-Henn Lee , Taylor Gregory J. 
Published: August 2003

Abstract
Aluminum (Al) toxicity is a major constraint for crop production in acid soils, although crop cultivars vary in their tolerance to Al. We have investigated the potential role of citrate in mediating Al tolerance in Al-sensitive yeast (Saccharomyces cerevisiae; MMYO11) and canola (Brassica napus cv Westar). Yeast disruption mutants defective in genes encoding tricarboxylic acid cycle enzymes, both upstream (citrate synthase [CS]) and downstream (aconitase [ACO] and isocitrate dehydrogenase [IDH]) of citrate, showed altered levels of Al tolerance. A triple mutant of CS (Δcit123) showed lower levels of citrate accumulation and reduced Al tolerance, whereas Δaco1- and Δidh12-deficient mutants showed higher accumulation of citrate and increased levels of Al tolerance. Overexpression of a mitochondrial CS (CIT1) in MMYO11 resulted in a 2- to 3-fold increase in citrate levels, and the transformants showed enhanced Al tolerance. A gene for Arabidopsis mitochondrial CS was overexpressed in canola using an Agrobacterium tumefaciens-mediated system. Increased levels of CS gene expression and enhanced CS activity were observed in transgenic lines compared with the wild type. Root growth experiments revealed that transgenic lines have enhanced levels of Al tolerance. The transgenic lines showed enhanced levels of cellular shoot citrate and a 2-fold increase in citrate exudation when exposed to 150 μm Al. Our work with yeast and transgenic canola clearly suggest that modulation of different enzymes involved in citrate synthesis and turnover (malate dehydrogenase, CS, ACO, and IDH) could be considered as potential targets of gene manipulation to understand the role of citrate metabolism in mediating Al tolerance.
Overproduction of Cytokinins in Petunia Flowers Transformed with PSAG12-IPT Delays Corolla Senescence and Decreases Sensitivity to Ethylene
Authors: Chang Hsiang , Jones Michelle L. , Banowetz Gary M. , Clark David G. 
Published: August 2003

AbstractPlant senescence is regulated by a coordinated genetic program mediated in part by changes in ethylene, abscisic acid (ABA), and cytokinin content. Transgenic plants with delayed senescence are useful for studying interactions between these signaling mechanisms. Expression of ipt, a cytokinin biosynthetic gene from Agrobacterium tumefaciens, under the control of the promoter from a senescence-associated gene (SAG12) has been one approach used to delay senescence. We transformed petunia (Petunia x hybrida cv V26) with PSAG12-IPT. Two independently transformed lines with extended flower longevity (I-1-7-22 and I-3-18-34) were used to study the effects of elevated cytokinin content on ethylene synthesis and sensitivity and ABA accumulation in petunia corollas. Floral senescence in these lines was delayed 6 to 10 d relative to wild-type (WT) flowers. Ipt transcripts increased in abundance after pollination and were accompanied by increased cytokinin accumulation. Endogenous ethylene production was induced by pollination in both WT and IPT corollas, but this increase was delayed in IPT flowers. Flowers from IPT plants were less sensitive to exogenous ethylene and required longer treatment times to induce endogenous ethylene production, corolla senescence, and up-regulation of the senescence-related Cys protease phcp1. Accumulation of ABA, another hormone regulating flower senescence, was significantly greater in WT corollas, confirming that floral senescence was delayed in IPT plants. These results extend our understanding of the hormone interactions that regulate flower senescence and provide a means of increasing flower longevity.
Microarray Analysis of the Genome-Wide Response to Iron Deficiency and Iron Reconstitution in the Cyanobacterium Synechocystis sp. PCC 6803
Authors: Singh Abhay K. , McIntyre Lauren M. , Sherman Louis A. 
Published: August 2003

Abstract
A full-genome microarray of the (oxy)photosynthetic cyanobacterium Synechocystis sp. PCC 6803 was used to identify genes that were transcriptionally regulated by growth in iron (Fe)-deficient versus Fe-sufficient media. Transcript accumulation for 3,165 genes in the genome was analyzed using an analysis of variance model that accounted for slide and replicate (random) effects and dye (a fixed) effect in testing for differences in the four time periods. We determined that 85 genes showed statistically significant changes in the level of transcription (P ≤ 0.05/3,165 = 0.0000158) across the four time points examined, whereas 781 genes were characterized as interesting (P ≤ 0.05 but greater than 0.0000158; 731 of these had a fold change &gt;1.25×). The genes identified included those known previously to be Fe regulated, such as isiA that encodes a novel chlorophyll-binding protein responsible for the pigment characteristics of low-Fe (LoFe) cells. ATP synthetase and phycobilisome genes were down-regulated in LoFe, and there were interesting changes in the transcription of genes involved in chlorophyll biosynthesis, in photosystem I and II assembly, and in energy metabolism. Hierarchical clustering demonstrated that photosynthesis genes, as a class, were repressed in LoFe and induced upon the re-addition of Fe. Specific regulatory genes were transcriptionally active in LoFe, including two genes that show homology to plant phytochromes (cph1 and cph2). These observations established the existence of a complex network of regulatory interactions and coordination in response to Fe availability.
Convergent Responses to Stress. Solar Ultraviolet-B Radiation and Manduca sexta Herbivory Elicit Overlapping Transcriptional Responses in Field-Grown Plants of Nicotiana longiflora
Authors: Izaguirre Miriam M. , Scopel Ana L. , Baldwin Ian T. , Ballaré Carlos L. 
Published: August 2003

