CHANGED DENSITIES AND DIAMETERS OF INTRAMEMBRANE TONOPLAST PARTICLES OF MESEMBRYANTHEMUM-CRYSTALLINUM IN CORRELATION WITH NACL-INDUCED CAM

Plants of Mesembryanthemum crystallinum L., a facultative halophyte and CAM plant, were treated with four different levels of salinity in the root medium, i.e. 0, 100, 200 and 400 mM NaCl. The degree of expression of CAM, as given by day/night changes of malate levels, and the densities and diameters of intramembraneous tonoplast particles were followed over a time course of 23 days after the beginning of the salt treatment. Particle densities and diameters were counted and measured, respectively, on electron micrographs of freeze-fracture replicas of purified tonoplast vesicles. Changes in the density and an increase of the diameters of these particles, which largely although perhaps not exclusively belong to the H+-transporting tonoplast ATPase, were observed in relation to the progressing salt treatment and ageing of the plants. Particle densities and diameters were strongly correlated with the actual degree of CAM-expression. Sodium-dodecylsulfate gel electrophoresis showed that the intramembraneous H+-channel subunit peptide (c-subunit) of the tonoplast ATPase increased in its staining density with the salt treatment and ageing of plants. It might be speculated that this is related to the observed changes in particle densities and diameters.