Auxin-binding-protein antibodies and peptides influence stomatal opening and alter cytoplasmic pH

Previous work has shown that stomatal opening induced by indole-3-acetic acid (IAA) in epidermal strips of the orchid Paphiopedilum tonsum L. is preceded by a reduction in cytoplasmic pH (pH_i) of the guard cells. We now report that Fab fragments of an auxin-agonist antibody (D16), directed against a putative auxin-binding domain of the auxin-binding protein ABP1, induce stomatal opening and decrease guard-cell pH_i, as monitored with the acetomethoxy ester of the ratiometric pH indicator Snarf-1. Similar activity was shown by a monoclonal antibody against the same domain. The C-terminal dodecapeptide, Pz152–163 of maize ABP1 (ABPzm1) induced guard-cell alkalinization and closed stomata, as did Fab fragments of a monoclonal antibody (MAC 256) recognising the C-terminal region of ABPzm1. By implicating, for the first time, an auxin-binding protein in mediation of an auxin-dependent physiological response, these findings strongly support an auxin-receptor role for ABP1.

Authors and Affiliations

1. Department of Botany, La Trobe University, Bundoora, Victoria, 3083, Australia, , , , , , AU

   Christoph A. Gehring, Robyn M. McConchie & Roger W. Parish

2. Horticulture Research International, Wellesbourne, Warwick, CV35 9EF, UK, , , , , , GB

   Michael A. Venis

Received: 23 December 1997 / Accepted: 16 January 1998

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