Patch-clamp analysis establishes a role for an auxin binding protein in the auxin stimulation of plasma membrane current in Zea mays protoplasts |
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Authors: | Annegret Rück Klaus Palme Michael A Venis Richard M Napier Hubert H Felle |
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Institution: | Institut für Botanik I, Justus-Liebig-Universität Gießen, Senckenbergstr. 17–21, D-6300 Gießen, Germany;Max-Planck-Institut für Züchtungsforschung, Carl-von- Linné-Weg 10, D-5000 Köln 30, Germany;Horticulture Research International, East Malling, Kent ME19 6BJ, UK |
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Abstract: | The electrical response of Zea mays protoplasts to different auxins and to antibodies raised against an ER-located auxin binding protein from maize (Zm-ERabp1), was investigated using the patch-clamp technique (whole-cell configuration). Following a lag-phase of 30–40 seconds, indole-3-acetic acid and 1-naphthylacetic acid induced an outwardly directed current of positive charge in a concentration-dependent manner. This current was further increased by the fungal toxin fusicoccin (FC). The current was observed only in the presence of Mg2+-ATP in the patch-pipette and was abolished after addition of erythrosin B, an inhibitor of H+-ATPase, to the protoplasts indicating that the plasma membrane H+-ATPase is activated by auxins and fusicoccin. Addition of antibodies directed against Zm-ERabp1 abolished the current induced by auxins, without affecting the response of protoplasts to fusicoccin. Antibodies directed against a peptide representing part of the putative auxin binding domain of Zm-ERabp1 showed auxin agonist activity, stimulating an outwardly directed membrane current in the absence of auxin. These results suggest that (i) Zm-ERabp1 or antigenically related proteins represent a site for auxin perception through which the plasma membrane H+-ATPase is activated, and (ii) that the activation of the H+-ATPase by such proteins is initiated from outside the plasma membrane. |
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