Effects of the mesophyll on stomatal responses in amphistomatous leaves

The role of the mesophyll in stomatal functioning in thin amphistomatous leaves was investigated by altering gas exchange for one surface and observing the effects on stomatal conductance for the other surface. Three methods of perturbing gas exchange on the adaxial surface were used. First, gas exchange for the adaxial surface was completely blocked with plastic wrap or vacuum grease. Second, leaves were inverted to induce closure of the adaxial stomata. And third, ambient humidity for the adaxial surface was reduced to induce stomatal closure on that surface. Experiments were performed at low light intensity and three different CO2 concentrations to test the idea that stomatal responses in thin amphistomatous leaves are partially controlled by a signal from the mesophyll that varies with light and CO2. In general, stomata on the abaxial surface opened when gas exchange on the adaxial surface was reduced, with the largest increases in conductance occurring at high CO2 concentration. The data are discussed with respect to role of a purported signal from the mesophyll and the partitioning of that signal between the two surfaces of the leaf.