GUARD-CELL PRESSURE APERTURE CHARACTERISTICS MEASURED WITH THE PRESSURE PROBE

Pressure within guard cells in strips of intact epidermis of Tradescan tia virginiana was controlled with a pressure probe apparatus after th e guard cells had been filled with silicone oil. Pressure was increase d and decreased incrementally between 0.0 and 4.1 MPa to cause inflati on and deflation of the guard cells. At steady-state guard cell pressu res, the width of the stomatal pore was recorded and plotted against p ressure. The pressure required for near-maximum aperture was 4.1 MPa. Aperture as a function of pressure was sigmoidal.