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

Modification of spectral and kinetic properties of fluorescence in Phosphatidylglycerol depleted thylakoid membrane. Masayuki Komura^*,1, Yutaka Shibata¹, Ildiko Domonkos², Zoltan Gombos², Hajime Wada³, Shigeru Itoh¹, ¹ Department of Material Science, Graduate School of Science, Nagoya university, Furoh-cho, chikusa-ku, Nagoya, Aichi-ken, Japan² Institute of Plant Biology, Biological Research Center of the Hungarian Academy of Sciences, Szeged, Hungary³ Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, komaba, Tokyo, Japan

ABSTRACT- Phosphatidylglycerol (PG) is a ubiquitous phospholipid in almost all organisms and has been considered to play an important role in the structural maintenance of the photosynthetic apparatus in thylakoid membranes. Earlier studies with pgsA deleted mutant cells of Synechocystis sp. PCC 6803 that are defective in PG synthase demonstrated the importance of PG in PS II dimerization as well as in PS I trimerization. We measured time-resolved fluorescence spectra of thylakoid membranes of this mutant by streak camera spectrograph at 5 K. Spectral and kinetic properties of fluorescence were measured upon PG abundance, deficiency and readdition. Fluorescence intensity of PS II was increased in a few days after the depletion of PG whereas PS I fluorescence did not change, indicating a decrease of PS II activity in this period. Phycobilisomes were removed from PS II in the next period (after 7 days), giving less fluorescence. A spectral blue shift of PS I fluorescence band was observed after 2 weeks of PG depletion in parallel with the monomerization of PS I trimer. Global exponential fitting analysis revealed that (1) the blue shift of PS I fluorescence was derived from a modification of longest lived component while the other components were unchanged, (2) lifetimes of F685 and F695, fluorescence components in PS II were not changed. However, the amplitude of F695 was increased upon the PG depletion. It suggests partial monomerization of PS II RC. Readdition of PG resulted in a total recovery of fluorescence kinetic properties even in the presence of Lincomycin that suppresses the protein synthesis. PG seems to be an essential structural factor both in PS I and PS II RC.

KEY WORDS: time-resolved fluorescence spectra, Phosphatidylglycerol, Global exponential fitting analysis