bluuebunny/crossref_metadata_2025_split huggingface dataset:
Correlation of defense gene induction defects with powdery mildew susceptibility inArabidopsisenhanced disease susceptibility mutants
Authors: Reuber T. Lynne , Plotnikova Julia M. , Dewdney Julia , Rogers Elizabeth E. , Wood William , Ausubel Frederick M. 
Published: March 2003

Summary We investigated the relative importance of specific

Arabidopsis thaliana

genes in conferring resistance to bacterial versus fungal pathogens. We first developed a pathosystem involving the infection of

Arabidopsis

accession Columbia with a virulent isolate of the obligate biotrophic fungal pathogen

Erysiphe orontii. E. orontii

elicited the accumulation of mRNAs corresponding to the defense‐related genes

PR1, BGL2 (PR2), PR5 and GST1

, but did not elicit production of the phytoalexin camalexin or the accumulation of defensin (

PDF1.2

) or thionin (

THI2.1

) mRNAs. We tested a set of 15 previously isolated

Arabidopsis

phytoalexin deficient

(pad),

non‐expresser of

PR (npr) and

enhanced disease susceptibility

(eds)

mutants that are more susceptible to

Pseudomonas syringae

for their susceptibility to

E. orontii.

Four of these mutants (

pad4–1, npr1–1, eds5–1 and

a double

npr1–1 eds5–1

mutant) as well as

Arabidopsis

lines carrying a

nahG

transgene exhibited enhanced susceptibility to

E. orontii

and reduced levels of

PR

gene expression

.

Comparison of the

PR

gene induction patterns in response to

E. orontii

in the various mutants and in the

nahG

transgenics suggests the existence of

NPR1

‐independent salicylate‐dependent and

NPR1

‐independent salicylate‐independent defense gene activation pathways. Eleven other

eds

and

pad

mutants did not show measurable enhanced susceptibility to

E. orontii

, suggesting that these mutants are defective in factors that are not important for the limitation of

E. orontii

growth.
High pressure freezing and freeze substitution reveal new aspects of fine structure and maintain protein antigenicity in barley aleurone cells
Authors: Lonsdale Jennifer E. , McDonald Kent L. , Jones Russell L. 
Published: March 2003

Summary High pressure freezing and freeze substitution (HPF‐FS) were used to prepare barley (

Hordeum vulgare

L. cv Himalaya) aleurone protoplasts for transmission electron microscopy (TEM). We show that HPF‐FS is superior to conventional chemical fixation and dehydration techniques for the preservation of cellular fine structure and antigenicity of proteins in barley aleurone protoplasts. HPF‐FS extracted fewer proteins from the cytosol and organelles of aleurone protoplasts and maintained the details of cellular structure. The cortical cytoskeleton, made up of microtubules, was observed for the first time by TEM in barley aleurone protoplasts prepared by HPF‐FS. Organelles such as protein storage vacuoles retained their proteinaceous contents, and other cellular organelles (including the Golgi apparatus, the nucleus and mitochondria) were also well preserved in protoplasts fixed by HPF‐FS. Antibodies to the vacuolar enzyme nuclease I, the tonoplast aquaporin α‐TIP and the glyoxysomal enzyme malate synthase showed that the antigenicity of organellar enzymes and membrane proteins was preserved in cells prepared by HPF‐FS. We conclude that HPF‐FS is superior to chemical fixation for the preparation of plant protoplasts for TEM and is the method of choice for the preservation of aleurone protoplasts for structural and immunochemical studies.
Analysis of alternative transcripts of the flaxL6rust resistance gene
Authors: Ayliffe Michael A. , Frost Donna V. , Finnegan E. Jean , Lawrence Gregory J. , Anderson Peter A. , Ellis Jeffery G. 
Published: March 2003

Summary The

L6

rust resistance gene from flax generates at least four transcript classes by alternative splicing of the third intron. The most abundant transcript class encodes a resistance protein containing domains that include nucleotide binding site motifs and a leucine‐rich repeat region (NBS‐LRR). The remaining three transcript classes encode truncated products which lack most of the C‐terminal part of the protein containing the leucine‐rich region (LRR). The four transcript classes occur in all plant organs examined and no induction of

L6

expression was observed following infection of resistant plants with an avirulent rust strain expressing the corresponding

