In Arabidopsis thaliana cell cultures, the peptaibol alamethicin induced a form of active cell death that was associated with cell shrinkage and DNA fragmentation. The transfer of mature A. thaliana plants from a peptide-free medium to a medium containing a moderate concentration of alamethicin caused the development of lesions in leaves after a few days. These lesions were characterized by cell death, deposition of callose, production of autofluorescent phenolic compounds, and transcription of defense genes, just like in the hypersensitive response to a pathogen attack. The induction of defense-like responses in Arabidopsis by other membrane-disrupting peptides was also evaluated. The peptides selected for comparison included the natural antimicrobial melittin and the peptaibol ampullosporin A, as well as synthetic analogues of the peptaibols cervinin and trichogin. The response amplitude in A. thaliana increased with the peptaibol's ability to permeabilize biological membranes through a pore-forming mechanism and was strongly associated with their content in the helicogenic α-aminoisobutyric acid residue.