EFFECT OF FOLIAR APPLICATIONS OF GLYCINEBETAINE ON STOMATAL CONDUCTANCE, ABSCISIC-ACID AND SOLUTE CONCENTRATIONS IN LEAVES OF SALT-STRESSEDOR DROUGHT-STRESSED TOMATO

Tomato (Lycopersicon esculentum Mill.) was used as a model system for investigating the effects of glycinebetaine applications on plants, as this species is unable to synthesise glycinebetaine, but is sensitive to exogenous supply. Glycinebetaine application significantly increas ed stomatal conductance of tomato plants grown in well-watered, water- deficient or saline conditions; however, glycinebetaine did not affect the leaf ABA concentration, relative water content, sap osmotic poten tial, or shoot water potential. Glycinebetaine applied to the foliage was readily absorbed, but the concentrations in the leaves made a negl igible contribution to the total leaf sap osmotic potential. Our resul ts indicate that applied glycinebetaine was involved in regulation of stomatal conductance but not via ABA metabolism or water relations. Gl ycinebetaine may have been accumulated in specific cells or cellular c ompartments, with consequences for stomatal functions. Further work is required to elucidate the cellular and subcellular localisation of ap plied glycinebetaine.