Phytophthora elicitor PB90 induced apoptosis in suspension cultures of tobacco

The protein elicitor PB90 secreted by Phy-tophthora boehmeriae is an efficient elicitor inducing the hypersensitive response and systemic acquired resistance in tobacco plants. Here, we observed cell death in suspension-cultured cells of Nicotiana tabacum BY-2 with PB90 treatment using Trypan blue staining method. And this cell death could be suppressed by cycloheximide, an inhibitor of proteins synthesis, which implies that PB90-induced cell death was an active cell death process requiring new protein synthesis. DAPI staining revealed that PB90 induce rapid chroma tin condensation, margination, apoptotic bodies' formation and DNA laddering, further TUNEL assay also observed the specific breakage of 3'-OH ends. All of the above common morphological characteristics indicated that PB90 induced apoptosis in suspension cultures of tobacco, suggesting that hypersensitive response induced by PB90 is an apoptotic process.