Increases in jasmonic acid caused by indole-3-acetic acid and auxin herbicides in cleavers (Galium aparine)

The effects of indole-3-acetic acid and auxin herbicides on endogenous jasmonic acid (JA) concentrations were studied in relation to changes in ethylene and abscisic acid (ABA) levels in cleavers (Galium aparine). When plants were root-treated with increasing concentrations of indole-3-acetic acid (IAA), ethylene biosynthesis was stimulated in response to the accumulation of endogenous IAA in the shoot tissue. Within 25 h of treatment, stimulated ethylene formation was accompanied by increases in immunoreactive concentrations of JA and ABA, which reached maxima of 4.5-fold and 26-fold of the control, respectively, at 100 μM of applied IAA. Corresponding effects were obtained using synthetic auxins and when the ethylene-releasing compound ethephon was applied exogenously. This represents the first report, to our knowledge, of an auxin-mediated increase in JA levels. The increase in JA may be triggered by ethylene.