Leaves of barley ( Hordeum vulgare L. cv. Salome) treated with jasmonic acid (JA), its methyl ester (JM), or its amino acid conjugates exhibit up-regulation of specific genes and down-regulation of house-keeping genes. This transcriptional regulation exhibits several specificities. (i) The (−)-enantiomers are more active, and conjugates are mainly active if they carry an l-amino acid moiety. (ii) The various JA-responsive genes respond differentially to enantiomeric and chiralic forms. (iii) Both JA and its amino acid conjugates exhibiting no or negligible interconversion induce/repress genes.