Involvement of actin filament association in hypersensitive reactions in potato cells

In potato tissues after either penetration by an incompatible race of Phytophthora infestans, the potato late blight fungus, or treatment with hyphal wail components (HWC) prepared from P. infestans, cytoplasmic aggregation is observed as one of the earliest resistance reactions. In potato protoplasts, the number of aggregated protoplasts increased after treatment with HWC. The increase was repressed by treatment with cytochalasin D, staurosporine, verapamil, ophiobolin and quinacrine prior to HWC treatment, suggesting that cytoplasmic aggregation in potato protoplasts was connected with actin filament association, protein phosphorylation, Ca2+, calmodulin and phospholipase reactions. The ratio of monomer-actin in potato tissues was decreased by treatment with HWC, while the decrease was repressed by treatment with cytochalasin D, staurosporine, ophiobolin and quinacrine prior to HWC treatment. These inhibitors inhibited the accumulation of rishitin, a potato phytoalexin, which occurs in potato tissues treated with HWC. The results imply that the factors involved in signal transduction might be connected with the cytoskeleton, especially actin filament association, during the initiation of defence responses in potato cells. (C) 1999 Academic Press.