This enzyme converts phytoene into zeta-carotene via the intermediary of phytofluene by the symmetrical introduction of two double bonds at the C-11 and C-11' positions of phytoene. Also active with phytofluene and 1,2-epoxyphytoene as substrates. 15-cis-phytoene + 2 a plastoquinone = 9,9',15-tri-cis-zeta-carotene + 2 a plastoquinol Inhibited by the herbicide norflurazon in a non-competitive way. Carotenoid biosynthesis; lycopene biosynthesis. Up-regulated by light. Can also use NAD(+) and NADP(+) as electron acceptor under anaerobic conditions. Belongs to the carotenoid/retinoid oxidoreductase family.