Effect of Photoperiod on Stomatal Opening in Vicia faba.

Stomatal apertures in darkness and subsequent average opening rates in light were measured in Vicia faba leaf discs throughout the nyctoperiods for plants grown on three light:dark cycles (8:16, 12:12, and 16:8). The time course of opening in darkness depended on the specific light:dark cycle with the maximum aperture always occurring at the time the lights normally went on. The light-induced opening rate was also maximum at the end of the nyctoperiod.