bluuebunny/crossref_metadata_2025 huggingface dataset:
AtOPT6 Transports Glutathione Derivatives and Is Induced by Primisulfuron
Authors: Cagnac Olivier , Bourbouloux Andrée , Chakrabarty Debasis , Zhang Ming-Yong , Delrot Serge
Published: July 2004

The oligopeptide transporter (OPT) family contains nine members in Arabidopsis. While there is some evidence that AtOPTs mediate the uptake of tetra- and pentapeptides, OPT homologs in rice (Oryza sativa; OsGT1) and Indian mustard (Brassica juncea; BjGT1) have been described as transporters of glutathione derivatives. This study investigates the possibility that two members of the AtOPT family, AtOPT6 and AtOPT7, may also transport glutathione and its conjugates. Complementation of the hgt1met1 yeast double mutant by plant homologs of the yeast glutathione transporter HGT1 (AtOPT6, AtOPT7, OsGT1, BjGT1) did not restore the growth phenotype, unlike complementation by HGT1. By contrast, complementation by AtOPT6 restored growth of the hgt1 yeast mutant on a medium containing reduced (GSH) or oxidized glutathione as the sole sulfur source and induced uptake of [3H]GSH, whereas complementation by AtOPT7 did not. In these conditions, AtOPT6-dependent GSH uptake in yeast was mediated by a high affinity (K  m = 400 μ  m) and a low affinity (K  m = 5 mm) phase. It was strongly competed for by an excess oxidized glutathione and glutathione-N-ethylmaleimide conjugate. Growth assays of yeasts in the presence of cadmium (Cd) suggested that AtOPT6 may transport Cd and Cd/GSH conjugate. Reporter gene experiments showed that AtOPT6 is mainly expressed in dividing areas of the plant (cambium, areas of lateral root initiation). RNA blots on cell suspensions and real-time reverse transcription-PCR on Arabidopsis plants indicated that AtOPT6 expression is strongly induced by primisulfuron and, to a lesser extent, by abscisic acid but not by Cd. Altogether, the data show that the substrate specificity and the physiological functions of AtOPT members may be diverse. In addition to peptide transport, AtOPT6 is able to transport glutathione derivatives and metal complexes, and may be involved in stress resistance.
Floral Meristem Identity Genes Are Expressed during Tendril Development in Grapevine
Authors: Calonje Myriam , Cubas Pilar , Martínez-Zapater José M. , Carmona María José
Published: July 2004

To study the early steps of flower initiation and development in grapevine (Vitis vinifera), we have isolated two MADS-box genes, VFUL-L and VAP1, the putative FUL-like and AP1 grapevine orthologs, and analyzed their expression patterns during vegetative and reproductive development. Both genes are expressed in lateral meristems that, in grapevine, can give rise to either inflorescences or tendrils. They are also coexpressed in inflorescence and flower meristems. During flower development, VFUL-L transcripts are restricted to the central part of young flower meristems and, later, to the prospective carpel-forming region, which is consistent with a role of this gene in floral transition and carpel and fruit development. Expression pattern of VAP1 suggests that it may play a role in flowering transition and flower development. However, its lack of expression in sepal primordia, does not support its role as an A-function gene in grapevine. Neither VFUL-L nor VAP1 expression was detected in vegetative organs such as leaves or roots. In contrast, they are expressed throughout tendril development. Transcription of both genes in tendrils of very young plants that have not undergone flowering transition indicates that this expression is independent of the flowering process. These unique expression patterns of genes typically involved in reproductive development have implications on our understanding of flower induction and initiation in grapevine, on the origin of grapevine tendrils and on the functional roles of AP1-and FUL-like genes in plant development. These results also provide molecular support to the hypothesis that Vitis tendrils are modified reproductive organs adapted to climb.
Root-Gel Interactions and the Root Waving Behavior of Arabidopsis
Authors: Thompson Matthew V. , Holbrook N. Michele
Published: July 2004

Arabidopsis roots grown on inclined agarose gels exhibit a sinusoidal growth pattern known as root waving. While root waving has been attributed to both intrinsic factors (e.g. circumnutation) and growth responses to external signals such as gravity, the potential for physical interactions between the root and its substrate to influence the development of this complex phenotype has been generally ignored. Using a rotating stage microscope and time-lapse digital imaging, we show that (1) root tip mobility is impeded by the gel surface, (2) this impedance causes root tip deflections by amplifying curvature in the elongation zone in a way that is distinctly nontropic, and (3) root tip impedance is augmented by normal gravitropic pressure applied by the root tip against the gel surface. Thus, both lateral corrective bending near the root apex and root tip impedance could be due to different vector components of the same graviresponse. Furthermore, we speculate that coupling between root twisting and bending is a mechanical effect resulting from root tip impedance.
Characterization of Arabidopsis Glutamine Phosphoribosyl Pyrophosphate Amidotransferase-Deficient Mutants
Authors: Hung Wei-Fon , Chen Lih-Jen , Boldt Ralf , Sun Chih-Wen , Li Hsou-min
Published: July 2004

