Abstract
Lotus japonicas is a model organism for leguminous plants and is used for a full genome sequencing project. To incorporate gene expression information in our metabolic studies, we investigated the biosynthesis of pyridine nucleotides and trigonelline in cell suspension cultures of L. Japonicas. The in situ metabolism of [3H]quinolinic acid and [14C]nicotinamide revealed that the activity of the de novo pathway for NAD synthesis was maximum in the exponential growth phase, whereas the salvage pathway was high in the lag phase. Transcript levels of NaPRT and NIC encoding salvage enzymes, were enhanced in the lag phase of cell growth whereas the maximum expression of NADS was found in the exponential growth phase. Correspondingly, the activities of the salvage enzymes, nicotinate phosphoribosyltransferase (EC 2.4.2.11) and nicotinamidase (EC 3.5.1.19), increased one day after transfer the stationary phase cells to the fresh medium. The greatest trigonelline synthesis was found in the stationary phase of cell growth. The role of trigonelline in leguminous plants is discussed.
