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

Spraying a zeatin solution on the mature leaf of an intact sunflowerplant (Helianthus annuus L. cv. Large Russian) caused a two-folddecrease in leaf temperature during the 20 min after treatment.Scanning electron microscope photographs taken 2 min after cytokinintreatment, however, showed a small but distinct stimulationof the opening of the central pore of the stomata, indicatingthat the latent period of cytokinin-induced stomatal openingis only 2 min. Five minutes after treatment with zeatin, thestomata at both the central pore and the outer ledge had openedwidely. On the other hand, zeatin riboside treatment did notshow a distinct effect on the stomatal opening within theseperiods. The stomata of a water-sprayed leaf closed within 1min after the treatment. (Received January 7, 1981; Accepted June 12, 1981)