The Biosynthesis of Nicotine and Related Alkaloids in Intact Plants, Isolated Plant Parts, Tissue Cultures, and Cell-Free Systems

The A622 gene in Nicotiana glauca (tree tobacco): evidence for a functional role in pyridine alkaloid synthesis

“…However, the fact that addition of nicotinic acid to hairy root lines containing the NgRNAi-A622 construct does not restore capacity to produce nicotine and anabasine, nor enable these cultures to synthesise anatabine unlike control root lines, does suggest a role for A622 in the steps between nicotinic acid biosynthesis (via the pyridine nucleotide cycle) and the synthesis of these alkaloids. In this respect, it is noteworthy that previous studies from the laboratory of Leete led to the suggestion that the synthesis of pyridine alkaloids involves reduction of nicotinic acid to 3,6-dihydronicotinic acid before its condensation with either 1-methyl-D 1 -pyrrolinium or D 1 -piperideine to form nicotine and anabasine respectively, or with nicotinic acid to produce anatabine (Leete and Slattery 1976;Leete 1992). Whether the activity of A622 does indeed function to enable synthesis of 3,6-dihydronicotinic acid as a necessary intermediate for production of pyridine alkaloids in Nicotiana remains to be determined but such an explanation would be compatible with the results presented in the present study.…”

“…Biochemical studies have indicated that biosynthesis of both anabasine and nicotine may involve the same enzyme complex which acts upon a common derivative from the pyridine nucleotide cycle to provide the pyridine rings of both alkaloids (Leete and Slattery 1976;Leete 1992). Independent studies also demonstrated that increased levels of cadaverine (derived from lysine) in roots of N. rustica or N. tabacum, resulted in substantial increases in anabasine concentrations at the expense of nicotine (Walton et al 1988;Fecker et al 1993).…”

“…However, the later stages of alkaloid synthesis remain rather uncharacterized in Nicotiana species, with only one study describing the characteristics of a 'nicotine synthase' complex via the in vitro assay of root extracts from Nicotiana glutinosa and N. tabacum (Friesen and Leete 1990). As noted by Leete (1992), this crude enzyme preparation may have contained a mixture of enzymes, including possibly an NADPH requiring enzyme which causes the stereospecific reduction of nicotinic acid to 3,6-dihydronicotinic acid-a proposed key intermediate in the synthesis of anabasine and anatabine as well as nicotine (Leete 1992).…”

Nicotine uptake by peppermint plants as a possible source of nicotine in plant-derived products

“…Either the plants incorporate the alkaloid from exogenous sources, or they are able to synthesise the alkaloid endogenously. In addition to nicotine-accumulating plants of the genus Nicotiana, the alkaloid has also been found in some other members of the Solanaceae family, such as potatoes, tomatoes and eggplants (Leete 1992). Although the corresponding nicotine concentrations in these vegetables (up to 0.24 mg kg −1 d.w.) (0.24 μg g −1 d.w. ;Siegmund et al 1999) are about 25 times higher than the official MRL, they are several magnitudes lower than those found in tobacco (more than 10,000 μg g −1 d.w.; Saithoh et al 1985).…”

Enantioselective Demethylation of Nicotine as a Mechanism for Variable Nornicotine Composition in Tobacco Leaf

“…Racemization of nornicotine was proposed to explain the high percentage of (R)-nornicotine accumulation (15), supported by the claim that (R)-nornicotine was observed in leaves when feeding (S)-nicotine (14). However, racemization was not confirmed when tested in cell culture assays (16,17).…”