Elevation of the cytosolic free [Ca2+] is indispensable for the transduction of the Nod factor signal in alfalfa.
In root hairs of alfalfa (Medicago sativa), the requirement of Ca(2+) for Nod factor signaling has been investigated by means of ion-selective microelectrodes. Measured 50 to 100 microm behind the growing tip, 0.1 microM NodRm-IV(C16:2,S) increased the cytosolic free [Ca2+] by about 0.2 pCa, while the same concentration of chitotetraose, the nonactive glucosamine backbone, had no effect. We demonstrate that NodRm-IV(C16:2,S) still depolarized the plasma membrane at external Ca(2+) concentrations below cytosolic values if the free EGTA concentration remained low (</=0.01 mM). Externally added Sr(2+) was able to replace Ca(2+), and to some extent even enhanced the Nod-factor-induced depolarization, whereas with Mg(2+) it was decreased. This suggests that the Nod factor response is triggered by Ca(2+) from external stores. The addition of the endomembrane Ca(2+)-ATPase inhibitor 2,5-di(t-butyl)-1, 4-benzohydroquinone, which presumably mobilizes Ca(2+) from Ins(1,4, 5)P(3)-sensitive stores, mimicked the Nod factor response, i.e. increased the cytosolic free [Ca2+], triggered Cl(-)-efflux, depolarized the plasma membrane, and alkalized the root hair space. In all cases a refractory state toward Nod factor perception was produced, indicating a shortcut of Nod factor signal transduction by releasing Ca(2+) from internal stores. These latter results strongly support the idea that an elevation of cytosolic free [Ca2+] is indispensable for the transduction of the Nod factor signal, which is consistent with the role of Ca(2+) as a second messenger.
Felle
H H
HH
Botanisches Institut I, Justus-Liebig-Universität, Senckenbergstrasse 17, D-35390 Giessen, Germany. hubert.felle@bio.uni-giessen.de
Kondorosi
E
E
Kondorosi
A
A
Schultze
M
M
D002118:Calcium / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism; D002614:Chelating Agents / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D006873:Hydroquinones / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000455:Medicago sativa / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D008839:Microelectrodes; D018517:Plant Roots / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D013324:Strontium / Q000494:pharmacology
D002614:Chelating Agents; D006873:Hydroquinones; D008070:Lipopolysaccharides; C019359:2,5-di-tert-butylhydroquinone; D004533:Egtazic Acid; D000252:Calcium-Transporting ATPases; D002118:Calcium; D013324:Strontium