Cytochrome P450 involved in brassinosteroids (BRs) inactivation and regulation of BRs homeostasis. Inactivates the BRs castasterone (CS) and brassinolide (BL) through carbon 26 hydroxylation. Acts in association with CYP72C1 to inactivate BRs and modulate photomorphogenesis. By brassinolide (BL), auxin and dark treatment. No visible phenotype under normal growth condition, but reduced responsiveness of hypocotyls to light and increased responsiveness to brassinolide (BL). Strong reduction of C-26 hydroxylase activity. Plants overexpressing CYP734A1 exhibit severe dwarfism. Belongs to the cytochrome P450 family.