pH Gradients in the Stomatal Complex of Tradescantia virginiana

pH of the vacuolar sap, cytoplasm, and apoplast of the cells of the stomatal complex of Tradescantia virginiana was measured using micro-electrodes. Marked differences in vacuolar and apoplastic pH were observed between leaves with open and closed stomata. Cytoplasmic pH appeared to be uniform in all the cells and did not change with stomatal aperture. The information obtained enabled proton motive force across the plasmalemma and tonoplast of the guard cells to be calculated. The results are discussed in relation to the accumulation of potassium by the guard cell on stomatal opening.