Abstract

Inorganic phosphate (Pi) uptake systems across the plasma membrane of plant cells have been extensively investigated. Physiological studies have established that Pi is transported into plant cells via co-transport with H⁺ , and in some plants with Na ⁺ , using the driving force provided by the electrogenic H ⁺ pump in the plasma membrane. Molecular studies have identified many genes for Pi transporters and are providing insights into the mechanisms of genetic control of Pi transport. There still remain, however, questions as to how Pi uptake systems are regulated at the physiological level. We have found that Pi uptake induces cytoplasmic acidification, and, conversely, that inducing cytoplasmic acidification causes the cytoplasmic Pi concentration to decrease. Both of these responses affect the operation of the H ⁺ -pump. These phenomena are discussed in relation to a possible mechanism for the physiological control of Pi uptake by plant cells.