A Relationship between Phosphate Uptake and Membrane Electrical Potential in Excised Roots ofHelianthus annuus

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Abstract
Phosphate uptake by excised roots of sunflower (Helianthus annuus) was determined by the disappearance of phosphate from the external solution and by the accumulation of phosphate labelled with 32P. Over a 24 h period it was observed that net phosphate uptake declined to zero whilst uptake of 32P continued unabated. The electrical PD of the cortical cell membranes declined in parallel with net phosphate uptake and it was found that both could be restored by creating a pH gradient across the plasmalemma. It was concluded that net phosphate uptake was responsible for a component of the membrane PD of the root cortical cells.