Abstract
Ultrastructure of Xanthomonas oryzae cultured on a medium, the degeneration process of the cultured bacteria induced by chemical treatment, and the ultrastructural changes of the bacteria growing in rice plants by the chemical treatment were studied using a streptomycin-resistant strain.
The bacterium is surrounded by a relatively electron-transparent cell wall, and a cytoplasmic membrane composed of a continuous unit membrane is present along the inside of this cell wall. Nuclear material of fibrillar appearance, ribosomes, polysomelike structures and two kinds of granules of different components were observed in the cytoplasm. Mitochondria, endoplasmic reticula, and mesosomes were not observed in the cytoplasm. Particles which seemed to be polysomes occurred occasionally in the cytoplasm. Granules of high electron density which appeared to be a certain kind of lipid and some of low density were observed in the cytoplasm.
Bacteria taken from the peripheral region of the inhibition zone induced by 2-amino-1, 3, 4-thiadiazole (ATDA) were examined. The electron density of cytoplasm decreased and few ribosomes were present. The coagulation of the cytoplasm caused irregular lysogenous spaces with no boundary. On the other hand, it was observed that the cytoplasm aggregated in a certain region and developed into a spherical body which was enclosed within 20-40nm in thick wall. Such bodies were observed only in the bacteria at the peripheral region of the inhibition zone. The spherical body was enclosed by an electron-dense outer layer and an electron-transparent inner layer, and was filled with electron-dense material. The above observations of the body are consistent with the ultrastructure of spore. The author temporarily termed it sporelike structure. In the bacteria taken from the central region of the inhibition zone, fibrillar structure coagulated and then disappeared.
In the vessels of rice plants treated with ATDA, especially the bacteria in pitted vessels showed drastic degeneration. Their cell wall and cytoplasmic membrane collapsed, resulting in the flowing out of the cytoplasm. On the other hand, the bacteria in spiral and ring vessels did not show any prominent change in their cell organelles. Such a difference probably depends on the quantitative difference of ATDA in those vessel types.
