Biomedical subjects

J P Geiger

Publications and source records attributed to J P Geiger.

At least 19 recordsLinked to original sources

PubMed2003

Activity of class III peroxidases in the defense of cotton to bacterial blight.

Cotton cotyledons displayed a hypersensitive reaction (HR) in the cultivar Réba B50 after infiltration with the avirulent race 18 from Xanthomonas campestris pv. malvacearum. Two sets of peroxidases were associated with the HR time course. Early but transient accumulation of peroxidase in material encapsulating the bacteria in intercellular areas was observed by immunocytochemistry at 3 h postinfection and coincided with the oxidative burst. Total guaiacol-peroxidase activity was highly increased in cells undergoing HR, from 12 h after treatment. Molecular characterization of seven cloned peroxidase genes revealed highly conserved B, D, and F domains, with similarities to plant class III peroxidases. Analysis of gene expression showed variation in transcript accumulation during both compatible (race 20) and incompatible interactions for four of these genes: pod2, pod3, pod4, and pod6. Pod4 and pod6 were more intensely up-regulated during resistance than during disease and in the control, while pod3 was specifically down-regulated during the HR after the oxidative burst. Pod2 was induced by pathogen infection and weakly stimulated in the control. These data suggest that cotton peroxidases may have various functions in the defense response to Xanthomonas infections.

Amino Acid Sequence↗

PubMed2002

Lipid peroxidation in cotton: Xanthomonas interactions and the role of lipoxygenases during the hypersensitive reaction.

Lipid peroxidation, often associated with hypersensitive cell death, may be initiated either by active oxygen species (AOS) or lipoxygenases (LOX). Here we report a detailed analysis of this oxidative process in both incompatible and compatible interactions between the cotton cultivar Reba B50 and Xanthomonas campestris pv. malvacearum (Xcm). The hypersensitive reaction (HR) was characterized by a massive production of polyunsaturated fatty acid (PUFA) hydroperoxides together with typical tissue dehydration. Among these, isomers peroxidized on carbon 9, largely predominant, were chiral, showing an excess in the S enantiomer. The HR process was accompanied by an increase in 9S-LOX activity and preceded by transcription of a LOX gene (GhKLox1). These results showed that: (i) AOS produced during the oxidative burst were not involved in PUFA peroxidation during HR; and (ii) as previously described in elicited leaves of tobacco, the massive enzymatic lipid peroxidation was closely associated with hypersensitive cell death. During disease development in this cotton cultivar, the 9-lipoxygenation of PUFAs was late, weak, preceded by a faint accumulation of GhKLox1 transcripts, and associated with chlorosis but not with necrosis. Consequently, the main difference between incompatible and compatible interactions was in the precocity and intensity of the oxidative process, rather than in its nature. These data provide the evidence for a correlation between lipid peroxidation and hypersensitive cell death induced by pathogens.

Apoptosis↗

PubMed2000

Salicylic acid mediated by the oxidative burst is a key molecule in local and systemic responses of cotton challenged by an avirulent race of Xanthomonas campestris pv malvacearum.

We analyzed the production of reactive oxygen species, the accumulation of salicylic acid (SA), and peroxidase activity during the incompatible interaction between cotyledons of the cotton (Gossypium hirsutum) cv Reba B50/Xanthomonas campestris pv malvacearum (Xcm) race 18. SA was detected in petioles of cotyledons 6 h after infection and 24 h post inoculation in cotyledons and untreated leaves. The first peak of SA occurred 3 h after generation of superoxide (O(2)(.-)), and was inhibited by infiltration of catalase. Peroxidase activity and accumulation of SA increased in petioles of cotyledons and leaves following H(2)O(2) infiltration of cotyledons from 0.85 to 1 mM. Infiltration of 2 mM SA increased peroxidase activity in treated cotyledons and in the first leaves, but most of the infiltrated SA was rapidly conjugated within the cotyledons. When increasing concentrations of SA were infiltrated 2. 5 h post inoculation at the beginning of the oxidative burst, the activity of the apoplastic cationic O(2)(.-)-generating peroxidase decreased in a dose-dependent manner. We have shown that during the cotton hypersensitive response to Xcm, H(2)O(2) is required for local and systemic accumulation of SA, which may locally control the generation of O(2)(.-). Detaching cotyledons at intervals after inoculation demonstrated that the signal leading to systemic accumulation of SA was emitted around 3 h post inoculation, and was associated with the oxidative burst. SA produced 6 h post infection at HR sites was not the primary mobile signal diffusing systemically from infected cotyledons.

