Influx of double labelled glutamine into mistletoes (Viscum album) from the xylem sap of its host (Abies alba)

The flux of glutamine into the mistletoe Viscum album from the xylem sap of a coniferous host was analyzed. For this purpose, a perfusion system was used in which the xylem sap of the host was replaced by an artificial perfusion solution. With this system, flux rates into the mistletoe were determined in feeding experiments with the organic nitrogen source U13C/15N-Gln. At the end of the experiments the δ values of C and N were significantly depleted in the outflow compared to the percolation solution. Since this depletion was higher for C than for N, a combination of Gln uptake and simultaneous uploading of organic compounds in the host xylem can be assumed. Gln was strongly metabolized during its allocation in the mistletoe. As a consequence, the C skeleton of Gln was equally distributed between leaf and stem tissue, whereas N of Gln preferentially accumulated in the stem. Apparently, the C atoms of the Gln taken up are transported faster in the mistletoe to the sink tissues than the N atoms. It is concluded that C liberated from Gln is transported rapidly to different sink tissues, whereas N in the oversupplied mistletoes is transported slowly to sinks in the leaves.