A methyltransferase for synthesis of the phytoalexin 6‐methoxymellein in carrot cells

Carrot ( Daucus carota L.) roots treated with 2‐chloroethylphosphonic acid or uronide elicitor accumulated the phytoalexin 6‐methoxymellein. The extracts of these cells catalyzed methylation of 6‐hydroxymellein to 6‐methoxymellein with S ‐adenosyl‐L‐methionine as a methyl donor. Activity of the O ‐methyltransferase was not found in fresh carrot roots but increased when they were treated with either type of elicitor in parallel with the increase in 6‐methoxymellein content. The enzyme did not methylate 6‐methoxymellein, 3,4‐dehydro‐6‐methoxymellein, and some coumarin derivatives, though 3,4‐dehydro‐6‐hydroxymellein accepted methyl moiety at the same rate as in 6‐hydroxymellein.