Salicylic Acid and Systemic Acquired Resistance to Pathogen Attack

New insights into the phenomenon of systemic acquired resistance have been gained in recent years, by the use of techniques in molecular genetics and biology that have replaced the largely descriptive approach of earlier work. The isolation of mutants in the signal transduction pathway from induction to expression of resistance as well as the use of transgenic plants over-expressing or suppressing the expression of putative candidate genes involved in systemic acquired resistance and its signalling have identified several steps in the establishment of plant resistance. In this review the latest developments implicating salicylic acid as a signal molecule in systemic resistance are discussed and contrasted with new signalling pathways which, seemingly, are based on alternative mechanisms.