Involvement of actin filament association in hypersensitive reactions in potato cells

In potato tissues after either penetration by an incompatible race of Phyto phthora infestans, the potato late blight fungus, or treatment with hyphal wail components (HWC) prepared from P. infestans, cytoplasmic aggregation i s observed as one of the earliest resistance reactions. In potato protoplas ts, the number of aggregated protoplasts increased after treatment with HWC . The increase was repressed by treatment with cytochalasin D, staurosporin e, 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 phosph olipase reactions. The ratio of monomer-actin in potato tissues was decreas ed by treatment with HWC, while the decrease was repressed by treatment wit h cytochalasin D, staurosporine, ophiobolin and quinacrine prior to HWC tre atment. These inhibitors inhibited the accumulation of rishitin, a potato p hytoalexin, which occurs in potato tissues treated with HWC. The results im ply that the factors involved in signal transduction might be connected wit h the cytoskeleton, especially actin filament association, during the initi ation of defence responses in potato cells. (C) 1999 Academic Press.