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

(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-ad enosyl-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 a gainst enzyme purified from cultured Coptis cells. Content and activit y of SMT were measured in extracts from different tissues of Coptis pl ants and the relationship between SMT expression and the accumulation of alkaloids was examined. In intact plants, berberine accumulated pre dominantly in the main roots, while other tissues contained fewer alka loids. However, SMT activity and protein levels indicated that the mai n roots were a rather poor site for biosynthesis, and that perhaps oth er 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 relat ive 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 biosy nthesis and it did not determine the ratio of coptisine to berberine i n cultured cells.