Vacuoles from Sugarcane Suspension Cultures

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Abstract
The electrochemical proton gradient across the tonoplast of isolated (Saccharum sp.) vacuoles and vacuoles in situ was measured. The isolated vacuoles had no significant protonmotive potential difference, the pH gradient of 0.8 (inside acid) was balanced by a membrane potential of .apprx. -80 mV (inside negative). From pH and uncoupler insensitivity and K+ sensitivity, the experimentally caused K+ gradient created the electric potential. Qualitatively different results were obtained on vacuoles in situ: the pH gradient is greater (1.3) and the membrane potential is positive inside. Uncoupler sensitivity is evidence for an enzyme system transducing protons inward as cause for the considerable protonmotive force at the tonoplast in situ.