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 (Weidh ase 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 re tardant tetcyclacis at concentrations as low as 1 mu M. In parallel wi th the decrease of jasmonates, JIP gene expression was reduced as refl ected 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 overc ome the inhibition by tetcyclacis and increases both the endogenous ja smonate content and transcript accumulation. This suggests that tetcyc lacis acts upstream of 12-oxo-phytodienoic acid and in keeping with th is proposal, an increase in relative LOX activity was detected after t etcyclacis treatment. Although tetcyclacis was shown to inhibit the de gradation of ABA to phaseic acid, its effect on jasmonate synthesis is much more pronounced.