SYNTHETICINHIBITORS OF GA BIOSYNTHESIS AND METABOLISM Many chemical inhibitors are known which block GA biosynthesis. Several inhibitors, e.g., AMO-16182 and cycocel, block the A activity of ent-kaurene synthesis. Other inhibitors block the pathway at the next stage, i.e., during the oxidation of ent-kaurene. These include ancymidol, tetcyclacis(structure 4), paclobutrazol(structure 5), and uniconazole(structure 6). These inhibitors are known to perturb the activity of P-450 mono-oxygenases. The modes of action and comparable activities of these inhibitors, all of which are effective growth retardants, have been extensively reviewed(20, 41)