Amitrole↗

PubMed1998

Fot 1 insertions in the Fusarium oxysporum f. sp. albedinis genome provide diagnostic PCR targets for detection of the date palm pathogen.

Populations of Fusarium oxysporum f. sp. albedinis, the causal agent of Bayoud disease of date palm, are derivatives of a single clonal lineage and exhibit very similar Fot 1 hybridization patterns. In order to develop a sensitive diagnostic tool for F. oxysporum f. sp. albedinis detection, we isolated several DNA clones containing a copy of the transposable element Fot 1 from a genomic library of the date palm pathogen. Regions flanking the insertion sites were sequenced, and these sequences were used to design PCR primers that amplify the DNA regions at several Fot 1 insertion sites. When tested on a large sample of Fusarium isolates, including 286 F. oxysporum f. sp. albedinis isolates, 17 other special forms, nonpathogenic F. oxysporum isolates from palm grove soils, and 8 other Fusarium species, the primer pair TL3-FOA28 allowed amplification of a 400-bp fragment found only in F. oxysporum f. sp. albedinis. Sequence analysis showed that one of the Fot 1 copies was truncated, lacking 182 bp at its 3' terminus. The primer pair BI03-FOA1 amplified a 204-bp fragment which overlapped the Fot 1 truncated copy and its 3' site of insertion in the F. oxysporum f. sp. albedinis genome and identified 95% of the isolates. The primer pairs BIO3-FOA1 and TL3-FOA28 used in PCR assays thus provide a useful diagnostic tool for F. oxysporum f. sp. albedinis isolates.

Cloning, Molecular↗

PubMed1997

Extracellular polysaccharides from Xanthomonas axonopodis pv. manihotis interact with cassava cell walls during pathogenesis.

The location of lipopolysaccharides produced by Xanthomonas axonopodis pv. manihotis during pathogenesis on cassava (Manihot esculenta) was determined by fluorescence and electron microscopy immunolabeling with monoclonal antibodies. During the early stages of infection, pathogen lipopolysaccharides were detected on the outer surface of the bacterial envelope and in areas of the plant middle lamellae in the vicinity of the pathogen. Later in the infection process, lipopolysaccharide-specific antibodies bound to areas where the plant cell wall was heavily degraded. Lipopolysaccharides were not detected in the fibrillar matrix filling intercellular spaces of infected cassava leaves. Monoclonal antibodies specific for the exopolysaccharide xanthan side chain labeled the bacteria, the fibrillar matrix, and portions of the host cell wall. The association of Xanthomonas lipopolysaccharides with host cell walls during plant infection is consistent with a role of these bacterial extracellular polysaccharides in the infection process.

Blotting, Western↗

PubMed1996

Primary sternal closure and mediastinal decompression by inlay autologous rib grafts.

Hemodynamic instability and arrhythmia after cardiopulmonary bypass occasionally requires delayed sternal closure or placement of a stenting device. A primary sternal closure with autologous inlay rib grafts can ensure a secure, stable sternal repair and avoids prolonged ventilator support and the concerns, risks, and expense associated with a secondary sternotomy repair.

Aortic Valve↗

PubMed1994

Molecular characterization of races and vegetative compatibility groups in Fusarium oxysporum f. sp. vasinfectum.

Restriction fragment length polymorphism (RFLP) and vegetative compatibility analyses were undertaken to assess genetic relationships among 52 isolates of Fusarium oxysporum f. sp. vasinfectum of worldwide origin and representing race A, 3, or 4 on cotton plants. Ten distinct vegetative compatibility groups (VCGs) were obtained, and isolates belonging to distinct races were never in the same VCG. Race A isolates were separated into eight VCGs, whereas isolates of race 3 were classified into a single VCG (0113), as were those of race 4 (0114). Ribosomal and mitochondrial DNA (rDNA and mtDNA) RFLPs separated four rDNA haplotypes and seven mtDNA haplotypes. Race A isolates displayed the most polymorphism, with three rDNA haplotypes and four mtDNA haplotypes; race 4 isolates formed a single rDNA group but exhibited three mtDNA haplotypes, while race 3 isolates had unique rDNA and mtDNA haplotypes. Two mtDNA molecules with distinct sizes were identified; the first (45-kb mtDNA) was found in all race A isolates and seven race 4 isolates, and the second (55-kb mtDNA) was found in all race 3 isolates and in two isolates of race 4. These two mtDNA molecules were closely related to mtDNAs of F. oxysporum isolates belonging to other formae speciales (conglutinans, lycopersici, matthioli, and raphani). Isolates within a VCG shared the same rDNA and mtDNA haplotypes, with the exception of VCG0114, in which three distinct mtDNA haplotypes were observed. Genetic relationships among isolates inferred from rDNA or mtDNA site restriction data were different, and there was not a strict correlation between race and RFLPs.(ABSTRACT TRUNCATED AT 250 WORDS)

