New Compounds Induce Brassinosteroid Deficient-like Phenotypes in Rice
Abstract: Brassinosteroids (BRs) are steroidal plant hormones with potent plant growth
promoting activity. Because BR-deficient mutants of rice exhibit altered plant architecture
and important agronomic traits, we conducted a systemic search for specific inhibitors of
BR biosynthesis to manipulate the BR levels in plant tissues. Although previous studies
have been conducted with BR biosynthesis inhibitors in dicots, little is known regarding
the effects of BR biosynthesis inhibition in monocot plants. In this work, we used
potent inhibitors of BR biosynthesis in Arabidopsis, and we performed a hydroponic
culture of rice seedlings to evaluate the effects of BR biosynthesis inhibition. Among the
test compounds, we found that 1-[[2-(4-Chlorophenyl)-4-(phenoxymethyl)-1,3-dioxolan-2-
yl]methyl]-1H-1,2,4-triazole (1) is a potent inhibitor that could induce phenotypes in rice
seedlings that were similar to those observed in brassinosteroid deficient plants. The
IC 50 value for the retardation of plant growth in rice seedlings was approximately
1.27 ± 0.43 μM. The IC 50 value for reducing the bending angle of the lamina joint was
approximately 0.55 ± 0.15 μM.