A‐L6

avirulence gene. Flax plants transgenic for an intronless

L6

gene, incapable of encoding truncated resistance proteins by alternative splicing, expressed

L6

resistance indistiguishable from that of the wild‐type gene. Therefore, a definitive role for alternative transcripts and their predicted truncated products could not be assigned in the flax/flax rust system.
Mutations at therug4locus alter the carbon and nitrogen metabolism of pea plants through an effect on sucrose synthase
Authors: Craig Josephine , Barratt Paul , Tatge Helma , Déjardin Annabelle , Handley Linda , Gardner Christopher D. , Barber Lorraine , Wang Trevor , Hedley Cliff , Martin Cathie , Smith Alison M. 
Published: March 2003

Summary The biochemical and molecular basis of the wrinkled‐seeded phenotype of

rug4

mutants of pea (

Pisum sativum

L.) has been investigated. Mutant embryos have reduced starch contents and only 5% of the sucrose synthase activity of wild‐type embryos during development. Activities of other enzymes involved in the conversion of sucrose to starch are unaffected. A gene encoding an isoform of sucrose synthase expressed in the embryo co‐segregates with the

rug4

locus, and one of the three mutant alleles has been show to carry a point mutation in this gene that converts a highly conserved arginine residue to a lysine residue. It is highly likely that the reduced starch content of the mutant embryo is a direct consequence of the loss of sucrose synthase activity. The mutations reduce the activity of sucrose synthase in the testa and the leaf by 50% or less, but activity in

Rhizobium

‐infected root nodules is reduced by 85%. Although the nodules of mutant plants contain metabolically active bacteroids, the N content and δ15N values of these plants in the field indicate that, unlike wild‐type plants, they derive little of their N from N2 fixation via

Rhizobium

. Sucrose synthase thus appears to be essential for the supply of carbon for bacteroid metabolism and/or ammonia assimilation during nitrogen assimilation.
Glyoxalase I fromBrassica juncea: molecular cloning, regulation and its over‐expression confer tolerance in transgenic tobacco under stress
Authors: Veena  , Reddy Vanga S. , Sopory Sudhir K. 
Published: March 2003

Summary Despite its ubiquitous presence, the role of glyoxalase I has not been well investigated in plants. In order to find out its physiological functions, we have cloned and characterized a cDNA from

Brassica juncea

encoding glyoxalase I (

Gly I

) and made transgenic tobacco plants harbouring

Gly I

in both sense and antisense orientation. The transgenic nature of the plants was confirmed by Southern blotting, and the estimated number of genes inserted ranged from one to six. The transcript and protein levels of glyoxalase I were also monitored in transgenic plants. The expression of glyoxalase I in

B. juncea

was upregulated in response to salt, water and heavy metal stresses. In response to a high concentration of salt, the transcript level averaged threefold higher in 72 h, and an increase in the protein was also seen by immunoblotting. The transgenic plants over‐expressing glyoxalase I showed significant tolerance to methylglyoxal and high salt, as tested in detached leaf disc senescence assay. A comparison of plants expressing high and low levels of glyoxalase I showed that the tolerance to different salt concentrations was correlated with the degree of glyoxalase I expression. Our results suggest an important role of glyoxalase I in conferring tolerance to plants under stress conditions.
Green fluorescent protein as a marker to investigate targeting of organellar RNA polymerases of higher plantsin vivo
Authors: Hedtke Boris , Meixner Martin , Gillandt Sabine , Richter Ekkehard , Börner Thomas , Weihe Andreas 
Published: March 2003

Summary The recent identification of phage‐type RNA polymerases encoded in the nuclear genome of higher plants has provided circumstantial evidence for functioning of these polymerases in the transcription of the mitochondrial and plastid genomes, as demonstrated by sequence analysis and
in vitro
import experiments. To determine the subcellular localization of the phage‐type organellar RNA polymerases
in planta
, the putative transit peptides of the RNA polymerases RpoT;1 and RpoT;3 from
Arabidopsis thaliana
and RpoT from
Chenopodium album
were fused to the coding sequence of a green fluorescent protein (GFP). The constructs were used to stably transform
A. thaliana
. Transgenic plants were examined for green fluorescence with epifluorescence and confocal laser scanning microscopy. Plants expressing the GFP fusions under control of the CaMV35S promoter exhibited a distinct subcellular localization of the GFP fluorescence for each of the fusion constructs. In plants expressing GFP fusions with the putative transit peptides of ARAth;RpoT;1 and CHEal;RpoT, fluorescence was found exclusively in mitochondria, both in root and leaf cells. In contrast, GFP fluorescence in plants expressing the ARAth;RpoT;3‐GFP construct accumulated in chloroplasts of leaf cells and non‐green plastids (leucoplasts) of root cells. By demonstrating targeting
in planta
, the data add substantial evidence for the phage‐type RNA polymerases from
C. album
and
A. thaliana
to function in the transcriptional machinery of mitochondria and plastids.
Transporters for ammonium, amino acids and peptides are expressed in pitchers of the carnivorous plantNepenthes
Authors: Schulze Waltraud , Frommer Wolf B. , Ward John M. 
Published: March 2003

