Fluorescence Properties of Chlorophyll-Protein Complexes From Spinach Chloroplasts — on the Specificity of the Emission Bands

Abstract

Interpretation of chlorophyll fluorescence signals from leaves and chloro-plasts rely on a number of assumptions regarding fluorescence yields, fluorescence emitters, energy transfer probabilities etc. One of the assumptions which has not been clearly resolved yet is the assignment of the emission peaks of chloroplast fluorescence at 77K to specific chlorophyll-protein complexes. The 685 and 695 nm emissions are usually attributed to PSII and that in the 710–730 nm region to PSI. The purified light harvesting complex of PSII (LHCII) has an emission peak at 681 nm but also emissions at 695 nm and 735 nm. Under certain conditions of isolation, the long wavelength emission in LHC is of comparable intensity to that of the 695 nm shoulder (Fuad et al. 1983). Such an LHC, named LHC736, has no apparent contamination from PSI. The fluorescence properties of chlorophyll-protein complexes were therefore studied in detail to obtain more information on the specificity of the emission bands of chloroplasts at 77K. Three approaches were used i) analysis of fluorescence spectra by deconvolution into gaussian components, ii) measurements of fluorescence lifetimes at 77K and iii) study of the temperature dependence of fluorescence intensity. These approaches were applied to thylakoids, and the purified chlorophyll-protein complexes: PSI, PSII, LHCII, LHC736 and aged LHCII.