PARENT SESSION
Posters P4Aa Chlorophyll and bilin based antenna systems. Abstracts (239-271)

When a lumenal protein interferes with stromal side affairs: Synechocystis PCC 6803 mutants lacking PsbU. John Veerman^*,1, Julian Eaton-Rye², Doug Bruce¹, ¹ Department of Biological Sciences, Brock University, St.Catharines, Ontario, Canada² Department of Biology, University of Otago, Dundein, New Zealand

ABSTRACT- The lumenal side structural protein psbU present in cyanobacteria and red algae PSII complexes enhances the structural stability of PSII and has been implicated in the regulation of S-state transitions of the oxygen evolution complex. The present study was undertaken to investigate the alterations in energy transfer in the psbU- mutant. We have used a combination of fluorescence spectroscopy, pulse amplitude modulation and picosecond time-resolved fluorescence spectroscopy to characterize energy transfer in the Synechocystis PCC 6803 psbU- cells. The absolute 77K fluorescence spectra with 590nm excitation has shown a marked increase in the 680nm peak in the psbU- mutant as compared to the wild-type, while with 435nm excitation the psbU- mutant and wild-type absolute 77K fluorescence spectra were not significantly different. Gaussian deconvolution of the absolute 77K fluorescence spectra with 590nm excitation revealed that the APC terminal emitter/PSII component at 680nm increases out of proportion with the PSII component at 690nm in the psbU- mutant cells. In addition, the absolute value of Fo was greater in the psbU- mutant and this increase was a good deal less pronounced when using a 450nm measuring light as opposed to a 665nm measuring light. These results indicate that the phycoilisome/PSII energy coupling is less efficient in the psbU- mutant. Picosecond time-resolved fluorescence spectroscopy was undertaken to corroborate the idea of decreased PSII/phycobilisome energy coupling in the psbU- mutant and has yielded slower decay kinetics for the psbU- mutant cells as compared to the wild-type cells at Fo using both a 407nm and 650nm laser. The global lifetime analyses of the fluorescence decay data suggests that PSII possesses altered decay kinetics in the psbU- mutant. Therefore, the existing data indicates that the psbU- mutant has both a relatively decoupled phycobilisome/PSII connection and a PSII complex with altered excitation transfer and/or primary photochemistry.

KEY WORDS: phycobilisome, picosecond, PSII, psbU