The role of the apoplastic transport barriers for radial water and ion uptake in rice (Oryza sativa L.) and corn (Zea mays L.) roots
type: CreativeWork
description: For rice, the overall radial hydraulic conductivity (Lpr) was lower than those of other cereal roots. The stele/endodermis, aerenchyma, and the outer part of roots (OPR) arrange in series and their resistances to the overall radial water flow are additive. However, the hydraulic resistance of the OPR was smaller by a factor of 30 than the overall values of root Lpr. Hence, the endodermis rather than the OPR limits water uptake. It appears that the OPR is constructed to provide a substantial barrier for oxygen rather than for water. The latter is transported down to root tips limiting root extension, which resulted to develop small rice root systems. Both cultivars used here (IR64 and Azucena) developed strong barriers to radial oxygen loss (ROL). The rates of ROL dramatically decreased along the root and reached values close to zero in basal parts. The data from this thesis show for the first time that radial uptake of water by rice roots is not limited by the OPR. Theoretical estimations suggested that the endodermis limits the rate of radial water flow and the resistance of the aerenchyma is in between that of the endodermis and the OPR. High values of the LpOPR could be either brought about by a large apoplastic component of water transport or by a high permeability of membranes of the living cells in the OPR or by both together. In order to quantify the relative contribution of the apoplastic vs cell-to-cell paths to the overall LpOPR, apoplastic pores of the OPR were either partially blocked by China ink particles or clogged with copper ferrocyanide precipitates. In another experiment, water channels (aquaporins) of the OPR were blocked with water channel blocker HgCl2. Resulted LpOPR values after the treatments suggested that proportionately greater apoplastic water flow across the OPR compared to cell-to-cell water flow. On average, 66-75% of water used extraprotoplastic path. This finding was further supported by substantial increases of the reflection coeff…
abstract: For rice, the overall radial hydraulic conductivity (Lpr) was lower than those of other cereal roots. The stele/endodermis, aerenchyma, and the outer part of roots (OPR) arrange in series and their resistances to the overall radial water flow are additive. However, the hydraulic resistance of the OPR was smaller by a factor of 30 than the overall values of root Lpr. Hence, the endodermis rather than the OPR limits water uptake. It appears that the OPR is constructed to provide a substantial barrier for oxygen rather than for water. The latter is transported down to root tips limiting root extension, which resulted to develop small rice root systems. Both cultivars used here (IR64 and Azucena) developed strong barriers to radial oxygen loss (ROL). The rates of ROL dramatically decreased along the root and reached values close to zero in basal parts. The data from this thesis show for the first time that radial uptake of water by rice roots is not limited by the OPR. Theoretical estimations suggested that the endodermis limits the rate of radial water flow and the resistance of the aerenchyma is in between that of the endodermis and the OPR. High values of the LpOPR could be either brought about by a large apoplastic component of water transport or by a high permeability of membranes of the living cells in the OPR or by both together. In order to quantify the relative contribution of the apoplastic vs cell-to-cell paths to the overall LpOPR, apoplastic pores of the OPR were either partially blocked by China ink particles or clogged with copper ferrocyanide precipitates. In another experiment, water channels (aquaporins) of the OPR were blocked with water channel blocker HgCl2. Resulted LpOPR values after the treatments suggested that proportionately greater apoplastic water flow across the OPR compared to cell-to-cell water flow. On average, 66-75% of water used extraprotoplastic path. This finding was further supported by substantial increases of the reflection coeff…
author: Ranathunge, Kosala Manjupriya
date published: 2005-09-19
date modified: 2026-07-27T18:49:29Z
provider: Universität Bayreuth
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Universität Bayreuth