Evidence that fusicoccin and indole-3-acetic acid induce cytosolic acidification of Zea mays cells

Abstract

Microelectrodes were used to measure simultaneously the effects of fusicoccin on cytosolic pH and membrane potential in a maize root cell. The cytosolic pH began to fall within seconds of adding fusicoccin, whereas the membrane hyperpolarization commenced after a lag of 2 min. The pH microelectrode could not be used with coleoptile cells for technicalreasons. However, the dual-wavelength absorbance technique showed that fusicoccin also induced a rapid cytosolic acidification in coleoptile cells. Indole-3-acetic acid lowered the cytosolic pH of these cells. The effect was less pronounced than with fusicoccin and began after 5 min well before membrane hyperpolarization (10 min) and extracellular acidification (30 min) were detectable. Procaine, which penetrates the plasma membrane and gains protons in the cytosol, was shown to depolarize root cells and inhibit indole-3-acetic acid-induced growth of coleoptiles. 1-Naphthylacetate, which acidifies the cytosol, hyperpolarized root cells and stimulated coleoptile growth. The results support the concept that fusicoccin and auxins induce elongation growth by lowering the cytosolic pH. Auxin Coleoptile Cytosolic pH Fusicoccin Growth Membrane potential Zea mays