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Fungal Attack (fungal + attack)
Selected AbstractsEndochitinase activity in the apoplastic fluid of Phellinus weirii -infected Douglas-fir and its association with over wintering and antifreeze activityFOREST PATHOLOGY, Issue 5 2003A. Zamani Summary Extracellular proteins were extracted from Phellinus weirii infected Douglas-fir (Pseudotsuga menziesii var. menziesii) roots and needles to examine endochitinase activity. Chitinases have been associated with the plant's defence response against fungal attack because they hydrolyse chitin, a structural component of fungal cell walls. Protein separation using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) followed by Western immunoblot analysis using a polyclonal antibody specific to an endochitinase-like protein (ECP) resulted in the detection of up to three polypeptides between 27 and 30 kDa in size. Two-dimensional gel electrophoresis (2-D PAGE) followed by Western immunoblot analysis revealed that the apoplastic fluid contained multiple ECP isoforms with isoelectric points (pIs) ranging from 5.3 to 5.8 and molecular masses of 27,30 kDa. Chitinase activity in needle and root tissues was measured spectrophotometrically using a colorimetric assay. A gel overlay technique using glycol chitin as a substrate for endochitinase was applied to confirm that the ECP antibody detected an enzymatically active protein. The apoplastic fluid collected from P. weirii -infected winter Douglas-fir needles showed anti-freeze activity and seasonal analysis of needle tissue showed some evidence of ECP accumulation in winter months. ECP was distributed systemically throughout the tree. Increased levels of endochitinase activity in the region of P. weirii infection supports a physiological role for ECP in the plant defence response. Résumé Les protéines extra-cellulaires ont été extraites des racines et aiguilles de douglas (Pseudotsuga menziesii var menziesii) infectés par Phellinus weirii (Murr.) Gilbn., pour étudier l'activité endochitinase. Les chitinases ont été associées aux réactions de défense des plantes contre les attaques fongiques parce-qu'elles hydrolysent la chitine, un composant de la paroi des cellules fongiques. La séparation des protéines, réalisée par électrophorèse en gel de polyacrylamide avec sodium dodecyl sulfate (SDS-PAGE), suivie par une analyse par Western immunoblot en utilisant un anticorps polyclonal spécifique d'une protéine de type endochitinase (ECP), a permis la détection de 3 polypeptides de taille comprise entre 27 et 30 kDa. Une électrophorèse sur gel en 2-dimensions (2-D PAGE) suivie par une analyse par Western immunoblot a révélé que le fluide apoplastique contient de multiples isoformes d'ECP avec des pI dans une gamme de 5.3 à 5.8 et des masses moléculaires de 27 à 30 kDa. L'activité chitinase dans les aiguilles et tissus racinaires a été mesurée par spectrophotométrie par une méthode colorimétrique. Une technique d'overlay utilisant de la chitine glycol comme substrat de l'endochitinase a été appliquée pour confirmer que l'anticorps ECP avait détecté une protéine active du point de vue enzymatique. Le fluide apoplastique d'aiguilles récoltées en hiver sur des douglas infectés par P. weirii a montré une activité antigel et l'analyse saisonnière des tissus foliaires a montré une certaine accumulation d'ECP pendant l'hiver. L'ECP est répartie de façon systémique dans l'ensemble de l'arbre. Les niveaux accrus d'activité endochitinase dans la zone infectée par P. weirii suggère un rôle physiologique de l'ECP dans les réactions de défense de la plante. Zusammenfassung Aus Wurzeln und Nadeln von mit Phellinus weirii infizierten Douglasien (Pseudotsuga menziesii var. menziesii) wurden extrazelluläre Proteine extrahiert, um die Endochitinase-Aktivität zu bestimmen. Chitinasen werden mit der pflanzlichen Abwehrreaktion auf Pilzinfektionen in Verbindung gebracht, da sie Chitin, eine Strukturkomponente der pilzlichen Zellwand, hydrolysieren. Die Proteine wurden mit Natrium-Dodecyl-Sulfat-Polyacrylamid-Gelelektrophorese (SDS-PAGE) getrennt, gefolgt von einer Western Immunoblot-Analyse mit einem gegen ein Endochitinase-ähnliches Protein (ECP) spezifischen polyklonalen Antikörper. Hiermit liessen sich bis