<jats:title>Abstract</jats:title> <jats:p>Treatment of opium poppy (Papaver somniferum L.) cell cultures with autoclaved mycelial homogenates of Botrytis sp. resulted in the accumulation of sanguinarine. Elicitor treatment also caused a rapid and transient induction in the activity of tyrosine/dopa decarboxylase (TYDC, EC 4.1.1.25), which catalyzes the conversion of L-tyrosine and L-dopa to tyramine and dopamine, respectively, the first steps in sanguinarine biosynthesis. TYDC genes were differentially expressed in response to elicitor treatment. TYDC1-like mRNA levels were induced rapidly but declined to near baseline levels within 5 h. In contrast, TYDC2-like transcript levels increased more slowly but were sustained for an extended period. Induction of TYDC mRNAs preceded that of phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) mRNAs. An elicitor preparation from Pythium aphanidermatum was less effective in the induction of TYDC mRNA levels and alkaloid accumulation; however, both elicitors equally induced accumulation of PAL transcripts. In contrast, treatment with methyl jasmonate resulted in an induction of TYDC but not PAL mRNAs. The calmodulin antagonist N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide and the protein kinase inhibitor staurosporine partially blocked the fungal elicitor-induced accumulation of sanguinarine. However, only staurosporine and okadaic acid, an inhibitor of protein phosphatases 1 and 2A, blocked the induction of TYDC1-like transcript levels, but they did not block the induction of TYDC2-like or PAL tanscript levels. These data suggest that activation mechanisms for PAL, TYDC, and some later sanguinarine biosynthetic enzymes are uncoupled.