Fluorescence emission spectra of chloroplasts and subchloroplast preparations at low temperature |
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Authors: | CP Rijgersberg J Amesz APGM Thielen JA Swager |
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Institution: | Department of Biophysics, Huygens Laboratory, Rijksuniversiteit Leiden, P.O. Box 9504, Wassenaarseweg 78, 2300 RA Leiden The Netherlands |
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Abstract: | A study was made of the chlorophyll fluorescence spectra between 100 and 4.2 K of chloroplasts of various species of higher plants (wild strains and chlorophyll b mutants) and of subchloroplast particles enriched in Photosystem I or II. The chloroplast spectra showed the well known emission bands at about 685, 695 and 715–740 nm; the System I and II particles showed bands at about 675, 695 and 720 nm and near 685 nm, respectively. The effect of temperature lowering was similar for chloroplasts and subchloroplast particles; for the long wave bands an increase in intensity occurred mainly between 100 and 50 K, whereas the bands near 685 nm showed a considerable increase in the region of 50-4.2 K. In addition to this we observed an emission band near 680 nm in chloroplasts, the amplitude of which was less dependent on temperature. The band was missing in barley mutant no. 2, which lacks the lightharvesting chlorophyll a/b-protein complex. At 4.7 K the spectra of the variable fluorescence (Fv) consisted mainly of the emission bands near 685 and 695 nm, and showed only little far-red emission and no contribution of the band at 680 nm.From these and other data it is concluded that the emission at 680 nm is due to the light-harvesting complex, and that the bands at 685 and 695 nm are emitted by the System II pigment-protein complex. At 4.2 K, energy transfer from System II to the light-harvesting complex is blocked, but not from the light-harvesting to the System I and System II complexes. The fluorescence yield of the chlorophyll species emittting at 685 nm appears to be directly modulated by the trapping state of the reaction center. |
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Keywords: | Fluorescence emission spectroscopy Low temperature Chlorophyll (Chloroplast) reaction center chlorophylls primary electron donors of System I and II respectively System I pigment protein complexes containing about 90 and 40 chlorophyll molecules per reaction center respectively PS I Photosystem I respectively PS II Photosystem II respectively Chl chlorophyll |
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