Catalyzes the reduction of the 7-8 double bond of phenylpropanal substrates, such as p-coumaryl aldehyde and coniferyl aldehyde (in vitro). Has activity towards toxic substrates, such as 4-hydroxy-(2E)-nonenal (in vitro) (By similarity). May play a distinct role in plant antioxidant defense and is possibly involved in NAD(P)/NAD(P)h homeostasis. an n-alkanal + NAD(+) = an alk-2-enal + H(+) + NADH an n-alkanal + NADP(+) = an alk-2-enal + H(+) + NADPH Homodimer. Belongs to the NADP-dependent oxidoreductase L4BD family.