Nonheme diiron monooxygenase involved in the biosynthesis of xanthophylls. Specific for beta-ring hydroxylations of beta-carotene. Produces beta-cryptoxanthin and zeaxanthin. 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] all-trans-beta-carotene + 2 H(+) + O2 + 2 reduced [2Fe-2S]-[ferredoxin] = beta-cryptoxanthin + H2O + 2 oxidized [2Fe-2S]-[ferredoxin] beta-cryptoxanthin + 2 H(+) + O2 + 2 reduced [2Fe-2S]-[ferredoxin] = all-trans-zeaxanthin + H2O + 2 oxidized [2Fe-2S]-[ferredoxin] Inhibited by o-phenanthroline and 8-hydroxyquinoline. Up-regulated during chloroplast to chromoplast transition stage. The histidine box domains may contain the active site and/or be involved in iron binding. Belongs to the sterol desaturase family.