Amino acid conjugates as metabolites of the plant growth regulator dihydrojasmonic acid in barley (Hordeum vulgare)

The biotransformation of 2-¹⁴C](±)9, 10-dihydrojasmonic acid (DJA) was studied in excised shoots of 6-day-old barley seedlings after 72 h. From the ethyl acetate extract, some minor metabolites were isolated and purified by DEAE-Sephadex A-25 chromatography, thin-layer chromatography (TLC), C₁₈-cartridges, and high-performance liquid chromatography (HPLC). The structural identification of these metabolites was performed by gas chromatography-mass spectrometry (GC-MS), circular dichroism (CD), and amino acid analysis, and the following amino acid conjugates were found:N-(?)9,10-dihydrojasmonoyl]valine,N-(?)9,10-dihydrojasmonoyl]isoleucine,N-9,10-dihydrojasmonoyl]leucine,N-11-hydroxy-9,10-dihydrojasmonoyl]valine,N-11-hydroxy-9,10-dihydrojasmonoyl]isoleucine,N-12-hydroxy-9,10-dihydrojasmonoyl]isoleucine; and the cucurbic acid-related compoundsN-{3-hydroxy-2(4-hydroxypentyl)-cyclopent-1-yl]-acetyl}isoleucine andN-{3-hydroxy-2(5-hydroxypentyl)-cyclopent-1-yl]-acetyl}isoleucine. The results suggest conjugation with isoleucine and valine, as well as preferential hydroxylation at position C-11 or hydrogenation at position C-6, as being important steps in the metabolism of (±)DJA in barley shoots.