Chemical elicitors of systemic acquired resistance-Salicylic acid and its functional analogs

Any interaction of plants with phytopathogens involves the generation of various chemical molecules that are critical for activation of their defense machinery. One of the chemicals, salicylic acid (SA) induces systemic acquired resistance (SAR) in plants. The activation of SAR provides a broad-spectrum resistance against a wide range of related or unrelated pathogens. There has been considerable progress in the biochemical and molecular understanding of SAR activation in various plants. In addition, several chemicals including SA and its analogs are known to provide a direct or indirect defense against pathogens when applied to plants. Molecular mechanism of plant defense induced by synthetic chemical inducers is not very well understood. This review highlights the importance of salicylic acid and its most studied analog, Acibenzolar-S-methyl in inducing SAR and it also provides a description of other major chemical elicitors of plant defenses and their possible molecular mechanism.