9-hydroxy-3,5,7,11,13,15,17,19-octaoxohenicosanoyl-[acp] + NADP+ ← NADPH + 3,5,7,9,11,13,15,17,19-nonaoxohenicosanoyl-[acp] + H+
(6Z,9Z,12Z,15Z)-3-hydroxy-2-[(2Z,5Z,8Z,11Z)-tetradeca-2,5,8,11-tetraen-1-yl]octadeca-6,9,12,15-tetraenoate + NADP+ ← NADPH + (6Z,9Z,12Z,15Z)-3-oxo-2-[(2Z,5Z,8Z,11Z)-tetradeca-2,5,8,11-tetraen-1-yl]octadeca-6,9,12,15-tetraenoate + H+