Calcium Requirement for Indoleacetic Acid-induced Acidification by Avena Coleoptiles

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Abstract
The ionic specificity of IAA-induced acidification by A. [sativa] coleoptiles was studied, using zwitterionic, presumably impermeant buffers. The acidification was almost totally dependent on divalent cations with an order of effectiveness of Ca2+ .gtoreq. Sr2+ > Mn2+, Mg2+; other polyvalent cations tested were ineffective. The Ca2+ response was IAA-dependent. The CaCl2 concentration was optimal at 0.3-1 mM and inhibitory at higher concentrations. Sr2+ inhibited Ca2+-dependent acidification and monovalent cations such as K+ did not induce additional acidification in the presence of optimal CaCl2. These data are consistent with a mechanism for IAA-induced acidification involving a Ca2+ -H+ exchange.