Influence of Certain Amino Acids and of Nicotinic Acid upon the Nicotine Content of Tobacco Leaves.

The tobacco alkaloid nicotine possesses a molecular structure by which it may be related empirically to the amino acid proline. Proline is a-pyrrolidinecarboxylic acid. Nicotine may be considered as an N-methylated proline containing a 3-pyridine rino attached to the alpha position in place of the carboxyl. These similarities have been pointed out by TOTTINGHAM (9) and have been employed by TRIER (12) as a basis for extensive speculations on the probable origin of nicotine in the tobacco plant. According to TRIER, nicotine may be formed in vivo from proline and nicotinic acid by a simultaneous oxidative decarboxylation of the two molecules. The methylation of the pyrrolidine nitrogen was accounted for by the action of methyl alcohol as a dismutation product of formaldehyde. TRIER postulated the formation of the pyridine portion of the nicotine molecule from proline through the intervention of formic acid as the second dismutation product of formaldehyde. In short, the hypothesis of TRIER assigned to proline the role of precursor of both the fiveand the six-membered rings of the nicotine molecule. It should be noted, however, that TRIER'S theory was advanced at a time when nicotinic acid was practically unknown in the literature of plant chemistry. KLEIN and LINSER (7) tested TRIER's hvpothesis by culturing the excised leafy shoots of tobacco plants in dilute aqueous solutions of proline. These investigators obtained large increases in the nicotine content of the leaves and stems of the plants to which proline had been supplied. The hydrochlorides of glutamic acid and of ornithine were found to possess similar effects. GORTER (5) critically reviewed the work of KLEIN and LINSER and presented data of his own to show that both those plants provided with proline and those cultured in KNOP'S solution after a period of 4 or 5 days contained less nicotine than at the beginning of the experiment. The increase in nicotine content of the leaves of the plants supplied with proline was onlly apparent and represented merely a less extensive decrease rather than an actual synthesis of nicotine. In the present study attention was given to the influences of proline, pyrrolidonecarboxylic acid, glutamic acid, ornithine, nicotinic acid, and other substances upon the nicotine content of tobacco leaves by the use of methods of culture and of expression of data 1 Contribution from the Osborn Botanical Laboratory, Yale,University.