Involved in the biosynthesis of pyridine alkaloid natural products, leading mainly to the production of anabasine, anatabine, nicotine and nornicotine, effective deterrents against herbivores with antiparasitic and pesticide properties (neurotoxins); nornicotine serves as the precursor in the synthesis of the carcinogen compound N'-nitrosonornicotine (NNN) (PubMed:19002761, PubMed:31276744). Probable NADPH-dependent oxidoreductase that binds NADPH in vitro. Does not seem to be involved in the NADPH-dependent reduction of phenylcoumaran benzylic ethers (PubMed:12369619). Reductase that may be involved in a late step of tobacco alkaloid biosynthesis. Maybe involved in either the formation of a nicotinic acid-derived precursor or the final condensation reaction of tobacco alkaloids (PubMed:19002761). Alkaloid biosynthesis; nicotine biosynthesis. Monomer. Expressed in roots. Induced by methyl jasmonate in roots (PubMed:12369619, PubMed:19002761). Down-regulated by auxin (PubMed:8038607). Accumulates upon the removal of flower heads and young leaves (PubMed:8038607). Root cells silencing A622 exhibit inhibition of cell growth, severely decreased formation of several alkaloids, and accumulation of nicotinic acid beta-N-glucoside and N-methylpyrrolinium cation. Belongs to the NmrA-type oxidoreductase family. Isoflavone reductase subfamily.