Electric properties of thylakoid membranes from pea mutants with modified carotenoid and chlorophyll-protein complex composition

Surface electric properties of thylakoid membranes from wild type and two mutant forms, Coeruleovireus 2/16 and Costata 2/133, of pea are investigated by electric light scattering and microelectrophoretic measurements. Characterization of the chlorophyll-protein complexes in thylakoid membranes reveals that the relative ratio of oligomeric (LHC II1) to monomeric (LHC II3) forms of the light-harvesting Chl a/b complex of Photosystem II is lower (3.34) in 2/133 mutant and higher (6.62) in 2/16 mutant than in wild type (4.57). This is accompanied by elevated amounts and a considerable reduction of all carotenoids in 2/16 and 2/133 mutant, respectively, as compared to the wild type. The concomitant variations of the permanent dipole moment (transversal charge asymmetry), electric polarizability and electrokinetic charge of the thylakoid membranes from both the mutants are discussed in terms of the differences in the supramolecular (oligomeric) organization of the light-harvesting complexes II within the photosynthetic apparatus.