Abstract
Recent research has underscored the importance of nicotinamide adenine dinucleotide (NAD) biosynthesis. In Arabidopsis, genes involved in the NAD biosynthetic pathway have not been fully determined. Previously, we identified the gene encoding NAD synthetase (NADS), which acts in the final step of NAD biosynthesis. Transcriptional analysis revealed that guard cells (GCs) have relatively high levels of NAD biosynthetic gene expression. The NAD level in the epidermis including GCs was transiently decreased by abscisic acid (ABA), whereas nicotinate mononucleotide adenyltransferase (NMNAT) activity was increase by ABA; however, the increase was significantly delayed compared to the decrease in NAD. The activity of NADS was in a steady state during NAD fluctuation. Stomatal movement and drought tolerance were correlated to the activity of NMNAT. We proposed that NAD biosynthetic activity is involved in regulation of stomatal aperture, possibly via the regulation of NMNAT activity.
