Nonheme diiron monooxygenase involved in the biosynthesis of xanthophylls. Specific for beta-ring hydroxylations of beta-carotene. Has also a low activity toward the beta- and epsilon-rings of alpha-carotene. No activity with acyclic carotenoids such as lycopene and neurosporene. Uses ferredoxin as an electron donor. all-trans-beta-carotene + 4 H(+) + 2 O2 + 4 reduced [2Fe-2S]-[ferredoxin] = all-trans-zeaxanthin + 2 H2O + 4 oxidized [2Fe-2S]-[ferredoxin] Homodimer. Expressed in leaves, flowers, stems, roots and siliques. The histidine box domains may contain the active site and/or be involved in iron binding. The N-terminal part of the mature protein (70-129) is probably involved in the formation of a functional homodimer. No visible phenotype when grown under normal light conditions; due to redundancy with BCH2. Bch1 and bch2 double mutant has no visible phenotype but lower levels of beta, beta-xanthophylls and increased beta-carotene and lutein. Cyp97c1, bch1 and bch2 triple mutant is paler and smaller than wild-type. A protein lacking the first 69 amino acids has a normal in vitro activity, while a protein lacking 129 N-terminal amino acids produces predominantly the monohydroxy intermediate beta-cryptoxanthin. Belongs to the sterol desaturase family.