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Host plant stimulates the tryptophan betaine, hypaphorine,
accumulation in Pisolithus tinctorius hyphae during
ectomycorrhizal infection. Fungal hypaphorine controls
K+ uptake, H+ extrusion and root hair
development
Talk. Thursday session 7: Systematics, Specificity and Recognition
BEGUIRISTAIN THIERRY, JIANGUO HUANG & FREDERIC LAPEYRIE
Equipe de Microbiologie Forestière, I.N.R.A., Centre de
Nancy, 54280 Champenoux, France
ICOM1 Abstract
Hypaphorine, the betaine of tryptophan, is the major indolic
compound which accumulates in Pisolithus tinctorius hyphae.
Hypaphorine is over-accumulated in P. tinctorius tissues as
soon as hyphae are in contact with host plant root surface.
This phenomenon observed, 24 hours after inoculation was
recorded as well in several month old ectomycorrhizae. Such
over-accumulation is controlled by specific root diffusible
molecules, it could be induced through a membrane, but non-
host plants are inactive.
Hypaphorine solutions (0.1-10 µM) applied to fungal colonies
stimulated net K+ uptake and net H+
extrusion. Hypaphorine
and IAA activities were in the same range of magnitude, while
tryptophane, a precursor of IAA and hypaphorine in P.
tinctorius, was inactive. P. tinctorius, a hypaphorine
producer, was much less responsive to exogenous micromolar
hypaphorine solutions, than Paxillus involutus, a non-
hypaphorine producer. Hypaphorine might be in some way
contributing to ion fluxes regulation through plasma
membrane, in hyphal tip for cell elongation and in
mycorrhizae for nutrient exchange between hyphae and root
cortical cells.
Fungal hypaphorine had no IAA like activity on Eucalyptus
root elongation and ramification and therefore could not be
considered as an auxin analogue, instead a strong reduction
of root hairs elongation was recorded (10-1000 µM)