Saturation Kinetics of the Velocity of Stomatal Closing in Response to CO(2).

Stomatal closing movements in response to changes from CO(2)-free to CO(2)-containing air were recorded in leaf sections of Zea mays using air flow porometers. The response to CO(2) was fast; the shortest lag between the application of 300 microliters CO(2) per liter of air and the beginning of a stomatal response was 3 seconds. The velocity of stomatal closing increased with CO(2) concentration and approached its maximal value between 10(3) and 10(4) microliters CO(2) per liter of air. The CO(2) concentration at which the closing velocity reached half its maximal value was approximately 200 microliters CO(2) per liter of air, both in the light and in darkness. This indicates that the mechanism of stomatal responses to CO(2) is the same in both light regimes and that the range of stomatal sensitivity to changes in CO(2) concentration coincides with the range of CO(2) concentrations known to occur in the intercellular spaces of illuminated leaves.