Changes in the activities of ornithine decarboxylase, putrescine N-methyltransferase and N-methylputrescine oxidase in tobacco roots in relation to nicotine biosynthesis

Changes in ornithine decarboxylase, putrescine N-methyltransferase and N-methylputrescine oxidase activities in response to some treatments were investigated using hydroponically grown tobacco plants. Decapitation of shoots brought about marked elevation of the three enzyme activities, which reached their peaks 24 hr after decapitation, then declined. An excellent correlation was observed between the accumulation of nicotine and changes in the three root enzyme activities. Administration of IAA at 2.5 to 5 μconcentration significandy increased these enzyme activities in roots of decapitated plants but higher concentrations of IAA prevented the rise in enzyme activities promoted by decapitation. Nicotine strongly inhibited the rise in enzyme activities in roots of decapitated plants in all cases. The results suggest that these enzymes are under the control of a common regulatory system, in which auxin and nicotine are important components. Ornithine decarboxylase was present in all the plants examined, but putrescine N-methyltransferase and N-mediylputrescine oxidase were detected only in the roots of tobacco, Datura and Atropa plants.