FACTORS INFLUENCING PS-II PARTICLE ARRAY FORMATION IN ARABIDOPSIS-THALIANA CHLOROPLASTS AND THE RELATIONSHIP OF SUCH ARRAYS TO THE THERMOSTABILITY OF PS-II

Chloroplasts of the thermal-stable fatty acid desaturase mutants JB67 and LK3 of Arabidopsis thaliana are characterised by the presence of regular arrays of freeze-fracture particles associated with the core and light-harvesting antennae of Photosystem II (Tsvetkova et al. (1994) Biochim. Biophys. Acta 1192, 263-271). Similar arrays were found to be induced in the membranes of chloroplasts isolated from wild-type plants by resuspending the chloroplasts in media containing Tricine and/or high concentrations of compatible co-solutes such as sorbitol. The thermal stability of their chloroplasts was also increased under such conditions. The increased tendency to form PS II particle arrays, and the enhanced thermal stability of PS II, in chloroplasts isolated from the mutants and wild-type chloroplasts suspended in different media, appear to be reflections of the increased stability of protein-protein interactions between and within PS II units, respectively. The role of lipids in determining the formation of freeze-fracture particle arrays in the mutants is discussed in terms of the observed changes in lipid composition and their possible role in the control of lipid/protein synthesis.