Perception of the auxin signal at the plasma membrane of tobacco mesophyll protoplasts |
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Authors: | Hélène Barbier-Brygoo Geneviève Ephritikhine Dieter Klämbt Christophe Maurel Klaus Palme Jeff Schell Jean Guern |
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Institution: | Institut des Sciences Végétales, Centre National de la Recherche Scientifique, Bât 22, Avenue de la Terrasse, F91198 Gif-sur-Yvette Cedex, France;Botanisches Institut der Universität Bonn, Meckenheimer Allee 170, D-5300 Bonn 1;, Germany Max Planck Institut für Züchtungforschung, D-5000 Köln 1;, Germany |
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Abstract: | Auxin-induced variations of transmembrane potential difference have been shown to be a useful tool for analyzing hormone sensitivity in tobacco protoplasts. Using this technique, we demonstrated that protoplasts derived from wild-type, an auxin-resistant mutant and Agrobacterium-rhizogenes transformed plants differed widely in the sensitivity of their electrical response to naphthalene acetic acid. We have used different antibodies, raised to auxin binding proteins (ABP) from maize coleoptiles, or to the axr1 gene product (ABP1), to test whether changes in auxin sensitivity can be correlated with the presence of tobacco proteins immunologically related to this ABP. Titrations indicated that 0.4 nM anti-ABP IgG inhibited 50% of the auxin-specific response of wild-type protoplasts, whereas 0.04 nM or 4 nM anti-ABP IgG were necessary to inhibit the response of mutant and transformed protoplasts, respectively, to the same extent. On wild-type protoplasts, blocking part of the immunoreactive sites with anti-ABP antibodies resulted in a decrease in auxin sensitivity of the electrical response (0.4 nM anti-ABP IgG inducing a 10–fold decrease), whereas addition of maize ABP increased this auxin sensitivity (1 pM ABP1 raised the sensitivity more than 1000–fold). The results obtained suggest that the auxin sensitivity detected by our assay system correlates with the amount of tobacco proteins immunologically related to the axr1 gene product from maize. A hypothesis accounting for the presence of these proteins at the external surface of tobacco protoplasts and for the effects of hetero-logous maize ABP on auxin sensitivity is proposed. |
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