zu drei Polypeptide zwischen 27-30 kDa nachweisen. Eine zweidimensionale Gelelektrophorese (2-D PAGE) mit anschliessender Western Immunoblot-Analyse ergab, dass die Apoplastenflüssigkeit multiple ECP-Isoformen enthielt (mit pIs von 5,3 bis 5,8 und Molekularmassen von 27 bis 30 kDa). Die Chitinase-Aktivität wurde auch im Nadel- und Wurzelgewebe spektrophotometrisch mit einer Farbreaktion gemessen. Um sicher zu stellen, dass der ECP-Antikörper ein enzymatisch aktives Protein nachwies, wurde eine Gel-Overlay-Methode verwendet, mit Glycolchitin als Substrat für die Endochitinase. Die Apoplastenflüssigkeit der Nadeln von mit P. weirii infizierten Douglasien zeigte in Winterzustand eine Antifrost-Aktivität, ihre Analyse während des gesamten Jahres ergab aber keine Hinweise auf eine ECP-Anreicherung während der Wintermonate. ECP war systemisch im gesamten Baum enthalten. Die erhöhte Endochitinase-Aktivität in Bereichen mit P. weirii -Infektion lässt auf eine physiologische Rolle von ECP in der Pflanzenabwehr schliessen. [source] Composites of rigid polyurethane foam and cellulose fiber residueJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010M. C. Silva Abstract Rigid polyurethane composite foams were prepared with cellulose fibers as a filler. The cellulose fibers were an industrial residue of blanched cellulose pulp production. The influence of the cellulose fiber concentration on the structural, thermal, mechanical, and morphological properties of the foams was investigated. We also studied the influence of the cellulose fibers on the foam's resistance to fungal attack by placing a suspension of known fungus in contact with the surface of the foam and following the morphological evolution as a function of time (for 60 days). The increase in the cellulose filler concentration in the foams, up to 16% w/w with respect to the polyol, changed their properties as follows: (1) the cell size decreased, (2) the thermooxidative stability and mechanical properties remained approximately constant, (3) the thermal conductivity decreased slightly, and (4) fungal growth was observed. Therefore, a cellulosic fibrous industrial residue was rationally valorized as a filler in classical rigid polyurethane foams; this yielded materials with mechanical resistance and a susceptibility to fungi in a wet environment. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Transient expression of a vacuolar peroxidase increases susceptibility of epidermal barley cells to powdery mildewMOLECULAR PLANT PATHOLOGY, Issue 6 2001Brian Kåre Kristensen summary The expression of genes encoding the peroxidases, Prx7 and Prx8, is induced in barley leaf tissue after inoculation with the barley powdery mildew fungus, Blumeria graminis f.sp. hordei (DC) Speer (Bgh). The role of these peroxidases in general barley defence responses against fungal attack was investigated using a transient expression system. Colonization frequencies of Bgh on cells transfected with Prx7 or Prx8 expression-, mutant- or fusion-DNA constructs were compared to the frequencies on cells expressing a ,-glucuronidase (GUS) control construct. Twice the number of powdery mildew colonies were observed on cells expressing Prx7 as compared to control cells. Introduction of either mutant or truncated versions of Prx7 showed that decreased resistance against Bgh was dependent on the presence of the C-terminal signal peptide required for correct subcellular targeting, but not affected significantly by mutations in the catalytic centre. No impact on Bgh performance was observed after the introduction of Prx8 or mutant constructs. An enhanced accumulation of the apoplastic Prx8 was verified by immunocytology. These results indicate a more complex role of peroxidases in defence responses than was previously suspected. [source] Non-host resistance of barley is associated with a hydrogen peroxide burst at sites of attempted penetration by wheat powdery mildew fungusMOLECULAR PLANT PATHOLOGY, Issue 4 2001Ralph Hückelhoven Summary In barley, non-host resistance against the wheat powdery mildew fungus (Blumeria graminis f.sp. tritici, Bgt) is associated with the formation of cell wall appositions and a hypersensitive reaction in which epidermal cells die rapidly in response to fungal attack. In