ASSIMILATION OF NITROGEN IN ROOT NODULES OF ALDER (<i>ALNUS GLUTINOSA</i>)

Abstract

S ummary Citrulline is shown to be the predominant free amino acid in alder root nodules, while serine also occurs in relatively large amounts. Citrulline and glutamic acid are prominent free amino acids in alder xylem tissue. The activities of N 2 ‐ase, GS, GDH, and OCT in root nodule homogenates are reported. From the K m values of GDH for NH 4 + (16mM) and glutamate (0·9 mM) and the concentrations in the nodule of NH 4 + (1·5 HIM) and glutamate (0·5 mM) it is concluded that GDH in alder nodules is responsible for the deamination of glutamate. The important function of GDH in the nitrogen metabolism of alder nodules is confirmed by the much higher activity of this enzyme in homogenates of nodules as compared to that in homogenates of root‐tips and leaves. The vesicle clusters, which contain the N 2 ‐ase activity, did not show activity of GS, GDH and OCT. The cytoplasm of the host cells was shown to possess the GS activity, while GDH and OCT probably are localized in the organelles of the host cells.