DIRECT MEASUREMENTS OF TURGOR PRESSURE POTENTIALS .4. NATURALLY OCCURRING PRESSURES IN GUARD-CELLS AND THEIR RELATION TO SOLUTE AND MATRIC POTENTIALS IN THE EPIDERMIS

Measurements were made of turgor pressures in epidermal, subsidiary, and guard cells at different degrees of stomatal opening. The results are correlated with estimates of solute potentials of the different cell saps and with a postulated matric potential of cell walls. The results contribute to an understanding of the role of the subsidiary cells in the stomatal mechanism especially in the Graminaceous type and the role of 'tissue tension' as a pressure involved in turgor phenomena in epidermal tissue. The results make it possible to explain the abnormally large stomatal openings found after floating illuminated leaf tissue on water or keeping it in humid CO2-free air. © 1979 Oxford University Press.