Kinetics of Hormone-induced H⁺ Excretion

Abstract

A study has been made of the kinetics of hormone-induced H⁺ excretion from peeled Avena coleoptile sections using a new, simple technique involving direct application of the pH electrode to the surface of the section. Hormone-induced H⁺ excretion begins after lags and occurs at rates which are consistent with a role of H⁺ in regulating cell elongation. With fusicoccin, H⁺ excretion begins within the 1st minute, and an external pH of 5 (optimal for wall loosening) is reached in 5 to 8 minutes, while with auxin the lag averages 14 minutes and pH 5 is reached in 20 to 30 minutes. KCN, which inhibits cell elongation in 3 to 5 minutes, stops H⁺ excretion in less than 1 minutes, whereupon the external pH rises sharply. Cycloheximide stops auxin-induced H⁺ excretion in 3 to 8 minutes, and the pH then rises slowly. In the absence of hormones, the pH of the extracellular solution comes to equilibrium at 5.6, but the actual pH of the wall solution is probably about 0.3 unit below this due to Donnan effects.