TRANSPORT OF PHOSPHOCHOLINE IN HIGHER-PLANT CELLS - P-31 NUCLEAR-MAGNETIC-RESONANCE STUDIES

Phosphocholine (PC) is an abundant primary form of organic phosphate that is transported in plant xylem sap. Addition of PC to the perfusate of compressed P(i)-starved sycamore cells monitored by 31P NMR spectroscopy resulted in an accumulation of PC and all the other phosphate esters in the cytoplasmic compartment. Addition of hemicholinium-3, an inhibitor of choline uptake, to the perfusate inhibited PC accumulation but not inorganic phosphate (P(i)). When the P(i)-starved cells were perfused with a medium containing either P(i) or PC, the resulting P(i) distribution in the cell was the same. Addition of choline instead of PC to the perfusate of compressed cells resulted in an accumulation of PC in the cytoplasmic compartment from choline kinase activity. In addition, PC phosphatase activity has been discovered associated with the cell wall. These results indicate that PC was rapidly hydrolyzed outside the cell and that choline and P(i) entered the cytosolic compartment where choline kinase re-forms PC.