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Jasmonic acid (JA) and its various derivatives are lipid-derived signaling molecules which participate in the regulation of a number of plant processes, including growth, reproductive development, photosynthesis, and responses to biotic and abiotic stress factors. As compared to auxins, ABA, cytokinins, GAs, and ethylene, discovery of JA and elucidation of its roles in plants have been made in the relatively recent past. JA was first isolated from the fungus Lasiodiplodia theobromae as a plant growth inhibitor. Among green plants, the free acid (−JA) was first detected and identified as a growth inhibitor from the pericarp of Vicia faba (broad bean). The immature fruits of Vicia faba contain a mixture of (−) JA and its stereoisomer (+)-7-iso-jasmonic acid (+7-iso-JA) in 65–35% ratio (Fig. 21.1). Hydroxy-jasmon ester of chrysanthemic acid in pyrethrins (a class of insecticides), isolated from Chrysanthemum cinerariifolium (Pyrethrum), was the first JA metabolite discovered from plants. Active jasmonates, most importantly the methyl esters of jasmonates (JAMe), were initially detected as odorants from the flowers of Jasminum grandiflorum.