VIEW ARTICLE

Cytology and Histology

Ultrastructural Modifications in Apple Stems Induced by Erwinia amylovora and the Fire Blight Toxin. Pi -yu Huang, Postdoctoral Fellow, Department of Plant Pathology, University of Missouri, Columbia 65201; Robert N. Goodman, Professor, Department of Plant Pathology, University of Missouri, Columbia 65201. Phytopathology 66:269-276. Accepted for publication 1 October 1975. DOI: 10.1094/Phyto-66-269.

Ultrastructural changes in apple stem tissues induced by Erwinia amylovora and its toxin were investigated by electron microscopy. In bacteria-inoculated apple stem tissues, there was no significant ultrastructural change in host cells 24 hours after inoculation even though bacteria were found in xylem vessels and in the intercellular spaces between collenchyma and parenchyma cells. The earliest ultrastructural modification was plasmolysis of xylem parenchyma cells. This took place about 48 hours after inoculation and was followed by aggregation of cytoplasm and disorganization of subcellular organelles. Cytoplasm became a dark amorphous coagulum and lysigenous cavities developed in xylem by the third day after inoculation. In toxin-treated stem tissues, plasmolysis of xylem parenchyma cells took place 2 hours after treatment with 200 µg/ml of toxin and was the first sign of ultrastructural change. Four to five hours after the toxin treatment, membrane systems of subcellular organelles as well as the plasmalemma and tonoplasts were intensely deranged. These observations suggest that the ultrastructural changes induced by the fire blight toxin are much the same as those induced by the pathogen.