Abstract
We have already reported that NiA and related compounds had plant-growth-promoting and flower-inducing activities in duckweed, Lemna paucicostata 151. These effects may be concerned with the biosynthesis and metabolism of NAD. So, for the first step, the various enzyme activities related to them were investigated in this study to obtain some fundamental information on the action mechanism of these compounds and metabolites. Extremely high enzyme activity of nicotinamidase and very high enzyme activity of NAD glycohydrolase were found. The enzyme activities of nicotinate phosphoribosyltransferase, quinolinate phosphoribosyltransferase, and nicotinate methyltransferase were easily detected. In contrast, nicotinamide phosphoribosyltransferase and ADP-ribosyltransferase activities were very low and nicotinamide methyltransferase activity was not detectable. NiA and NAm administered to the plant were rapidly incorporated into NAD and metabolized to several compounds. Postulation of the action mechanism is discussed.
