Immune mechanisms of higher plants are characterized by high diversity. The consequence is sometimes in contact with the pathogen production of reactive oxygen species, cell wall modification, the local cell death with characteristics of apoptosis, production of phytoalexins and pathogenesis associated proteins (PR). Elicitors are compounds directly responsible for the induction of immune responses of plants. Among the effectors produced by micro-organisms can be distinguished elicitors specific to a particular strain of the pathogen and those commonly found in many pathogens. After binding to the receptors, elicitors in plant cells initiate plurality been well characterized signal transduction pathways. The first section discusses the mechanisms of some aspects of the identification and early signal transduction, gene transcription independent of plant defense responses, against the operating mechanisms in other organisms.