Nicotinic acid and nicotinamide metabolism and promotion of cell arrest in G2 in Pisum sativum

Abstract Nicotinic acid and nicotinamide are immediate precursors of trigonelline, a hormone present in cotyledons of Pisum sativum L. which promotes cell arrest in G2 during cell maturation in roots and shoots. All three compounds are members of the pyridine nucleotide pathway for the synthesis of NAD and NADP. Concentrations of nicotinic acid and nicotinamide in excised roots grown for 3 days in White's medium with sucrose were determined by HPLC. Results suggest that nicotinamide is rapidly converted first to nicotinic acid and then trigonelline. High nicotinic acid concentrations may occur in excised roots. Conversion of trigonelline to nicotinic acid in excised roots did not occur in these experiments. The concentrations of either nicotinamide or nicotinic acid in roots are not related to the proportions of cells arrested in G2. Trigonelline promotes cell arrest in G2, and nicotinic acid and nicotinamide are active only because they are converted to trigonelline.