Salicylic acid (SA) is a phenolic phytohormone and is found in plants with roles in plant growth and development, photosynthesis , transpiration , ion uptake and transport.  SA is involved in endogenous signaling, mediating in plant defense against pathogens .  It plays a role in the resistance to pathogens by inducing the production of pathogenesis-related proteins .  It is involved in the systemic acquired resistance in which a pathogenic attack on one part of the plant induces resistance in other parts. The signal can also move to nearby plants by salicylic acid being converted to the volatile ester, methyl salicylate .