Atsuko Kanazawa, Antony R. Crofts and David M. Kramer

Program in Biophysics and Computational Biology, Dept. of Microbiology and Dept. of Plant Biology. University of Illinois at Urbana-Champaign, 393 Morrill Hall, 505 S. Goodwin Ave., Urbana, IL 61801

Cryophilic algae are photosynthetic organisms normally found on the surface of permanent snow or ice. We have obtained ten strains of these isolated from the surface of Antarctic snow, and are making a comparative analysis of the energetics of photosystem II (PSII) in them. Previously, in temperate plants, we found high activation barriers for the electron transfer reactions from Qa to Qb, and recombination from S2Qa- and from S2Qb-. In the cryophilic algae, Chlorella antarctica, we found significant lower activation barriers for these reactions. We suggest these represent specific adaptations of PSII bioenergetics for life at low temperatures.