Guard cell pressure/aperture characteristics measured with the pressure probe

Pressure within guard cells in strips of intact epidermis of Tradescantia virginiana was controlled with a pressure probe apparatus after the guard cells had been filled with silicone oil. Pressure was increased and decreased incrementally between 0.0 and 4.1 MPa to cause inflation and deflation of the guard cells. At steady‐state guard cell pressures, the width of the stomatal pore was recorded and plotted against pressure. The pressure required for near‐maximum aperture was 4.1 MPa. Aperture as a function of pressure was sigmoidal.