Osmotic measurements on stomatal cells ofCommelina communis L.

Summary

Observations of aperture changes as sucrose is added to the solution bathing epidermal strips ofCommelina communis L. allow calculation of the osmotic changes required to open or close the stomatal pore, for comparison with changes in potassium content. With “isolated” guard cells, in strips in which all cells other than guard cells have been killed, the internal osmotic changes required are 83 mosmol kg⁻¹ μm⁻¹ below 10μm aperture, 129 mosmol kg⁻¹ μm⁻¹ in the range 10–15 μm, and 180 mosmol kg⁻¹ μm⁻¹ above 15 μm. For opening against subsidiary cell turgor in addition to guard cell turgor, in intact strips with live subsidiary and epidermal cells, these figures should each be increased by about 33 mosmol kg⁻¹ μm⁻¹. A change in subsidiary cell turgor is magnified in its effects on the water relations of the guard cell by a factor greater than 3.7 for equal changes in the water potential of the two cells, or greater than 4.7 at constant volume of the guard cell.