Dark Opening of Stomates of Vicia faba in CO2-free Air

Leaf epidermal strips of Vicia faba were floated on 10 millimolar KCl at temperatures of 10 to 45 C for several time periods in the dark. For the duration of the experiment, a jet of water-saturated, CO(2)-free air was passed over the strips. The width of the stomatal aperture was measured microscopically and the potassium content was estimated and expressed as the percentage of area of the guard cell pair stained with cobaltinitrite. Stomatal opening in the dark occurred at temperatures above 35 C. The high temperature aperture reduction previously observed at 45 C in the light was not observed in the dark. Potassium accumulation occurred at all temperatures except 10 C, with a maximum at 45 C, which appeared functionally different from that seen previously in the light.