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Uptake and metabolism of
[14C]glutamate and
[14C]malate by Betula
pendula/Paxillus involutus mycorrhizas
poster
BLAUDEZ DAMIEN, MICHEL CHALOT, PIERRE DIZENGREMEL & BERNARD
BOTTON
University Henri Poincaré-Nancy I, Faculty of
Sciences, Laboratory of Forest Biology, U.A. INRA 977, BP
239, F-54500 Vandoeuvre Cedex, France
ICOM1 Abstract
Modifications of nitrogen assimilation pathways during
mycorrhizas formation have been demonstrated by several
authors. Labelling experiments with
[14C]glutamate and [14C]malate were
performed with detached mycorrhizal (MYC) or non
mycorrhizal (NM) roots from 6 and 15 day-old and from 3
month-old seedlings. The newly-formed ECM roots (6 and 15
day-old) took up the label more efficiently than the oldest
one did. MYC roots took up the label at a 5- to 10-fold
higher rate, when compared with NM roots. Most of the label
in the MYC or NM root system was recovered in the soluble
fraction (amino and organic acids) but the ratio of the
radioactivity recovered in the soluble fraction on the
radioactivity recovered in the insoluble fraction was
higher in MYC roots. Under both [14C]glutamate
and [14C]malate feeding, glutamine was the main
labelled amino acid, the remaining radioactivity being
recovered in aspartate, glutamate, GABA and alanine in MYC
and NM roots. However, in MYC roots the ratio
[14C]glutamine/[14C]glutamate
remained higher compared with NM roots. The low recovery of
label in organic acids suggested that amino acid synthesis
is an important sink for TCA cycle intermediates. The
distribution of label differs also with the age of the
roots. For instance [14C]aspartate and
[14C]alanine were detected in 6 day-old MYC
roots but not in 15 day-old MYC roots. The implications of
such modifications for N and C interactions during the
early stages of mycorrhizas formation are discussed.