The invention concerns novel peptides, in particular plant peptides, having an antimicrobial activity and a cytotoxic activity, in particular for plant cells. The invention also concerns polynucleotides coding for said peptides, vectors comprising said polynucleotides, micro-organisms and cells transformed with said vectors, transgenic organisms whereof all of part of the cells contain and/or express said vectors, uses of said peptides and said polynucleotides, in particular as plant-specific antimicrobial agents. The invention further concerns an antimicrobial and/or cytotoxic method for treating plants.