Affiliation:
1. Botanisches Institut I, Justus-Liebig-Universität, Senckenbergstrasse 17, D–35390 Giessen, Germany (H.H.F.)
2. Institut des Sciences Végétales, Centre National de la Recherche Scientifique, Avenue de la Terrasse, F–91198 Gif-sur-Yvette, France (E.K., A.K., M.S.)
Abstract
Abstract
In root hairs of alfalfa (Medicago sativa), the requirement of Ca2+for Nod factor signaling has been investigated by means of ion-selective microelectrodes. Measured 50 to 100 μm behind the growing tip, 0.1 μm 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 Ca2+ concentrations below cytosolic values if the free EGTA concentration remained low (≤0.01 mm). Externally added Sr2+ was able to replace Ca2+, and to some extent even enhanced the Nod-factor-induced depolarization, whereas with Mg2+ it was decreased. This suggests that the Nod factor response is triggered by Ca2+ from external stores. The addition of the endomembrane Ca2+-ATPase inhibitor 2,5-di(t-butyl)-1,4-benzohydroquinone, which presumably mobilizes Ca2+ from Ins(1,4,5)P3-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 Ca2+ 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 Ca2+ as a second messenger.
Publisher
Oxford University Press (OUP)
Subject
Plant Science,Genetics,Physiology
Cited by
96 articles.
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