Reductase involved in lignan biosynthesis (PubMed:18347017, PubMed:25107662). Involved in secondary cell wall biosynthesis in fiber cells (PubMed:25107662). Unlike conventional pinoresinol reductases that can reduce both pinoresinol and lariciresinol, PRR1 shows a strict substrate preference toward pinoresinol (PubMed:18347017). Active on both (+) and (-)-pinoresinol (PubMed:18347017). Abstracts the 4R-hydride from the NADPH cofactor during catalysis (PubMed:18347017). (-)-lariciresinol + NADP(+) = (-)-pinoresinol + H(+) + NADPH (+)-lariciresinol + NADP(+) = (+)-pinoresinol + H(+) + NADPH Forms homodimers. Expressed in roots and stems. No significant difference in lariciresinol content (PubMed:18347017). Prr1 and prr2 double mutants show a complete inhibition of lariciresinol biosynthesis (PubMed:18347017). Elevated levels of pinoresinol, reduced lignin content in the fiber cells, and a slightly altered lignin structure with low abundance of cinnamyl alcohol end groups (PubMed:25107662). Belongs to the NmrA-type oxidoreductase family. Isoflavone reductase subfamily.