Using a transgene-based screening, we previously isolated several Arabidopsis mutants defective in protein import into chloroplasts. Positional cloning of one of the loci, CIA1, revealed that CIA1 encodes Gln phosphoribosyl pyrophosphate amidotransferase 2 (ATase2), one of the three ATase isozymes responsible for the first committed step of de novo purine biosynthesis. The cia1 mutant had normal green cotyledons but small and albino/pale-green mosaic leaves. Adding AMP, but not cytokinin or NADH, to plant liquid cultures partially complemented the mutant phenotypes. Both ATase1 and ATase2 were localized to chloroplasts. Overexpression of ATase1 fully complemented the ATase2-deficient phenotypes. A T-DNA insertion knockout mutant of the ATase1 gene was also obtained. The mutant was indistinguishable from the wild type. A double mutant of cia1/ATase1-knockout had the same phenotype as cia1, suggesting at least partial gene redundancy between ATase1 and ATase2. Characterizations of the cia1 mutant revealed that mutant leaves had slightly smaller cell size but only half the cell number of wild-type leaves. This phenotype confirms the role of de novo purine biosynthesis in cell division. Chloroplasts isolated from the cia1 mutant imported proteins at an efficiency less than 50% that of wild-type chloroplasts. Adding ATP and GTP to isolated mutant chloroplasts could not restore the import efficiency. We conclude that de novo purine biosynthesis is not only important for cell division, but also for chloroplast biogenesis.
Phloem Import and Storage Metabolism Are Highly Coordinated by the Low Oxygen Concentrations within Developing Wheat Seeds
Authors: van Dongen Joost T. , Roeb Gerhard W. , Dautzenberg Marco , Froehlich Anja , Vigeolas Helene , Minchin Peter E. H. , Geigenberger Peter
Published: July 2004

We studied the influence of the internal oxygen concentration in seeds of wheat (Triticum aestivum) on storage metabolism and its relation to phloem import of nutrients. Wheat seeds that were developing at ambient oxygen (21%) were found to be hypoxic (2.1%). Altering the oxygen supply by decreasing or increasing the external oxygen concentration induced parallel changes in the internal oxygen tension. However, the decrease in internal concentration was proportionally less than the reduction in external oxygen. This indicates that decreasing the oxygen supply induces short-term adaptive responses to reduce oxygen consumption of the seeds. When external oxygen was decreased to 8%, internal oxygen decreased to approximately 0.5% leading to a decrease in energy production via respiration. Conversely, increasing the external oxygen concentration above ambient levels increased the oxygen content as well as the energy status of the seeds, indicating that under normal conditions the oxygen supply is strongly limiting for energy metabolism in developing wheat seeds. The intermediate metabolites of seed storage metabolism were not substantially affected when oxygen was either increased or decreased. However, at subambient external oxygen concentrations (8%) the metabolic flux of carbon into starch and protein, measured by injecting 14C-Suc into the seeds, was reduced by 17% and 32%, respectively, whereas no significant effect was observed at superambient (40%) oxygen. The observed decrease in biosynthetic fluxes to storage compounds is suggested to be part of an adaptive response to reduce energy consumption preventing excessive oxygen consumption when oxygen supply is limited. Phloem transport toward ears exposed to low (8%) oxygen was significantly reduced within 1 h, whereas exposing ears to elevated oxygen (40%) had no significant effect. This contrasts with the situation where the distribution of assimilates has been modified by removing the lower source leaves from the plant, resulting in less assimilates transported to the ear in favor of transport to the lower parts of the plant. Under these conditions, with two strongly competing sinks, elevated oxygen (40%) did lead to a strong increase in phloem transport to the ear. The results show that sink metabolism is affected by the prevailing low oxygen concentrations in developing wheat seeds, determining the import rate of assimilates via the phloem.
The ANTHER INDEHISCENCE1 Gene Encoding a Single MYB Domain Protein Is Involved in Anther Development in Rice
Authors: Zhu Qian-Hao , Ramm Kerrie , Shivakkumar Ramani , Dennis Elizabeth S. , Upadhyaya Narayana M.
Published: July 2004

Using a two-element iAc/Ds transposon-tagging system, we identified a rice (Oryza sativa L. cv Nipponbare) recessive mutant, anther indehiscence1 (aid1), showing partial to complete spikelet sterility. Spikelets of the aid1 mutant could be classified into three types based on the viability of pollen grains and the extent of anther dehiscence. Type 1 spikelets (approximately 25%) were sterile due to a failure in accumulation of starch in pollen grains. Type 2 spikelets (approximately 55%) had viable pollen grains, but anthers failed to dehisce and/or synchronize with anthesis due to failure in septum degradation and stomium breakage, resulting in sterility. Type 3 spikelets (approximately 20%) had normal fertility. In addition, aid1 mutant plants had fewer tillers and flowered 10 to 15 d later than the wild type. The Ds insertion responsible for the aid1 mutation was mapped within the coding region of the AID1 gene on chromosome 6, which is predicted to encode a novel protein of 426 amino acids with a single MYB domain. The MYB domain of AID1 is closely related to that of the telomere-binding proteins of human, mouse, and Arabidopsis, and of single MYB domain transcriptional regulators in plants such as PcMYB1 and ZmIBP1. AID1 was expressed in both the leaves and panicles of wild-type plants, but not in mutant plants.
Identification and Characterization of Stretch-Activated Ion Channels in Pollen Protoplasts
Authors: Dutta Rajiv , Robinson Kenneth R.
Published: July 2004

