Guard cell wall properties are important in stomatal movement. Previous research focused on the structure and anatomy of guard cell walls, but little is known about the physical changes that take place within the walls during stomatal opening and closure. In this work, we investigate the volumetric elastic modulus (ε) of the guard cell wall at different pH values during stomatal opening in Vicia faba epidermal strips using a cell pressure probe. The volumetric elastic modulus of the guard cell wall decreased from 7.098 to 5.690 MPa when the pH of the cell wall decreased from 8.60 to 6.50. It is easier for guard cells to change their volume at a lower volumetric elastic modulus during stomatal movement. The results are suggestive of a putative role for pH in the regulation of stomatal movement.
