Involvement of BU1 in BR signaling. A and B, Effect of BRZ. Etiolated seedlings of the wild type (WT) and BU1:OX-4 were grown in complete darkness with or without 10 μm BRZ2001 for 2 weeks prior to measurement of the length of the second lower internodes and mesocotyls. Arrows indicate nodes. Arrowheads indicate mesocotyls, organs between lowest nodes and seeds. Bar = 5 cm. The error bars indicate sd (n = >9). C, Gross morphology of d61, a BR-insensitive mutant that has an inactive BR receptor OsBRI1 (left), and d61 overexpressing BU1 (right). The erect leaf phenotype of d61 was complemented by overexpression of BU1. Bar = 50 cm. D, Culm of d61 (left) and d61 overexpressing BU1 (right). Arrows indicate nodes. Bar = 10 cm.