Independent fluorescence emission of the chlorophyll spectral forms in higher plant Photosystem II

Abstract

Room-temperaure steady-state emission and Q 1 absorption spectra of light-harvesting chlorophyll a b protein complex II (LHCII) isolated from spinach have been analysed in terms of a linear combination of asymmetric gaussian bands. To investigate a possible correspondence between the absorption and emission bands, the thermal emission spectrum of each absorption band has been calculated. It is demonstrated that the calculated fluorescence bands correspond closely to those obtained by gaussian deconvolution. It is thus possible to associate an emission band with each absorbing chlorophyll spectral species: Chl 653 648, Chl 663 660, Chl 672 670, Chl 680 678, Chl 687 684, Chl 697 695 (Chl m n is the spectral species that absorbs with maximum at wavelength n and emits with maximum at wavelength m) and to interpret the emission spectrum of LHCII as a linear combination of the emission spectra of each absorbing chlorophyll spectral species. In particular, the correspondence between the 684 nm and 695 nm absorption bands and the emission bands with maximum at 687 nm and 697 nm lends support to the presence of long wavelength Chl a spectra forms in LCHII, the external antenna of PS II. A close correlation between the emission and absorption gaussian bands is also found in the analysis of the room temperature absorption and emission spectra of such membrane preparation as BBY-grana from spinach and thylakoids prepared from barley wild type and the chlorina f2 mutant (lacking LHCII). On the basis of these data, the commonly observed 5–7 nm wavelength difference between the absorption and emission spectra maxima of chlorophyll containing biological membranes is interpreted in terms of (a) the Stokes shifts of the single spectral forms together with (b) the increased emission contribution of the longer wavelength forms to the emission spectrum caused by energy transfer.