Arabidopsis leaf hydraulic conductance is regulated by xylem sap pH, controlled, in turn, by a P?type H ⁺ ?ATPase of vascular bundle sheath cells

The leaf vascular bundle sheath cells (BSCs) that tightly envelop the veins, are a selective and dynamic barrier to xylem sap water solutes radially entering mesophyll cells. Under normal conditions, pH below 6 is presumably important for driving regulating transmembranal solute transport. Having discovered recently differentially high expression of BSC proton pump, AHA2, we now test hypothesis it regulates radial fluxes. We monitored in veins detached leaves wild-type Arabidopsis, AHA mutants aha2 complemented with AHA2 gene solely BSCs. tested an inhibitor (vanadate) stimulator (fusicoccin), different buffers. their impact on hydraulic conductance (Kleaf ), effect osmotic permeability (Pf ) isolated BSCs protoplasts. found necessary acidification, turn, elevating Kleaf . Conversely, knockdown, which alkalinized sap, or, buffering its 7.5, reduced , external 7.5 decreased Pf All these showed causative link between activity conductance.