VIEW ARTICLE

Cytology and Histology

Ultrastructural Evidence for Immobilization of an Incompatible Bacterium, Pseudomonas pisi, in Tobacco Leaf Tissue. R. N. Goodman, Professor, Department of Plant Pathology, University of Missouri-Columbia, Columbia 65201; Pi-Yu Huang(2), and J. A. White(3). (2)(3)Post Doctoral Fellow, and Electronmicroscopist, respectively, Department of Plant Pathology, University of Missouri-Columbia, Columbia 65201. Phytopathology 66:754-764. Accepted for publication 20 January 1976. DOI: 10.1094/Phyto-66-754.

Incompatible (Pseudomonas pisi), compatible (P. tabaci ), and saprophytic (P. fluorescens) bacteria, 10⁹ cells/ml, were injected into tobacco leaf tissue. At 20 minutes, 2, 4, and 6 hours after injection, tissue was examined electronmicroscopically and the extent and manner of bacterial immobilization was determined. After 20 minutes, wall cuticle separated from the wall where incompatible bacteria were in close proximity to the wall surface. This was not noted in control tissue even after 6 hours. After 2, 4, and 6 hours the separated wall cuticle, which was filamentous at 20 minutes, became progressively thicker and more comprehensive by having large numbers of vesicles ≅ 25 nm in diameter, dense staining fibrils and membrane fragments integrated into it. During this period this structure appeared to envelope and immobilize some bacteria that had migrated to the plant wall surface. Not all bacteria became ensheathed by the wall cuticle. At 2 and 4 hours after injection, the plasmalemma vesiculated, the wall became swollen, and some elements of the cell wall became more intensely electrondense. Electronmicrographs suggest migration of some plant cell contents to and through the plant cell wall where they aggregate with remnants of the original wall cuticle to form a bacteria-ensheathing envelope. Some parts of the bacterial cell wall also seem to be incorporated into this structure. After 6 hours, plant cells show typical hypersensitive reaction symptoms. Pseudomonas fluorescens induced the separation of cell wall cuticle, which also enveloped bacterial cells, but the ensheathing cuticle remained very fine. Few vesicles were formed and distortion of neither plant nor bacterial cells was detected during the 6-hour course of the experiment. The compatible pathogen, P. tabaci, did not induce formation of a bacteria-limiting wall cuticle after 6 hours although host cell cytoplasm was disorganized. Plant cell wall fibrils aggregated loosely around the bacteria, but no vesicles or membrane fragments augmented the fibrillar debris.