Pollen tube growth requires a Ca2+ gradient, with elevated levels of cytosolic Ca2+ at the growing tip. This gradient's magnitude oscillates with growth oscillation but is always maintained. Ca2+ influx into the growing tip is necessary, and its magnitude also oscillates with growth. It has been widely assumed that stretch-activated Ca2+ channels underlie this influx, but such channels have never been reported in either pollen grains or pollen tubes. We have identified and characterized stretch-activated Ca2+ channels from Lilium longiflorum pollen grain and tube tip protoplasts. The channels were localized to a small region of the grain protoplasts associated with the site of tube germination. In addition, we find a stretch-activated K+ channel as well as a spontaneous K+ channel distributed over the entire grain surface, but neither was present at the germination site or at the tip. Neither stretch-activated channel was detected in the grain protoplasts unless the grains were left in germination medium for at least 1 h before protoplast preparation. The stretch-activated channels were inhibited by a spider venom that is known to block stretch-activated channels in animal cells, but the spontaneous channel was unaffected by the venom. The venom also stopped pollen tube germination and elongation and blocked Ca2+ entry into the growing tip, suggesting that channel function is necessary for growth.
Spermidine Synthase Genes Are Essential for Survival of Arabidopsis
Authors: Imai Akihiro , Matsuyama Takashi , Hanzawa Yoshie , Akiyama Takashi , Tamaoki Masanori , Saji Hikaru , Shirano Yumiko , Kato Tomohiko , Hayashi Hiroaki , Shibata Daisuke , Tabata Satoshi , Komeda Yoshibumi , Takahashi Taku
Published: July 2004

The cellular polyamines putrescine, spermidine, and spermine are ubiquitous in nature and have been implicated in a wide range of growth and developmental processes. There is little information, however, on mutant plants or animals defective in the synthesis of polyamines. The Arabidopsis genome has two genes encoding spermidine synthase, SPDS1 and SPDS2. In this paper, we describe T-DNA insertion mutants of both of these genes. While each mutant allele shows normal growth, spds1-1 spds2-1 double-mutant seeds are abnormally shrunken and they have embryos that are arrested morphologically at the heart-torpedo transition stage. These seeds contain significantly reduced levels of spermidine and high levels of its precursor, putrescine. The embryo lethal phenotype of spds1-1 spds2-1 is complemented by the wild-type SPDS1 gene. In addition, we observed a nearly identical seed phenotype among an F2 seed population from the cross between the spds2-1 allele and SPDS1 RNA interference transgenic lines. These data provide the first genetic evidence indicating a critical role of the spermidine synthase in plant embryo development.
Salt Cress. A Halophyte and Cryophyte Arabidopsis Relative Model System and Its Applicability to Molecular Genetic Analyses of Growth and Development of Extremophiles
Authors: Inan Günsu , Zhang Quan , Li Pinghua , Wang Zenglan , Cao Ziyi , Zhang Hui , Zhang Changqing , Quist Tanya M. , Goodwin S. Mark , Zhu Jianhua , Shi Huazhong , Damsz Barbara , Charbaji Tarif , Gong Qingqiu , Ma Shisong , Fredricksen Mark , Galbraith David W. , Jenks Matthew A. , Rhodes David , Hasegawa Paul M. , Bohnert Hans J. , Joly Robert J. , Bressan Ray A. , Zhu Jian-Kang
Published: July 2004

Salt cress (Thellungiella halophila) is a small winter annual crucifer with a short life cycle. It has a small genome (about 2 × Arabidopsis) with high sequence identity (average 92%) with Arabidopsis, and can be genetically transformed by the simple floral dip procedure. It is capable of copious seed production. Salt cress is an extremophile native to harsh environments and can reproduce after exposure to extreme salinity (500 mm NaCl) or cold to −15°C. It is a typical halophyte that accumulates NaCl at controlled rates and also dramatic levels of Pro (>150 mm) during exposure to high salinity. Stomata of salt cress are distributed on the leaf surface at higher density, but are less open than the stomata of Arabidopsis and respond to salt stress by closing more tightly. Leaves of salt cress are more succulent-like, have a second layer of palisade mesophyll cells, and are frequently shed during extreme salt stress. Roots of salt cress develop both an extra endodermis and cortex cell layer compared to Arabidopsis. Salt cress, although salt and cold tolerant, is not exceptionally tolerant of soil desiccation. We have isolated several ethyl methanesulfonate mutants of salt cress that have reduced salinity tolerance, which provide evidence that salt tolerance in this halophyte can be significantly affected by individual genetic loci. Analysis of salt cress expressed sequence tags provides evidence for the presence of paralogs, missing in the Arabidopsis genome, and for genes with abiotic stress-relevant functions. Hybridizations of salt cress RNA targets to an Arabidopsis whole-genome oligonucleotide array indicate that commonly stress-associated transcripts are expressed at a noticeably higher level in unstressed salt cress plants and are induced rapidly under stress. Efficient transformation of salt cress allows for simple gene exchange between Arabidopsis and salt cress. In addition, the generation of T-DNA-tagged mutant collections of salt cress, already in progress, will open the door to a new era of forward and reverse genetic studies of extremophile plant biology.
The Salt-Stress Signal Transduction Pathway That Activates the gpx1 Promoter Is Mediated by Intracellular H2O2, Different from the Pathway Induced by Extracellular H2O2
Authors: Avsian-Kretchmer Orna , Gueta-Dahan Yardena , Lev-Yadun Simcha , Gollop Rachel , Ben-Hayyim Gozal
Published: July 2004

