Catalyzes the C23-alpha-hydroxylation step in brassinosteroid biosynthesis (Probable). Converts 6-deoxocathasterone to 6-deoxoteasterone in the late C6-oxidation pathway and cathasterone to teasterone (TE) in the early C6-oxidation pathway of brassinolide (BL) biosynthesis (Probable). Plant hormone biosynthesis; brassinosteroid biosynthesis. Highly expressed in shoot apex and inflorenscence. Expressed in roots, stems, leaf blades and leaf sheaths. Down-regulated by brassinolide (BL). Belongs to the cytochrome P450 family.