EXPRESSION OF (S)-SCOULERINE 9-O-METHYLTRANSFERASE IN COPTIS-JAPONICA PLANTS

(S)-adenosyl-L-methionine: (S)-scoulerine 9-O-methyltransferase (SMT: EC 2.1.1.), which catalyses the transfer of the S-methyl group of S-adenosyl-L-Methionine (SAM) to the 9-hydroxyl group of (S)-scoulerine to form (S)-tetrahydrocolumbamine, is responsible for a late step in the biosynthesis of berberine. An antibody specific to SMT was prepared against enzyme purified from cultured Coptis cells. Content and activity of SMT were measured in extracts from different tissues of Coptis plants and the relationship between SMT expression and the accumulation of alkaloids was examined. In intact plants, berberine accumulated predominantly in the main roots, while other tissues contained fewer alkaloids. However, SMT activity and protein levels indicated that the main roots were a rather poor site for biosynthesis, and that perhaps other tissues, especially lateral roots and stems, were the primary sites for biosynthesis. This result suggests that main roots may be storage sites for berberine alkaloids synthesized in other tissues. The relative ease by which berberine is produced in cultured cells may reflect these characteristics of berberine biosynthesis. Furthermore, analysis of cultured cells with different alkaloid-producing abilities showed that SMT was not involved in the rate limiting step in berberine biosynthesis and it did not determine the ratio of coptisine to berberine in cultured cells.