Retarded Stomatal Closure by Phenylmercuric Acetate

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Abstract
Excised leaves of Nerium oleander, which were treated with phenylmercuric acetate (PMA) 11/2 h before excising, transpired faster than untreated excised leaves. Similarly, PMA‐treated oleander plants transpired more than untreated plants in the dark. These effects were due to retarded stomatal closure caused by PMA. Measurements of stomatal apertures on disks of Vicia faba leaves kept in the dark, and of diffusive resistance to water vapor from Phaseolus vulgaris leaves, confirmed that PMA retards stomatal closing as well as stomatal opening. However, day‐time reductions in transpiration by PMA greatly exceed night‐time increases in water loss. The mechanisms of stomatal movement, as affected by PMA, are discussed. PMA may conceivably decrease the permeability of guard cell membranes to solutes, thereby retarding all stomatal movements that are osmotically induced.