DNA, Fungal↗

PubMed1994

Pathological and Molecular Characterization of Xanthomonas campestris Strains Causing Diseases of Cassava (Manihot esculenta).

Fifty-one strains representing Xanthomonas campestris pv. manihotis and cassavae and different pathovars occurring on plants of the family Euphorbiaceae were characterized by ribotyping with a 16S+23S rRNA probe of Escherichia coli and by restriction fragment length polymorphism analysis with a plasmid probe from X. campestris pv. manihotis. Pathogenicity tests were performed on cassava (Manihot esculenta). Histological comparative studies were conducted on strains of two pathovars of X. campestris (vascular and mesophyllic) that attack cassava. Our results indicated that X. campestris pv. manihotis and cassavae have different modes of action in the host and supplemented the taxonomic data on restriction fragment length polymorphism that clearly separate the two pathovars. The plasmid probe could detect multiple restriction fragment length polymorphisms among strains of the pathovar studied. Ribotyping provides a useful tool for rapid identification of X. campestris pathovars on cassava.

Journal Article↗

PubMed1993

A Cytochemical Study of Extracellular Sheaths Associated with Rigidoporus lignosus during Wood Decay.

An ultrastructural and cytochemical investigation of the development of Rigidoporus lignosus, a white-rot fungus inoculated into wood blocks, was carried out to gain better insight into the structure and role of the extracellular sheaths produced by this fungus during wood degradation. Fungal sheaths had a dense or loose fibrillar appearance and were differentiated from the fungal cell wall early after wood inoculation. Close association between extracellular fibrils and wood cell walls was observed at both early and advanced stages of wood alteration. Fungal sheaths were often seen deep in host cell walls, sometimes enclosing residual wood fragments. Specific gold probes were used to investigate the chemical nature of R. lignosus sheaths. While labeling of chitin, pectin, beta-1,4- and beta-1,3-glucans, beta-glucosides, galactosamine, mannose, sialic acid, RNA, fucose, and fimbrial proteins over fungal sheaths did not succeed, galactose residues and laccase (a fungal phenoloxidase) were found to be present. The positive reaction of sheaths with the PATAg test indicates that polysaccharides such as beta-1,6-glucans are important components. Our data suggest that extracellular sheaths produced by R. lignosus during host cell colonization play an important role in wood degradation. Transportation of lignin-degrading enzymes by extracellular fibrils indicates that alteration of plant polymers may occur within fungal sheaths. It is also proposed that R. lignosus sheaths may be involved in recognition mechanisms in fungal cell-wood surface interactions.

Journal Article↗

PubMed1992

Immunocytochemical localization of laccase L1 in wood decayed by Rigidoporus lignosus.

The cellular distribution of laccase L1 during degradation of wood chips by Rigidoporus lignosus, a tropical white rot fungus, was investigated by using anti-laccase L1 polyclonal antisera in conjunction with immunolabeling techniques. The enzyme was localized in the fungal cytoplasm and was associated with the plasmalemma and the fungal cell wall. An extracellular sheath, often observed around fungal cells, often contained laccase molecules. Diffusion of laccase within apparently unaltered wood was seldom observed. The enzyme penetrated all degraded cell walls, from the secondary wall toward the primary wall, including the middle lamella. Xylem cells showing advanced stages of decay were sometimes devoid of significant labeling. These data suggest that the initial attack on wood was not performed by laccase L1 of R. lignosus. Previous alteration of the lignocellulose complex may facilitate the movement of laccase within the wood cell walls. This immunogold study revealed that laccase localization during wood degradation seems limited not in space but in time.

Basidiomycota↗

PubMed1974