Functional Epidermal Cells are Necessary for Abscisic Acid Effects on Guard Cells

Experimental results are presented which show that abscisicacid (ABA) causes stomatal closure only if the stomatal complexis adjacent to live epidermal cells. It is further shown thatABA acts by affecting solute fluxes into and out of epidermaland guard cells. Live epidermal cells function as recipientsfor solutes and thereby assist their movement out of the guardcells. ABA-mediated solute leakage from guard cells alone doesnot suffice to cause stomatal closure within one hour.