Involved in the biosynthesis of benzylisoquinoline alkaloids. N-methyltransferase methylating (S)-coclaurine. 4'-O-methylcoclaurine and norlaudanine can also be used as substrates. (S)-coclaurine + S-adenosyl-L-methionine = (S)-N-methylcoclaurine + H(+) + S-adenosyl-L-homocysteine Alkaloid biosynthesis; (S)-reticuline biosynthesis; (S)-reticuline from (S)-norcoclaurine: step 2/4. Expressed in roots, stems, flower buds and at lower levels, in leaves (PubMed:12946416, PubMed:16813579). Restricted to sieve elements of the phloem adjacent or proximal to laticifers (PubMed:16813579). Transiently induced from 4 to 7 days after seed imbibition. Up-regulated upon fungal elicitor treatment or wounding. Belongs to the CFA/CMAS family.