Abstract
Light and electron microscopic studies were carried out to clarify the relationships be tween cytoplasmic granulation and hypersensitive cell death in the inner epidermal cells of rice leaf-sheaths inoculated with an incompatible race of Pyricularia oryzae Cav. Hypersensitive cell death, as determined by the loss of capability for plasmolysis, was clearly observed by electron microscopy when the epidermal tissues were treated with a hypertonic sucrose solution. In the incompatible combination between race 037 and var. Toride 1 (resistance gene Pi-zt), fragmentation of plasma membranes and destruction of the unit membrane structure were observed in infected epidermal cells that did not plasmolyze. Disruption of the plasma membrane was also observed in non-plasmolyzed cells, suggesting that membrane disruption was not caused by the plasmolysis treatment. Infected epidermal cells in the incompatible combination were found to be alive until invagination and lomasome-like structures were formed in plasma membranes. In the compatible combination between race 037 and var. Koshihikari, ultrastructural changes were not observed in plasma membranes of infected epidermal cells and normal plasmolysis occurred. Thus, it is suggested that hypersensitive cell death may occur when plasma membranes invaginate and form lomasome-like structures then followed by disruption into vesicles which are observed light-microscopically as cytoplasmic granules.
