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Comparative Ultrastructure of Cucumbers Pretreated with Plant Growth-promoting Rhizobacteria,DL -3-aminobutyric Acid or Amino Salicylic Acid after Inoculation with Colletotrichum orbiculare

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The infection behaviour of Colletotrichum orbiculare was observed using a transmission electron microscope (TEM) in the leaves of cucumber plants preinoculated with plant growth-promoting rhizobacteria (PGPR) Serratia marcescens (90-166) or Pseudomonas fluorescens (89B61) after inoculation with the anthracnose pathogen. Moreover, the structural defence mechanisms mediated by pretreatingdl-3-amino butyric acid or amino salicylic acid was compared with those mediated by these two PGPR. In untreated plants broadly spread intercellular/intracellular hyphae were found in leaf tissues. The cytoplasm of fungal hyphae appeared intact and the electron densities of intercellular and intracellular hyphae were not high even at 5 days after fungal inoculation, indicating lack of defence responses. However, in the leaves of plants preinoculated with both PGPR active defence responses were observed, i.e. sheath formation at penetration sites, and accumulations of endoplasmic reticula or of numerous vesicles around intracellular hyphae. Furthermore, the electron densities of most intracellular and intercellular hyphae were higher than those of untreated control plants. In the leaves of plants pretreated with both chemicals, the hyphae of the pathogen were rarely observed at 5 days after challenge inoculation. Similar to the case of PGPR-pretreated plants, the most intercellular and intracellular hyphae in plant tissues were electron dense. However, no active defence responses were observed in leaf tissues. Moreover, in some cases, hyphal growth was restricted to the epidermal cell layer, and in particular, was not observed to develop in mesophyll cells of the plants. These results suggest that the mechanisms of systemically induced resistance are differently expressed by preinoculating with PGPR or by pretreating with chemicals.

Keywords: Colletotrichum orbiculare; Pseudomonas fluorescens; Serratia marcescens; amino salicylic acid; cucumber plants; dl-3-aminobutyric acid; induced systemic resistance; plant growth-promoting rhizobacteria; systemic-acquired resistance; ultrastructures

Document Type: Research Article


Affiliations: 1: Faculty of Bioscience and Industry, College of Applied Life Science, and the Research Institute for Subtropical Agriculture and Biotechnology, Cheju National University, Jeju 690-756, Korea 2: National Instrumentation Center for Environmental Management (NICEM), Seoul National University, Seoul 151-921, Korea 3: Division of Bioscience and Technology, Korea University, Seoul 136-701, Korea 4: Subtropical Environment Division, National Institute of Subtropical Agriculture, Rural Development Administration (RDA), Jeju 699-803, Korea (correspondence to Y. C. Jeun. ), Email:

Publication date: August 1, 2007

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