Plant cell transmembrane water transport, and in particular the contribution of aquaporin-mediated transcellular (ATC) pathway to that process, can play profound roles on drought defense mechanisms. In order to investigate the role that the ATC pathway plays during recovery mechanisms, several genotypes of Vitis spp. were cultivated in pots, water stressed, and root hydraulic conductance and shoot hydraulic conductivity were measured, both at the end of a drought period and after one day of recovery. To discriminate the ATC-path contribution, roots and shoots were treated in vivo with 0.5 mM HgCl2. To quantify embolism occurrence, hydraulic measurements were performed either before or after a pressure flushing (200 kPa) designed to eject out embolisms from shoots and roots. When grapevines were fully watered (leaf = -0.37 MPa), the incidence of the ATC pathway on hydraulic conductance was about 20% in root and 16% in shoot. At the end the water stress period (leaf = -0.95 MPa), the ATC incidence was 52%, and 6%, respectively, suggesting an up-regulation of expression and/or activity of mercury-sensitive aquaporins under drought at the root level, while a down-regulation at the shoot level. During recovery (leaf = -0.34 MPa), the ATC pathway contributed to 75% of the root, and to 39% of the shoot water transport, suggesting a vital role for cell-to-cell protein-mediated pathways in recovering embolisms. The important role of transcellular water transport during the recovery process seems to be due to two parallel mechanisms: i) a direct contribution of mercury-sensitive aquaporins, probably located in the cortical parenchyma and in the endodermis, to favour water movement through the root; ii) a contribution of mercury-sensitive aquaporins to embolism refilling, both at the root and the shoot level. In order to repair embolisms, water would have to exudate from parenchyma cells into the vessel lumen to compress the gas phase, forcing it into xylem solution; in this step aquaporin activity could enhance water movement.
Mercury-sensitive aquaporins enhance hydraulic conductance in Vitis spp. roots and shoots during recovery after drought
LOVISOLO, Claudio;STRANO, Tiziano Camillo;SCHUBERT, Andrea
2004-01-01
Abstract
Plant cell transmembrane water transport, and in particular the contribution of aquaporin-mediated transcellular (ATC) pathway to that process, can play profound roles on drought defense mechanisms. In order to investigate the role that the ATC pathway plays during recovery mechanisms, several genotypes of Vitis spp. were cultivated in pots, water stressed, and root hydraulic conductance and shoot hydraulic conductivity were measured, both at the end of a drought period and after one day of recovery. To discriminate the ATC-path contribution, roots and shoots were treated in vivo with 0.5 mM HgCl2. To quantify embolism occurrence, hydraulic measurements were performed either before or after a pressure flushing (200 kPa) designed to eject out embolisms from shoots and roots. When grapevines were fully watered (leaf = -0.37 MPa), the incidence of the ATC pathway on hydraulic conductance was about 20% in root and 16% in shoot. At the end the water stress period (leaf = -0.95 MPa), the ATC incidence was 52%, and 6%, respectively, suggesting an up-regulation of expression and/or activity of mercury-sensitive aquaporins under drought at the root level, while a down-regulation at the shoot level. During recovery (leaf = -0.34 MPa), the ATC pathway contributed to 75% of the root, and to 39% of the shoot water transport, suggesting a vital role for cell-to-cell protein-mediated pathways in recovering embolisms. The important role of transcellular water transport during the recovery process seems to be due to two parallel mechanisms: i) a direct contribution of mercury-sensitive aquaporins, probably located in the cortical parenchyma and in the endodermis, to favour water movement through the root; ii) a contribution of mercury-sensitive aquaporins to embolism refilling, both at the root and the shoot level. In order to repair embolisms, water would have to exudate from parenchyma cells into the vessel lumen to compress the gas phase, forcing it into xylem solution; in this step aquaporin activity could enhance water movement.
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