Analysis of Pigment Orientation in Photosystem II at Different Temperatures by Polarization Fluorescence and Molecular Exciton Theory

Abstract

The effect of temperature on pigment orientation in photosystem II (PSII) was studied by fl uorescence excitation and polarization fl uorescence spectra of spinach thylakoid solution and molecular exciton theory. Experimental results showed that at 15 to 45 °C, the absorption band of chlorophyll a at 436 nm at room tempe rature red-shifted with increased temperature. The excitation spectra intensity reached the maximum at 35 °C but signifi cantly dropped at 65 and 78 °C. The polarization fl uorescence spectra revealed that the fl uorescence peak of PSII did not change at 15 and 45 °C, and the calculated degree of fl uorescence polarization increased with increased temperature. Spectral and molecular exciton theory analyses indicated that temperature affected pigment orientation in PSII, as well as the coupling strength between pigments or pigment and protein, thereby changing photosynthetic effi ciency. These results can serve as a reference for studies on energy absorption, energy transmission, regulation mechanism, and prospective applications in solar cell materials.