PH OF CELL SAP AND VACUOLAR PH DURING SENESCENCE OF THE ROSE PETAL
The pH of cell sap (extracted using the freeze-thaw method) is generally assimilated to vacuolar pH since the vacuole occupies more than 90 % of cell volume. A study was undertaken, using radioactive probes, to determine the pH of different cell compartments : vacuole, cytoplasm. It was observed that during senescence of the petal the relatively acidic pH of vacuolar sap, unlike that of cell sap, fell slowly. Cytoplasm pH, which was much higher, also fell. This parallel evolution in the two compartments has been reported for several types of material, the modifications in the cytoplasm determining those in the vacuole (reviewed in Kurkdjian and Guern, 1989).
In order to explain the differences observed between vacuolar pH and cell sap pH, contamination of cell sap by the constituents of extra-vacuolar compartments (Kurkdjian and Guem, 1981) should be taken into account. The contrary evolution of cell sap pH and vacuolar pH is discussed in the light of the results obtained.