Summary Insect capture and digestion contribute substantially to the nitrogen budget of carnivorous plants. In
Nepenthes
, insect‐derived nitrogenous compounds are imported from the pitcher fluid and transported throughout the plant via the vascular tissue to support growth. Import and distribution of nutrients may require transmembrane nitrogen transporters. Representatives of three classes of genes encoding transporters for the nitrogenous compounds ammonium, amino acids and peptides were identified in
Nepenthes
pitchers. The expression at the cellular level of an ammonium transporter gene, three amino acid transporter genes, and one peptide transporter gene were investigated in the insect trapping organs of
Nepenthes
. Expression of the ammonium transporter gene
NaAMT1
was detected in the head cells of digestive glands in the lower part of the pitcher where NaAMT1 may function in ammonium uptake from the pitcher fluid. One amino acid transporter gene,
NaAAP1
, was expressed in bundle sheath cells surrounding the vascular tissue. To understand the locations where transmembrane transport could be required within the pitcher, symplasmic and apoplasmic continuity was probed using fluorescent dyes. Symplasmic connections were not found between cortical cells and vascular bundles. Therefore, the amino acid transporter encoded by
NaAAP1
may be involved in transport of amino acids into the vascular tissue. In contrast, expression of the peptide transporter gene
NaNTR1
was detected in phloem cells of the vascular tissue within pitchers. NaNTR1 may function in the export of nitrogen from the pitcher by loading peptides into the phloem.
Microtubules regulate tip growth and orientation in root hairs ofArabidopsis thaliana
Authors: Bibikova Tatiana N. , Blancaflor Elison B. , Gilroy Simon 
Published: March 2003

Summary The polarized growth of cells as diverse as fungal hyphae, pollen tubes, algal rhizoids and root hairs is characterized by a highly localized regulation of cell expansion confined to the growing tip. In apically growing plant cells, a tip‐focused [Ca2+]c gradient and the cytoskeleton have been associated with growth. Although actin has been established to be essential for the maintenance of elongation, the role of microtubules remains unclear. To address whether the microtubule cytoskeleton is involved in root hair growth and orientation, we applied microtubule antagonists to root hairs of
Arabidopsis
. In this report, we show that depolymerizing or stabilizing the microtubule cytoskeleton of these apically growing root hairs led to a loss of directionality of growth and the formation of multiple, independent growth points in a single root hair. Each growing point contained a tip‐focused gradient of [Ca2+]c. Experimental generation of a new [Ca2+]c gradient in root hairs pre‐treated with microtubule antagonists, using the caged‐calcium ionophore Br‐A23187, was capable of inducing the formation of a new growth point at the site of elevated calcium influx. These data indicate a role for microtubules in regulating the directionality and stability of apical growth in root hairs. In addition, these results suggest that the action of the microtubules may be mediated through interactions with the cellular machinery that maintains the [Ca2+]c gradient at the tip.
Sucrose transport into developing seeds of Pisum sativum L.
Authors: Tegeder Mechthild , Wang Xin‐Ding , Frommer Wolf B.. , Offler Christina E.. , Patrick John W.. 
Published: March 2003

