| Abstract: | Uptake experiments and efflux compartmental analysis of planthormones, osmotica and toxins using ‘isolated’ guardcells of Valerianella locusta and guard cell protoplasts (GCP)of Vicia faba were performed in order to study the permeabilityproperties of guard cell plasma membrane and tonoplast. Theplasma membrane of guard cells exhibits a higher permeabilitythan plasma membranes of mesophyll cells for most solutes investigated.The permeability coefficients (Ps calculated for the guard cellplasma membranes are also significantly higher than the Ps valuesfor the guard cell tonoplast. This applies also for protonatedABA. We suppose that the high permeability for ABAH could bepart of the target cell properties. A Collander analysis demonstratesa linear correlation between Ps, values and the ratio Kr/Mr1,5for both plasma membrane (r = 0.87) and for the tonoplast (r=0.93). Because of deviations from the observed correlations,the permeation of some solutes (ABA, GA, IAA through the tonoplast;methylamine through the plasma membrane) seems to be facilitatedby an additional transport mechanism. The Collander analysisof the plasma membrane of GCP shows very similar results tothe analysis of the plasma membrane of ‘isolated’guard cells, indicating that isolation of protoplasts does notalter the permeability of the guard cell plasma membrane. Key words: Permeability coefficient, guard cells, plasma membrane, tonoplast |
