Lipid lateral diffusion and local microviscosity in plant mitochondrial membranes with various length and unsaturation of fatty acids

Two main aspects of the lipid dynamics, local microviscosity and lateral di ffusion, were investigated in intact plant mitochondria isolated from diffe rent tissues exhibiting large differences in their fatty acids in terms of unsaturation (amount of linoleic and linolenic acids) or length of the hydr ocarbon chains. In addition, the same parameters were determined in the out er and inner membranes isolated from cauliflower mitochondria, which differ ed not only in the fatty acid composition but also by the lipid-to-protein ratio. In intact mitochondria, local microviscosity assayed with anthroylox y-fatty acids exhibited a transverse gradient from the surface to the cente r of the bilayer, which was mainly affected by the unsaturation index and t he content in linoleic or linolenic acids. In contrast, lipid lateral diffu sion increased as the content in linolenic or palmitic acids increased, but was not directly correlated to the unsaturation index. Interestingly, loca l microviscosity at the membrane surface was higher in the outer membrane t han in the inner membrane, whereas no significant difference was found in l ipid lateral diffusion, These results indicate that the influence of the fa tty acid composition of mitochondrial membranes on the dynamics of the phos pholipid bilayer depends on the type of movement considered and suggest tha t other parameters, such as the protein content of the bilayer, also affect membrane fluidity.