SummaryThe anatomy of developing pea seeds is characterized by transfer cells present in both coats and cotyledons at the maternal/filial interface. To determine the nature and cellular localization of sucrose transporters in pea seeds, a full‐length clone of a sucrose/H+ symporter ( PsSUT1) was isolated from a cotyledon cDNA library. Northern blot analyses of different organs showed that PsSUT1 is expressed in non‐seed tissues, including sucrose sinks and sources. Within developing seeds, transcripts of PsSUT1 and PsAHA1 genes were detected in all tissues, while transcripts of a sucrose binding protein ( GmSBP) were confined to cotyledon epidermal transfer cells. Signal intensities of PsSUT1 and PsAHA1 transcripts and protein products were most pronounced in the thin‐walled parenchyma cells of seed coats and epidermal transfer cells of cotyledons. For cotyledons, the highest transporter densities were localized to those portions of plasma membranes lining the wall ingrowth regions of epidermal transfer cells. Responses of [14C]sucrose influx to metabolic inhibitors indicated that proton‐coupled sucrose transport was operative in both seed coats and cotyledons. Cotyledon epidermal transfer cells were shown to support the highest sucrose flux. Maximal transport activity was found to account for the sucrose flux differences between seed tissues. Intercellular movement of the symplasmic tracer, 5‐(6)‐carboxyfluorescein (CF), demonstrated that symplasmic pathways interconnect the vascular tissues to thin‐walled parenchyma transfer cells of seed coats and, for cotyledons, epidermal transfer cells to storage parenchyma cells.
BELL1 and AGAMOUS genes promote ovule identity in Arabidopsis thaliana
Authors: Western Tamara L. , Haughn George W. 
Published: March 2003

SummaryMolecular and genetic analyses have demonstrated that the Arabidopsis thaliana gene BELL1 (BEL1) is required for proper morphogenesis of the ovule integuments. Several lines of evidence suggest that BEL1 may act, at least in part, to repress the function of the organ identity gene AGAMOUS (AG) during ovule development. To study the relative roles of BEL1 and AG, plants homozygous for ag, bel1 or both were constructed in an ap2 mutant background where ovules form even in the absence of AG function. The loss of either BEL1 or AG led to a decrease in the number of mature ovules, accompanied by an increase in primordial outgrowths. These data suggest that BEL1 and AG gene products act early in ovule development in a partially redundant manner to direct ovule identity. Development of the abnormal integuments characteristic of the Bel1– mutant phenotype was found to be dependent on AG function. Finally, BEL1 appears to be required for embryo sac development independent of both other aspects of ovule morphogenesis and AG function. This study therefore suggests that both BEL1 and AG are required for several distinct aspects of ovule morphogenesis.
Interactions between introns via exon definition in plant pre‐mRNA splicing
Authors: Simpson Craig G. , Clark Gillian P. , Lyon Jackie M. , Watters Jenny , McQuade Clare , Brown John W. S. 
Published: March 2003

SummaryExon definition is a mechanism whereby splice sites are selected initially via interactions between splicing factors across an exon, prior to spliceosome assembly and intron removal. It occurs in the splicing of vertebrate pre‐mRNAs and, recently, evidence for exon definition and the role of exon sequences has been obtained in plant intron splicing. Here we demonstrate that interactions between plant introns influence splicing efficiency and that these interactions are consistent with an exon definition process. The splicing efficiency of a UA‐poor, inefficiently spliced intron (wheat amylase) increases 3.5‐ to 4.4‐fold when placed in tandem with a UA‐rich, well spliced, intron (legumin). Enhanced splicing is also observed with partial pea legumin intron sequences. However, mutation of splice sites in the partial UA‐rich intron sequences abolished the enhanced splicing effect such that intact splice sites at the 5′ and 3′ ends of the exon were required, thus pointing to exon definition. This was further supported by reducing the size of the intervening exon or replacing with a UA‐rich sequence which leads to loss of splicing of the UA‐poor intron. Finally, the results support UA‐rich sequences functioning early in the splicing process in plants.
A simple method to enrich an Agrobacterium‐transformed population for plants containing only T‐DNA sequences
Authors: Hanson Bill , Engler Dean , Moy York , Newman Bob , Ralston Ed , Gutterson Neal 
Published: March 2003

