PARENT SESSION
Posters P7B Evolution of photosynthesis. Abstracts (579-591)

Optimization and evolution of light harvesting in photosynthesis. The role of antenna chlorophyll conserved between Photosystem II and Photosystem I. Doug Bruce^*,1, Sergej Vasilliev¹, ¹ Department of Biological Sciences, St Catharines, Ontario, Canada

ABSTRACT- The efficiency of oxygenic photosynthesis depends on the presence of core antenna chlorophyll (Chl) closely associated with the photochemical reaction centers of both photosystem II (PSII) and photosystem I (PSI). Although the number and overall arrangement of these Chl in PSII and PSI differ, structural comparison reveals a cluster of 26 conserved Chls in nearly identical positions and orientations. To explore the role of these conserved Chl within PSII and PSI we studied the influence of their orientation on the efficiency of photochemistry in computer simulations. We found that the native orientations of the conserved Chls were not optimal for light harvesting in either photosystem. However, PSII and PSI each contain two highly orientationally optimized antenna Chl, located close to their respective reaction centers, in positions unique to each photosystem. In both photosystems the orientation of these optimized "bridging" Chls had a much larger impact on photochemical efficiency than the orientation of any of the conserved Chls. The differential optimization of antenna Chl is discussed in the context of competing selection pressures for the evolution of light harvesting in photosynthesis.

KEY WORDS: OPTIMIZATION