SYNTHESIS OF JASMONATE-INDUCED PROTEINS IN BARLEY (HORDEUM-VULGARE) IS INHIBITED BY THE GROWTH RETARDANT TETCYCLACIS

Barley leaf segments treated with jasmonate respond with the synthesis of specific proteins,referred to as jasmonate-induced proteins (JIPs). Application of abscisic acid (ABA) also induced JIP synthesis (Weidhase et al. 1987). In this study the effects of inhibitors on sorbitol-induced increases of endogenous jasmonates and ABA were investigated. The promotion of jasmonates by sorbitol was inhibited by the growth retardant tetcyclacis at concentrations as low as 1 mu M. In parallel with the decrease of jasmonates, JIP gene expression was reduced as reflected by a decline in the level of a 23-kDa protein (JIP-23) and mRNAs of JIP-6 and JIP-23. 12-Oxo-phytodienoic acid, an intermediate in the lipoxygenase (LOX) pathway leading to jasmonic acid was able to overcome the inhibition by tetcyclacis and increases both the endogenous jasmonate content and transcript accumulation. This suggests that tetcyclacis acts upstream of 12-oxo-phytodienoic acid and in keeping with this proposal, an increase in relative LOX activity was detected after tetcyclacis treatment. Although tetcyclacis was shown to inhibit the degradation of ABA to phaseic acid, its effect on jasmonate synthesis is much more pronounced.