Stomatal sensitivity to abscisic acid (ABA) can be modified by variations in the xylem sap traits such as pH, Ca2+, NO3- and PO4(3-) concentrations. In order to verify this hypothesis, plants of Licopersicon esculentum L. cv. Santa Clara were submitted to sudden and slow onset of water stress by PEG 6000 addition to the nutritive solution. The stomatal sensitivity to ABA was estimated by changes in the transpiration/xylematic ABA ratio. To evaluate the inhibitory effect of Ca2+, NO3- and PO4(3-) at different concentrations, detached leaves were submerged in artificial sap containing exogenous ABA. In intact plants, under sudden stress treatment, the ion concentration increment gradually raised the stomatal sensitivity to xylem ABA. Under slow stress treatment the stomatal response to ABA was not modified by Ca2+. A dose of 2.5 µM exogenous ABA was needed to induce a drop in the transpiration rate of detached leaves. The presence of Ca2+ in the transpiration flux stimulated the ABA inhibitory effect on transpiration rate.The stomatal closure response to ABA was intensified when Ca2+ and NO3- were added to the artificial sap.
Lycopersicon esculentum L.; transpiration; water stress; xylem sap