Several genes encoding putative glutathione peroxidase have been isolated from a variety of plants, all of which show the highest homology to the phospholipid hydroperoxide isoform. Several observations suggest that the proteins are involved in biotic and abiotic stress responses. Previous studies on the regulation of gpx1, the Citrus sinensis gene encoding phospholipid hydroperoxide isoform, led to the conclusion that salt-induced expression of gpx1 transcript and its encoded protein is mediated by oxidative stress. In this paper, we describe the induction of gpx1 promoter:uidA fusions in stable transformants of tobacco (Nicotiana tabacum) cultured cells and plants. We show that the induction of gpx1 by salt and oxidative stress occurs at the transcriptional level. gpx1 promoter analysis confirmed our previous assumption that the salt signal is transduced via oxidative stress. We used induction of the fusion construct to achieve better insight into, and to monitor salt-induced oxidative stress. The gpx1 promoter responded preferentially to oxidative stress in the form of hydrogen peroxide, rather than to superoxide-generating agents. Antioxidants abolished the salt-induced expression of gpx1 promoter, but were unable to eliminate the induction by H2O2. The commonly employed NADPH-oxidase inhibitor diphenyleneiodonium chloride and catalase inhibited the H2O2-induced expression of gpx1 promoter, but did not affect its induction by salt. Our results led us to conclude that salt induces oxidative stress in the form of H2O2, its production occurs in the intracellular space, and its signal transduction pathway activating the gpx1 promoter is different from the pathway induced by extracellular H2O2.
Characterization of a Novel Calcium/Calmodulin-Dependent Protein Kinase from Tobacco
Authors: Ma Li , Liang Shuping , Jones Russell L. , Lu Ying-Tang
Published: July 2004

A cDNA encoding a calcium (Ca2+)/calmodulin (CaM)-dependent protein kinase (CaMK) from tobacco (Nicotiana tabacum), NtCaMK1, was isolated by protein-protein interaction-based screening of a cDNA expression library using 35S-labeled CaM as a probe. The genomic sequence is about 24.6 kb, with 21 exons, and the full-length cDNA is 4.8 kb, with an open reading frame for NtCaMK1 consisting of 1,415 amino acid residues. NtCaMK1 has all 11 subdomains of a kinase catalytic domain, lacks EF hands for Ca2+-binding, and is structurally similar to other CaMKs in mammal systems. Biochemical analyses have identified NtCaMK1 as a Ca2+/CaMK since NtCaMK1 phosphorylated itself and histone IIIs as substrate only in the presence of Ca2+/CaM with a K  m of 44.5 μ  m and a V  max of 416.2 nm min−1 mg−1. Kinetic analysis showed that the kinase not previously autophosphorylated had a K  m for the synthetic peptide syntide-2 of 22.1 μ  m and a V  max of 644.1 nm min−1 mg−1 when assayed in the presence of Ca2+/CaM. Once the autophosphorylation of NtCaMK1 was initiated, the phosphorylated form displayed Ca2+/CaM-independent behavior, as many other CaMKs do. Analysis of the CaM-binding domain (CaMBD) in NtCaMK1 with truncated and site-directed mutated forms defined a stretch of 20 amino acid residues at positions 913 to 932 as the CaMBD with high CaM affinity (K  d = 5 nm). This CaMBD was classified as a 1-8-14 motif. The activation of NtCaMK1 was differentially regulated by three tobacco CaM isoforms (NtCaM1, NtCaM3, and NtCaM13). While NtCaM1 and NtCaM13 activated NtCaMK1 effectively, NtCaM3 did not activate the kinase.
Cytoskeletal Proteins Are Coordinately Increased in Maize Genotypes with High Levels of eEF1A
Authors: Lopez-Valenzuela Jose A. , Gibbon Bryan C. , Holding David R. , Larkins Brian A.
Published: July 2004

The opaque2 (o2) mutation increases the Lys content of maize (Zea mays) endosperm by reducing the synthesis of zein storage proteins and increasing the accumulation of other types of cellular proteins. Elongation factor 1A (eEF1A) is one of these proteins, and its concentration is highly correlated with the amount of other Lys-containing proteins in the endosperm. We investigated the basis for this relationship by comparing patterns of protein accumulation and gene expression between a high (Oh51Ao2) and a low (Oh545o2) eEF1A inbred, as well as between high and low eEF1A recombinant inbred lines obtained from their cross. The content of α-zein and several cytoskeletal proteins was measured in high and low eEF1A inbred lines, and the levels of these proteins were found to correlate with that of eEF1A. To extend this analysis, we used an endosperm expressed sequence tag microarray to examine steady-state levels of RNA transcripts in developing endosperm of these genotypes. We identified about 120 genes coordinately regulated in association with eEF1A content. These genes encode proteins involved in several biological structures and processes, including the actin cytoskeleton, the endoplasmic reticulum, and the protein synthesis apparatus. Thus, higher levels of eEF1A in o2 mutants may be related to a more extensive cytoskeletal network surrounding the rough endoplasmic reticulum and increased synthesis of cytoskeleton-associated proteins, all of which contribute significantly to the Lys content of the endosperm.
Evolution and Function of the Sucrose-Phosphate Synthase Gene Families in Wheat and Other Grasses
Authors: Castleden C. Kate , Aoki Naohiro , Gillespie Vanessa J. , MacRae Elspeth A. , Quick W. Paul , Buchner Peter , Foyer Christine H. , Furbank Robert T. , Lunn John E.
Published: July 2004