the interaction of barley with the pathogenic barley powdery mildew fungus (Blumeria graminis f.sp. hordei, Bgh), these defence reactions are also associated with accumulation of H2O2. To elucidate the mechanism of non-host resistance, the accumulation of H2O2 in response to Bgt was studied in situ by histochemical staining with diaminobenzidine. H2O2 accumulation was found in cell wall appositions under appressoria from Bgt and in cells undergoing a hypersensitive reaction. A mutation (mlo5) at the barley Mlo locus, that confers broad spectrum resistance to Bgh, did not influence the barley defence phenotype to Bgt. Significantly, Bgt triggered cell death on mlo5 -barley while Bgh did not. [source] Changes in abscisic acid, salicylic acid and phenylpropanoid concentrations during cold acclimation of androgenic forms of Festulolium (Festuca pratensis × Lolium multiflorum) in relation to resistance to pink snow mould (Microdochium nivale)PLANT BREEDING, Issue 4 2009E. Pociecha Abstract We investigated changes in concentrations of abscisic (ABA) and salicylic acid (SA), phenolic compounds and phenylalanine ammonia-lyase (PAL) activity in relation to cold-induced tolerance of four androgenic genotypes of Festulolium (Festuca × Lolium hybrids) to frost and to the snow mould fungus Microdochium nivale. Cold acclimation increased frost tolerance and resistance to snow mould. Resistant genotypes were characterized by higher ABA concentrations during the first 54 h of cold acclimation and lower concentrations of SA than susceptible genotypes. After cold acclimation, the content of phenolics was significantly lower in genotypes tolerant to frost and M. nivale infection than in susceptible genotypes, while PAL activity was significantly higher. Signalling networks controlling cold acclimation to frost (abiotic) and mould infection (biotic) appears to involve increases in foliar concentrations of ABA and decreases in the SA level during successful cold acclimation. Higher PAL activity and lower concentrations of phenolic compounds also appear to be associated with enhanced tolerance to frost and fungal attack. [source] Effects of foliar- and root-applied silicon on the enhancement of induced resistance to powdery mildew in Cucumis sativusPLANT PATHOLOGY, Issue 5 2005Y. C. Liang Two cucumber (Cucumis sativus) cultivars differing in their resistance to powdery mildew, Ningfeng No. 3 (susceptible) and Jinchun No. 4 (resistant), were used to study the effects of foliar- and root-applied silicon on resistance to infection by Podosphaera xanthii (syn. Sphaerotheca fuliginea) and the production of pathogenesis-related proteins (PRs). The results indicated that inoculation with P. xanthii significantly suppressed subsequent infection by powdery mildew compared with noninoculation, regardless of Si application. Root-applied Si significantly suppressed powdery mildew, the disease index being lower in Si-supplied than in Si-deprived plants, regardless of inoculation treatment. The resistant cultivar had a more constant lower disease index than the susceptible cultivar, irrespective of inoculation or Si treatment. Moreover, with root-applied Si, activities of PRs (for example peroxidase, polyphenoloxidase and chitinase) were significantly enhanced in inoculated lower leaves or noninoculated upper leaves in inoculated plants of both cultivars. Root-applied Si significantly decreased the activity of phenylalanine ammonia-lyase in inoculated leaves, but increased it in noninoculated upper leaves. However, Si treatment failed to change significantly the activity of PRs in plants without fungal attack. Compared to the control (no Si), foliar-applied Si had no effects either on the suppression of subsequent infection by P. xanthii or on the activity of PRs, irrespective of inoculation. Based on the findings in this study and previous reports, it was concluded that foliar-applied Si can effectively control infections by P. xanthii only via the physical barrier of Si deposited on leaf surfaces, and/or osmotic effect of the silicate applied, but cannot enhance systemic acquired resistance induced by inoculation, while continuously root-applied Si can enhance defence resistance in response to infection by P. xanthii in cucumber. [source] | ||||||||||