Metabolism of the Methyl Group of Nicotine in Nicotiana rustica

The methyl group of nicotine has been shown to participate in transmethylation reactions involving methionine (3) and choline (8). De novo synthesis of radioactive nicotine from nornicotine, methioninemethyl-C14 and ATP was demonstrated recently in leaves of Nicotiana alata (9). In the present study the rate of metabolism of the methyl group of nicotinemethyl-C14 and the rate of transmethylation from methionine-methyl-C14 to nicotine were investigated in mature N. rustica plants. It has been suggested that metabolism of nicotine takes place in the roots of tobacco plants (8). After translocation to the upper parts of the plant, nicotine is thought,to remain metabolically inert. This was confirmed in part by studying metabolism of methyland ring-labeled nicotine and methyl-labeled methionine in rootless N. rustica plants. In contrast to plants with roots, rootless plants showed little or no ability to metabolize ringlabeled nicotine or to transfer methyl groups from methionine to nicotine. However, methyl groups of methyl-labeled nicotine were metabolized by plants without roots to the extent of 39 % of the total nicotine methyl metabolism in whole plants.