Suc-phosphate synthase (SPS) is a key regulatory enzyme in the pathway of Suc biosynthesis and has been linked to quantitative trait loci controlling plant growth and yield. In dicotyledonous plants there are three SPS gene families: A, B, and C. Here we report the finding of five families of SPS genes in wheat (Triticum aestivum) and other monocotyledonous plants from the family Poaceae (grasses). Three of these form separate subfamilies within the previously described A, B, and C gene families, but the other two form a novel and distinctive D family, which on present evidence is only found in the Poaceae. The D-type SPS proteins lack the phosphorylation sites associated with 14-3-3 protein binding and osmotic stress activation, and the linker region between the N-terminal catalytic glucosyltransferase domain and the C-terminal Suc-phosphatase-like domain is 80 to 90 amino acid residues shorter than in the A, B, or C types. The D family appears to have arisen after the divergence of mono- and dicotyledonous plants, with a later duplication event resulting in the two D-type subfamilies. Each of the SPS gene families in wheat showed different, but overlapping, spatial and temporal expression patterns, and in most organs at least two different SPS genes are expressed. Analysis of expressed sequence tags indicated similar expression patterns to wheat for each SPS gene family in barley (Hordeum vulgare) but not in more distantly related grasses. We identified an expressed sequence tag from rice (Oryza sativa) that appears to be derived from an endogenous antisense SPS gene, and this might account for the apparently low level of expression of the related OsSPS11 sense gene, adding to the already extensive list of mechanisms for regulating the activity of SPS in plants.
Targeted Modification of Homogalacturonan by Transgenic Expression of a Fungal Polygalacturonase Alters Plant Growth
Authors: Capodicasa Cristina , Vairo Donatella , Zabotina Olga , McCartney Lesley , Caprari Claudio , Mattei Benedetta , Manfredini Cinzia , Aracri Benedetto , Benen Jacques , Knox J. Paul , De Lorenzo Giulia , Cervone Felice
Published: July 2004

Pectins are a highly complex family of cell wall polysaccharides comprised of homogalacturonan (HGA), rhamnogalacturonan I and rhamnogalacturonan II. We have specifically modified HGA in both tobacco (Nicotiana tabacum) and Arabidopsis by expressing the endopolygalacturonase II of Aspergillus niger (AnPGII). Cell walls of transgenic tobacco plants showed a 25% reduction in GalUA content as compared with the wild type and a reduced content of deesterified HGA as detected by antibody labeling. Neutral sugars remained unchanged apart from a slight increase of Rha, Ara, and Gal. Both transgenic tobacco and Arabidopsis were dwarfed, indicating that unesterified HGA is a critical factor for plant cell growth. The dwarf phenotypes were associated with AnPGII activity as demonstrated by the observation that the mutant phenotype of tobacco was completely reverted by crossing the dwarfed plants with plants expressing PGIP2, a strong inhibitor of AnPGII. The mutant phenotype in Arabidopsis did not appear when transformation was performed with a gene encoding AnPGII inactivated by site directed mutagenesis.
Role of Hsp17.4-CII as Coregulator and Cytoplasmic Retention Factor of Tomato Heat Stress Transcription Factor HsfA2
Authors: Port Markus , Tripp Joanna , Zielinski Dirk , Weber Christian , Heerklotz Dirk , Winkelhaus Sybille , Bublak Daniela , Scharf Klaus-Dieter
Published: July 2004

HsfA2 is a heat stress (hs)-induced Hsf in peruvian tomato (Lycopersicon peruvianum) and the cultivated form Lycopersicon esculentum. Due to the high activator potential and the continued accumulation during repeated cycles of heat stress and recovery, HsfA2 becomes a dominant Hsf in thermotolerant cells. The formation of heterooligomeric complexes with HsfA1 leads to nuclear retention and enhanced transcriptional activity of HsfA2. This effect seems to represent one part of potential molecular mechanisms involved in its activity control. As shown in this paper, the activity of HsfA2 is also controlled by a network of nucleocytoplasmic small Hsps influencing its solubility, intracellular localization and activator function. By yeast two-hybrid interaction and transient coexpression studies in tobacco (Nicotiana plumbaginifolia) mesophyll protoplasts, we found that tomato (Lycopersicon esculentum) Hsp17.4-CII acts as corepressor of HsfA2. Given appropriate conditions, both proteins together formed large cytosolic aggregates which could be solubilized in presence of class CI sHsps. However, independent of the formation of aggregates or of the nucleocytoplasmic distribution of HsfA2, its transcriptional activity was specifically repressed by interaction of Hsp17.4-CII with the C-terminal activator domain. Although not identical in all aspects, the situation with the highly expressed, heat stress-inducible Arabidopsis HsfA2 was found to be principally similar. In corresponding reporter assays its activity was repressed in presence of AtHsp17.7-CII but not of AtHsp17.6-CII or LpHsp17.4-CII.
Long Term Transcript Accumulation during the Development of Dehydration Adaptation in Cicer arietinum
Authors: Boominathan P. , Shukla Rakesh , Kumar Arun , Manna Dipak , Negi Divya , Verma Praveen K. , Chattopadhyay Debasis
Published: July 2004

