EFFECTS OF MERCURIC-CHLORIDE ON THE HYDRAULIC CONDUCTIVITY OF TOMATO ROOT SYSTEMS - EVIDENCE FOR A CHANNEL-MEDIATED WATER PATHWAY

A pressure-flux approach was used to evaluate the effects of HgCl2 on water transport in tomato (Lycopersicon esculentum) roots. Addition of HgCl2 to a root-bathing solution caused a large and rapid reduction i n pressure-induced root water flux; the inhibition was largely reversi ble upon addition of beta-mercaptoethanol. Root system hydraulic condu ctivity was reduced by 57%. There was no difference between treatments in the K+ concentration in xylem exudate. The results are consistent with the presence of a protein-mediated path for transmembrane water f low in tomato roots.