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Arabidopsis leaf hydraulic conductance is regulated by xylem sap pH,controlled, in turn,by a P-type H+-ATPase of vascular bundle sheath cells |
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| Authors: | Yael Grunwald Noa Wigoda Nir Sade Adi Yaaran Tanmayee Torne Sanbon Chaka Gosa Nava Moran Menachem Moshelion |
| Affiliation: | 1. The R.H. Smith Institute of Plant Sciences and Genetics in Agriculture, The R.H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, 76100 Israel;2. The R.H. Smith Institute of Plant Sciences and Genetics in Agriculture, The R.H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, 76100 Israel These authors contributed equally to this work.;3. The R.H. Smith Institute of Plant Sciences and Genetics in Agriculture, The R.H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, 76100 Israel School of Plant Sciences and Food Security, The George S. Wise Faculty of Life Sciences at Tel-Aviv University, Tel Aviv, 6997801 Israel |
| Abstract: | The leaf vascular bundle sheath cells (BSCs) that tightly envelop the leaf veins, are a selective and dynamic barrier to xylem sap water and solutes radially entering the mesophyll cells. Under normal conditions, xylem sap pH below 6 is presumably important for driving and regulating the transmembranal solute transport. Having discovered recently a differentially high expression of a BSC proton pump, AHA2, we now test the hypothesis that it regulates the xylem sap pH and leaf radial water fluxes. We monitored the xylem sap pH in the veins of detached leaves of wild-type Arabidopsis, AHA mutants and aha2 mutants complemented with AHA2 gene solely in BSCs. We tested an AHA inhibitor (vanadate) and stimulator (fusicoccin), and different pH buffers. We monitored their impact on the xylem sap pH and the leaf hydraulic conductance (Kleaf), and the effect of pH on the water osmotic permeability (Pf) of isolated BSCs protoplasts. We found that AHA2 is necessary for xylem sap acidification, and in turn, for elevating Kleaf. Conversely, AHA2 knockdown, which alkalinized the xylem sap, or, buffering its pH to 7.5, reduced Kleaf, and elevating external pH to 7.5 decreased the BSCs Pf. All these showed a causative link between AHA2 activity in BSCs and leaf radial hydraulic water conductance. |
| Keywords: | AHA AHA2 ABA Arabidopsis thaliana (Thale cress) barrier bundle sheath H+-ATPase leaf hydraulic conductivity (Kleaf) proton pump water valve Xylem sap pH |