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Induction of Apoptotic Cell Death Leads to the Development of Bacterial Rot Caused by Pseudomonas cichorii

¹Laboratory of Plant Pathology and Biotechnology, Faculty of Agriculture, Kochi University, Nankoku 783-8502, Japan; ²Research institute of Molecular Genetic, Kochi University, Nankoku 783-8502, Japan; ³The Graduate School of Science and Technology, Kobe University, Rokkodai, Nadaku, Kobe 657-8501, Japan

Pseudomonas cichorii is the major causal agent of bacterial rot of lettuce. Collapse and browning symptoms were observed in lettuce leaf tissue from 15 to 24 h after inoculation (HAI) with P.cichorii; superoxide anion generation was detected at 1 to 6 HAI; and cell death was induced at 6 HAI, reaching a maximum at approximately 9 and 12 HAI. Heterochromatin condensation and DNA laddering also were observed within 3 HAI. Pharmacological studies showed that induction of cell death and DNA laddering was closely associated with de novo protein synthesis, protein kinase, intracellular reactive oxygen species, DNase, serine protease, and caspase III-like protease. Moreover, chemicals, which inhibited the induction of cell death and DNA laddering, also suppressed the development of disease symptoms. These results suggest that apoptotic cell death might be closely associated with the development of bacterial rot caused by P. cichorii.

Additional keywords: programmed cell death.