Continuous recognition of the elicitor signal for several hours is prerequisite for induction of cell death and prolonged activation of signaling events in tobacco BY-2 cells.

To provide insights into the mechanisms by which receptors for pathogenic elicitors activate defense signaling, we investigated the duration of cryptogein treatment required for induction of various defense responses including programmed cell death in synchronized tobacco BY-2 cells. Transient cryptogein treatment induced only a rapid and transient phase of oxidative burst and mitogen-activated protein kinase (MAPK) activation. Prolonged production of *O(2)(-) and prolonged activation of MAPKs, as well as accumulation of transcripts of defense-related genes and cell death, required continuous recognition of cryptogein for several hours. In contrast, desensitization was gradually induced in the absence of the elicitor.