Effect of cytochalasin D on defense responses of potato tuber discs treated with hyphal wall components of Phytophthora infestans

Cytoplasmic aggregation, the rapid translocation of cytoplasm and organelle s to the site of fungal penetration of a cell, occurs in potato tissue afte r penetration of an incompatible race of Phytophthora infestans, the late b light fungus, or treatment with hyphal wall components (HWC) prepared from P. infestans. This phenomenon is thought to be one of the defense reactions of plant against pathogens, but the exact function of cytoplasmic aggregat ion is currently unknown. To evaluate the relationship between cytoplasmic aggregation and defense reactions, we suppressed the cytoplasmic aggregatio n by treatment with cytochalasin D, an inhibitor of the polymerization of a ctin, and examined the effect of inhibition on certain defense responses ca used by HWC treatment. In potato tuber discs treated simultaneously with HW C and cytochalasin D, a delay in the induction of phenylalanine ammonia-lya se mRNA, decrease in the accumulation of PR (pathogenesis-related) proteins and partial suppression of cell death were observed, while the generation of superoxide anions was not affected. These results suggested that cytopla smic aggregation was essential for the timely induction of defense reaction s manifested at late resistant stage. (C) 1999 Elsevier Science Ireland Ltd . All rights reserved.