Abstract
Using abraded Zea mays L. coleoptile segments, proton extrusion has been measured in the presence of growth promoting auxins and their inactive structural analogues. Prior to application, the segments spontaneously acidified the external medium to pH 4.8 within 7h. Indole-3-acetic acid (IAA) concentration dependently decreases external pH to 4.2, fusicoccin (FC) to below 3.5. Whereas the IAA-effect spontaneously recovers and can be repeated, the FC-effect is final and irreversible. The growth promoting auxins 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), indole-3-butyric acid (IBA) and 1-naphthylacetic acid (1-NAA) all stimulate proton extrusion similar to IAA. The growth inactive structural analogues 2,3-dichlorophenoxyacetic acid (2,3-D) and 2-naphthylacetic acid (2-NAA) also acidify the external medium, but quantitatively to a lesser extent. p-chlorophenoxyisobutyric acid (PCIB) does not inhibit the IAA response. No effects were obtained with deactivated H+-ATPase (anoxia) and in the presence of benzoic acid.
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