THE EFFECTS OF CADMIUM ON THE FLUIDITY AND H+-ATPASE ACTIVITY OF PLASMA-MEMBRANE FROM SUNFLOWER AND WHEAT ROOTS

The effects of cadmium on the H+-ATPase activity and on the membrane fluidity were studied in plasma membrane prepared from roots of sunflower and wheat. Plasma membrane purified from the microsomal fraction by phase partitioning showed a decreased ATPase activity by in vivo Cd2+ treatment (30% and 90% decrease in wheat and sunflower, respectively) and the in vitro application caused an inhibition, as well. The ordering state of the membrane at the C-5 and C-16 levels of the fatty acid chains and at the membrane surface was determined by electron spin resonance (ESR) and by fluorescence spectroscopy, respectively. The presence of Cd2+ increased the ordering of the plasma membrane in both in vivo treatments and in vitro experiments. Under Cd2+ treatment, a more rigid structure of the PM was found at different depths in the membrane; changes were larger in sunflower than in wheat. The alterations can be the results of direct effects on the membrane constituents (proteins, lipids) or of the modification in lipid composition. Preliminary studies suggest that there are changes caused by Cd2+ in the fatty acid composition of the phospholipid fraction in PM, which were different in the case of wheat and sunflower.