Abstract
Susceptible plant tissues were treated with several host-specific toxins from host-selective pathotypes of Alternaria alternata. Three different types of toxin-induced changes were detected by electron microscopy. The first and most common type was toxin-induced change in the plasma membrane. Many invaginations appeared in the membrane, along with much fragmentation and vesiculation. Cell walls were degraded, and desmotubules extended from plasmodesmata. Such effects were induced by AK-toxin in pear petals in addition to leaves, by AM-toxin I in apple and pear leaves, by AF-toxin I in strawberry and pear leaves, and by AF-toxin II in pear leaves. The initial effects in this type of response appeared to be at the interface between the cell wall and the plasma membrane. The second type of response to a toxin was a change in the chloroplast, resulting in detachment and vesiculation of grana lamellae; this response was induced by AM-toxin I in apple and pear leaves. A third type occurred in tomato leaves exposed to AL-toxin ; the mitochondria became swollen, the mitochondrial cristae were reduced and the matrix appeared to be leached. In addition, the endoplasmic reticulum was swollen and vesiculated. AF-toxin II caused collapse of cells in leaf veins of strawberry, but the electron micrographs did not show the location of early cellular effects. Electron micrographs showed no effects of the toxins on cells of resistant host genotypes.
