1IRD, UMR « DGPC », “Résistance des Plantes”, BP 64501, 34394 Montpellier, France; 2INRA, Service Commun de Microscopie Electronique, BV 1540, Dijon cedex 21034 France; 3S.O.F.T. Laboratoire GBSA, Case Courrier 024, Université Montpellier II, Place Eugène Bataillon, 34095 Montpellier Cedex 05, France
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Accepted 30 June 2003.
Cotton cotyledons displayed a hypersensitive reaction (HR) in the cultivar Réba B50 after infiltration with the aviru-lent 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.
© 2003 The American Phytopathological Society