AtMEK5 DD is an active mutant of AtMEK5, a MAP kinase kinase in Arabidopsis. Induction of AtMEK5 DD expression in transgenic plants leads to activation of 44 and 48 kD MAPKs and causes a rapid cell death. To compare the cell death induced by the expression of AtMEK5 DD with the HR-cell death induced by avirulence pathogen infection, we analyzed the activation of downstream MAP Kinase and induction of PR genes expression in permanent transgenic Arabidopsis plants. In-gel kinase activity assay revealed that the infection of Pseudomonas syringae DC3000 harboring Avr Rpt2 gene also lead to activation of 44 and 48 kD MAPKs. PAL, PR1 and PR5 were strongly induced in plants undergoing HR-cell death caused by the infection of P. syringae DC3000, while only the expression of PR5 was strongly induced in transgenic plants expressing AtMEK5 DD protein. NahG protein in AtMEK5 DD × NahG plants cannot suppress the cell death induced by AtMEK5 DD. And AtMEK5 DD protein expressed AtMEK5 DD × NahG plants showed no significant change in salicylic acid (SA) level. All these suggest that the cell death induced by the activation of AtMEK5 is salicylic acid-independent.