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

Changes in energy transfer dynamics by unstacking of the chloroplast membrane. Chantal de Wit^*,1, Janne Ihalainen¹, Henny van Roon¹, Ivo van Stokkum¹, Rienk van Grondelle¹, Jan Dekker¹, ¹ Department of Physics and Astronomy, Faculty of Sciences, Amsterdam, The Netherlands

ABSTRACT- In green plant photosynthesis, photosystem I and II (PSI, PSII) work in series to convert light into chemically stored energy. Plants are able to optimize the photosynthetic output under varying light conditions by state transitions. A mobile pool of light harvesting complex II (LHCII) realizes excitation redistribution between the two photosystems. This process is known to involve reversible phosphorylation of the LHCII. The disappearance of phosphorylated LHCII from the stacked regions of the membranes can perhaps be partially mimicked by unstacking induced by removal of divalent cations. Fluorescence emission spectra at 5K were recorded of spinach chloroplast membranes, both native and artificially unstacked. These spectra show a significant increase in the PSI/PSII and LHCII/PSII emission ratios for the blebs with respect to the native membranes. It is concluded that LHCII bound to PSII in the grana is released from PSII upon unstacking. Recently, it was published (Zhang and Scheller, 2004) that PSI binds a significant amount of LHCII in state 2. Question is whether unstacking of the chloroplast membrane mimicks a state-transition, i.e. whether LHCII released from PSII by unstacking will associate with PSI. For this purpose, time-resolved fluorescence measurements, performed at room temperature with a streak camera with 3 ps time-resolution, will be presented at the meeting. These experiments may shed light on the kinetics and extent of LHCII to PSI energy transfer in native membranes and blebs.

KEY WORDS: unstacking, chloroplast membrane, state transitions, time-resolved fluorescence