Effect of osmotic shock on auxin-induced cell extension, cell wall changes and acidification in Avena coleoptile segments

Abstract

The effect of plasma membrane alteration caused by osmotic shock of different strengths on the auxin-induced responses of Avena coleoptile cells was observed. Osmotic shock brought about by 0.5–0.7 M mannitol solution for 10 or 30 min, followed by phosphate-buffer (1 mM, pH 6.0) treatment for 10 min at 4°C caused no significant inhibition of auxin-induced cell extension. The osmotic shock did not affect auxin-induced cell wall loosening represented by stress-relaxation time and a decrease in the noncellulosic glucose level of the cell wall. The shock caused only a temporary inhibition of transmembrane potential and no inhibition of oxygen consumption. However, it inhibited auxin-stimulated H⁺ secretion which was reversed by 0.1 mM CaCl₂. We concluded that the Osmotic shock may partly modify the plasma membrane related to the hydrogen ion pump which interacts with auxin, but this modification which is reflected little by the transmembrane potential and cellular metabolism, is not closely related to auxin-induced cell wall loosening and thus cell extension in Avena coleoptiles.