STRUCTURAL CHARACTERISTICS OF THYLAKOID MEMBRANES OF ARABIDOPSIS MUTANTS DEFICIENT IN LIPID FATTY-ACID DESATURATION

The ultrastructure of thylakoid membranes from Arabidopsis thaliana wi ld-type, JB67 and LK3 fatty acid desaturation deficient mutants was st udied by thin-section and freeze-fracture electron microscopy. There w as a decrease in the amount of the appressed and non-appressed membran es in JB67 and LK3 Arabidopsis mutants when compared to the wild type, resulting in a reduction in the length of photosynthetic membrane per plastid. The results from freeze-fracture showed a decrease in size a nd a marked increase in packing density of membrane-associated particl es on the exo- and endoplasmic fracture faces of the mutants. In addit ion, areas of the appressed membranes of the mutants contained particl es in regular arrays under conditions where no such arrays were observ ed in wild-type thylakoid membranes. These observations suggest, that the decreased level of lipid fatty acid unsaturation affects the abili ty of the lipid matrix to mediate the assembly of chloroplast membrane components. The role of polyunsaturated membrane lipids is considered in terms of their ability to promote functional oligomeric assemblies of components of the photosynthetic apparatus.