Barzda, V., Faculty of Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1081, Amsterdam, Netherlands, Department of Physics, University of Toronto at Mississauga, Toronto, Canada
Ionov, M., Sadykov Inst. of Bioorg. Chemistry, Uzbekistan Academy of Sciences, Tashkent, Uzbekistan, Institute of Horticulture, Volcani Center, Bet Dagan, Israel
Van Amerongen, H., Faculty of Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1081, Amsterdam, Netherlands, Laboratory of Biophysics, Wageningen University, Wageningen, Netherlands
Gussakovsky, E.E., Institute of Horticulture, Volcani Center, Bet Dagan, Israel, Faculty of Life Sciences, Bar Ilan University, Ramat Gan, Israel
Shahak, Y., Institute of Horticulture, Volcani Center, Bet Dagan, Israel

Circularly polarized luminescence (CPL) is a powerful technique to study the macroorganization of photosynthetic light-harvesting apparatus in vivo and in vitro. It is particularly useful for monitoring environmental stress induced molecular re-organization of thylakoid membranes in green leaves. The current study focuses on two questions which are important to perform and interpret such experiments: how does CPL depend on the excitation wavelength and how on the orientation of the granal thylakoids. CPL and circular dichroism (CD) of pea chloroplasts were complementarily applied when chloroplasts were either in suspension or trapped in a polyacrylamide gel (PAAG) after alignment in a magnetic field. In contrast to the CD spectrum, the CPL signal was found to be independent of the excitation wavelength in both the Soret and the Qy absorption region for chloroplasts in both suspension and PAAG. The improved resolution of luminescence measurements revealed a relatively small negative CPL band in addition to the previously described large positive band. No effect of photoselection upon excitation on the CPL spectra was detected. The CPL intensity at 690 nm at the edge of the granal thylakoids was found to be higher than at the face of the grana suggesting the CPL anisotropy.