GUARD-CELL RESPONSES TO POTASSIUM FERRICYANIDE

Micromolar concentrations of potassium ferricyanide inhibit light-indu ced stomatal opening. The extent of the inhibition is dependent on the presence of carbon dioxide and the concentration of potassium ferricy anide needed to obtain 50% inhibition of stomatal opening is 40-fold h igher in CO2-free air than in normal air. The fungal toxin, fusicoccin (1 mu M), overcame the ferricyanide inhibition of stomatal opening in dicating that the electron acceptor may interact more or less directly with the activity of the plasma membrane H+-ATPase. Although potassiu m ferricyanide strongly inhibited stomatal opening, it had only minor effects on stomatal maintaining or stomatal closure due to darkness or ABA.