Has a 11,12(11',12') 9-cis epoxycarotenoid cleavage activity. Catalyzes the first step of abscisic-acid biosynthesis from carotenoids. Contributes probably to abscisic acid synthesis for the induction of seed dormancy. a 9-cis-epoxycarotenoid + O2 = 2-cis,4-trans-xanthoxin + a 12'-apo-carotenal 9-cis-violaxanthin + O2 = (3S,5R,6S)-5,6-epoxy-3-hydroxy-5,6-dihydro-12'-apo-beta-caroten-12'-al + 2-cis,4-trans-xanthoxin 9'-cis-neoxanthin + O2 = (3S,5R,6R)-3,5-dihydroxy-6,7-didehydro-5,6-dihydro-12'-apo-beta-caroten-12'-al + 2-cis,4-trans-xanthoxin Binds 1 Fe(2+) ion per subunit. Partially bound to the thylakoid. Expressed before fertilization in male and female gametophytes, and then immediately after pollination, restricted to seed endosperm. Expressed in seeds at early and mid-maturation stages. Low induction by drought stress. Plants exhibit abscisic-acid-deficient phenotypes in seeds, but not in vegetative tissues. Belongs to the carotenoid oxygenase family.