Evidence that circularly dichroic chlorophyll forms a-682 and a-710 are oriented at right angles to the thylakoid membranes of whole chloroplasts, and that the circular dichroism is light-dependent

Self-assembly and structural-functional flexibility of oxygenic photosynthetic machineries: personal perspectives

This short review, with a bit of historical aspect and a strong personal bias and emphases on open questions, is focusing on the (macro-)organization and structural-functional flexibilities of the photosynthetic apparatus of oxygenic photosynthetic organisms at different levels of the structural complexity-selected problems that have attracted most my attention in the past years and decades. These include (i) the anisotropic organization of the pigment-protein complexes and photosynthetic membranes-a basic organizing principle of living matter, which can, and probably should be adopted to intelligent materials; (ii) the organization of protein complexes into chiral macrodomains, large self-assembling highly organized but structurally flexible entities with unique spectroscopic fingerprints-structures, where, important, high-level regulatory functions appear to 'reside'; (iii) a novel, dissipation-assisted mechanism of structural changes, based on a thermo-optic effect: ultrafast thermal transients in the close vicinity of dissipation of unused excitation energy, which is capable of inducing elementary structural changes; it makes plants capable of responding to excess excitation with reaction rates proportional to the overexcitation above the light-saturation of photosynthesis; (iv) the 3D ultrastructure of the granum-stroma thylakoid membrane assembly and other multilamellar membrane systems, and their remodelings-associated with regulatory mechanisms; (v) the molecular organization and structural-functional plasticity of the main light-harvesting complex of plants, in relation to their crystal structure and different in vivo and in vitro states; and (vi) the enigmatic role of non-bilayer lipids and lipid phases in the bilayer thylakoid membrane-warranting its high protein content and contributing to its structural flexibility.

Dichroism and polarized fluorescence of chlorophyll a, chlorophyll c and bacteriochlorophyll a dissolved in liquid crystals

Three photosynthetic pigments were studied: chlorophyll a, chlorophyll c and bacteriochlorcphyll a in nematic liquid crystal matrixes. The polarized absorption and fluorescence spectra as a function of the electric field have been measured. From the polarized components of the absorption A( parallel) and A( perpendicular) of the pigments in liquid crystals two reduced components A(x) and A(y) are calculated (x and y are the direction of the axis which is going through the second, fourth pyrrol rings, and the first, third rings, respectively). From these results the orientation of chlorophylls in liquid crystals and the configuration of the transition moments in the skeleton of the pigment molecules were determined.

The development of the intense circular-dichroic signal during granum formation in greening etiolated maize

In greening maize mesophyll, circular dichroism (c.d.) revealed the early formation of protein-chlorophyll complexes, followed by unorganized chlorophyll. The intense c.d. [Gregory & Raps (1974) Biochem. J. 142, 193-201] appeared later still, whereas membrane-membrane contact (stacking), measured from electron micrographs, appeared much earlier. Isolated grana, which still showed stacking, lost 92% of their original intense c.d.; intense c.d. is not therefore simply dependent on stacking.