Fig. 2.

Chl fluorescence emission spectra of spinach thylakoids at 77K. The excitation wavelength was 435 nm and the band width was 20 nm. The emission wavelength was 650–750 nm and the band width was 2.5 nm. The typical fluorescence emission spectra (green curves) are shown with Gaussian decompositions. The curve with little noise is the original fluorescence emission spectrum, while the smooth curve corresponds to the sum of the six Gaussian curves showing the validity of the decomposition results. Six main components were identified in accordance with Stoitchkova et al. (2006) and are referred to as F680 (red curves: peak, 681 nm; half band width, 10.1 nm), F685 (green-yellow curves: peak, 685 nm; half band width, 9.3 nm), F695 (blue-purple curves: peak, 693 nm; half band width, 9.2 nm), F700 (orange curves: peak, 700 nm; half band width, 15.8 nm), F720 (blue curves: peak 720 nm; half band width, 21.9 nm) and F735 (red-purple curves: peak 735 nm; half band width 23.4 nm), respectively. The curves correspond to the fluorescence maxima of the trimeric and monomeric forms of LHCII (F680), the PSII reaction center complex (F685), the core antenna complex of PSII (F695), the aggregated trimers of LHCII (F700), the core complex of PSI (F720) and LHCI (F735). Low emission of PSI fluorescence at the long wavelength is the consequence of a decrease in the quantum efficiency of the photomultiplier used in the fluorescence spectrophotometer. (A) Fluorescence from thylakoids incubated in the dark. (B) Fluorescence from thylakoids illuminated with high light (light intensity: 1,000 µmol photons m⁻² s⁻¹). An increase in the ratio of F700:F680 at high light indicates conversion of free LHCIIs to aggregated LHCIIs.