Seasonal Dynamics of Nitrogenous Compounds in a Nitrophilic Weed II. The Role of Free Amino Acids and Proteins as Nitrogen Store in Urtica dioica

The free amino acid fraction, representing the most importantnitrogen store in the overwintering below ground plant partsof Urtica dioica, consisted mainly (up to 80%) of asparagineand arginine. While asparagine was dominant in rhizomes, upto one year old, argrnine was specifically accumulated in theolder rhizomes and roots. In spring first the nitrogen storedin asparagine and with a delay of about three weeks that inarginine was mobilized and translocated to the rapidly growingshoots. Proteins may function as nitrogen store too, in particularin the case of the seeds. In the below ground organs, however,a special storage protein, rich in amides and/or arginine, whichwould correspond to the large quantities of these amino acidsin the overwintering organs, could not be detected. (Received September 3, 1984; Accepted November 2, 1984)