Cool season crops face intermittent drought. Exposure to drought and other abiotic stresses is known to increase tolerance of the plants against subsequent exposure to such stresses. Storage of environmental signals is also proposed. Preexposure to a dehydration shock improved adaptive response during subsequent dehydration treatment in a cool season crop chickpea (Cicer arietinum). We have identified 101 dehydration-inducible transcripts of chickpea by repetitive rounds of cDNA subtraction; differential DNA-array hybridization followed by northern-blot analysis and analyzed their responses to exogenous application of abscisic acid (ABA). Steady-state expression levels of the dehydration-induced transcripts were monitored during the recovery period between 2 consecutive dehydration stresses. Seven of them maintained more than 3-fold of expression after 24 h and more than 2-fold of expression level even at 72 h after the removal of stress. Noticeably, all of them were inducible by exogenous ABA treatment. When the seedlings were subjected to recover similarly after an exposure to exogenous ABA, the steady-state abundances of 6 of them followed totally different kinetics returning to basal level expression within 24 h. This observation indicated a correlation between the longer period of abundance of those transcripts in the recovery period and improved adaptation of the plants to subsequent dehydration stress and suggested that both ABA-dependent and -independent mechanisms are involved in the maintenance of the messages from the previous stress experience.
Expression in Multigene Families. Analysis of Chloroplast and Mitochondrial Proteases
Authors: Sinvany-Villalobo Galit , Davydov Olga , Ben-Ari Giora , Zaltsman Adi , Raskind Alexander , Adam Zach
Published: July 2004

The proteolytic machinery of chloroplasts and mitochondria in Arabidopsis consists primarily of three families of ATP-dependent proteases, Clp, Lon, and FtsH, and one family of ATP-independent proteases, DegP. However, the functional significance of the multiplicity of their genes is not clear. To test whether expression of specific isomers could be differently affected by growth conditions, we analyzed transcript abundance following short-term exposure to different environmental stimuli, using 70-mer oligonucleotide arrays. This analysis revealed variability in the response to high light and different temperatures within members of each family. Thirty out of the 41 tested genes were up-regulated in response to high light, including both chloroplast and mitochondrial isozymes, whereas only six and five genes responded to either high or low temperature, respectively. The extent of response was variable, ranging from 2- to 20-fold increase in the steady-state levels. Absolute transcript levels of the tested genes, compiled from one-channel arrays, were also variable. In general, transcripts encoding mitochondrial isozymes were accumulated to a lower level than chloroplastic ones. Within the FtsH family, transcript abundance of most genes correlated with the severity of mutant phenotypes in the relevant genes. This correlation was also evident at the protein level. Analysis of FtsH isozymes revealed that FtsH2 was the most abundant species, followed by FtsH5 and 8, with FtsH1 being accumulated to only 10% of FtsH2 level. These results suggest that, unlike previous expectations, the relative importance of different chloroplast protease isozymes, evidenced by mutant phenotypes at least in the FtsH family, is determined by their abundance, and not necessarily by different specific functions or specialized expression under certain conditions.
Loss of Highly Branched Arabinans and Debranching of Rhamnogalacturonan I Accompany Loss of Firm Texture and Cell Separation during Prolonged Storage of Apple
Authors: Peña María J. , Carpita Nicholas C.
Published: July 2004

Growth and maturation of the edible cortical cells of apples (Malus domestica Borkh) are accompanied by a selective loss of pectin-associated (1→4)-β-d-galactan from the cell walls, whereas a selective loss of highly branched (1→5)-α-l-arabinans occurs after ripening and in advance of the loss of firm texture. The selective loss of highly branched arabinans occurs during the overripening of apples of four cultivars (Gala, Red Delicious, Firm Gold, and Gold Rush) that varied markedly in storage life, but, in all instances, the loss prestages the loss of firm texture, measured by both breaking strength and compression resistance. The unbranched (1→5)-linked arabinans remain associated with the major pectic polymer, rhamnogalacturonan I, and their content remains essentially unchanged during overripening. However, the degree of rhamnogalacturonan I branching at the rhamnosyl residues also decreases, but only after extensive loss of the highly branched arabinans. In contrast to the decrease in arabinan content, the loss of the rhamnogalacturonan I branching is tightly correlated with loss of firm texture in all cultivars, regardless of storage time. In vitro cell separation assays show that structural proteins, perhaps via their phenolic residues, and homogalacturonans also contribute to cell adhesion. Implications of these cell wall modifications in the mechanisms of apple cortex textural changes and cell separation are discussed.
The Biosynthesis of d-Galacturonate in Plants. Functional Cloning and Characterization of a Membrane-Anchored UDP-d-Glucuronate 4-Epimerase from Arabidopsis
Authors: Mølhøj Michael , Verma Rajeev , Reiter Wolf-Dieter
Published: July 2004

Pectic cell wall polysaccharides owe their high negative charge to the presence of d-galacturonate, a monosaccharide that appears to be present only in plants and some prokaryotes. UDP-d-galacturonate, the activated form of this sugar, is known to be formed by the 4-epimerization of UDP-d-glucuronate; however, no coding regions for the epimerase catalyzing this reaction have previously been described in plants. To better understand the mechanisms by which precursors for pectin synthesis are produced, we used a bioinformatics approach to identify and functionally express a UDP-d-glucuronate 4-epimerase (GAE1) from Arabidopsis. GAE1 is predicted to be a type II membrane protein that belongs to the family of short-chain dehydrogenases/reductases. The recombinant enzyme expressed in Pichia pastoris established a 1.3:1 equilibrium between UDP-d-galacturonate and UDP-d-glucuronate but did not epimerize UDP-d-Glc or UDP-d-Xyl. Enzyme assays on cell extracts localized total UDP-d-glucuronate 4-epimerase and recombinant GAE1 activity exclusively to the microsomal fractions of Arabidopsis and Pichia, respectively. GAE1 had a pH optimum of 7.6 and an apparent K  m of 0.19 mm. The recombinant enzyme was strongly inhibited by UDP-d-Xyl but not by UDP, UDP-d-Glc, or UDP-d-Gal. Analysis of Arabidopsis plants transformed with a GAE1:GUS construct showed expression in all tissues. The Arabidopsis genome contains five GAE1 paralogs, all of which are transcribed and predicted to contain a membrane anchor. This suggests that all of these enzymes are targeted to an endomembrane system such as the Golgi where they may provide UDP-d-galacturonate to glycosyltransferases in pectin synthesis.
RNAi-Mediated Tocopherol Deficiency Impairs Photoassimilate Export in Transgenic Potato Plants
Authors: Hofius Daniel , Hajirezaei Mohammad-Reza , Geiger Michael , Tschiersch Henning , Melzer Michael , Sonnewald Uwe
Published: July 2004

