Induction of defense-related ultrastructural modifications in pea root tissues inoculated with endophytic bacteria

• Published in: Plant physiology (Bethesda) 1996-11, Vol.112 (3), p.919-929
• Main Authors: Benhamou, N. (Universite Laval, Sainte-Foy, Quebec, Canada.), Kloepper, J.W, Quadt-Hallman, A, Tuzun, S
• Format: Article
• Language: English
• Subjects: Apposition; BACILLUS; Bacteria; Biological and medical sciences; Biological control; CANAL INTERCELLULAIRE; CANAL INTERCELULAR; Cell walls; COMPOSE PHENOLIQUE; COMPUESTOS FENOLICOS; Control; ESTRUCTURA CELULAR; EXPERIMENTACION IN VIVO; EXPERIMENTATION IN VIVO; Extracellular space; Fundamental and applied biological sciences. Psychology; Fungal plant pathogens; FUSARIUM OXYSPORUM; HOTE; HUESPEDES; Hyphae; IMMUNITE; INFECCION EXPERIMENTAL; INFECTION EXPERIMENTALE; INMUNIDAD; MECANISME DE DEFENSE; MECANISMOS DE DEFENSA; PARED CELULAR; PAROI CELLULAIRE; Pathogens; Peas; Phytopathology. Animal pests. Plant and forest protection; PISUM SATIVUM; Plant diseases; Plant roots; Plant-Microbe and Plant-Insect Interactions; PLANTAS TRANSGENICAS; PLANTE TRANSGENIQUE; Plants; POLISACARIDOS; POLYHOLOSIDE; RACINE; RAICES; RESISTANCE AUX MALADIES; RESISTENCIA A LA ENFERMEDAD; STRUCTURE CELLULAIRE; TRANSFERENCIA DE GENES; TRANSFERT DE GENE; ULTRAESTRUCTURA; ULTRASTRUCTURE
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.112.3.919

The stimulation exerted by the endophytic bacterium Bacillus pumilus strain SE34 in plant defense reactions was investigated at the ultrastructural level using an in vitro system in which root-inducing T-DNA pea (Pisum sativum L.) roots were infected with the pea root-rotting fungus Fusarium oxysporum f. sp. pisi. In nonbacterized roots, the pathogen multiplied abundantly through much of the tissue including the vascular stele, whereas in prebacterized roots, pathogen growth was restricted to the epidermis and the outer cortex. In these prebacterized roots, typical host reactions included strengthening the epidermal and cortical cell walls and deposition of newly formed barriers beyond the infection sites. Wall appositions were found to contain large amounts of callose in addition to being infiltrated with phenolic compounds. The labeling pattern obtained with the gold-complexed laccase showed that phenolics were widely distributed in Fusarium-challenged, bacterized roots. Such compounds accumulated in the host cell walls and the intercellular spaces as well as at the surface or even inside of the invading hyphae of the pathogen. The wall-bound chitin component in Fusarium hyphae colonizing bacterized roots was preserved even when hyphae had undergone substantial degradation. These observations confirm that endophytic bacteria may function as potential inducers of plant disease resistance