Compartmental analysis of phosphate in roots of intact barley seedlings

Elution profiles of 32P-labelled inorganic phosphate (Pi) from roots of intact barley plants were observed and were found to conform to the pattern theoretically derived for three compartments in series. An allowance was made for the movement of labelled phosphate from the cytoplasm into the root xylem. Transformations of labelled phosphate within metabolically labile organic pools seem to be invisible kinetically because their rate constants are generally higher than that for Pi efflux across the plasmalemma and tonoplast. It is concluded that compartmentation of phosphate between cytoplasm and vacuole can be explored usefully by this technique especially if used in conjunction with other methods which can measure the size of cytoplasmic organic phosphate pools.