Effects of a New Plant Growth Regulator Prohexadione Calcium (BX-112) on Shoot Elongation Caused by Exogenously Applied Gibberellins in Rice (<italic>Oryza sativa</italic> L.) Seedlings

The effects of a novel plant growth regulator (PGR) prohexadione calcium (BX-112; calcium 3,5-dioxo-4-propionylcyclohexanecarboxylate) on shoot elongation caused by exogenously applied GA1, GA3, GA4) GA19 and GA20 were investigated in rice (Oryza sativa L. cv. Nihonbare and cv. Tan-ginbozu) seedling test. Depending on the dose, BX-112 reduced shoot elongation in both cultivars caused by GA19 and GA20, but not by GA1. When a high dose of BX-112 (e.g. 250 ng/plant and over) was applied with GA1, or GA4, shoot elongation was even promoted. This promotive effect, however, was not observed with GA3. These results suggest that BX-112 inhibits gibberellin (GA) biosynthesis in the rice plant at the 3β- and 2β-hydroxylation of GAs, namely steps of activation and inactivation, respectively.