Emission spectra of two thermoluminescence (TL) components emitted from the photosynthetic apparatus were determined by the use of an imaging photon detector system. The following results were obtained: (i) The TL B-band emitted from whole thylakoids and PS II core complex showed the same emission spectrum peaking at about 690 nm (uncorrected for wavelength dependence of the photocathode) with a broad tailing in far-red region. This spectrum agrees with the reported emission spectrum of delayed luminescence, consistent with the view that the TL B-band arises from thermally stimulated recombination of charge pairs in PS II. (ii) The emission spectrum of TL Z-band was variant, depending on the PS I/PS II ratio in the sample. This was because the Z-band consists of two spectral components emitting at about 740 nm and 690 nm (also uncorrected for the wavelength dependence of the photocathode); the former originates exclusively from PS I and the latter from PS II. (iii) Light-harvesting chlorophyll protein complexes (LHCI and LHCII) emit the respective spectral components of Z-band more strongly than do their respective core complexes, indicating that reaction center photochemistry is not involved in energy storage for the Z-band. (iv) A methanol extract of thylakoids emitted only a weak Z-band at 690 nm, but the formation of a chlorophyll aggregate markedly enhanced the Z-band intensity, concomitant with a shift in emission maximum to 740 nm. The mechanism of energy storage for Z-band is discussed in relation to the local chlorophyll concentration.
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