Abstract
Hypersensitive cell death plays a critical role in the plant defense system, constituting a major component of HR to restrict pathogen multiplication. Screening early responding genes during HR against TMV infection, we identified that encoding ornithine decarboxylase (ODC). Subsequent analyses showed not only ODC but also other genes involved in polyamine biosynthesis to be up-regulated, resulting in accumulation of polyamines in apoplast of TMV-infected leaves. Treatment of inhibitors for polyamine biosynthesis reduced the rate of HR and accumulation of polyamines. These results suggested polyamines to have critical role(s) in HR. This was experimentally confirmed, showing that H2O2 was generated in leaves infiltrated with polyamines. Further analyses revealed that accumulated polyamines were indeed degraded by polyamine oxidase detected in apoplast. It was concluded that, when HR is triggered, polyamines are synthesized, transported to apoplast, and degraded to induce H2O2, eventually resulting in hypersensitive cell death.
