Effect of Low O₂ Concentration and Azide on Hydraulic Conductivity and Osmotic Volume of the Cortical Cells of Wheat Roots

Abstract

The short-term effects of O₂ deficiency and sodium azide (NaN₃) on the hydraulic conductivity of cortical cells in wheat roots was studied using the pressure probe. Hydraulic conductivities were obtained by measuring either turgor relaxation, or volume relaxation under pressure clamp. Both low O₂ concentration and NaN₃ increased the half times of pressure and volume relaxations. The increases in T½ were found to be due to a decrease in the hydraulic conductivity (Lp) of the cells. The mean values of Lp from pressure relaxation experiments were 7.75 × 10^-1m s^-1 Mpa^-1 in the fully aerated solution and 1.15 and 2.17 x 10^-1m s^-1 Mpa^-1 in low O₂ concentration and 1 mol m^-3 NaN₃ solutions respectively. The pressure clamp experiments yielded similar results to pressure relaxation experiments for both low O₂ concentration and 1 mol m^-3 NaN₃ treatments. In addition to determination of Lp, pressure and volume relaxation experiments were also used to evaluate osmotic volume of the cells. In aerated solutions the osmotic volume of the cells was about twice that of their geometric volume, but in low O₂ concentration and NaN₃ solutions the osmotic cell volume was reduced and approximately equal to the geometric volume. The decrease in osmotic volume and part of the reduction in Lp may be explained by the occlusion of plasmodesmata induced by low O₂ concentration and NaN₃.