Tocopherols (vitamin E) are lipophilic antioxidants presumed to play a key role in protecting chloroplast membranes and the photosynthetic apparatus from photooxidative damage. Additional nonantioxidant functions of tocopherols have been proposed after the recent finding that the Suc export defective1 maize (Zea mays) mutant (sxd1) carries a defect in tocopherol cyclase (TC) and thus is devoid of tocopherols. However, the corresponding vitamin E deficient1 Arabidopsis mutant (vte1) lacks a phenotype analogous to sxd1, suggesting differences in tocopherol function between C4 and C3 plants. Therefore, in this study, the potato (Solanum tuberosum) ortholog of SXD1 was isolated and functionally characterized. StSXD1 encoded a protein with high TC activity in vitro, and chloroplastic localization was demonstrated by transient expression of green fluorescent protein-tagged fusion constructs. RNAi-mediated silencing of StSXD1 in transgenic potato plants resulted in the disruption of TC activity and severe tocopherol deficiency similar to the orthologous sxd1 and vte1 mutants. The nearly complete absence of tocopherols caused a characteristic photoassimilate export-defective phenotype comparable to sxd1, which appeared to be a consequence of vascular-specific callose deposition observed in source leaves. CO2 assimilation rates and photosynthetic gene expression were decreased in source leaves in close correlation with excess sugar accumulation, suggesting a carbohydrate-mediated feedback inhibition rather than a direct impact of tocopherol deficiency on photosynthetic capacity. This conclusion is further supported by an increased photosynthetic capacity of young leaves regardless of decreased tocopherol levels. Our data provide evidence that tocopherol deficiency leads to impaired photoassimilate export from source leaves in both monocot and dicot plant species and suggest significant differences among C3 plants in response to tocopherol reduction.
Cloning and Functional Characterization of a Phospholipid:Diacylglycerol Acyltransferase from Arabidopsis
Authors: Ståhl Ulf , Carlsson Anders S. , Lenman Marit , Dahlqvist Anders , Huang Bangquan , Banaś Walentyna , Banaś Antoni , Stymne Sten
Published: July 2004

A new pathway for triacylglycerol biosynthesis involving a phospholipid:diacylglycerol acyltransferase (PDAT) was recently described (Dahlqvist A, Stahl U, Lenman M, Banas A, Lee M, Sandager L, Ronne H, Stymne S, [2000] Proc Natl Acad Sci USA 97: 6487–6492). The LRO1 gene that encodes the PDAT was identified in yeast (Saccharomyces cerevisiae) and shown to have homology with animal lecithin:cholesterol acyltransferase. A search of the Arabidopsis genome database identified the protein encoded by the At5g13640 gene as the closest homolog to the yeast PDAT (28% amino acid identity). The cDNA of At5g13640 (AtPDAT gene) was overexpressed in Arabidopsis behind the cauliflower mosaic virus promoter. Microsomal preparations of roots and leaves from overexpressers had PDAT activities that correlated with expression levels of the gene, thus demonstrating that this gene encoded PDAT (AtPDAT). The AtPDAT utilized different phospholipids as acyl donor and accepted acyl groups ranging from C10 to C22. The rate of activity was highly dependent on acyl composition with highest activities for acyl groups containing several double bonds, epoxy, or hydroxy groups. The enzyme utilized both sn-positions of phosphatidylcholine but had a 3-fold preference for the sn-2 position. The fatty acid and lipid composition as well as the amounts of lipids per fresh weight in Arabidopsis plants overexpressing AtPDAT were not significantly different from the wild type. Microsomal preparations of roots from a T-DNA insertion mutant in the AtPDAT gene had barely detectable capacity to transfer acyl groups from phospholipids to added diacylglycerols. However, these microsomes were still able to carry out triacylglycerol synthesis by a diacylglycerol:diacylglycerol acyltransferase reaction at the same rate as microsomal preparations from wild type.
Strategies for accommodating individuals’ styles and preferences in flexible learning programmes
Authors: Sadler‐Smith Eugene , J. Smith Peter
Published: July 2004

There has been a considerable growth in the use of flexible methods of delivery for workplace learning and development. However, in designing programmes of flexible learning there is often the assumption that learners will exhibit uniformity in the ways in which they process and organise information (cognitive style), in their predispositions towards particular learning formats and media (instructional preferences) and the conscious actions they employ to deal with the demands of specific learning situations (learning strategies). In adopting such a stance one runs the risk of ignoring important aspects of individual differences in styles, preferences and strategies. Our purpose in this paper will be to: (i) consider some aspects of individual difference that are pertinent to the delivery of flexible learning in the workplace; (ii) identify some of the challenges that extant differences in styles and preferences between individuals  may  raise  for  instructional  designers  and  learning  facilitators;  (iii)  suggest  ways  in  which  models  of  flexible  learning  design  and  delivery may acknowledge and accommodate individual differences in styles and preferences through the use of an appropriate range of instructional design, learning and support strategies.
Non‐linear instructional design model: eternal, synergistic design and development
Authors: Crawford Caroline
Published: July 2004

