ASSIMILATION OF NITROGEN IN ROOT NODULES OF ALDER (ALNUS GLUTINOSA)

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Abstract
Summary: 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 N2‐ase, GS, GDH, and OCT in root nodule homogenates are reported. From the Km values of GDH for NH4+ (16mM) and glutamate (0·9 mM) and the concentrations in the nodule of NH4+ (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 N2‐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.