Formation of jasmonates from octadecanoids (A) and endogenous levels of free JA upon treatment with deuterated JA (B) in barley leaf segments. A, 50 μm OPDAME or 50 μm OPDA was applied, and the formation of JA (black columns), JAME (white columns), and OPDA (hatched columns) were measured. B, 45 μm [2H6]JA was applied, and its portion taken up (hatched columns) and the endogenous levels of JA (black columns) were determined.