Relationship between stomatal conductance and light intensity in leaves of Zea mays L., derived from experiments using the mesophyll as shade.

Attached leaves of Zea mays were illuminated with monochromatic light, with either the upper or the lower epidermis facing the light source. The mesophyll absorbed between 99.5 and 99.6% of the red or blue light used. An inversion of the light direction therefore caused a 200- to 250-fold change in the quantum flux into each epidermis. This variation in quantum flux did not affect stomatal conductance. Stomatal conductance was however correlated with intercellular CO2 concentration, ci, and the relationship between stomatal conductance and ci appeared also to remain the same if changes in ci were brought about by changes in atmospheric CO2 concentration instead of light. A close inspection of the data showed that stomata of the upper (adaxial) epidermis exhibited a small increase in conductance (<0.1 cm s(-1)) in response to blue light that was superimposed on the dominating response to ci.