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Plant Physiol, November 2000, Vol. 124, pp. 1373-1380
How Alfalfa Root Hairs Discriminate between Nod Factors and
Oligochitin Elicitors1
Hubert H.
Felle,*
Éva
Kondorosi,
Ádam
Kondorosi, and
Michael
Schultze
Botanisches Institut I, Justus-Liebig-Universität,
Senckenbergstrasse 17, D-35390 Giessen, Germany (H.H.F.); Institut des
Sciences Végétales, Centre National de la Recherche
Scientifique, Avenue de la Terrasse, F-91198 Gif-sur-Yvette, France
(É.K., Á.K.); Institute of Genetics, Biological Research
Center, Hungarian Academy of Sciences, P.O. Box 521, H-6701 Szeged,
Hungary (Á.K.); and The Plant Laboratory, Department of Biology,
University of York, Heslington, York Y01 5YW, United Kingdom
(M.S.)
Using ion-selective microelectrodes, the problem of how signals
coming from symbiotic partners or from potential microbial intruders
are distinguished was investigated on root hairs of alfalfa
(Medicago sativa). The Nod factor, NodRm-IV(C16:2,S), was used to trigger the symbiotic signal and (GlcNAc)8 was
selected from (GlcNAc)4-8, to elicit defense-related
reactions. To both compounds, root hairs responded with initial
transient depolarizations and alkalinizations, which were followed by a
hyperpolarization and external acidification in the presence of
(GlcNAc)8. We propose that alfalfa recognizes tetrameric
Nod factors and N-acetylchitooligosaccharides (n = 4-8) with separate perception sites: (a)
(GlcNAc)4 and (GlcNAc)6 reduced the
depolarization response to (GlcNAc)8, but not to
NodRm-IV(C16:2,S); and (b) depolarization and external alkalization
were enhanced when NodRm-IV(C16:2,S) and (GlcNAc)8 were
added jointly without preincubation. We suggest further that changes in
cytosolic pH and Ca2+ are key events in the transduction,
as well as in the discrimination of signals leading to symbiotic
responses or defense-related reactions. To (GlcNAc)8, cells
responded with a cytosolic acidification, and they responded to
NodRm-IV(C16:2,S) with a sustained alkalinization. When both agents
were added jointly, the cytosol first alkalized and then acidified.
(GlcNAc)8 and NodRm-IV(C16:2,S) transiently increased
cytosolic Ca2+ activity, whereby the response to
(GlcNAc)8 exceeded the one to NodRm-IV(C16:2,S) by at least
a factor of two.
1
This work was supported by the European Union
(grant no. ERBFMRXCT980243) and by the Deutsche Forschungsgemeinschaft.
*
Corresponding author; e-mail Hubert.Felle{at}bio.uni-giessen.de;
fax 49-641-99-35119.
© 2000 American Society of Plant Physiologists
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