Latent Periods of Cytokinin-induced Stomatal Opening in the Sunflower Leaf

Abstract

Spraying a zeatin solution on the mature leaf of an intact sunflower plant (Helianthus annuus L. cv. Large Russian) caused a two-fold decrease in leaf temperature during the 20 min after treatment. Scanning electron microscope photographs taken 2 min after cytokinin treatment, however, showed a small but distinct stimulation of the opening of the central pore of the stomata, indicating that the latent period of cytokinin-induced stomatal opening is only 2 min. Five minutes after treatment with zeatin, the stomata at both the central pore and the outer ledge had opened widely. On the other hand, zeatin riboside treatment did not show a distinct effect on the stomatal opening within these periods. The stomata of a water-sprayed leaf closed within 1 min after the treatment.