| Abstract: | Two experiments indicate that abscisic acid (ABA) may influencestomatal behaviour of Commelina communis L. Stomatal conductancecould not be correlated with bulk leaf ABA content but whenthe abaxial epidermis was assayed for ABA, small increases inABA content correlated well with limitations of leaf conductance.Restricted conductance of the abaxial surface of leaves wasassociated with an increase of approximately 40 amole ABA perstomatal complex. This agrees with previously published figures. When roots of individual plants were split between two containers,drying the soil around one part of the root system restrictedleaf conductance, even though leaf water relations were notaffected. Increased ABA content of the epidermis coincided withincreased ABA content of the roots in drying soil. Other rootsof the same plant in moist soil did not show increased ABA content.These results suggest that in drying soil, ABA can move fromthe roots to the epidermis and restrict stomatal aperture evenwhen leaf water potentials and turgors remain constant. Theimportance of this mechanism in providing a sensitive foliarresponse to decreasing soil moisture is discussed. Key words: Soil drying, ABA, roots, stomata, water relations |
