Pyrrolidines, Piperidines, and Pyridines

Publisher Summary Alkaloids are derivatives of pyrrolidine, piperidine, and pyridine, which have simple structures. The alkaloids belonging to these groups have divergent physiological activities. This chapter focusses on restricted secondary metabolites in cultured plant cells. The alkaloid contents are lower in the cultures than in the intact plant. Nicotinic acid and nicotinamide adenine dinucleotide are metabolized to other compounds of the pyridine nucleotide cycle, and either trigonelline or nicotinic acid ν-α-L-arabinoside. The latter two compounds are metabolized to nicotinic acid and other compounds. These two types of nicotinic acid conjugates are believed to be a storage form of nicotinic acid. With a few exceptions, alkaloid concentrations in tobacco tissue cultures generally decrease with prolonged periods of subculture. The culture conditions inducing organogenesis stimulate alkaloid accumulation in tobacco tissue cultures. The activities of several enzymes involved in or related to pyridine nucleotide cycle are determined in connection with the regulation of nicotine accumulation in tobacco roots and calli. Nicotinic acid is replenished through two routes: directly from nicotinic acid mononucleotide and via the synthesis and degradation of NAD.