Abstract
The effects of solar ultraviolet (UV)-B (280–315 nm) on plants have been studied intensively over the last 2 decades in connection with research on the biological impacts of stratospheric ozone depletion. However, the molecular mechanisms that mediate plant responses to solar (ambient) UV-B and their interactions with response mechanisms activated by other stressors remain for the most part unclear. Using a microarray enriched in wound- and insect-responsive sequences, we examined expression responses of 241 genes to ambient UV-B in field-grown plants of Nicotiana longiflora Cav. Approximately 20% of the sequences represented on the array showed differential expression in response to solar UV-B. The expression responses to UV-B had parallels with those elicited by simulated Manduca sexta herbivory. The most obvious similarities were: (a) down-regulation of several photosynthesis-related genes, and (b) up-regulation of genes involved in fatty acid metabolism and oxylipin biosynthesis such as HPL (hydroperoxide lyase), α-DIOX (alpha-dioxygenase), LOX (13-lipoxygenase), and AOS (allene oxide synthase). Genes encoding a WRKY transcription factor, a ferredoxin-dependent glutamate-synthase, and several other insect-responsive genes of unknown function were also similarly regulated by UV-B and insect herbivory treatments. Our results suggest that UV-B and caterpillar herbivory activate common regulatory elements and provide a platform for understanding the mechanisms of UV-B impacts on insect herbivory that have been documented in recent field studies.
Constitutive E2F Expression in Tobacco Plants Exhibits Altered Cell Cycle Control and Morphological Change in a Cell Type-Specific Manner
Authors: Kosugi Shunichi , Ohashi Yuko 
Published: August 2003

Abstract
The E2F family plays a pivotal role in cell cycle control and is conserved among plants and animals, but not in fungi. This provides for the possibility that the E2F family was integrated during the development of higher organisms, but little is known about this. We examined the effect of E2F ectopically expressed in transgenic tobacco (Nicotiana tabacum) plants on growth and development using E2Fa (AtE2F3) and DPa from Arabidopsis. E2Fa-DPa double transgenic lines exhibited altered phenotypes with curled leaves, round shaped petals, and shortened pistils. In mature but not immature leaves of the double transgenic lines, there were enlarged nuclei with increasing ploidy levels accompanied by the ectopic expression of S phase- but not M phase-specific genes. This indicates that a high expression of E2F promotes endoreduplication by accelerating S phase entry in terminally differentiated cells with limited mitotic activity. Furthermore, mature leaves of the transgenic plants contained increased numbers of small cells, especially on the palisade (adaxial) side of the outer region toward the edge, and the leaf strips exhibited hormone-independent callus formation when cultured in vitro. These observations suggest that an enhanced E2F activity modulates cell cycle in a cell type-specific manner and affects plant morphology depending on a balance between activities for committing to S phase and M phase, which likely differ between organs or tissues.
The Putative Arabidopsis Arp2/3 Complex Controls Leaf Cell Morphogenesis
Authors: Li Shundai , Blanchoin Laurent , Yang Zhenbiao , Lord Elizabeth M. 
Published: August 2003

Abstract
The evolutionarily conserved Arp2/3 complex has been shown to activate actin nucleation and branching in several eukaryotes, but its biological functions are not well understood in multicellular organisms. The model plant Arabidopsis provides many advantages for genetic dissection of the function of this conserved actin-nucleating machinery, yet the existence of this complex in plants has not been determined. We have identified Arabidopsis genes encoding homologs of all of the seven Arp2/3 subunits. The function of the putative Arabidopsis Arp2/3 complex has been studied using four homozygous T-DNA insertion mutants for ARP2, ARP3, and ARPC5/p16. All four mutants display identical defects in the development of jigsaw-shaped epidermal pavement cells and branched trichomes in the leaf. These loss-of-function mutations cause mislocalization of diffuse cortical F-actin to the neck region and inhibit lobe extension in pavement cells. The mutant trichomes resemble those treated with the actin-depolymerizing drug cytochalasin D, exhibiting stunted branches but dramatically enlarged stalks due to depolarized growth suggesting defects in the formation of a fine actin network. Our data demonstrate that the putative Arabidopsis Arp2/3 complex controls cell morphogenesis through its roles in cell polarity establishment and polar cell expansion. Furthermore, our data suggest a novel function for the putative Arp2/3 complex in the modulation of the spatial distribution of cortical F-actin and provide evidence that the putative Arp2/3 complex may activate the polymerization of some types of actin filaments in specific cell types.
The Role of Joint Attention in Later Development Among Preterm Children: Linkages Between Early and Middle Childhood
Authors: Smith Lars , Ulvund Stein Erik 
Published: August 2003

