Abstract
The effects of preillumination were investigated on ion-stimulated stomatal opening of epidermal strips isolated from Commelina communis L. leaves, which are dark-starved 24 hours or more. The rate and the extent of ion-stimulated stomatal openings were increased by preexposure of epidermal strips to light. The evidences are interpreted as indicating that the energy induced by preillumination can be conserved in guard cells for considerable time periods and then used for a delayed stomatal opening in the presence of higher concentration of potassium or sodium ions. Action spectrum showed two peaks, one in blue and one in the red light region. The ratio of the blue peak to the red peak is 1.2; which is the smallest reported value in action spectra of stomatal movements. 3-(4-chlorophenyl)-1,-1-Dimethylurea suppressed the ion-stimulated stomatal opening induced by the preillumination. We conclude that the photosynthetic electron transport system, containing photosystem II, in guard cell chloroplasts is a basic system of energy acquirement for stomatal opening.