Stickstoff-Assimilation in der Wurzel und Transport von N-Verbindungen mit dem Blutungssaft der Wurzeln in Abhängigkeit von der Mn-Versorgung

Nitrogen Assimilation in Roots and the Transport of Nitrogen Compounds in the Bleeding Sap of Roots in relation to Manganese Nutrition. The assimilation of nitrogen in the roots of 27 days old pumpkin plants was examined in relation to manganese nutrition. The transport of nitrogen compounds in the xylem was determined in roots and in the bleeding sap of roots using nitrate as the N-source. The maximum NO₃ content in the roots was observed in the Mn treatment which resulted in the highest shoot yields (0.05 ppm Mn). The bleeding sap of this treatment was lowest in nitrate concentration, but showed the highest rate of transport of organic nitrogen compounds. In experiments with ¹⁵N in the nutrient solution the isotope was found in the roots in organic and in inorganic compounds. The composition of the fraction of free amino acids differed between roots and xylem sap. In the bleeding sap glutamine was especially dominant. In the roots the amino acid composition depended on the extent of Mn-supply. Lowest glutamine concentrations were found in the xylem sap from the treatment with maximum shoot yields. A numerical difference was found in the xylem sap between organic N (N_(org)) and the amino acid nitrogen. This difference which account for more than 50 % of the organically bound nitrogen is suggested to be made up in part by low molecular weight peptides, amino sugars and other compounds. In Mn deficiency a general reduction in the intensity of nitrogen metabolism was found. With Mn toxicity the N assimilation activity was more intensive than for the low Mn supply. Simultaneously, however, the transport of organic N compounds from the root was lower.