SummaryA simple modification to standard binary vector design has been utilized to enrich an Agrobacterium‐transformed population for plants containing only T‐DNA sequences. A lethal gene was incorporated into the non‐T‐DNA portion of a binary vector, along with a screenable marker. The resulting class of vectors is designated as NTL T‐DNA vectors (non‐T‐DNA lethal gene‐containing T‐DNA vectors). The lethal gene used here is a CaMV 35S‐barnase gene with an intron in the coding sequence (barnase‐INT); the screenable marker is a pMAS‐luciferase gene with an intron in the coding sequence (LUC‐int). To evaluate the utility of this vector design, tobacco plants were transformed with either the NTL T‐DNA vector or a control vector from which most of the barnase‐INT gene was deleted. Populations of 50 transgenic plants were scored for LUC expression. The results indicated a dramatic reduction in the presence of non‐T‐DNA sequences in the transgenic population using the NTL T‐DNA vector. Only one transgenic plant was found to be LUC+ using the NTL vector, compared with 42 of 50 plants using the control vector. Importantly, the efficiency with which transformed tobacco plants was obtained was reduced by no more than 30%. The reduction in LUC+ transgenics was partially reversed when a barstar‐expressing tobacco line was trans‐ formed, indicating that barnase expression was responsible for the reduced frequency of incorporating non‐T‐DNA sequences. Similar transformation results were obtained with tomato and grape. The incorporation of a barnase‐INT gene outside the left border appears to provide a generally applicable tool for enriching an Agrobacterium‐transformed population for plants con‐ taining only T‐DNA sequences.
The RCN1‐encoded A subunit of protein phosphatase 2A increases phosphatase activity in vivo
Authors: Deruère Jean , Jackson Karin , Garbers Christine , Söll Dieter , DeLong Alison 
Published: March 2003

SummaryProtein phosphatase 2A (PP2A), a heterotrimeric serine/threonine‐specific protein phosphatase, comprises a catalytic C subunit and two distinct regulatory subunits, A and B. TheRCN1gene encodes one of three A regulatory subunits inArabidopsis thaliana. A T‐DNA insertion mutation at this locus impairs root curling, seedling organ elongation and apical hypocotyl hook formation. We have usedin vivoandin vitroassays to gauge the impact of thercn1mutation on PP2A activity in seedlings. PP2A activity is decreased in extracts fromrcn1mutant seedlings, and this decrease is not due to a reduction in catalytic subunit expression. Roots of mutant seedlings exhibit increased sensitivity to the phosphatase inhibitors okadaic acid and cantharidin in organ elongation assays. Shoots of dark‐grown, but not light‐grown seedlings also show increased inhibitor sensitivity. Furthermore, cantharidin treatment of wild‐type seedlings mimics thercn1defect in root curling, root waving and hypocotyl hook formation assays. In roots of wild‐type seedlings,RCN1mRNA is expressed at high levels in root tips, and accumulates to lower levels in the pericycle and lateral root primordia. In shoots,RCN1is expressed in the apical hook and the basal, rapidly elongating cells in etiolated hypocotyls, and in the shoot meristem and leaf primordia of light‐grown seedlings. Our results show that the wild‐typeRCN1‐encoded A subunit functions as a positive regulator of the PP2A holoenzyme, increasing activity towards substrates involved in organ elongation and differential cell elongation responses such as root curling.
Subcellular localization of ozone‐induced hydrogen peroxide production in birch (Betula pendula) leaf cells
Authors: Pellinen Riikka , Palva Tapio , Kangasjärvi Jaakko 
Published: March 2003

SummaryThe atmospheric air pollutant ozone (O3) is one of the environmental stresses that induce formation of reactive oxygen species (ROS) in plants. Previously, the toxicity of O3 has been believed to be a result of ROS formation from O3‐degradation. Recently, however, it has been shown that O3 induces active ROS production, which suggests that O3‐responses may be mechanistically similar to pathogen‐induced responses and that O3‐damage could be a result of deleterious firing by the ROS of pathways normally associated with the HR. The subcellular localization of O3‐induced H2O2 production was studied in birch (Betula pendula). O3 induced H2O2 accumulation first on the plasma membrane and cell wall. Experiments with inhibitors of possible sources for H2O2 in the cell wall suggested that both NADPH‐dependent superoxide synthase and the cell wall peroxidases are involved in this H2O2 production. The H2O2 production continued in the cytoplasm, mitochondria and peroxisomes when the O3‐exposure was over, but not in chloroplasts. The timing of mitochondrial H2O2 accumulation coincided with the first symptoms of visible damage and, at the same time, the mitochondria showed disintegration of the matrix. These responses may not be directly connected with defense against oxidative stress, but may rather indicate changes in oxidative balance within the cells that affect mitochondrial metabolism and the homeostasis of the whole cell, possibly leading into induction of programmed cell death.