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

Dynamic interaction between LHCII and PSII in grana membranes fused with liposomes. Silvia Haferkamp^*,1, Winfried Haase², Helmut Kirchhoff¹, ¹ Institut fuer Botanik, Muenster, Germany² Max-Planck-Institut fuer Biophysik, Frankfurt am Main, Germany

ABSTRACT- A preparation protocol was developed to incorporate lipids in grana membranes (BBY) by fusion with liposomes (from native or non-native lipids). The incorporation was monitored and quantified by density gradient centrifugation and electron microscopy of freeze-fractured fusion products. We estimate that the relative membrane area occupied by lipids increases from 20 % (control grana) up to 70 % in the fusion products. The membranes are characterized by 77 K fluorescence spectroscopy, absorption spectroscopy and Fo measurements. The data indicate a detachment of LHCII from PSII in the fusion products. This can be concluded from an increase in the Fo level (about 4.6 times the control value), a blue-shift in the absorption maxima in the Qy region (from 680 nm to 673 nm) and the occurrence of a new emission band at 681 nm in the 77 K fluorescence spectra. Interestingly, the increased Fo level shows a characteristic temperature dependency. Above the gel to fluid transition temperature of the lipids Fo decreases to the value of non-fused grana. We conclude that the fluidity of the lipids facilitates the intermolecular protein interaction in grana membranes required for efficient energy transfer in the PSII antenna. The protein density seems to be of minor significance. Chlorophyll-a-fluorescence induction measurements to analyze the light harvesting of PSII in the fusion product are planned.

KEY WORDS: excitation transfer, grana membranes, lipids, transition temperature