Abstract
AK-toxin from the Japanese pear pathotype of Alternaria alternata caused plasma membrane modifications in cells of susceptible Japanese pear leaves 1hr after toxin exposure, but not in cells of resistant leaves even after 10hr of toxin exposure. In susceptible cells, modifications were characterized as invagination and fragmentation of plasma membrane, accumulation of amorphous materials exterior to plasma membrane, and occurrence of tubular structures from plasmodesmata. Additionally, Golgi vesicles increased in number within 6hr after toxin exposure, but markedly decreased at 10hr in susceptible cells. An alkaline bismuth stain for carbohydrates well reacted with both Golgi vesicles and the materials inside them. Golgi vesicles which were observed in peripheral cytoplasm beneath invaginated plasma membrane appeared to fuse with the plasma membrane and to secrete bismuth-reactive amorphous materials containing carbohydrates. Ultrastructural changes were not observed in cell wall near modified plasma membrane of toxin-treated susceptible cells. Activation of Golgi activity which was observed in toxin-treated susceptible cells did not occur in toxin-treated resistant cells. These ultrastructural results suggested that the bismuth-reacted amorphous materials were not degenerated products from cell wall, but rather were formed by secretory products from Golgi vesicles.
