Abstract: | Earlier observations of Dawson on the relative incorporation of [2-3H]- and [6-3H]-nicotinic acid into nicotine have been confirmed in intact Nicotiana tabacum plants. All the tritium in the nicotine derived from [2-3H]-nicotinic acid was located at C-2 of the pyridine ring. However the radioactive nicotine derived from [6-3H]-nicotinic acid was not labelled specifically at C-6 with tritium. By carrying out feeding experiments with [6-14-C, 2-3H]- and [6-14C, 3H]-nicotinic acids, it was established that there was very little loss of tritium from C-2 and C-6 of nicotinic acid during 5 days of metabolism in the tobacco plant. |