THE EFFECT OF PLANT HORMONE ABSCISIC-ACID ON MODEL MEMBRANES - DIFFERENTIAL SCANNING CALORIMETRY AND PLANAR BILAYER-MEMBRANES INVESTIGATIONS

The effect of abscisic acid on the thermotropic properties of dipalmitoylphosphatidylcholine (DPPC) and on phosphatidylethanolamines (natural (PE) and dipalmitoylphosphatidylethanolamine (DPPE)) bilayers was investigated by differential scanning calorimetry (DSC). Abscisic acid eliminates the pretransition of DPPC, causes a downward shift of its temperature of melting (Tm) and broadens the melting peak without changing the enthalpy of melting. In natural PE bilayers interacting with abscisic acid a small decrease in the enthalpy of melting almost without change of Tm was detected, whereas in synthetic DPPE abscisic acid caused a small shift of Tm and small broadening of the melting peak without changing the enthalpy of melting. Abscisic acid increases the conductance to Na+ or K+ by three orders of magnitude in planar lipid membranes formed from PE monolayers and by less than two orders of magnitude in membranes formed from PC monolayers.