Zeaxanthin epoxidase that plays an important role in the xanthophyll cycle and abscisic acid (ABA) biosynthesis. Converts zeaxanthin into antheraxanthin and subsequently violaxanthin. all-trans-zeaxanthin + 4 H(+) + 2 O2 + 4 reduced [2Fe-2S]-[ferredoxin] = all-trans-violaxanthin + 2 H2O + 4 oxidized [2Fe-2S]-[ferredoxin] Plant hormone biosynthesis; abscisate biosynthesis. Expressed in flower buds, lips and leaves. Detected in roots. Expressed during floral development. High expression of beta-hydroxylase (BHY) and zeaxanthin epoxidase (ZEP) results in the accumulation of violaxanthin, 9-cis-violaxanthin and neoxanthin in the yellow cultivar Gower Ramsey, while the down-regulation of BHY and ZEP results in the accumulation of beta-carotene and orange coloration in floral tissues of the cultivar Sunkist.