AbstractJoint attention is a hallmark of human cognition. It refers to the capacity to coordinate attention to objects and events with attention to other people. Infants display considerable individual differences in this capacity. This longitudinal study of 13‐month‐old preterms was conducted to examine the hypothesis that two different types of joint‐attention skills assessed in an infant–tester paradigm are related to verbal and nonverbal IQ measures through middle childhood. Data are reported separately for the children's tendency to initiate such skills and to respond to an experimenter's offers to share in such behaviours. The results provide support for the hypothesis that the initiation of joint attention makes a unique contribution to later nonverbal IQ apart from variance associated with biomedical risk status and infant development. The results of this study have implications for the conceptualisation of joint‐attention skills, as well as for understanding the relation between joint attention and later cognition.
Extremely Premature and Very Low Birthweight Infants: A Double Hazard Population?
Authors: Nadeau Line , Tessier Réjean , Boivin Michel , Lefebvre Francine , Robaey Philippe 
Published: August 2003

AbstractThis article evaluates the contributions of birth status (defined by gestational age and birthweight) and family adversity at birth and at age 7 to explaining behavior problems at age 7. The behaviors of 96 extremely preterm and very low birth‐weight children and 66 full‐term children were assessed in a school setting by peers, teachers and parents. The results show that a significant relationship exists between birth status and isolation and social withdrawal problems as well as between birth status and social immaturity and inattention problems. Family adversity at birth has a significant contribution to aggressive behaviors reported by the three sources whereas, at age 7, this index is associated only with aggressive behaviors and social immaturity problems reported by parents. In conclusion, the results of the present study qualify the findings of studies that suggest that at school age, the effect of prematurity decreases and that behavior problems are explained chiefly by family environment characteristics. Our results indicate that the findings must take into account the cohort studied, the environmental measures used, the type of behaviors assessed as well as the type of informants.
Urban land rent theory: a regulationist perspective
Authors: Jäger Johannes 
Published: August 2003

Whilst real estate capital became a driving force in analyses of urban development, urban land rent theory has made only very limited progress during the past decade. There are a number of reasons for this – such as a weak conceptualization of the role of political agency, for example. Hence, a way out of this relative stagnation, by attempting to systematically develop an integrated view on structure and agency in the context of urban land rent, is offered in this article. Advances in critical theory, thinking about space and dialectic reasoning contribute to the development of a new perspective on land rent. Land rent is conceptualized as a middle‐range theory. In order to bring together concrete urban phenomena with the general process of political‐economic development, a systematic link between land rent theory and the theoretical apparatus of the French Regulation School is developed. The reformulation of land rent theory from a regulationist perspective underlines the importance of the institutional context (and its changes) for an understanding of rent and its role in the urban context. In so doing, land rent theory proves to be a very useful tool for providing an integrated political‐economic perspective for analyses of urban phenomena. This is illustrated briefly in the cases of Vienna and Montevideo.Si le capital immobilier est devenu un point central des analyses du développement urbain, la théorie n'a guère progressé au cours de la dernière décennie. Plusieurs facteurs sont en cause, telle la faible conceptualisation du rôle politique d'agence. Cet article propose donc une porte de sortie à cette relative stagnation, en tentant de construire systématiquement une vision intégrée de la structure et l'agence dans le cadre de la rente urbaine. Les progrès en matière de théorie critique, réflexion en termes d'espace et raisonnement dialectique facilitent l'élaboration d'une nouvelle perspective sur la location foncière, laquelle est conceptualisée en tant que théorie intermédiaire. Afin de regrouper phénomènes urbains concrets et processus général d'aménagement politico‐économique, une relation systématique est établie entre la théorie sur la rente foncière et l'appareil théorique de l'École Française de Régulation. Reformuler la théorie sur la rente foncière d'un point de vue régulationiste souligne combien le contexte institutionnel (et ses changements) est important pour comprendre la rente et son rôle dans le cadre urbain. Ce faisant, la théorie sur la rente foncière se révèle un outil très utile pour créer une perspective politico‐économique intégrée permettant d'analyser les phénomènes urbains. Cet aspect est brièvement illustré dans les cas de Vienne et Montevideo.