Reductase involved in lignan biosynthesis. Catalyzes the enantioselective sequential conversion of (+)-pinoresinol into (+)-lariciresinol and of (+)-lariciresinol into (-)-secoisolariciresinol. Abstracts the 4R-hydride from the NADPH cofactor during catalysis. (+)-lariciresinol + NADP(+) = (+)-pinoresinol + H(+) + NADPH (-)-secoisolariciresinol + NADP(+) = (+)-lariciresinol + H(+) + NADPH Optimum pH is 7.4. Optimum temperature is 30 degrees Celsius. Dimer. Expressed in young stems, young roots and petioles. In stems, expressed in radial parenchyma cells and in the cambial cells of developing secondary xylem. Belongs to the NmrA-type oxidoreductase family. Isoflavone reductase subfamily.