Ultrastructural effects of thaxtomin A produced by Streptomyces scabies onmature potato tuber tissues

The cytological and ultrastructural modifications induced by thaxtomin A, a phytotoxin produced by Streptomyces scabies, were analyzed on mature field -grown potato tuber tissues. In tissue sampled during the first 12 h after treatment with thaxtomin A, the plasmalemma of parenchyma cells was detache d from the cell wall in several places. However, the plasmalemma did not ap pear ruptured. The intercellular spaces between the retracted plasmalemma a nd the cell wall often contained fibrillar material. After a longer period of time, cells from tissues treated with thaxtomin A showed significant dis organization, such as detachment and invagination of the plasmalemma, the p resence of a fibrillar-like material in the cytoplasm, and electron-dense m aterial associated with moribund cellular features.