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.

A Negative Hydraulic Message from Oxygen-Deficient Roots of Tomato Plants? (Influence of Soil Flooding on Leaf Water Potential, Leaf Expansion, and Synchrony between Stomatal Conductance and Root Hydraulic Conductivity)

“…We assume changes in these gases in the flood water (Table I) interfere with the normal increase and decrease of L, during the 1st d of flooding and induce a temporary depression of conductivity across membranes (Zhang and Tyerman, 1991). Such effects may be mediated by conformational changes in the water channel proteins (aquaporins).…”

A New Pressure Probe Method to Determine the Average Volumetric Elastic Modulus of Cells in Plant Tissue

“…Perhaps some improvement in the determination of V may be obtained by the method of Malone and Tomos (19901, and this will hopefully improve the accuracy of qnst estimates. However, Zhang and Tyerman (1991) found that for cortical cells of wheat roots, the calculated cell volumes were about twice the optically determined volumes, unless the roots were subjected to anoxia or azide. Cosgrove and Steudle (1981) were not able to determine the pressure dependence of einst for cortical cells of pea.…”

Polarity of Water Transport across Epidermal Cell Membranes in Tradescantia virginiana

“…Routine correction for dynamic (K h ) effects required measurement of either tip pneumatic conductance (K p ) or tip size (Fig. 2C), but because the data for K p was routinely available as part of microcapillary manufacturing (Wada et al, 2011) , very similar to the hydraulic resistance of tips of a similar size reported by Zhang and Tyerman (1991). From Equation 2 (P cell 2 P oil = a/r m + dV/ dt 3 1/K h ), the differences between measured P oil and P cell due to K h were generally less than 0.0001 MPa; hence, for the tips and cells used in this study, the effects of K h and surface tension were very small, but the magnitude of both of these effects will increase if smaller tips are used.…”

“…In the PC method, first developed by Wendler and Zimmermann (1982), V o (and, given reasonable assumptions about cell geometry, A) is estimated without the need for optical measurements, and L p can be measured without the need to determine dP/dV or «. However, this method is technically more demanding because it requires precise P control as well as a continuous record of the volume flow of water across the cell membrane (as measured by changes in the position of the cell solution/oil meniscus within the glass capillary over time) and has rarely been used Zimmermann, 1982, 1985;Cosgrove et al, 1987;Moore and Cosgrove, 1991;Zhang and Tyerman, 1991;Murphy and Smith, 1998). Since volume (V) is continuously changing over time, this approach may also be influenced by the hydraulic conductance of the capillary tip (K h ) used to make the measurements as well as surface tension effects due to the progressive changes in capillary diameter with meniscus position, and these influences have not been quantitatively addressed.…”