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JXB Advance Access published online on March 31, 2003
Journal of Experimental Botany, doi:10.1093/jxb/erg146
© 2003 by Oxford University Press
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Received October 21, 2002; accepted January 20, 2003
© 2003 Society for Experimental Biology

RESEARCH PAPER

Bidirectional exchange of amino compounds between phloem and xylem during long-distance transport in Norway spruce trees (Picea abies [L.] Karst)

Arthur Geßler 1, Paul Weber 1, Stephan Schneider 1, Heinz Rennenberg 1*

1 Institut für Forstbotanik und Baumphysiologie, Professur für Baumphysiologie, Albert-Universität Freiburg, Georges-Köhler-Allee Geb 053/054, D-79110 Freiburg i. Br., Germany

* To whom correspondence should be addressed. E-mail: Heinz.rennenberg{at}ctp.uni-freiburg.de.


  Abstract

14C-Gln, 14C-Asp, 15N-Gln, and 15N-Asp were fed to cut tips of 2- or 3-year-old needles of spruce twigs, still attached to the tree. After incubation, distribution of the radiolabel and 15N enrichment was studied in needles, bark and wood tissues of girdled twigs and untreated controls. Analysis of the twig tissues showed that between 22% and 26% of the total amount of the tracers applied had been taken up. Since export out of the application segment and distribution between needles, bark and wood was comparable for 14C and 15N tracer, it was concluded that, mainly the amino compounds that had been fed were subject to long- distance transport within the plant and supplied the new sprout with nitrogen. Asp was exported to a greater extent to developing needles compared with Gln. This difference in export between the two amino compounds applied may be explained by the different pool sizes of Gln and Asp in xylem and phloem or differences in xylem and phloem loading. Girdling of the stem showed that the transport of reduced nitrogen compounds from older needle generations to current-year needles proceeded in both xylem and phloem. In addition, an intensive bidirectional exchange of Gln and Asp between xylem and phloem was observed during long-distance transport.

Key words: Amino acids, girdling, long-distance transport, Picea abies, phloem-xylem exchange, spruce.


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