PARENT SESSION
Posters P8B Supermolecular organization of the photosynthetic apparatus. Abstracts (592-611)

Entropy-assisted generation of local order in photosynthetic membranes. Eun-Ha Kim^*,1, Wah Soon Chow¹, Peter Horton², Jan Anderson¹, ¹ Photobioenergetics group, Research School of Biological Sciences, Australian National University, GPO Box 475, Canberra, ACT, Australia² Robert Hill Institute, Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, UK

ABSTRACT- Grana formation is a ubiquitous feature of the ultrastructure of chlorophyll b-containing chloroplasts. We have studied the hypothesis that increasing entropy in chloroplasts contributes to the formation of grana (Chow, Aust. J. Plant Physiol. 26, 641-647). The addition of water-soluble macromolecules such as bovine serum albumin or dextran to a suspension of initially unstacked, envelope-free chloroplasts induced local order at both the inter- and intra membrane level. Restacking of thylakoids occurred spontaneously accompanied by lateral segregation of PSII from PSI, thus mimicking thylakoid membrane system in vivo. We suggest that grana formation driven via increasing entropy is explained partially by the need for greater volume for free diffusion of the macromolecules under crowding conditions. This mechanism may be important in vivo where molecules have to diffuse to their destinations efficiently resulting in enhanced metabolic fluxes. Furthermore, we propose that a general thermodynamic principle of maximizing entropy drives the evolutionary selection for grana in chlorophyll b-containing plants.

KEY WORDS: grana, entropy, chloroplast ultrastructure