Jarin-1, an inhibitor of JA-Ile biosynthesis in Arabidopsis thaliana , acts differently in other plant species.

Jasmonates (JAs), including jasmonic acid (JA) and its biologically active derivative JA-Ile, are lipid-derived plant signaling molecules. They govern plant responses to stresses, such as wounding and insect herbivory. Wounding elicits a rapid increase of JA and JA-Ile levels as well as the expression of JAR1, coding for the enzyme involved in JA-Ile biosynthesis. Endogenous increase and application of JAs, such as MeJA, a JA methylester, result in increased defense levels, often accompanied by diminished growth. A JA-Ile biosynthesis inhibitor, jarin-1, was shown to exclusively inhibit the JA-conjugating enzyme JAR1 in Arabidopsis thaliana . To investigate whether jarin-1 does function similarly in other plants, we tested this in Medicago truncatula , Solanum lycopersicum , and Brassica nigra seedlings in a root growth inhibition assay. Application of jarin-1 alleviated the inhibition of root growth after MeJA application in M. truncatula seedlings, proving that jarin-1 is biologically active in M. truncatula . Jarin-1 did not show, however, a similar effect in S . lycopersicum and B. nigra seedlings treated with MeJA. Even JA-Ile levels were not affected by application of jarin-1 in wounded leaf disks from S. lycopersicum . Based on these results, we conclude that the effect of jarin-1 is highly species-specific. Researchers intending to use jarin-1 for studying the function of JAR1 or JA-Ile in their model plants, must test its functionality before use.