Instructional design is at the heart of each educational endeavour. This process revolves around the steps through which the thoughtful productions of superior products are created. The ADDIE generic instructional design model emphasises five basic steps within the instructional design process: analyse, design, develop, implement and evaluate. The simplistic nature of the ADDIE model, including the ease of application and possibilities towards the cyclical features of the process, enable a more holistic overview of the instructional design process. The Eternal, Synergistic Design Model emphasises the non‐linear nature of the instructional design process. The continuous design and development focuses upon the core evaluation of the product, wherein the Pareto principle emphasises the feedback related to the 20% of difficulties while maintaining an eye upon the 80% neutral and positive aspects of the product.
Recognising and promoting collaboration in an online asynchronous discussion
Authors: Murphy Elizabeth
Published: July 2004

This paper reports on a study involving the identification and measurement of collaboration in an online asynchronous discussion (OAD). A conceptual framework served for the development of a model which conceptualises collaboration on a continuum of processes that move from social presence to production of an artefact. From this model, a preliminary instrument with six processes was developed. Through application of the instrument to an OAD, the instrument was further developed with indicators added for each process. Use of the instrument to analyse an OAD showed that it is effective for gaining insight into collaborative processes in which discussants in an OAD do or do not engage. Use of the instrument in other contexts would test and potentially strengthen its reliability and provide further insight into the collaborative processes in which individuals engage in OADs. Analysis of an OAD using the instrument revealed that participants engaged primarily in processes related to social presence and articulating individual perspectives, and did not reach a stage of sharing goals and producing shared artefacts. The results suggest that the higher‐level processes related to collaboration in an OAD may need to be more explicitly and effectively promoted in order to counteract a tendency on the part of participants to remain at the level of individual rather than group or collaborative effort.
Learning productivity: a case analysis of the ‘e‐BOSNO’ course for manager teams
Authors: Winnips Koos , Collis Betty
Published: July 2004

Action learning in a workplace context, focused on projects relating to real business needs, is the basis of the management seminars offered by the BOSNO (in Dutch, ‘BedrijfsOpleiding voor Samenwerkende Nederlandse Ondernemingen’[Company training for Dutch companies working in cooperation with each other]) consortium in The Netherlands. In the seminars, managers from participating companies work in teams on multiple‐step problem analysis and solution strategies, supported by workplace coaches. The teams also interact with each other so that peer learning is stimulated. To extend the BOSNO management seminar model in both depth and flexibility, a new approach called e‐BOSNO was designed in which a web‐based learning support environment played a critical role. This paper describes the e‐BOSNO design process and gives results from the first cycle of e‐BOSNO. The results showed the participants to be much more active and interactive than in previous e‐BOSNO seminars, even though there were fewer face‐to‐face meetings. Workplace‐oriented learning occurred and was shared in a way which makes it available for reuse in subsequent e‐BOSNO seminars.
Developing critical thinking skills in computer‐aided extended reading classes
Authors: Daud Nuraihan Mat , Husin Zamnah
Published: July 2004

One of the skills that can be taught in an English proficiency class that adopts literary texts for teaching the language is critical thinking. The background, characters and their motives are among those that invite critical inquiry and interpretation. Although it has been claimed that discussing literary texts in the traditional way can help develop students’ critical thinking skills, it is yet to be proved whether the use of a teaching aid can help the process. This study is, therefore, carried out to see if the use of computer software can help to develop such skills. It specifically looks at the potential of a literary text,Othello, and a concordancer in developing and enhancing critical thinking abilities of 40 English as a Second Language (ESL) students at the International Islamic University Malaysia. An experimental study was carried out, where an experimental group was exposed to text analysis using a concordancer whilst the control group analysed the text manually. The Cornell Critical Thinking Test was used to analyse the critical thinking ability of the students. The experimental group outperformed the control group in all the subscales measured, but the percentage of variance in the scores was low.
Phenotypic plasticity in pigmentation in Daphnia induced by UV radiation and fish kairomones
Authors: TOLLRIAN R. , HEIBL C.
Published: July 2004

Planktonic organisms are exposed to harmful ultraviolet (UV) radiation. Pigmentation offers protection but at the same time increases visibility, and therefore vulnerability, to visually orienting predators such as fish. As an adaptation against fish predation, zooplankton should be transparent, though this would leave them less protected against UV radiation. Thus both adaptations would appear to be mutually exclusive. However, phenotypic plasticity in pigmentation could allow flexible adaptation to both environmental situations.

We tested the hypothesis that Daphnia should be able to change their level of pigmentation in response to fish kairomone and/or UV radiation using four species of Daphnia.

Daphnia hyalina Leydig increased pigmentation under UV radiation and D. pulex Leydig reduced pigmentation in the fish kairomone treatment. Both species live in habitats with variable UV and fish impact.

Daphnia cucullata Sars and D. middendorffiana Fischer showed no reaction, probably because of their extreme adaptations: D. middendorffiana is strongly pigmented and seems to be adapted to high UV‐B impact and an absence of fish in its arctic habitat. In contrast, D. cucullata has evolved in coexistence with fish. It can afford being nearly transparent because it lives in eutrophic lakes where UV‐B is not relevant.

Our data on four species suggest that plasticity in pigmentation might be common in Daphnia adapted to environments with contrasting or variable selection pressures.