Epidermal and Guard Cell Interactions on Stomatal Aperture in Epidermal Strips and Intact Leaves

Despite the observation first made by von Mohl in 1856, thatepidermal cells greatly influence stomatal aperture, subsequentstudies have failed to pay adequate attention to epidermal cellviability or to quantify the degree of its influence on aperturein epidermal strips and leaf sections. Using Vicia faba stripsand leaf sections we found the following: (i) a non-linear relationshipbetween aperture and guard cell contact with live epidermalcells; (ii) epidermal cell viability on isolated strips hada threshold at about 25 °C; (iii) epidermal strips withdead epidermal cells had wider apertures and lower variabilitythan strips with live cells or intact leaf sections; (iv) afterepidermal cell viability was accounted for, stomatal aperturesshowed no significant differences between isolated strips orstrips removed from leaf sections treated in the same manner;(v) highly variable apertures appeared to be the normal conditionof the intact leaf. Caution should therefore be used in interpretingstomatal behaviour from epidermal strips without first takinginto account mechanical interactions between the guard and surroundingepidermal cells. Vicia faba L, broad bean, epidermal strips, leaf impressions, stomata, guard cells, temperature effects