Determination of apoplastic K+ in intact leaves by ratio imaging of PBFI fluorescence

Abstract

The tetraammonium salt of the K+ binding fluorescent dye benzofuran isophthalate (PBFI) was used to investigate the influence of potassium nutrition (0.1-2.1 mol m-3) on apoplastic K+ in Vicia faba leaves by means of ratio imaging. As a reference the infiltration-centrifugation method was used. Both methods reflected the influence of K+ supply on apoplastic K+ concentration. The abaxial leaf side revealed significantly higher K+ concentrations (20-25 mol m-3) than the adaxial side (5-8 mol m-3). Application of COOP led to an immediate increase in apoplastic K+ demonstrating the reliability of the PBFI method.