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 (pHi) 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 pHi, 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.
Department of Botany, La Trobe University, Bundoora, Victoria, Australia.
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D000818:Animals; D000906:Antibodies / Q000276:immunology; D000911:Antibodies, Monoclonal / Q000276:immunology; D001665:Binding Sites; D003593:Cytoplasm; D006863:Hydrogen-Ion Concentration; D007210:Indoleacetic Acids / Q000378:metabolism; D051379:Mice; D010455:Peptides / Q000378:metabolism; D010937:Plant Growth Regulators; D010940:Plant Proteins / Q000276:immunology / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000276:immunology / Q000378:metabolism*
D000906:Antibodies; D000911:Antibodies, Monoclonal; D007210:Indoleacetic Acids; D010455:Peptides; D010937:Plant Growth Regulators; D010940:Plant Proteins; D011956:Receptors, Cell Surface; C046131:auxin receptor, plant