Supramolecular Structure of Pigment-Protein Complexes in Relation to the Chlorophyll a Fluorescence of Chloroplasts at 25° C or at -196° C: Cation Effect, pH Effect and Trypsinolysis

Abstract

The oligomeric forms of the thylakoid pigment-protein complexes (LHCP¹, LHCP² and CPIa) are dissociated to their constituents in the presence of cations (Argyroudi-Akoyunoglou, 1980). Cations have been also found to increase drastically the 77 K F685/F730 ratio of the pigment-protein complexes, and especially of CPIa, isolated by SDS-sucrose density gradient centrifuga-tion (Argyroudi-Akoyunoglou et al., 1982; Argyroudi-Akoyunoglou, Thomou, 1981) These results suggested that the increase in the F685/F730 ratio may arise from changes in the organization of the pigment-protein complexes, i.e. the dissociation of the complexes to their components. Support to this came also from the finding that in developing chloroplasts the the fluorescence yield (Fmax/Chl) at 25° C, follows an initial rise and then a sharp decline to a plateau (Castorinis et al., 1982); these changes follow closely the pigment-protein complex monomer to oligomer organization, which occurs during chloro-plast development (Kalosakas et al, 1981). Thus high Fmax/Chl is found when monomers predominate, and low when oligomers get organized. To check this hypothesis further, we studied whether various conditions, known to induce or not affect changes in the Chl a fluorescence yield of chloroplasts at 25° C, or in the F685/F730 ratio at 77 K, can also induce changes in the pigment-protein complex organization.