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 an d CAM plant, were treated with four different levels of salinity in th e root medium, i.e. 0, 100, 200 and 400 mM NaCl. The degree of express ion of CAM, as given by day/night changes of malate levels, and the de nsities and diameters of intramembraneous tonoplast particles were fol lowed over a time course of 23 days after the beginning of the salt tr eatment. Particle densities and diameters were counted and measured, r espectively, on electron micrographs of freeze-fracture replicas of pu rified tonoplast vesicles. Changes in the density and an increase of t he diameters of these particles, which largely although perhaps not ex clusively belong to the H+-transporting tonoplast ATPase, were observe d in relation to the progressing salt treatment and ageing of the plan ts. Particle densities and diameters were strongly correlated with the actual degree of CAM-expression. Sodium-dodecylsulfate gel electropho resis showed that the intramembraneous H+-channel subunit peptide (c-s ubunit) 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 diam eters.