Plants respond to several environmental stresses such as pathogen attack, mechanical or herbivorous insect-driven wounding and the presence of pollutants by the synthesis of secondary metabolites that mediate interplant communication for defense responses. Among these signalling molecules are phytohormones: jasmonic acid (JA), salicylic acid (SA) and abscisic acid (ABA). They are considered to be the major regulators of plant defense responses. The role of salicylic acid in influencing plant resistance to pathogens (aphids, bacteria, fungi) is well documented, whereas jasmonic acid is commonly believed to play an important role in plant responses to insect herbivores and abiotic stress. The soluble jasmonic acid acts as a direct defense to herbivores or others injuries, whereas the volatile form, methyl jasmonate, represents a plant signal molecule, which serves as an indirect defense mechanism.